Examination of Grain Moisture Meters
Using Air-Oven Reference Method
Transfer Standards
PART 1: Laboratory Grain Sample Preparation and Testing
PART 2: Field Inspection and Evaluation

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159

NIST Handbook

2017

INSIDE FRONT COVER - BLANKExamination of Grain Moisture Meters
Using Air-Oven Reference Method
Transfer Standards
Part 1:
Part 2:

Laboratory Grain Sample Preparation and Testing
Field Inspection and Examination

G. Diane Lee, Physical Scientist
Dr. Douglas Olson, Chief
Office of Weights and Measures
Physical Measurement Laboratory

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March 2017
U.S. Department of Commerce
Wilbur L. Ross, Jr., Secretary
National Institute of Standards and Technology
Kent Rochford, Acting Director and Under Secretary of Commerce for Standards and Technology

NIST
Handbook

159

Certain commercial entities, equipment, or materials may be identified in this document to describe an
experimental procedure or concept adequately. Such identification is not intended to imply
recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended
to imply that the entities, materials, or equipment are necessarily the best available for the purpose.

National Institute of Standards and Technology Handbook 159, 2017 Edition
Natl. Inst. Stand. Technol. Handb. 159, 2017 Ed., 80 pages (March 2017)

WASHINGTON: 2017

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PrefaceState and local weights and measures jurisdictions or other testing laboratories that use transfer standards
developed using the air-oven reference methods (referred to as “air-oven reference standards) to testcommercial grain moisture meters collect grains that are typically grown and traded in their State andtransport them to their laboratory for testing. In the laboratory, these grains are cleaned, mixed, and tested
to determine moisture content and test weight. The grains are then divided into smaller grain samples andassigned moisture and test weight reference values.
These samples with known reference moisture and weight per bushel values are issued to weights andmeasures officials to test commercial grain moisture meters in accordance with NIST Handbook 44,
Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices,
Section 5.56.(a) “Grain Moisture Meters.” Commercial grain moisture meters are meters that provide rapid
measurement of grain moisture content during the sale of a quantity of grain. The moisture content of grain
is used to determine the amount of money a seller will receive for the grain. For example, if grain moisture
content is too high, the buyer must dry the grain before storage, so cost adjustments are made by the buyer
to offset the cost for drying. Conversely, if the moisture is too low the grain quality may be affected andcost adjustments may be made for low moisture.
This reference manual provides technical guidelines for: (1) laboratory grain sample preparation andtesting; and (2) the field evaluation of grain moisture meters and multi-constituent grain analyzers thatmeasure moisture in accordance with NIST Handbook 44, Section 5.56.(a) for field testing using air-ovenreference method transfer standards.
This manual is one of a number of manuals published by the National Institute of Standards and Technologythat are designed to present, in compact form, comprehensive technical guidance for state and local weights
and measures officials. Individual reference manuals for the various types of measuring devices in NIST
Handbook 44 are being considered in acknowledgement of the rapidly developing technological characterof commercial measurement and the ever-changing equipment used in the measurement process.
Although this handbook is prepared primarily for use by State and local weights and measures officials, theinformation may also be useful to manufacturers and commercial and industrial establishments interested
in evaluating grain moisture meters.

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Acknowledgements
Special thanks go to the following individuals and groups for their technical contributions, reviews, andinput in the preparation of this handbook:
National Type Evaluation Technical Committee (NTETC), Grain Analyzer Sector EPO Work Group:
John W. Barber, JB Associates
Cathleen Brenner, USDA, GIPSA
Randy Burns, Arkansas
Sid Colbrook, Illinois (Illinois Weights and Measures, Retired)
Bob Davis, Illinois
John Fecht, Nebraska
Richard Pierce, (USDA, GIPSA, Retired)Fred Seeber, Shore Sales Company, Inc.
Cheryl Tew, (North Carolina Weights and Measures, Retired)
Bob Wittenberger, (Missouri Weights and Measures, Retired)
Will Wotthlie, (Maryland Weights and Measures, Retired)
NIST Office of Weights and Measures Staff:
Tina Butcher
Linda Crown

References
T. Butcher, L. Crown, R. Harshman, J. Williams, NIST Handbook 44 – Specifications and Tolerances andother Technical Requirements for Weighing and Measuring Devices, latest edition.
USDA, GIPSA, Technical Services Division, Air-Oven Moisture Reference Laboratory Working
Instructions, latest edition.
USDA GIPSA, Moisture Handbook, January 1999.
USDA, GIPSA, Equipment Handbook, October 1996.
J. W. Barber, JB Associates, Grain Moisture Meters from Theory to Practice (slide presentation), 2001.

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Acronyms
CC ............................................................................................................ NTEP Certificate of Conformance
EPO ............................................................................................................... Examination Procedure Outline
GA .......................................................................................................................................... Grain Analyzer
GIPSA ...................................................................Grain Inspection Packers and Stockyards Administration
GMM ........................................................................................................................... Grain Moisture Meter
Handbook 44 ..................................................... NIST Handbook 44, Specifications, Tolerances, and Other
Technical Requirements for Weighing and Measuring Devices
NCWM......................................................................... National Conference on Weights and Measures, Inc.
NIST.....................................................................................National Institute of Standards and Technology
NTEP ..................................................................................................... National Type Evaluation Program
OWM .......................................................................................................... Office of Weights and Measures
USDA............................................................................................................U.S. Department of Agriculture
USNWG ............................................................................................................... U.S. National Work Groupv

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TABLE OF CONTENTSPREFACE .................................................................................................................................... III
ACKNOWLEDGEMENTS ....................................................................................................... IV
REFERENCES ............................................................................................................................ IV
ACRONYMS ................................................................................................................................ V
PART 1: LABORATORY GRAIN SAMPLE PREPARATION AND TESTING ................ 1
SCOPE .................................................................................................................................. 1
GENERAL GUIDANCE ON SAFETY ............................................................................. 1
DEFINITIONS ..................................................................................................................... 2
equilibrate .............................................................................................................................................2
laboratory standard meters .................................................................................................................2
naturally moist grains ..........................................................................................................................2
parent sample........................................................................................................................................2
test weight..............................................................................................................................................2
working sample .....................................................................................................................................2

EQUIPMENT ....................................................................................................................... 3
Breathing Apparatus ............................................................................................................................3
Grain Sample Cleaning and Mixing Equipment ...............................................................................3
Automatic or Hand Sieves .........................................................................................................3
Dockage Tester ..........................................................................................................................3
Dividers......................................................................................................................................3
Test Weight per Bushel Equipment ....................................................................................................4
Basic Air-Oven Test Equipment .........................................................................................................4
Analytical Balance .....................................................................................................................4
Glass Vacuum Desiccator ..........................................................................................................4
Laboratory Mill ..........................................................................................................................5
Mechanical Convection (forced-draft) Oven .............................................................................5
Moisture Dishes (tins) ................................................................................................................5
Thermometer ..............................................................................................................................6
Top-loading Balance ..................................................................................................................6

GENERAL ............................................................................................................................ 6
Grain Handling .....................................................................................................................................6
Air-Oven Test Procedures ...................................................................................................................7
Test Weight per Bushel Procedures ....................................................................................................7

PARENT GRAIN SAMPLE PREPARATION ................................................................. 7
Collection...............................................................................................................................................7vii

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Cleaning ................................................................................................................................................7
Storage and Labeling ...........................................................................................................................8

WORKING SAMPLE PREPARATION ........................................................................... 8
Laboratory Conditions.........................................................................................................................9
Temperature: ..............................................................................................................................9Maximum Rate of Change: ........................................................................................................9
Relative Humidity: .....................................................................................................................9
Preparing Working Samples for Testing............................................................................................9TESTING THE WORKING SAMPLE ............................................................................. 9Laboratory Standard Meter Moisture Measurements......................................................................9
Reference Air-Oven Moisture Measurements ...................................................................................9
Laboratory Standard Meter Moisture vs. Reference Air-Oven Moisture Bias ............................ 10
Requirement for Laboratory Standard Meter Moisture vs. Reference Air-Oven Moisture Bias.............................................................................................................................................................. 10
Determine the Test Weight ................................................................................................................ 10
Records ................................................................................................................................................ 10
Parent and Working Samples ................................................................................................... 10
Field Samples ........................................................................................................................... 11

SELECTING AND PREPARING OFFICIAL GRAIN SAMPLES ............................. 11
Official Grain Samples for Field Testing.......................................................................................... 11Time Lapse .......................................................................................................................................... 13

RETESTING AND REUSING OFFICIAL GRAIN SAMPLES .................................. 13
Retesting Samples ............................................................................................................................... 13
Reusing Samples ................................................................................................................................. 13

PART 2: FIELD INSPECTION AND EVALUATION .......................................................... 15
EPO NO. 50 (2017) NIST EXAMINATION PROCEDURE OUTLINE (EPO) FOR GRAIN
MOISTURE METERS ............................................................................................................... 15
SCOPE ................................................................................................................................ 15
GENERAL GUIDANCE ON SAFETY ........................................................................... 15
DEFINITIONS ................................................................................................................... 16
audit trail............................................................................................................................................. 16
cereal grain and oil seeds ................................................................................................................... 16
constituent ........................................................................................................................................... 16
back-up sample. .................................................................................................................................. 16
drop...................................................................................................................................................... 16
grain calibration ................................................................................................................................. 17
grain moisture meter .......................................................................................................................... 17
kind of grain ........................................................................................................................................ 17
moisture content (wet basis) .............................................................................................................. 17
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official grain samples.......................................................................................................................... 17
grain sample ........................................................................................................................................ 17
security seal ......................................................................................................................................... 18
specification......................................................................................................................................... 18
test site ................................................................................................................................................. 18
test weight............................................................................................................................................ 18
tolerance .............................................................................................................................................. 18
warmed ................................................................................................................................................ 18

FIELD EQUIPMENT AND GRAIN SAMPLES ............................................................ 18
Apparatus and Equipment ................................................................................................................ 19
Breathing Apparatus ................................................................................................................ 19
Thermometer ............................................................................................................................ 19
Container.................................................................................................................................. 20
Cooler ...................................................................................................................................... 20
Fire Extinguisher...................................................................................................................... 20
First Aid Kit ............................................................................................................................. 20
Portable Refrigerator................................................................................................................ 20
Grain Sample Racks ................................................................................................................. 21
Official Grain Samples ............................................................................................................ 21
Personal Protection Equipment (PPE) ..................................................................................... 22
Two-inch Aluminum Angle Gage............................................................................................ 22
Calculator ................................................................................................................................. 22
Safety Shoes ............................................................................................................................. 22
Security Seal ............................................................................................................................ 22
Approval Tags and Stickers ..................................................................................................... 22

INSPECTION..................................................................................................................... 23
General Consideration ....................................................................................................................... 24
Suitability, Installation, and Visibility of Identification .......................................................... 24
Level ........................................................................................................................................ 25
Position of Equipment.............................................................................................................. 26
Location and Access ................................................................................................................ 26
Assistance ................................................................................................................................ 27
Use and Maintenance ............................................................................................................... 27
Determination of Quantity and Temperature ........................................................................... 28
Operating Instructions .............................................................................................................. 29
Indicating and Recording Elements .................................................................................................. 29
General ..................................................................................................................................... 29
Design ...................................................................................................................................... 29
Selecting or Recording Grain or seed Type and Class ............................................................. 30
Operating Ranges and Temperatures ....................................................................................... 31
Electrical Power Supply........................................................................................................... 34
Units and Readability ............................................................................................................... 34
Recorded Representation ......................................................................................................... 35
Provisions for Sealing .............................................................................................................. 35
Marking Requirements ...................................................................................................................... 38
General Identification .............................................................................................................. 38
Interchange or Reversal of Parts .............................................................................................. 41
Marking, Operational Controls, Indications and Features ....................................................... 41
Values ...................................................................................................................................... 42
Permanence .............................................................................................................................. 42
On Devices that Indicate or Record in more than One Unit .................................................... 42
Lettering ................................................................................................................................... 42ix

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Other Devices not used for Commercial Measurements .......................................................... 43
Measuring Element ............................................................................................................................ 43
Accessory Devices/Equipment ................................................................................................ 43
Current Calibration Data .......................................................................................................... 43
Figure 2-13. Calibration Data from a GMM Certificate of Conformance. ................................................. 44

PRETEST DETERMINATIONS ..................................................................................... 44
Grains and Constituents .................................................................................................................... 44
Tolerances ........................................................................................................................................... 44
How to Apply Tolerances ........................................................................................................ 44

TEST NOTES ..................................................................................................................... 46
Official Grain Sample Maintenance, Test Methods and Documentation ...................................... 46
Storage ..................................................................................................................................... 46
Official Grain Samples used for Field Testing......................................................................... 46
Warming Official Grain Samples in Preparation for Testing................................................... 46
Minimum Test and Maximum Number of Drops .................................................................... 46
Preparation of the Official Grain Samples upon Arrival at the Test Site ................................. 47
Field Inspection and Test Method ............................................................................................ 48
Documentation ......................................................................................................................... 48
Official Grain Samples (Transfer Standards), Minimum Test, Minimum Sample Size. ............. 49

TEST ................................................................................................................................... 50
Minimum Test .................................................................................................................................... 50

POST TEST TASKS .......................................................................................................... 52
Provisions for Sealing ......................................................................................................................... 52
Record Results .................................................................................................................................... 52
Review Results ........................................................................................................................ 53

APPENDIX A. GRAIN MOISTURE METER SAMPLE TEST REPORT FORM ............. 1
APPENDIX B. GRAIN MOISTURE AIR-OVEN REFERENCE METHODS IN THE
UNITED STATES......................................................................................................................... 1
APPENDIX C. DETERMINING REFERENCE TEST WEIGHT PER BUSHEL VALUE
OF GRAINS .................................................................................................................................. 1x

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Part 1: Laboratory Grain Sample Preparation and Testing
Scope
Part 1 of this Handbook provides: (1) technical guidelines for determining the moisture content ofgrain samples using reference air-oven test procedures; (2) a description of the laboratory equipment
needed to determine the moisture in grain; and (3) instructions for preparing the parent and working
samples used to test commercial moisture meters and multi-constituent grain analyzers in accordancewith NIST Handbook 44, “Specifications, Tolerances, and Other Technical Requirements for
Weighing and Measuring Devices,” Section 5.56.(a) “Grain Moisture Meters (GMM).”

General Guidance on Safety
Many policies and regulations will vary among jurisdictions. It is essential that inspectors or service
persons be aware of all safety regulations and policies in place in the laboratory and to practice theiremployers’ safety policies. The safety reminders included in this manual contain general guidelines
useful in alerting laboratory persons to the importance of taking adequate precautions to avoid
personal injuries. These guidelines can only be effective in improving safety when coupled withtraining in hazard recognition and controls.
Always be familiar with emergency procedures BEFORE testing. After an emergency has
developed, crucial time can be lost if emergency procedures are not known. Be familiar with theprocedures to follow in the event of an equipment malfunction or the development of a dangerous
situation with the equipment or in the vicinity of the laboratory when operating specialized testing
equipment.
Be familiar with the nature of any product being dispensed by a device or being used in or near thelaboratory. Know the emergency procedures to be followed when a spill of a hazardous product has
occurred or a person has been exposed to the product. Knowledge of emergency procedures andrelated information should include the correct selection and use of fire extinguishers, the location of
emergency shut-offs, and evacuation procedures.
Keep a list of emergency phone numbers handy at all times in a notebook or on a card. Examples ofnumbers to keep are the local fire department, emergency medical facility, and other appropriate
public safety agencies. Prior to testing, carefully check the laboratory for safety hazards and takeappropriate precautions including:
•
•
•
•
•
•
•
•
•

Inspect all electrical cords and connections for damage to prevent electrical shock.
Learn the nature of hazardous products used in or near the laboratory.
Know the emergency evacuation routes for the laboratory.
Use personal protection equipment appropriate for the laboratory and for particular testing.
Wear safety shoes to prevent possible injury from falling weights, grain sample containers,
and other equipment and to prevent slipping on wet or slick surfaces.
Wear proper breathing apparatus, if necessary, for protection from dust and other airborne
contaminants.
Be sure that a first aid kit is available and that the kit is appropriate for the type of activity.
Practice safe and proper lifting techniques.
Use a lid opener if grain sample container lids are too tight to be removed comfortably byhand. Do not strain. Firmly grasp the container with good hand and wrist positioning;1

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Dry condensation from the outside of the grain sample container to prevent slippage andpossible breakage of container and/or injury to feet and toes; andWatch for chips, cracks, or breakage of glass containers. If found, dispose of the container
properly to prevent injury to the inspector. A damaged container may also affect the
integrity of the grain sample moisture.

Definitions
equilibrate
To be in or bring about equilibrium. In the case of preparing grain samples for moisture
testing, it refers to uniform distribution of moisture in the grain samples.
Note: Variations in moisture content may exist at the top, middle, and/or bottom of a onegallon working sample of grain. To reduce errors introduced by these variations, onegallon working samples of grain are not tested until they are refrigerated for at least
72 hours; this allows any moisture variations within the grain sample to equilibrate.

laboratory standard meters
Grain moisture meters of each type of meter used commercially in the State that are
maintained in the laboratory and used to select and/or screen grains for testing and fielduse. These meters are used to determine the moisture values of grain samples; these values
are compared to the moisture results obtained using the air-oven reference method andcannot exceed 0.3 % if the grain sample is to be used to test the same moisture meter typein the field. Some laboratories also collect data on the laboratory meters that is shared withthe meter manufacturer.

naturally moist grains
Grains that have not been artificially moistened by adding water to the grain after it has
been harvested.

parent sample
The “parent sample” is a bulk sample of a given type of grain from which a “working
sample” will be taken in order to create a set of official grain samples.

test weight
A measurement to determine the weight per volume (bulk density) of a particular lot ofgrain. For example, kg/hL or lb/bu.

working sample
The “working sample” is taken from a “parent sample” of grain and used to create a set of
official grain samples. See Example 1. “Preparing Samples for One Inspector to Conduct
Field Testing” in Part 1. Section 9.1. “Official Grain Samples for Field Testing.”

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EquipmentThis list includes a brief description of the equipment used in grain sample cleaning and mixing, test
weight determination, and air-oven testing. The USDA, GIPSA Equipment Handbook provides
additional information to include maintenance of the equipment included in this list. Pictures(figures) are included to provide examples of equipment used in some laboratories.

Breathing Apparatus
A mask or other appropriate apparatus used to prevent excessive inhalation of dust or othercontaminants.

Grain Sample Cleaning and Mixing Equipment
Automatic or Hand Sieves
Automatic or hand sieves are used to remove
larger or smaller materials from smaller samplesof grain. See Figure 1-1. “Automatic or Hand
Sieves.”Figure 1-1. Automatic or Hand
Sieves.

Dockage Tester
This device automatically removes and separates smaller orlarger materials from large portions of grain. State grainlaboratories use dockage testers to clean large samples ofgrain. After running samples through the dockage tester the
samples of grain are cleaner and more uniform in size. See
Figure 1-2. “Dockage Tester.”Figure 1-2. Dockage
Tester.

Dividers
Dividers are used to reduce a parent sample of grain tosmaller, representative working samples. When a sample
is placed in the divider it is separated into equal parts.
Dropping grain through the divider several times also
mixes the grain samples so that a representative sample
can be tested. See Figure 1-3. “Dividers.”

Figure 1-3. Dividers.

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Test Weight per Bushel Equipment
This equipment is used to determine the test weight
per bushel of the grain sample that is weighed.
Figure 1-4. “Test Weight per Bushel Equipment” shows
an example of a scale in which one quart of a grain
sample is weighed on the scale that is designed tomultiply the weight by 32. Since there are 32 quarts toa dry bushel of grain, the scale provides a direct readingof the weight per bushel of the grain that is weighed.
Figure 1-4. Test Weight per
Bushel Equipment.

Basic Air-Oven Test Equipment
Below is a list of basic equipment needed to perform single- and two-stage air-ovenmoisture testing and 72-hour air-oven tests for corn and beans. See Appendix B for
additional information concerning air-oven test procedures. USDA, GIPSA Air-Oven
Working Instructions provide a specific equipment list for each air-oven test described in
the working instructions.

Analytical Balance
An analytical balance is used to take the final weight of
the ground grain sample just before placing the samples
in the oven for air-oven moisture testing and to get theweight of the sample after oven testing. The balancemust be accurate to 0.1 mg. An example of an analyticalbalance is shown in Figure 1-5. “Analytical Balance.”

Figure 1-5.
Balance.

Analytical

Glass Vacuum Desiccator
A desiccator is used for cooling moisture dishes and ground grain
samples after oven testing. Cooling grain samples in a desiccator isnecessary to prevent the dry grain from absorbing moisture from theatmosphere during the cool-down period. The desiccator must be of
the glass vacuum type and have an inside diameter of approximately
250 mm, with a porcelain desiccator plate. Activated alumina,“molecular sieves” Type 4A desiccant must be placed in the bottomof the desiccator. See Figure 1-6. “Glass Vacuum Desiccator” with a
Porcelain Plate.
Figure 1-6. Glass Vacuum
Desiccator with a Porcelain
Plate.

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Laboratory MillA laboratory mill is a device used to grind the grain
sample in preparation for air oven testing. Studies
have shown that the use of different types of mills
yields different test results. The laboratory millshould be the type listed in the USDA, GIPSA Airoven Moisture Reference Laboratory Work
Instructions: The Wiley Intermediate Model Mill
with a 20 mesh (0.850 mm) opening (Arthur
H. Thomas Company, Philadelphia, Pennsylvania).
See Figure 1-7. “Laboratory Mill.”

Figure 1-7. Laboratory Mill.

Mechanical Convection (forced-draft) OvenOvens are used to dry grain samples at thetemperatures that are specified in the USDA, GIPSA
Air-Oven Working Instructions. Ovens must be
capable of maintaining a uniform temperature within±1 °C of the oven temperature specified for the specificair-oven test being conducted. See an example of a
“Mechanical Convection (forced draft) Oven” inFigure 1-8. “Mechanical Convection (forced-draft)
Oven.”
Figure 1-8. Mechanical
Convection (forced-draft)
Oven.

Moisture Dishes (tins)
Moisture dishes are used to hold groundgrain samples. The moisture dish with aground sample of grain is place in anoven for a time period and temperature
specified in the test procedure. The
moisture dishes are constructed of heavy
aluminum, with a diameter of about
55 mm and a height of about 15 mm. For
high moisture corn, moisture dishes witha diameter of 92 mm and a height of
Figure 1-9. Moisture Dishes (tins).
53 mm are needed. Intermediate size
dishes with a diameter of 70 mm and a height of 30 mm may be used on large
kernel samples. Follow the USDA, GIPSA air-oven working instructions (seeAppendix B) to determine the correct size moisture dish for testing. The dishesmust have fitted slip-in covers. Each individual dish and lid must be labeledwith an identifying mark such as a unique number that is marked on both the lid
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marking the dishes. Clearly labeling lids and dishes allows for tracking the dishtare weights over time and for storing dish weights to eliminate the need forreweighing after each use. See Figure 1-9. “Moisture Dishes (tins).”

Thermometer
An ASTM No. 96C, NIST traceable, partial-immersion thermometer is used tomeasure oven temperature. These thermometers are placed in the opening at the
top of the oven with the immersion mark aligned with the oven ceiling. See
Figure 1-10. “Partial Immersion Thermometers.” For 72-hour, air-oven testing,laboratories may consider using thermometers with charting capabilities in
addition to the partial immersion thermometers to ensure the oven temperature
is consistent during the entire test. Partial-immersion or digital Thermometers
are also used to determine grain sample temperatures.

Figure 1-10. Partial-Immersion Thermometers.

Top-loading Balance
A top loading balance is used in grain sample preparation to weigh the required
amount of grain that is placed in the moisture dishes for air-oven testing. Thebalance must be accurate to 0.01 g. Examples of these balances are shown in
Figure 1-11. “Top Loading Balances.”

Figure 1-11. Top-loading Balances.

GeneralGrain Handling
When not required for immediate use, grain samples must remain in sealed bags or jars
under refrigeration at a temperature of 1 °C to 3 °C (34 °F to 37 °F). Prior to use, samples
must be allowed to equilibrate to room temperature ± 10 degrees of the ambient
temperature before sample bags or jars are opened. This is necessary to prevent
condensation which will have adverse effects on subsequent tests.

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Air-Oven Test Procedures
The laboratory must follow the air-oven test procedures in the USDA, GIPSA Technical
Services Division, air-oven moisture laboratory working instructions. These procedures
are included in training material provided by NIST, OWM or a copy may be obtained
directly from:
USDA, GIPSA, FGIS
National Grain Center
10383 N Ambassador Drive
Kansas City, MO 64153

Telephone: 816-891-0401
Fax: 816-872-1258

See Appendix B for additional information concerning air-oven test procedures.

Test Weight per Bushel Procedures
To determine the reference test weight per bushel value of grains, the laboratory must
follow the test weight procedures in Appendix C of this reference manual. This procedure
may also be downloaded from NIST, OWM website at www.nist.gov/pml/wmd/. Selectthe link titled “Weights and Measures Connection Newsletter,” then select the link titled“Newsletter Article Archives,” then select “Grain Moisture Meters/NIR,” then look forSeries Number C-012 “Determining Reference Test Weight per Bushel Value of Grains.”

Parent Grain Sample Preparation
Grains used to test commercial grain moisture meters are collected from field locations within aweights and measures jurisdiction and brought to the jurisdiction’s laboratory. In the laboratory, thegrains are cleaned and stored in appropriate containers in preparation for testing. This section
describes collection, cleaning, and proper storage of this grain.

Collection
Parent samples of “naturally moist grains” are typically collected at harvest time for eachgrain that is typically grown and traded in a state’s jurisdiction. Low moisture and highmoisture grain samples will be needed to test commercial grain moisture meters. As such,an attempt should be made to obtain samples covering a range of moistures for each grain
type. (e.g., 13.0 % and 16.0 % moisture wheat samples). Low and high moisture ranges
will vary per jurisdiction. Sufficient grain should be collected to provide enough samples
needed to test all of the grain moisture meters in the jurisdiction. See Section 9, Example 1.
“Preparing Samples for One Inspector to Conduct Field Testing” for guidance on theamount of grain to collect.

Cleaning
The parent samples are cleaned immediately upon receipt using dockage testers andautomatic and/or hand sieves or equivalent grain or seed cleaning devices. Additional handpicking of the sample may be required to remove foreign material. Cleaned samples should
consist of whole, sound seeds or kernels and be free of spoilage, dust, dirt, and foreignmaterial. Follow the grain handling procedures in Part 1, Section 5.1. “Grain Handling”
of this manual when cleaning the grain.

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Storage and LabelingAfter samples are cleaned, mix each parent sample using a divider or other method toensure that any portion of the parent grain sample is representative of the entire sample.
After mixing, seal the grain in appropriate gallon storage containers (barrier, anti-static
plastic bags or glass jars). See Figure 1-12. “Sample Storage-Glass Gallon Jars and Barrier,Anti-static Plastic Bags.” The samples are labeled with grain type, date of collection,collection point, and approximate moisture content and are assigned and labeled with aunique identification number for each grain sample. A number of jars or bags may be partof the parent sample so the unique identification number should include a sequential
number following the identification number. For example, a unique ID number is 0714.
Each jar or bag of grain with this ID number can be given the sequential number as follows
0714-1, 0714-2, 0714-3, etc. denoting this is a part of the parent sample 0714. Place thesesamples in refrigeration for 72 hours at 2 °C to 4 °C (35 °F to 40 °F) prior to extracting
working samples for testing to allow the moisture of the sample within the container toequilibrate.

Figure 1-12. Sample Storage – Glass Gallon Jars and Barrier, Anti-static Gallon Plastic Bags.

Working Sample Preparation
Working samples are taken from a “parent sample” of grain and used to create a set of official grain
samples. Since each gallon in the parent sample is representative of the entire parent lot, the first
gallon working sample that is tested provides the information needed to determine if working
samples within the parent sample lot can be used to create official grain samples. For example,
whether or not the parent sample meets laboratory standard meter moisture and reference air-ovenmoisture bias.

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Laboratory Conditions
When preparing and testing working samples, the laboratory must be maintained under thefollowing conditions:Temperature:
68 °F to 73 °F (20 °C to 23 ° C)

Maximum Rate of Change:
1.8 °F/hr (1.0 °C/hr)

Relative Humidity:
40 % to 60 %Preparing Working Samples for Testing
When you have collected enough grain to make testing practical, which is typically when
you have enough grain samples to test reference air-oven moisture and laboratory standard
meter moisture within a workday, remove grain samples that have been refrigerated for atleast 72 hours at the conditions specified in Part 1, Section 6.3. “Storage and Labeling.”
Remove a one-gallon sample from each parent sample to serve as your working sample.
Allow the sample to reach to within 10 degrees of the ambient temperature. Thoroughly
mix each working sample by running it through a divider three times.

Testing the Working Sample
Each one-gallon working sample will be tested to determine a laboratory standard meter moisture;reference air-oven moisture; laboratory standard meter moisture vs. reference air-oven moisture bias;
and test weight. Keep any remaining grain from the working sample in its original container (i.e.,barrier, antistatic plastic bag or glass jar) during testing.

Laboratory Standard Meter Moisture Measurements
Determine the laboratory standard meter moisture of a sample from the one-gallon working
sample selected for testing. Following meter manufacturers’ instructions, place anappropriate amount of the working sample in each of the laboratory standard meters. Testeach gallon working sample three times on each laboratory standard meter and calculate
an average laboratory standard meter moisture value for each gallon working sample andrecord the results. Then return the remaining sample used to obtain a laboratory metermoisture to its appropriate container.

Reference Air-Oven Moisture Measurements
Upon completion of the laboratory standard meter moisture measurement described inPart 1, Section 8.1. “Laboratory Meter Moisture Measurements,” immediately withdraw
from each of the one-gallon working samples an amount sufficient to determine thereference air-oven moisture, as specified in the USDA, GIPSA air-oven test procedures.
Record the average of three reference air-oven moisture results for each one-gallon
working sample. See Appendix B “Grain Moisture Air-Oven Reference Methods in the
United States” for additional information on the USDA GIPSA air-oven test procedures.

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Note: Keep ground grain samples tightly sealed and limit the time between grinding andweighing the grain samples to reduce error in reference air-oven moisture results.

Laboratory Standard Meter Moisture vs. Reference Air-Oven Moisture Bias
Calculate the bias between the average laboratory standard meter moisture measurement
and the average reference air-oven moisture measurement for each one-gallon working
sample. Record the results and retain this information in your laboratory records. Markthe containers of all the working samples in the parent lot that meet the bias requirements
in Part 1, Section 8.4. “Requirements for Laboratory Standard Meter Moisture vs.
Reference Air-Oven Moisture Bias.” For example, an “A” that represents “Accepted” canbe mark on the containers. Working samples and parent samples from which they weredivided, which do not meet the criteria in Part 1, Section 8.4. “Requirements for Laboratory
Standard Meter Moisture vs. Reference Air-Oven Moisture Bias” for all the laboratory
standard meters may be discarded and record that the samples were discarded.
Note: The laboratory standard meter moisture and reference air-oven moisture bias is only
determined on a one-gallon working sample from each parent sample. The result of thistest applies to the entire parent sample.

Requirement for Laboratory Standard Meter Moisture vs. Reference AirOven Moisture Bias
For any working sample, the difference between the average standard laboratory metermoisture and the average reference air-oven moisture result shall not exceed plus or minus
0.3 % moisture. This bias is applied to each laboratory standard meter.
Note: As meter technology improves (for example, the use of high frequency dielectricmoisture meters with uniform algorithms across meters), variations between grain moisture
meters will likely improve; however, grain variations may still influence meter moisturemeasurements.

Determine the Test Weight
While the reference air-oven testing is conducted, the working samples can be tested toobtain the test weight values. Test weight per bushel values are determined by following
the procedures in Appendix C. “Determining Reference Test Weight per Bushel Value ofGrains.” An average of 10 repeat test weight per bushel measurements is used to determine
the test weight value for a working sample.

Records
Maintaining appropriate laboratory records provides an inventory of the grains andmoisture ranges of those grains. This aids the laboratory in making any necessary changes
to sample collection. Maintaining records of field data provides evidence of the integrityof the field samples. Records for all parent and working samples and field samples must
be maintained in the laboratory. At a minimum, records must include:

Parent and Working Samples
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b. identification number;c. meter moisture result (the measurement of a one-gallon working sample applies
to the entire parent sample lot);d. air-oven moisture results;
e. meter moisture and air-oven moisture bias result (the measurement of a onegallon working sample applies to the entire parent sample lot);f.

test weight results; andg. whether or not a parent sample lot was discarded after testing.

Field Samples
a. identification number of field samples issued;b. date field samples were issued;c. date field samples returned;
d. retested oven results; ande. number of times field samples were warmed, opened, and dropped.

Selecting and Preparing Official Grain Samples
Make official grain samples from the one-gallon working samples that have an air-oven moisture vs.
meter moisture bias that meets the requirements of Part 1, Section 8.4. “Requirements for Laboratory
Meter Moisture vs. Air-Oven Moisture Bias” and were tested and have an assigned value for airoven moisture and test weight. The reference air-oven moisture and laboratory standard metermoisture bias is a one-time test and the values are assigned to all working samples within a parent
sample based on the test results of a one-gallon working sample. But, it is necessary to test eachgallon working sample within a parent sample for air-oven and test weight per bushel to avoid
changes in moistures within the individual gallon working samples. These tests must be performed
just prior to issuing the grain samples for field testing.

Official Grain Samples for Field Testing
Official grain samples used for field testing must be the grains that are representative of
the grain types and moisture ranges normally traded in a jurisdiction. A one-gallon
working sample of high moisture grain and a one-gallon working sample of the same grain
type with a low moisture are selected for each grain type to prepare official grain samples.
Each gallon working sample is divided into three or more official grain samples with a highmoisture content and three or more official grain samples with a low moisture content foreach grain type. (See Example 1. “Preparing Samples for One Inspector to Conduct Field
Testing.”)
Samples are prepared by following these Steps:

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If the working samples are mixed and tested in accordance with Part 1, Section 8 “Testing
the Working Sample,” on the same day that official grain samples are prepared, follow Part
1, Section 9.1, Step c, below.
If the working samples were recently mixed and tested in accordance with Part 1,
Section 8 “Testing the working sample” and then refrigerated, allow the sample to reach
within 10 degrees of the ambient temperature, then follow Part 1, Section 9.1. “Official
Grain Samples for Field Testing,” Steps a and c below.
If there has been a significant lapse of time since a refrigerated working sample has beentested in accordance with Part 1, Section 8 “Testing the Working Sample,” repeat test inPart 1, Section 8.2. “Reference Air-Oven Moisture Measurements” and Section 8.5.
“Determine the Test Weight” then follow Part 1, Section 9.1. “Official Grain Samples for
Field Testing,” Step c, below.
If it is the first time a working sample is tested, allow the sample to reach within 10 degreesof the ambient temperature, then follow Part 1, Section 9.1. “Official Grain Samples for
Field Testing,” Steps a to c below.
a. Thoroughly mix each gallon working sample for each grain type and moisture content
by running it through a divider three times.
b. Test the working sample in accordance with Part 1, Section 8.1. “Laboratory Standard
Meter Moisture Measurements” to 8.5. “Determine the Test Weight” of this manual.
c. Extract three grain samples of sufficient size from each grain type and moisture level ofeach working sample. Place the official grain samples in the appropriate containers (SeePart 2, Section 4.1.9. “Official Grain Samples.”) and keep any additional portions for lab
verification. Refrigerate the samples until distributed to field inspection staff. (SeeExample 1. “Preparing Samples for One Inspector to Conduct Field Testing.”)
Example 1. Preparing Official Grain Samples for One Inspector to Conduct Field Testing.
Working Grain
Samples (Numberof Gallons)

Grain Type

Moisture Content

Field Samples –Number of Pint or
Quart, Jars or Bags

1

Corn

18.3 % (High)

3

1

Corn

15.0 % (Low)

3

1

Wheat

16.0 % (High)

3

1

Wheat

13.5 % (Low)3

1

Soybeans

16.2 % (High)

3

1

Soybeans

14.0 % (Low)3

Official grain samples must be of sufficient size for meter testing; this is typically one pint
or one quart. Different meter models may require different sample sizes. Place the official
grain samples in glass jars or poly bags and mark the official grain samples with thefollowing information:a. working sample ID number;

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b. grain type;c. date the official grain sample was prepared;d. reference moisture value (as determined by the USDA GIPSA Air-Oven Method);e. test weight value; andf.

space for the inspector to record number of times the sample was warmed, opened, anddropped.
Next, return the field samples and the remaining portion of the parent sample torefrigeration until needed by field inspectors.

Time Lapse
To prevent moisture loss and/or deterioration of the official grain samples that may occur
over time, official grain samples should be issued to field inspectors as soon as practicalafter testing and preparation. If substantial time has elapsed from the initial determinationof moisture and test weight measurements or there are concerns that these values havechanged, another working sample from the parent sample should be tested to obtain acurrent moisture and test weight value and then used to prepare another set of official grain
samples, prior to issuing the official grain samples for use in field testing.

Retesting and Reusing Official Grain Samples
Official grain samples are used for a limited number of drops when testing grain moisture meters as
specified in Part 2, Section 7.1.4. “Minimum Test and Maximum Number of Drops,” Paragraph d.
After a grain sample is used for the specified maximum number of drops, the samples must be
returned to the laboratory for retesting and/or reuse.

Retesting Samples
In the event that problems or concerns arise with any field tests conducted with a given
official grain sample, perform an air-oven test on those official grain samples returned to
the laboratory. This will provide evidence of whether or not the official grain sample
moisture was maintained during field testing.
Periodically retest official grain samples that are returned to the laboratory after use tomonitor and maintain a check on the system. If retesting reveals that moisture values arechanging significantly, this may indicate a need to change field handling procedures;
reduce the permitted number of drops; or take after actions to ensure that grain samples aremaintaining their stability during field testing.
Keep a record of all retest results and action taken to resolve issues resulting from retests.

Reusing Samples
Official grain samples may be reused if they are returned to the laboratory in goodcondition. To reuse these samples, recombine official grain samples of the same type andidentification number in a gallon container and mix the grain. Next, place the sample in13Part 1: Laboratory Grain Sample Preparation and Testing_______________________________________________________________________________________________
This publication is available free of charge from: https://doi.org.10.6028.NIST.HB.159-2017refrigeration as specified in Laboratory Grain Sample Preparation and Testing, Part 1,
Section 6.3. “Storage and Labeling.” After 72 hours, the working sample can be tested forreference air-oven moisture and test weight and then reissued as official grain samples.

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PART 2: Field Inspection and Evaluation
EPO No. 50 (2017)
NIST Examination Procedure Outline (EPO) for Grain Moisture Meters
ScopePart 2 of this Handbook provides technical guidelines for the field evaluation of grain moisture
meters and multi-constituent grain analyzers that measure moisture in accordance with NIST
Handbook 44, Section 5.56.(a) “Grain Moisture Meters” for field testing using air-oven reference
method transfer standards. The requirements of NIST Handbook 44 are grouped into the following
sections as outlined in NIST Examination Procedure Outlines:
•
•
•
•
•
•
•
•

SafetyDefinitions
Equipment
Inspection
Pretest Determination
Test notes
Test
Post Tasks

General Guidance on Safety
Many policies and regulations will vary among jurisdictions. It is essential that the inspector orservice persons be aware of all safety regulations and policies in place at the inspection site and topractice their employers’ safety policies. The safety reminders included in this manual containgeneral guidelines useful in alerting inspectors and service persons to the importance of taking
adequate precautions to avoid personal injuries. These guidelines can only be effective in improving
safety when coupled with training in hazard recognition and controls.
Always be familiar with emergency procedures BEFORE beginning an inspection. After an
emergency has developed, crucial time can be lost if emergency procedures are not known. Be
familiar with the procedures to follow in the event of an equipment malfunction or the developmentof a dangerous situation with the equipment or in the vicinity of the inspection site when operating
specialized testing equipment.
Be familiar with the nature of any product being dispensed by a device or being used in or near theinspection area. Know the emergency procedures to be followed when a spill of a hazardous producthas occurred or a person has been exposed to the product. Knowledge of emergency procedures andrelated information should include the correct selection and use of fire extinguishers, the location of
emergency shut-offs, and evacuation procedures.
Keep a list of emergency phone numbers handy at all times in a notebook or on a card. Examples ofnumbers to keep are the local fire department, emergency medical facility, and other appropriate
public safety agencies. Prior to inspection and evaluation of a moisture meter carefully check thesite for safety hazards and take appropriate precautions including:15

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•
•
•
•
•
•
•
•
•
•
•
•
•
•

Inspect all electrical cords and connections for damage to prevent electrical shock.
Learn the nature of hazardous products used at or near the inspection site.
Know the emergency evacuation routes at each inspection site.
Use personal protection equipment appropriate for the site and for the particular job.
Wear safety shoes to prevent possible injury from falling weights, grain sample containers, andother equipment and to prevent slipping on wet or slick surfaces.
Wear proper breathing apparatus, if necessary, for protection from dust and other airborne
contaminants.
Wear a hard hat for protection from overhead hazards, when appropriate.
Be sure that a first aid kit is available and that the kit is appropriate for the type of activity.
Practice safe and proper lifting techniques.
Use a lid opener if grain sample container lids are too tight to be removed comfortably by hand.
Do not strain. Firmly grasp the container with good hand and wrist positioning.
Dry condensation from the outside of the grain sample container to prevent slippage andpossible breakage of container and/or injury to feet and toes.
Watch for chips, cracks, or breakage of glass containers. If found, dispose of the container
properly to prevent injury to the inspector. A damaged container may also affect the integrityof the grain sample moisture.
Be sure all equipment being transported by the inspector or service technician is properly
secured in the vehicle.
Practice defensive driving when traveling between sites.

Definitions
audit trail
An electronic count and/or information record of changes to the values of the calibrationor configuration parameters of a device.
[NIST Handbook 44]

cereal grain and oil seeds
Agricultural commodities including, but not limited to, corn, wheat, oats, barley, flax, rice,sorghum, soybeans, peanuts, dry beans, safflower, sunflower, fescue seed, etc.
[NIST Handbook 44]

constituent
A component of a grain, such as protein, oil, starch, or moisture that a grain analyzer iscapable of measuring.

back-up sample.
An official grain sample used only when a change is suspected in the moisture content of
an official grain sample that will affect the test results.

drop
Each time a grain sample is passed through the measurement cycle of a moisture meter.

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grain calibration
A quantitative standardization established by a meter manufacturer for a specific grain andmeter type.

grain moisture meter
Any device indicating either directly or through conversion tables and/or correction tables
the moisture content of cereal grains and oil seeds. Also termed “moisture meter.”[NIST Handbook 44]
Note: This Handbook is primarily oriented toward the preparation and use of samples fortesting GMMs covered under NIST Handbook 44, Section 5.56.(a). However, Part 1 andsome sections of Part 2 of this handbook may be used to develop official grain samples foruse in evaluating meters that require conversion and correction tables to determine grainmoisture content. Part 2, Sections 5.1. “Indicating and Recording Elements” to 9. Post Test
Tasks” are requirements from NIST Handbook 44, Code 5.56.(a) and are not applicable tometers that require conversion and correction tables to determine grain moisture content.

kind of grain
Corn as distinguished from soybeans as distinguished from wheat, etc.
[NIST Handbook 44]

moisture content (wet basis)
The mass of water in a grain or seed sample (determined by the reference method) divided
by the mass of the grain or seed sample expressed as a percentage (%).
[NIST Handbook 44]

openedEach time grain is removed from and returned to the sample storage container, it has been
“opened” once.
Note: The time required to change lids to enable thermometer insertion should be so short
as not to constitute an opening.

official grain samples
Grain or seed used by the official as the official transfer standard from the reference
standard method to test the accuracy and precision of grain moisture meters.
[NIST Handbook 44]

grain sample
That portion of grain or seed taken from a bulk quantity of grain or seed to be bought orsold and used to determine the moisture content of the bulk.
[NIST Handbook 44]

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security seal
A uniquely identifiable physical seal, such as a lead-and-wire seal or other type of locking
seal; a pressure-sensitive seal sufficiently permanent to reveal its removal; or similar
apparatus attached to a weighing or measuring device for protection against or indicationof access to adjustment.
[NIST Handbook 44]

specification
A requirement usually dealing with the design, construction, or marking of a weighing or
measuring device. Specifications are directed primarily to the manufacturers of devices.
[NIST Handbook 44]

test site
A location housing a grain moisture meter or accessory device, which is subject to official
inspection and testing.

test weight
A measurement to determine the weight per volume (bulk density) of a particular lot ofgrain. For example, kg/hL or lb/bu.

tolerance
A value fixing the limit of allowable error or departure from true performance or value.
[NIST Handbook 44]

warmedEach time a sample of grain is brought to within 10 ºF of the ambient temperature, it has
been “warmed.”

Field Equipment and Grain Samples
A brief description of the equipment needed for the field evaluation and testing of grain moisture
meters are included in this section. Pictures (figures) are included to provide examples of equipmentused in some states. See Figure 2-1. “Apparatus, Equipment and Documents for Field Testing ofGrain Moisture Meters.”

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Figure 2-1. Apparatus, Equipment, and Documents for Field Testing of Grain Moisture Meters.

Apparatus and Equipment
Breathing Apparatus
A mask or other appropriate apparatus used to prevent excessive inhalation ofdust or other contaminants.

Thermometer
Thermometers can be digital or liquid-in-glass and must meet NIST
Handbook 105-6, “Specifications and Tolerances for Thermometers,”
requirements. These thermometers are used to monitor the grain sample temperatures.
(see Figure 2-2. “Examples of Thermometers”). A partial immersion thermometer isa thermometer that is designed to be used partially immersed in fluid or producttypically to a designated immersion mark on the thermometer. If using a partialimmersion thermometer it should be placed into the grain sample to thesubmersion line on the thermometer.

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Figure 2-2. Examples ofThermometers.

Container
A container of sufficient size may be used to safely carry accessory equipment.

Cooler
A cooler is needed for the sample jars of grain after removing the jars from therefrigerator. This will allow them to stabilize to ambient temperature andminimize exposure to temperature extremes and fluctuations. Ice must not be
used in the cooler since it can cause condensation on sample jars and potentiallyaffect the moisture content of the grain and stability of the sample. The cooler
must be of adequate size to accommodate the number of samples that will be
used for testing. See Figure 2-1. “Apparatus, Equipment, and Documents Field
testing of Grain Moisture Meters.”

Fire Extinguisher
Know the proper use and selection of fire extinguishers for a given application.
Contact your local fire department for current information and training.

First Aid Kit
An appropriate first aid kit should be maintained in your vehicle. Consideration
should be given to the type of work that the inspector, or service person typically
performs and the types of hazards typically encountered in these types ofactivities. Items in addition to those contained in a basic first aid kit may need
to be added to address the potential hazards which may be encountered by the
person who will be most likely to use the first aid kit. Check with your local
OSHA office or with your departmental safety officer for input on the items to
be included in each kit.

Portable Refrigerator
Portable refrigerators are used to keep the samples cold before and after testing
to help maintain grain sample stability and condition. A connection to an energy
source is needed to maintain cold conditions. For example, some portablerefrigerators may be attached to the cigarette lighter in a motor vehicle. See an
example in Figure 2-3. “Portable Refrigerator.”

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Figure 2-3. Portable Refrigerator (front and side views).

Grain Sample Racks
Racks are used to carry standard grain samples from meter to meter during
testing.

Figure 2-4. Grain Sample Rack.

Figure 2-5. Pint Grain Samples.

Figure 2-6. Labeled Quart and Pint Grain
Samples.

Official Grain Samples
At least three samples per grain type and moisture level (one high and one low
moisture grain sample) are used to test meters; jurisdictions may choose to use
additional official grain samples. The official grain samples must be stored inglass jars with lids or anti-static plastic bags. For additional details on
preparation and handling of grain samples, see Part 1, Section 9.1. “Official
Grain Samples for Field Testing” and Part 2, Section 7.1.2. “Official Grain
Samples for Field Testing.” Examples of storage containers are shown in21Part 2: Field Inspection and Evaluation_______________________________________________________________________________________________
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Figures 2-5. “Pint Grain Samples” and 2-6. “Labeled Quart and Pint Grain
Samples.”

Personal Protection Equipment (PPE)The appropriate PPE for testing grain moisture meters may include goggles orsafety glasses, hardhats, safety shoes, and other equipment deemed necessary by
your organization to complete the tests.

Two-inch Aluminum Angle Gage
Use a ruler or other aid to verify the distance between the kettle and funnel heightof the test weight per bushel equipment. A two-inch aluminum angle gage that
rests on top of the kettle and maintains a perpendicular orientation to the topedge of the funnel is recommended as an aid in making this measurement. See
Figure 2-7. “Aluminum Angle Gage” for an example of a gage used to measure
the distance between the kettle and funnel height.

Figure 2-7. Aluminum Angle Gage.

Calculator
A calculator may be necessary to assist with error and other test calculations.

Safety Shoes
Safety shoes to prevent possible injury from falling weights or equipment andalso to provide protection from slippage.

Security Seal
A uniquely identifiable physical seal, such as a lead-and-wire seal or other typeof locking seal, a pressure-sensitive seal sufficiently permanent to reveal its
removal, or similar apparatuses attached to a weighing or measuring device forprotection against or indication of access to adjustment.
[NIST Handbook 44]

Approval Tags and Stickers
Tags or stickers applied to grain moisture meters to indicate approval or rejectionof the meter and may include the date of inspection. Devices may be tagged
and/or removed from service due to large testing errors that exceed the allowable
tolerances.

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Inspection
The most current requirements of NIST Handbook 44, Section 5.56.(a) must be applied wheninspecting grain moisture meters in accordance with this manual. NIST Handbook 44,
Section 5.56.(a) applies to all NTEP meters and meters manufactured or placed into service afterJanuary 1, 1998. Sections 5.1. “General Consideration,” to 9. “Post Test Tasks,” are therequirements of NIST Handbook 44, Section 5.56.(a) used to inspect and test grain moisture meters
using air-oven transfer standards.

Safety Reminders
Location.
•

Carefully examine the inspection site prior to beginning an inspection and testing procedure.
Look for potentially dangerous situations such as:
o wet areas which may be slippery (see also Wet/Slick Conditions);o adjacent activities which may contribute a potential hazard to the inspection;o obstructions in the area which may prove to be safety hazards (e.g., objects on the groundwhich the inspector might trip over, objects in the path of the inspector to and from thedevice being tested, exits blocked by test equipment or vehicles, etc. – see also
Obstructions);o pedestrian or vehicle traffic (see also Traffic),o steep or narrow stairways;
o overhead hazards (e.g., feed bins, loading rack equipment, low-hanging beams in feedmills and warehouses, overhead activities, low doorways, etc. – see also Overhead
Hazards);o lack of or defective handrails; ando loose or exposed wiring (see also Electrical Hazards). Use great care when movingaround and working in areas in which these potential hazards are present.
o When using flammable products (e.g., testing metering devices), note the location of thefire extinguisher, emergency shut-offs, etc. prior to beginning the inspection.

Electrical Hazard.
•••

Be particularly aware of potential electrical hazards in or near the inspection site when
testing electronic devices or working in the vicinity of electrical equipment.
Loose or exposed wiring and a frayed or worn electrical cord should be brought to theattention of management at the inspection site.
Avoid standing on wet surfaces unless the electrical equipment is properly insulated andgrounded.

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Safety Reminders (continued)
Obstructions.
•

Care should be taken to avoid injury from obstructions in the work area during the course of aninspection. Obstructions which might prove to be safety hazards include:
o objects on the ground which the inspector might trip over;
o objects in the path of the inspector to and from the device being tested;o steep or narrow stairways; ando exits blocked by test equipment or vehicles, etc.

Overhead Hazards.
••

Note any overhead hazards such as feed bins, loading rack equipment, low-hanging beams in feedmills and warehouses, activities overhead, and low doorways prior to the inspection.
Take precautions, such as wearing a hardhat, to avoid potential injuries as the situation dictates.

Wet/Slick Conditions.
••••

Caution should be exercised when working in wet, slippery, or icy conditions to avoid slipping or
possible injury from electrical sources.
Shoes with non-skid soles should be worn to provide adequate traction to prevent slipping.
Be sure all equipment being transported by the inspector or service technician is properly
secured in the vehicle.
Practice defensive driving when traveling between sites.

General Consideration
This section includes NIST Handbook 44 General Codes requirements used to determine
if the device is suitable for its use; installed appropriately; and its markings are readily
observable and understood.

Suitability, Installation, and Visibility of Identification[Code References: NIST Handbook 44, Section 1.10. General Code, G-UR.1.1.,
G-UR.1.2., G-UR.2.1., UR.2. and G-UR.2.1.1.]
Commercial equipment shall be:a. suitable for the service in which it is used with respect to the elements of its design
including but not limited to its weighing capacity (for weighing devices), its
computing capability (for computing devices), its rate of flow (for liquidmeasuring devices), the character, number, size, and location of its indicating or
recording elements, and the value of its smallest unit and unit prices. ....................
.................................................................................................... G-UR.1.1., UR.2.

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Guidance:□ Current calibrations for a GMM are located in its Certificate of Conformance.
Verify that the moisture meter has current grain calibrations for all grains being
traded at the location.
b. suitable for the environment in which it is used, including, but not limited to, theeffects of wind, weather, and RFI. .......................................................... G-UR.1.2.
Guidance:□ Grain Moisture meters have specified operating conditions. Verify that a moisture
meter is being used in accordance with the temperature ranges specified in the
NTEP CC.
□ If there are sources of RFI near the moisture meter, look for any fluctuations inreading results during testing that affect the measurements.
c. a device shall be installed in accordance with the manufacturer’s instructions,
including any instructions marked on the device. A device installed in a fixedlocation shall be installed so that neither its operation nor its performance will be
adversely affected by any characteristic of the foundation, supports, or any otherdetail of the installation........................................................................... G-UR.2.1.
Guidance:□ Review the manufacturer’s operating instructions to verify that the moisture meter
installation is appropriate.
d. equipment shall be installed in such a manner that all required markings are readily
observable. ......................................................................................... G-UR.2.1.1.
Guidance:□ Ensure that you are able to view the marking such as serial number, model number
and other identifiable markings needed to operate or identify the grain moisture
meter.

Level[Code References: NIST Handbook 44, Section 5.56.(a) GMM, S.2.3, UR.3.8.]
A meter shall be equipped with a level indicator and leveling adjustments if its
performance is changed by an amount greater than the applicable tolerance whenthe meter is moved from a level position to a position that is out of level in any
upright direction by up to 5 % (approximately three degrees). The levelindicating means shall be readable without removing any meter parts requiring atool. .......................................................................................................... S.2.3.
a. If equipped with a level indicator, a meter shall be maintained in a level condition.
..................................................................................................................... UR.3.8.
Guidance:□ Figure 2-8. “A Level Indicating Means Showing an In-level Condition” shows one
type of level indicating means (a level bubble) on a grain moisture meter. Other

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level indicating means may be available on grain moisture meters. Using the levelindicating means on a meter, determine that the device is in level prior to testing.

□ If no level indicating means is available, place shims under the meter to raise it toa position out of level in any upright direction 5 % or approximately three degrees,
then verify that the performance has not changed in the non-level condition.

Figure 2-8. A Level Indicating Means Showing an
In-level Condition.

Position of Equipment[Code Reference: NIST Handbook 44, Section 1.10. General Code, G-UR.3.3.,
Section 5.56(a) UR.3.7]
a. A device or system equipped with a primary indicating element and used in direct
sales, except for prescription scales, shall be positioned so that its indications may
be accurately read and the weighing or measuring operation may be observed fromsome reasonable “customer” and “operator” position. The permissible distance
between the equipment and a reasonable customer and operator position shall be
determined in each case upon the basis of the individual circumstances,
particularly the size and character of the indicating element. ... G-UR.3.3., UR.3.7.
Guidance:□ When grain is traded, grain samples are taken from truckloads of grain to
determine its moisture content along with other dockage factors. Moisture testingis typically performed in a separate location. At this location verify that a customer
is able to read the indications of the moisture meter and observe the measurement
process. Also see Section 5.3.2. “Interchange or Reversal of Parts” below or NIST
Handbook 44, Section 5.56.(a), S.1.1.(b) for minimum height requirements of thedigits used to display moisture content.

Location and Access[Code Reference: NIST Handbook 44, Section 1.10. General Code, G-UR.2.3.]
a. A device shall be located, or such facilities for normal access thereto shall be
provided to permit:
1. the inspecting and testing of the device;
2. the inspecting and applying security seals to the device; and26

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3. readily bringing the testing equipment of the weights and measures official tothe device by customary means and in the amount and size deemed necessary
by such official for the proper conduct of the test.
b. Otherwise, it shall be the responsibility of the device owner or operator to supply
such special facilities, including such labor as may be needed to inspect, test, andseal the device, and to transport the testing equipment to and from the device, as
required by the weights and measures official. ....................................... G-UR.2.3.
Guidance:□ Grain moisture meters may be located in areas where it would be difficult to transport
the official grain samples and other equipment necessary for testing. In these
instances, the device owner must provide access for the inspector and his or her
equipment so that testing can be performed.

Assistance[Code Reference: NIST Handbook 44, Section 1.10. General Code, G-UR.4.4.]
If the design, construction, or location of any device is such as to require a testingprocedure involving special equipment or accessories or an abnormal amount oflabor, such equipment, accessories, and labor shall be supplied by the owner or
operator of the device as required by the weights and measuresofficial. ..............................................................................................G-UR.4.4.
Guidance:□ If the design, construction, or location of a grain moisture meter requires special
equipment to test the device, the device owner is responsible for providing theequipment needed to test the meter. For example, if the meter is located in a locked
room, the device owner or operator must unlock the location or provide the inspector
with keys to the room where the moisture meter is located. Likewise, if transporting
the official samples requires an abnormal amount of labor or pose significant
difficulty, the inspector can require assistance in transporting the equipment needed
for the inspection.

Use and Maintenance[Code Reference: NIST Handbook 44, Section 1.10. General Code, G-UR.4.1.,
G-UR.4.2., G-UR.4. and Section 5.56.(a) GMM, UR.3.1.]
a. All equipment in service and all mechanisms and devices attached thereto or usedin connection therewith shall be continuously maintained in proper operating
condition throughout the period of such service. Equipment in service at a single
place of business shall not be considered “maintained in a proper operating
condition” if predominately, equipment of all types or applications are found to
be in error in a direction favorable to the device user; or predominantly,
equipment of the same type or application is found to be in error in a direction
favorable to the device user. .................................................................. G-UR.4.1.
b. Unstable indications or other abnormal equipment performance observed during
operation shall be corrected and, if necessary, brought to the attention ofcompetent service personnel. ................................................................ G-UR.4.2.

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c. Weighing elements and measuring elements that are adjustable shall be adjusted
only to correct those conditions that such elements are designed to control andshall not be adjusted to compensate for defective or abnormal installation oraccessories or for badly worn or otherwise defective parts of the assembly. Any
faulty installation conditions shall be corrected, and any defective parts shall berenewed or suitably repaired, before adjustments are undertaken. Wheneverequipment is adjusted, the adjustments shall be so made as to bring performanceerrors as close as practicable to zero value............................................. G-UR.4.3
Guidance:□ All equipment must be maintained in proper operating condition.

□ Since calibrations for all NTEP meters are based on a national sample set and/or auniform algorithm, the issue of setting equipment predominately favorable to thedevice owner may be more difficult to identify for grain moisture meters than forother devices such as retail motor fuel dispensers. However, if more than one typeof meter is available, these meters should not be used to take advantage of theindividual meter accuracy, such as buying grain on one type of meter where theaccuracy of the meter is in favor of the device owner and selling grain on anothermeter type that would also benefit the device owner.

□ Adjustment shall not be made to compensate for malfunctions of the meter. These
malfunctions and faulty operations such as inappropriate blinking of indications
that may cause difficulty in obtaining a measurement or cause an inaccurate
reading must be corrected. Also any defective parts must be replaced.

Determination of Quantity and Temperaturea. The moisture meter system shall not require the operator to judge the precise
volume or weight and temperature needed to make an accurate moisturedetermination. External grinding, weighing, and temperature measurement
operations are not permitted. In addition, if the meter is capable of measuring test
weight per bushel, determination of sample volume and weight for thismeasurement shall be fully automatic and means shall be provided to ensure thatmeasurements of test weight per volume are not allowed to be displayed or printed
when an insufficient sample volume is available to provide an accurate
measurement. .................................................................................................. S.2.6.
[Nonretroactive as of January 1, 2004]
Guidance:□ Some non-NTEP GMM moisture meters require a specific weight of grain and/or
external temperature measurements (to apply a temperature correction) to determine
the moisture content of grain. In order to eliminate some of the potential user errors
associated with making these external measurements or grinding a grain, NTEP
moisture meters must make these measurements automatically if they are needed.
Verify that the meter does not require external measurements of temperature or
weight or require the use of correction charts or tables to obtain a moisturemeasurement.

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Operating Instructions
a. Operating instructions are readily available to the user, service technician, andweights and measures official to include a list of accessory equipment and thekinds of grain or seed to be measured with the moisture meter. .................. UR.3.1.
Guidance:□ Some jurisdictions prepare a notebook which includes operating instructions alongwith the grains traded on meters in their jurisdiction. Although some jurisdictions
may distribute this information, device owners are responsible for making
information about their specific meters available to the inspector.

Indicating and Recording Elements“Indicating and Recording Elements” refer to those NIST Handbook 44 code requirementsthat address requirements for how a grain moisture meter shall indicate and record themeasurement results. It also includes the minimum abbreviations for the identification of
the grain types on a moisture meter.

General[Code References: NIST Handbook 44, Section 1.10. General Code, G.S.5.1.]
All weighing and measuring devices shall be provided with indicating or
recording elements appropriate in design and adequate in amount. Primary
indications and recorded representations shall be clear, definite, accurate, andeasily read under any conditions of normal operation of the device. ...... G-S.5.1.
Guidance:□ The indications and recorded information on or from a grain moisture meter
include the grain type, the percent moisture, weight per bushel, and the constituent
label (moisture, protein, etc.) as appropriate, and may include other transaction
information. This information must be clear, accurate, and easily read.

Design[Code References: NIST Handbook 44, Section 5.56.(a) GMM, S.1.1.(a)-(g), S.1.2.,
Table S.1.2., S.1.3., S.1.5.]
a. Meters shall be equipped with a digital indicating element. .......................S.1.1.(a)b. The minimum height for the digits used to display moisture content shall be
10 mm. ....................................................................................................... S.1.1.(b)c. Meters shall be equipped with a communication interface that permits interfacingwith a recording element and transmitting the date, grain type, grain moistureresults, test weight per volume results, and calibration version
identification. ..............................................................................................S.1.1.(c)d. A digital indicating element shall not display, and a recording element shall notrecord, any moisture content values or test weight per volume values before theend of the measurement cycle. ................................................................... S.1.1.(d)29Part 2: Field Inspection and Evaluation_______________________________________________________________________________________________
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e. Moisture content results shall be displayed and recorded as percent moisture
content, wet basis. Test weight per bushel results shall be displayed and recorded
as pounds per bushel. Subdivisions of these units shall be in terms of decimal
subdivisions (not fractions). ........................................................................S.1.1.(e)f.

A meter shall not display or record any moisture content or test weight per volume
values when the moisture content of the grain sample is beyond the operating rangeof the device, unless the moisture and test weight representations include a clear
error indication (and recorded error message with the recorded
representation). ........................................................................................... S.1.1.(f)g. On multi-constituent meters (e.g., meters which also measure grain protein),provision shall be made for displaying and recording the constituent label (such as
moisture, protein, etc.) to make it clear which constituent is associated with eachof the displayed and recorded values. ........................................................ S.1.1.(g)Selecting or Recording Grain or seed Type and Class[Code References: NIST Handbook 44, Section 5.56.(a) GMM, S.1.2., Table S.1.2.]
a. Provision shall be made for selecting and recording the type and class or multiclass group (as appropriate) of grain or seed to be measured. The means to selectthe type and class or multi-class group of grain or seed shall be readily visible andthe type and class or multi-class group of grain or seed selected shall be clearlyand definitely identified. Abbreviations for grain types and multi-class groups
indicated on the meter must meet the minimum acceptable abbreviations listed inTable S.1.2. “Grain Types and Multi-Class Groups Considered for Type
Evaluation
andCalibration
and
Their
Minimum
Acceptable
Abbreviations.” ............................................................................................... S.1.2.
See examples of multiclass groups in table S.1.2.

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Table S.1.2.
Grain Types and Multi-Class Groups Considered for Type Evaluation and Calibration and
Their Minimum Acceptable Abbreviations
Grain Type

BarleyGrain Class

Minimum Acceptable Abbreviation

All-Class Barley*

BARLEY

Six-Rowed Barley

SRB

Two-Rowed Barley

TRB

Corn

---

CORN

Grain Sorghum---

SORG or MILO

Oats

---

OATS

All-Class Rough Rice*Long Grain Rough Rice
Medium Grain Rough Rice

Rice
Small Oil Seeds(under consideration)
Soybeans
Sunflower seed (Oil)

Wheat

RGHRICE
LGRR
MGRR

---

---

-----

SOYB
SUNF

All-Class Wheat*

WHEAT

Durum Wheat

DURW

Hard Red Spring Wheat

HRSW

Hard Red Winter Wheat
Hard White Wheat

HRWW
HDWW

Soft Red Winter Wheat

SRWW

Soft White Wheat
Wheat Excluding Durum*

SWW
WHTEXDUR

Note: Grain Types marked with an asterisk (*) are “Multi-Class Calibrations.”[[Nonretroactive as of January 1, 1998]

Guidance:□ During accuracy testing verify that the meter is in compliance with the design
requirement of NIST Handbook 44, Section 5.56.(a), S.1.1 (a)-(h) or Part 2.
Section 5.2.2. “Design” of this manual to include minimum height for digits,
display requirements, and minimum acceptable abbreviations used to identify
grains. Also print a receipt and examine it for compliance.

Operating Ranges and Temperatures[Code References:
UR.3.10.(a)-(d)]NIST Handbook 44, Section 5.56.(a) GMM, S.1.3.(a)-(d),a. A meter shall automatically and clearly indicate when the operating range ofthe meter has been exceeded. The operating range shall specify the following:............................................................................................................... S.1.3.

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1. Temperature Range of the Meter – The temperature range over which
the meter may be used and still comply with the applicable requirements
shall be specified. The minimum temperature range shall be 10 °C to
30 °C. No moisture value may be displayed when the temperature range
is exceeded. An appropriate message shall be displayed when thetemperature of the meter is outside its specified operating
range. .......................................................................................... S.1.3.(a)2. Temperature Range of each Grain or Seed –The temperature range foreach grain or seed for which the meter is to be used shall be specified.
The minimum temperature range for each grain shall be 0 °C to 40 °C.
No moisture value may be displayed when the temperature range is
exceeded. An appropriate error message shall be displayed when thetemperature of the grain sample exceeds the specified temperature range
for the grain. .............................................................................. S.1.3.(b)3. Moisture Range of the Grain or Seed – The moisture range for each grain
or seed for which the meter is to be used shall be specified. Moistureand test weight per bushel values may be displayed when the moisture
range is exceeded if accompanied by a clear indication that the moisture
range has been exceeded. ........................................................... S.1.3.(c)4. Maximum Allowable Meter/Grain Temperature Difference – The
maximum allowable difference in temperature between the meter andthe sample for which an accurate moisture determination can be madeshall be specified. The minimum temperature difference shall be 10 °C.
No moisture value may be displayed when the maximum allowabletemperature difference is exceeded. An appropriate error message shallbe displayed when the difference in temperature between the meter andthe sample exceeds the specified difference. ............................. S.1.3.(d)Guidance:□ Meter operating ranges are included on the NTEP certificates of conformance.
Figure 2-9. “Meter Operating Ranges Listed on a NTEP Certificate ofConformance” shows an example of operating ranges that are listed on a grainmoisture certificate of conformance. Meter operating ranges are not typicallyverified in the field because meters will likely be maintained within their operating
ranges. If conditions exist where these ranges can be verified, a test may be
performed to ensure that the meter responds with the appropriate error messages.
Operating Ranges:
Ambient Temperature Range (Environment): 10 °C to 40 °C (50 °F to 104 °F)*With Hardware/Software Modification 2 °C to 45 °C (35.6 °F to 113 °F)
Temperature Difference (Room to Grain Temperature): 20 °C (36 °F), see comments on page 3
Grain Temperature Range: 0 °C to 40 °C (32 °F to 104 °F)
Grain Moisture Range: Refer to pages 4 - 7

Figure 2-9. Meter Operating Ranges Listed on a NTEP Certificate of Conformance.

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b. Posting and availability of Operating Ranges
The operating range of the grain moisture meter shall be clearly andconspicuously posted in the place of business such that the information is readily
visible from a reasonable customer position. The posted information shall
include the following: .......................................................................... UR.3.10.
1. The temperature range over which the meter can be used and, if thetemperature range varies for different grains or seed, the range must be
specified for each. .......................................................................... UR.3.10.(a)2. The moisture range for each grain or seed for which the meter is to be
used. ............................................................................................... UR.3.10.(b)3. The temperature range for each grain or seed for which the meter is to be used.
........................................................................................................ UR.3.10.(c)4. The maximum allowable difference in temperature that may exist between themeter and the sample for which an accurate moisture determination can be
made. .............................................................................................. UR.3.10.(d)5. Operating instructions are readily available to the user, service technician, andweights and measures official to include a list of accessory equipment and thekinds of grain or seed to be measured with the moisture meter. ........... UR.3.1.
Guidance:□ The device owner is responsible for posting the correct ranges of operation for themeter. Verify that the ranges specified in NIST Handbook 44, Section 5.56(a),S.1.3.(a)-(d) or Part 2, Section 5.2.4. “Operating Ranges and Temperatures”
items (a) (1- 4) of this manual are posted in the place of business and visible to thecustomer. This information should be in close proximity to the meter so that it isreadily visible to a customer observing the transaction.
c. Operating Temperature
1. Warm-up Period. When a meter is turned on it shall not display or record any
usable values until the operating temperature necessary for accurate
determination has been attained, or the meter shall bear a conspicuous
statement adjacent to the indication stating that the meter shall be turned on
for a time period specified by the manufacturer prior to use. .............S.1.5.(a.)
2. A meter shall meet the requirements of T.2. Tolerances when operated in thetemperature range of 10 °C to 30 °C (50 °F to 86 °F) or within the range
specified by the meter manufacturer. .................................................. S.1.5.(b)3. If the manufacturer specifies a temperature range, the range shall be at least
20 °C (36 °F). .......................................................................................S.1.5.(c)Guidance:□ The warm-up test is not typically performed in the field since meters areusually in use and the temperatures at the test location are within the operating

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temperatures of the meter. When testing at a location where the meters havenot been in use for a period of time and the temperature of the location exceeds
the operating temperature of the meter, the warm-up can be tested by turning
the meters on and testing the meters with grain sample to verify that usablevalues are not recorded or displayed until the meter reaches its operating
temperature.

□ When testing for meter accuracy within the operating ranges for the meter, themeter must meet the tolerances as specified in NIST Handbook 44,
Section 5.56.(a).

□ When looking at the operating ranges for the meter verify the manufactures
specified temperature range is at least 20 °C (36 °F)

Electrical Power Supply[Code References: NIST Handbook 44, Section 5.56.(a) GMM, S.2.2., S.2.2.1, S.2.2.2]
a. Power Supply, Voltage and Frequency. A meter that operates using alternating
current
must
performwithinthetolerances
definedin
Section T.2. “Tolerances” over the line voltage range 100 V to 130 V, or 200 V
to 250 V rms as designed, and over the frequency range of 59.5 Hz to 60.5 Hz.
Battery-operated instruments shall not indicate or record values outside theapplicable tolerance limits when battery power output is excessive or deficient.
............................................................................................................ S.2.2.1.
b. Power Interruption. A power interruption shall not cause an indicating or
recording element to display or record any values outside the applicabletolerance limits. ................................................................................... S.2.2.2.
Guidance:□ The power supply, voltage and frequency test is not typically conducted in the field
on electrically powered grain moisture meters because this test requires a source
to change the voltage and frequency in the power supply. However, the power
supply, voltage and frequency test may be performed on battery operated
instruments if it can be determined that the battery power is in excessive or
deficient and then by verifying that the meter performs in tolerance while thebattery power is in this condition.

□ If interruptions to the power can be made that do not disrupt the normal flow ofbusiness, such as turning a room switch on and off that controls the power to amoisture meter, observations may be made to verify that this interruption does notcause an indicating or recording element to display or record any values outside
the applicable tolerance limit.

Units and Readability[Code References: NIST Handbook 44, Section 5.56.(a) GMM, S.1.4.]
The display permits moisture value determination to both 0.01 % and 0.1 %resolution. The 0.1 % resolution is for commercial transactions; the 0.01 %34

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resolution is for type evaluation and calibration purposes only, not forcommercial purposes. Test weight per bushel values shall be determined to thenearest 0.1 pound per bushel. .................................................................... S.1.4.
Guidance:□ Meters are allowed to display in two different percent resolutions for moisture.
The 0.01 % resolution is a finer resolution to allow for rounding during typeevaluation and calibration of the meter. There is a single resolution for test weight
per bushel which is 0.1 pounds per bushel. The 0.1 % resolution for moisture andthe 0.1 pounds per bushel must be used for commercial transactions. Prior toaccuracy testing, ensure that the meter is indicating in 0.1 % resolution for moistureand in 0.1 pounds per bushel for test weight. If the meter is indicating in a different
resolution record the “as found” resolution on your report form; explain therequirement to the device owner; and have the device owner change the resolution
to the appropriate resolution for field testing following instructions in the operation
manual.

Recorded Representation[Code References: NIST Handbook 44, Section 5.56.(a) GMM, G-S.5.6., UR.3.4. (a), (b)]a. Insofar as they are appropriate, the requirements for indicating and recording
elements shall also apply to recorded representations. All recorded values shallbe printed digitally. In applications where recorded representations are
required, the customer may be given the option of not receiving the recorded
representation. For systems equipped with the capability of issuing anelectronic receipt, ticket, or other recorded representation, the customer may
be given the option to receive any required information electronically (e.g., viacell phone, computer, etc.) in lieu of or in addition to a hard copy. ..... G-S.5.6.
b. Printed tickets must be free from any previous indication of moisture content
or type of grain or seed selected. The customer shall be given a printed ticketat the time of the transaction or as otherwise specified by the customer. The
printed ticket shall include the date, grain type, grain moisture results, test
weight per bushel, and calibration version identification. The ticket shall be
generated by the grain moisture meter system. ........................... UR.3.4.(a),(b)Guidance:□ Observe transactions to ensure that a printed ticket is given to customers and theprinted results show all of the information listed in NIST Handbook 44, Section
5.56.(a), UR.3.4. or in Part 2, Section 5.2.7. “Recorded Representation” of thismanual. Also verify that the receipt is printed from the grain moisture metersystem. This may be printed by a printer integral to the grain moisture meter or by
an external printer interfaced to the meter; the receipt may not be generated bymanual operation. During accuracy testing print out and review a ticket.

Provisions for Sealing[Code References: NIST Handbook 44, Section 1.10. General Code, G-S.8., G-S.9.,
G-UR.4.5., Section 5.56.(a) GMM, S.2.5., Table S.2.5.]

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a. A device shall be designed with provision(s) for applying a security seal thatmust be broken, or for using other approved means of providing security (e.g.,
data change audit trails available at the time of inspection), before any changethat detrimentally affects the metrological integrity of the device can be madeto any electronic mechanism. ................................................................. G-S.8.
[Nonretroactive as of January 1, 1990]
b. A software update that changes the metrologically significant software shall beconsidered a sealable event ....................................................................G-S.9.
(Added 2016)c. A security seal shall be appropriately affixed to any adjustment mechanism
designed to be sealed. ......................................................................G-UR.4.5.
d. Provision shall be made for applying a security seal in a manner that requires
the security seal to be broken, or for using other approved means of providing
security (e.g., audit trail available at the time of inspection as defined inTable S.2.5. “Categories of Device and Methods of Sealing,” NIST
Handbook 44, Section 5.56.(a) before any change that affects the metrologicalintegrity of the device can be made to any mechanism. ........................... S.2.5.
Guidance:□ If a feature or parameter of the moisture meter can be changed, that will affect themeasurement of a device, there must be a means for sealing that feature orparameter to ensure that there is evidence that a change was made to the device.
A list of the features and parameters to be sealed are included in Publication 14.
Acceptable forms of sealing are a physical seal, an event counter or an event
logger. These types of sealing are applied according to the category of the device.
Meters are classified as category 1, 2, 3, 3a, and 3b devices:o

If a meter is classified as a Category 1 device, which is a meter that does nothave remote configuration, the method for sealing can be a physical seal or
two event counters.

o

If a meter is classified as a Category 2 device, which is a device with remoteconfiguration but access is controlled by physical hardware, the hardware foraccess to remote communication must have a physical seal or two event
counters.

o

If a meter is classified as a Category 3 device, which is a device with remoteconfiguration, a Category 3a, device which is a device with no remoteconfiguration but the operator is able to make slope and bias changes or a
Category 3b device, which is a device with no remote configuration but
metrological changes can be made through a software switch such as a
password, these categories require an event logger.

□ The NTEP certificate of conformance for a grain moisture meter provides
information on the type of sealing associated with the meter and includes thelocation of a physical seal or guidelines for accessing event logger and/or event
counter information. Most NTEP meters are Category 3 devices requiring an audit
trail (an event logger or event counter). Figure 2-10. “Audit Trail and Key for36

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Description of Audit Trail Changes,” contains a printout of an event logger from a
NTEP grain moisture meter and a key to identify the codes on the event log.
During testing, review the CC to determine the type of sealing associated with themeter being tested then print and review the event logger or event counter to ensurethat it meets the requirements of NIST Handbook 44, Section 5.56.(a), Table S.2.5.
“Categories of Device and Methods of Sealing” or observe the physical seal toensure that the seal is secure and provides adequate security. For meters with event
loggers or event counters, review the printed event logger or counter for any
patterns that may indicate inappropriate changes. For example, one pattern that
may indicate inappropriate changes may be excessive changes during peak harvest
times. Note on your inspection report whether or not physical seals are intact, notesettings for any event counters, and attach a copy of the event log if applicable.

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Figure 2-10. Audit Trail and Key for Description of Audit Trail Changes.
Date

Time

Calibration

Constituent

Description

ChangeCount

ID

Description of metrological changes

ID

Description of metrological changes

1

Import an application model

12

A-constant (residual) (constituent parameter).

2

Delete an application model.

13

B-constant(leverage) (constituent parameter).

3

The date setting is changed.

14

Low limit (constituent parameter).

4

The time setting is changed.

15

High limit (constituent parameter).

5

The P Constant is changed

16

C-constant (standard deviation (std dev)) (constituent
parameter).

6

The O constant is changed

17

Number of printed decimals (constituent parameter).

7

The S constant is changed

18

Slope changes (constituent parameter)

8

The min temperature is changed (constituent parameter)

19

Changes of BIAS (constituent parameter).

9

The max temperature is changed (constituent parameter)

20

Moisture correction (constituent parameter).

10

Instrument temperature limit.

21

Correction of constituent (constituent parameter).

11

Number of subsamples (application model parameter).

22

Make correction (constituent parameter).

Marking Requirements
Marking requirements specify what must be marked on the grain moisture meter for proper
identification of the device and marking requirements for operational controls; graduations;indications; and features.

General Identification[Code Reference: NIST Handbook 44, Section 1.10. General Code, G-S.1.(a)-(e)]a. All equipment, except weights and separate parts necessary to themeasurement process but not having any metrological effect, shall be clearly

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and permanently marked for purposes of identification with the following
information: ............................................................................. G-S.1.(a)-(e)1. the name, initials, or trademark of the manufacturer or distributor;... G-S.1.(a)2. a model identifier that positively identifies the pattern or design of thedevice; ............................................................................................. G.S.1.(b)-The model identifier shall be prefaced by the word “Model,” “Type,”or “Pattern.” These terms may be followed by the word “Number” oran abbreviation of that word. The abbreviation for the word “Number”
shall, as a minimum, begin with the letter “N” (e.g., No or No.). The
abbreviation for the word “Model” shall be “Mod” or “Mod.” Prefix
lettering may be initial capitals, all capitals, or all lower case.
[Nonretroactive as of January 1, 2003](Added 2000) (Amended 2001)

3. a nonrepetitive serial number, except for equipment with no moving orelectronic component parts and software; ..................................... G-S.1.(c)[Nonretroactive as of January 1, 1968](Amended 2003 and 2016)-

The serial number shall be prefaced by words, an abbreviation, or asymbol, that clearly identifies the number as the required serial
number.
[Nonretroactive as of January 1, 1986]-

Abbreviations for the word “Serial” shall, as a minimum, begin withthe letter “S,” and abbreviations for the word “Number” shall, as aminimum, begin with the letter “N” (e.g., S/N, SN, Ser. No., and
S. No.).
[Nonretroactive as of January 1, 2001]

4. the current software version or revision identifier for not-built-for-purpose,software-based devices manufactured as of January 1, 2004, and allsoftware-based devices (or equipment) manufactured as of January 1, 2022;........................................................................................................ G-S.1.(d)[Nonretroactive as of January 1, 2004](Added 2003) (Amended 2016)-

The version or revision identifier shall be prefaced by words, anabbreviation, or a symbol, that clearly identifies the number as therequired version or revision.
[Nonretroactive as of January 1, 2007](Added 2006)-

Abbreviations for the word “Version” shall, as a minimum, begin withthe letter “V” and may be followed by the word “Number.”Abbreviations for the word “Revision” shall, as a minimum, begin withthe letter “R” and may be followed by the word “Number.” The

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abbreviation for the word “Number” shall, as a minimum, begin withthe letter “N” (e.g., No or No.). Prefix lettering may be initial capitals,
all capitals, or all lower case.
[Nonretroactive as of January 1, 2007](Added 2006) (Amended 2016)
5. a National Type Evaluation Program (NTEP) Certificate of Conformance(CC) number or a corresponding CC Addendum Number for devices thathave a CC. The CC Number or a corresponding CC Addendum Number
shall be prefaced by the terms “NTEP CC,” “CC,” or “Approval.” These
terms may be followed by the word “Number” or an abbreviation of thatword. The abbreviation for the word “Number” shall, as a minimum, begin
with the letter “N” (e.g., No or No.). ............................................. G-S.1.(e)[Nonretroactive as of January 1, 2003]
Guidance:□ Meters must be marked in accordance with NIST Handbook 44, Section 1.10.
General Code, G.S.1.(a)-(e). Much of the marking information required by GS.1. is often found on an identification badge. However, the information is not
required to be marked on a badge and may be located at various places on thedevice, provided it complies with visibility and permanence requirements.
Devices must be marked with the appropriate information to ensure that eachdevice is uniquely identified so that proper records and inspection trails can be
maintained by weights and measures jurisdictions and service agencies.
Appropriate markings are also necessary to track devices that may have beensold or transferred to different business locations in or out of jurisdictions.
Prior to testing locate the identification information on the meter. Confirm that
identification of the meter includes all the requirements included in NIST
Handbook 44, Section 1.10. General Code, G.S.1.(a)-(e) and record thenecessary information on the test report. Figure 2-11. “Examples of pre 2003
Identification Badge” shows a sample identification badge. In this sample, theID badge does not include a CC number. Although this ID badge does notinclude a CC number, it meets the requirements of NIST Handbook 44 because
it was manufactured prior to January 1, 2003. The requirement for including a
CC number only applies to meters manufactured after January 1, 2003. The
NTEP CC includes information on where to locate the identification badge andidentification information that can be assessed from the instrument display.

Figure 2-11. Example of pre 2003 Identification
Badge. (Note: The ID badge does not include a CC
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Interchange or Reversal of Parts
a. Parts of a device that may readily be interchanged or reversed in the course of
field assembly or of normal usage shall be: ........................ G-S.4.(a),G-S.4.(b)1. so constructed that their interchange or reversal will not affect the performanceof the device; or
2. so marked as to show their proper positions.
Guidance:□ During an inspection of any new meter designs with interchangeable orreversible parts, testing should be performed to ensure that these parts aremarked appropriately and if not marked they do not affect the performance. If
the part is not properly marked to show its proper position, a test can be
performed by first testing the meter with the part attached in one direction thenreattaching the part in another direction to determine if the reversal of the partaffected the performance of the device. This is to ensure that reversing a partdoes not cause inaccurate measurements. Current designs of NTEP grainmoisture meters do not have parts that can be readily interchanged during
normal use. As with other Handbook 44 requirements, compliance with theserequirements is verified during type evaluation.

Marking, Operational Controls, Indications and Featuresa. All operational controls, indications, and features, including switches, lights,
displays, push buttons, and other means, shall be clearly and definitely
identified. The use of approved pictograms or symbols shall be acceptable.
............................................................................................................ G-S.6.
[Nonretroactive as of January 1, 1977]
Guidance:□ Review the identification of operational controls, indications, switches, light
displays, and push buttons to ensure that they are clearly identified. These
requirements help to ensure that device owners can operate the device
appropriately and ensures consumers can understand the transaction andinformation displayed and recorded.
This identification may include
pictograms or symbols that have been approved by the weights and measurescommunity and that would be readily understood by an operator or consumer.
Information on identification of the operational controls is typically located in
the manufacturer’s operations manual. Figure 2-12. “Identified Operational
Controls” below shows the identification of operational controls on one NTEP
meter.

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Figure 2-12. Identified
Operational Controls.

Values
If graduations, indications, or recorded representations are intended to havespecific values, these shall be adequately defined by a sufficient number of
figures, words, symbols, or combinations thereof, uniformly placed withreference to the graduations, indications, or recorded representations and as close
thereto as practicable, but not so positioned as to interfere with the accuracy ofreading. ............................................................................................. G-S.5.2.4.
Guidance:□ Grain moisture meters and multi-constituent meters measure moisture and/or
protein, starch, and oil of grains in percent (%) value and grain test weight inpound per bushel (lb/bu) or Kilogram per hectoliter (kg/hl). Abbreviations forgrain type may also be used in accordance with NIST Handbook 44, Section
5.56.(a), Table S.1.2. “Grain Types and Multi-Class Groups Considered forType Evaluation and Calibration and Their Minimum Acceptable
Abbreviations.” Observations should be made while testing to ensure that theconstituents are properly labeled; that minimum acceptable abbreviations areused for the various grain types; and that the measurement values are identified
appropriately.

Permanence
Graduations, indications, or recorded representations and their defining figures,words, and symbols shall be of such character that they will not tend easily to
become obliterated or illegible. .......................................................... G-S.5.2.5.

On Devices that Indicate or Record in more than One Unit
On devices designed to indicate or record in more than one unit of measurement,
the values indicated and recorded shall be identified with an appropriate word,
symbol, or abbreviation. .................................................................... G-S.5.3.1.

Lettering
All required markings and instructions shall be distinct and easily readable andshall be of such character that they will not tend to become obliterated orillegible. ..................................................................................................G-S.7.

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Other Devices not used for Commercial Measurements
If there are other moisture meters on the premises not used for trade or
determining other charges for services, these devices shall be clearly andconspicuously marked “Not for Use in Trade or Commerce.”..............................................................................................................UR.3.2.
Guidance:□ Examine the markings on all meters on the premises. For those not usedcommercially ensure that they are marked “Not for Use in Trade. For all others
observe that:osymbols, words and figures are not easily obliterated;odifferent units are properly identified; andomarking and instruction are easily read.

Measuring Element
Accessory Devices/Equipment
When the operating instructions for a moisture meter require accessory
equipment separate from and external to the moisture meter, such equipment
shall be appropriate and complete for the measurement and Accessory devices,
if necessary in the determination of a moisture content value, shall be in close
proximity to the moisture meter and allow immediate use. ............. S.3., UR.3.5.

Current Calibration Dataa. Grain moisture determinations must be made using only the most recently
published calibration data. .................................................................UR.3.9.
b. A meter must be capable of displaying either calibration constants, a uniquecalibration name, or a unique calibration version number for use in verifyingthat the latest version of the calibration is being used to make moisture content
and test weight per bushel determinations. ......................................... S.2.4.1.
Guidance:□ Grain moisture meter calibrations are based on how the meter reacts to grain
samples, which vary with each crop year. As such, the calibrations of grainmoisture meter may change on an annual basis. Meter manufacturers provide
meter owners with the most current calibrations annually. Device owners are
responsible for ensuring that the latest calibrations are installed on the meter.
Calibration constants, unique calibration name, or calibration versions numbers
for grain moisture meters are listed on the NTEP CC. An example of thecalibrations and calibration version number on a CC are shown in
Figure 2-13. “Calibrations Data from a GMM Certificate of Conformance.”
Compare the meter calibrations, unique calibration name or calibration version
on the meter to the values on the most current CC to verify that the most recent
calibrations are installed on the meter.

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Hard Red Winter Wheat
Designation: Wheat HRW
Calibration Version: 060308n
Moisture Range - Approved: 6 % – 20 %Moisture Range - Pending: 6 % – 22 %Calibration Constants:
K1 = 0673 K4 = 0738 K7 = 2206
K2 = 1716 K5 = 2500 K8 = 9948
K3 = 1247 K6 = 1074 K9 = 1045
Test Weight per bushel: Approved

Figure 2-13. Calibration Data from a GMM Certificate of Conformance.

Pretest Determinations

Grains and Constituents
Determine the kind of grains, and constituents the device is used to measure and select thegrains for use in inspecting and testing the meter.

Tolerances[Code References: NIST Handbook 44, Section 5.56.(a) GMM, T.1., T.2., T.3.]

How to Apply Tolerancesa. Tolerances shall be applied to the average of at least three measurements oneach official grain sample for moisture and weight per bushel measurements)b. The tolerances hereinafter prescribed shall be applied to errors ofunderregistration and errors of overregistration. ...................................... T.1.
c. Air Oven Reference Method. – Maintenance and acceptance tolerances shallbe as shown in Table T.2.1. “Acceptance and Maintenance Tolerances AirOven Reference Method.” Tolerances are expressed as a fraction of thepercent moisture content of the official grain sample, together with a minimum
tolerance. ..................................................................................... T.2., T.2.1.

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Table T.2.1.
Acceptance and Maintenance Tolerances Air-Oven Reference Methods
Type of Grain, Class, or Seed

Tolerance

Minimum Tolerance

Corn, oats, rice, sorghum,
sunflowers

0.05 of the percent
moisture content

0.8 %in moisture content

All other cereal grains an doil
seeds

0.04 of the percent
moisture content

0.7 %in moisture content(Amended 2001)

d. The maintenance and acceptance tolerances on test weight per bushel
indications or recorded representations are shown in Table T.3. “Acceptanceand Maintenance Tolerances Test Weight per Bushel.” ........................... T.3.
Table T.3.
Acceptance and Maintenance Tolerances Test Weight per Bushel
Type of Grain or Seed
Corn, oats
All wheat classes
Soybeans, all barley classes, all riceclasses, sunflower, sorghum

Tolerance(Pounds Per Bushel)
0.8
0.5
0.7

(Added 2003)

Guidance:□ The following is an example of calculating the tolerance for a wheat sample:
Per Table T.2.1. “Acceptance and Maintenance Tolerances Air-Oven
Reference Methods,” the tolerance for wheat is 0.04 of the percent moisture
content of the standard grain sample, with a minimum tolerance of ± 0.7 %. If
the wheat sample moisture is 16 %, the tolerance is calculated by multiplying
the tolerance by the percent moisture:± 0.04 × 16 % = 0.64 %So the tolerance to be applied to this test is ± 0.64 %. However, since theminimum tolerance to be applied is ± 0.7 %, the tolerance for the test is± 0.7 %.
□The tolerances for test weight measurements are applied directly to themeasurement. The sample used for test weight has a test weight value assignedby the laboratory. The sample is placed in the meter and the test weightindicated by the meter is compared to the laboratory assigned test weight valuesof the sample.

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Test Notes
Official Grain Sample Maintenance, Test Methods and Documentation
The moisture of official grain samples will change over time due to temperature,environmental conditions, and stability of the grain samples. To maximize the use of theofficial grain example and ensure that the moisture value of the sample is maintained
throughout testing, field inspectors must follow guidelines and test procedures included inthis section. The test methods and documentation needed to perform inspection and testing
are also included in this section.

Storage
Official grain samples received from the laboratory are to be stored in arefrigerator and maintained at 2 ºC (35 °F) to 4 ºC (40 °F) until needed.

Official Grain Samples used for Field Testing
Official grain samples for field testing are grains that are representative of thegrain types and moisture ranges normally traded in a jurisdiction. Three or more
official grain samples with a high moisture content and three or more official
grain samples with a low moisture content for each grain type are used for fieldtesting commercial grain moisture meters. One of the three or more official grain
samples is retained as a backup for each grain type and moisture. Each of theremaining samples is used as an official sample until it has been dropped for thenumber of times described in Part 2, Section 7.1.4. “Minimum Test andMaximum Number of Drops” of this manual.

Warming Official Grain Samples in Preparation for Testing
Approximately two hours before use (consider travel time in this two-hour
period), remove only the official grain standards from the refrigerator that will
be used for moisture meter field evaluation for that day of testing and shake thesample several times (for homogeneity). Place the samples in a transport cooler
WITHOUT ICE. This will allow the grain sample to stabilize to ambient
temperature and minimize exposure to temperature extremes and fluctuations.
The sample jars or bags should be spread out to allow the air to move freely
about them. Official grain samples which are being used to test moisture meters
for the current day should be stored in the transport cooler when not in use. If
there are significant down times between tests during the day, grain standards
should be stored in the refrigerator until two hours before they are needed. Backup samples must remain in the portable refrigerator until needed by the inspector.
When it is determined that the back-up sample is needed that day, the back-up
sample should be placed in the cooler along with the day’s primary samples.
Note: Throughout the handling period when the grain is not refrigerated,occasionally shake each grain sample to mix the grain several times and also be
sure to shake the grain sample before removing the sealing lid for any purpose.

Minimum Test and Maximum Number of Drops
a. A minimum test of a grain moisture meter consists of testing the moisture and if
applicable, test weight meter measurements.

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b. When testing for moisture, the meter is to be tested using official grain samples
having at least two different moisture content values (“high” and “low” moisture
content) within the operating range of the device and representing the “high” and“low” moisture values at which a specific grain is traded within a jurisdiction.
c. When applicable, the test weight feature on the meter should be tested using an
official grain sample with the lowest moisture value.
d. The moisture value of grain samples may begin to change in moisture during
meter testing. High moisture corn and soybeans and other grains and moistures
have a maximum number of drops during testing. High moisture corn andsoybeans and rough rice standard samples can be used for a maximum numberof 18 drops. Corn and soybeans below 18 % and all other grains and moistures
have a maximum number of 24 drops. Extended use of grains for more than thespecified maximum number of drops must be supported by data to show that
testing is not affected by the extended use of the grain samples.

Preparation of the Official Grain Samples upon Arrival at the Test Site
a. Upon arrival at the test site, transport the official grain samples to the meter
location in the transport cooler. The grain samples should be taken into the room
where the moisture meter is located; taken out of the transport cooler; and placednear the moisture meter to allow them to reach the temperature of the room
before the jar is opened. Jars should not be opened until the grain is within
10 degrees of the room temperature. Moisture will condense on the grain if acold grain standard is opened before its temperature stabilizes. Except wheninserting a thermometer to take the temperature of the grain, the jar containing
the official grain sample is never opened without first allowing the grain tostabilize and is only exposed while conducting the moisture meter test.
b. Take the temperature of the grain sample with the least amount of exposure to
the environment. One method is to quickly replace the lid on the sample with arubber stopper or lid with a hole that allows a thermometer to be inserted into
the sample.
c. In order to ensure a valid result, care must be taken so that the moisture valuesof the samples are carefully maintained. High moisture samples are more
susceptible to moisture loss and spoilage; therefore, it is recommended that theinspection begin with the sample having the highest moisture value and proceed
to the samples with the lower moisture values to limit the amount of time thatthe high moisture samples are exposed to ambient conditions.
d. Work with only one sample at a time to avoid the possibility of confusing/mixing
the samples.
e. Carefully monitor each sample in order to detect any erratic meter readings orfoul odor which could indicate sample deterioration.
f.

To avoid contamination of the official samples, the meter, its parts, andaccessory equipment must be clear of other grain before using the official grain
samples in the meter. Prior to using an official grain sample in a GMM under

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test, check to ensure that the GMM dump cells, filling hoppers, grain drawers(receiving trays), etc. are clean and there is no buildup of residue.
g. Before opening the sample to begin testing the GMM, review all the details of
the inspection so that handling of the grain and the time the sample is out of thesealed container can be minimized.
h. Field inspectors are responsible for refrigerating samples at the end of each day
and for keeping samples in a cooler or refrigerator between inspection points.
Inspectors are also responsible for monitoring sample conditions and possible
moisture changes to determine when replacement is necessary. This includes
keeping the sample free of contamination from other grains, souring or molding
grain, and insects, all of which may cause erratic readings. A primary grain
sample that begins to fail on all meters may be indicative of a moisture change
in the primary grain sample. If a primary sample is compromised as noted above,
the back-up sample should be used to confirm the readings. If meters pass withthe back-up sample, place the previously used official grain sample in the
refrigerator for return to the laboratory, and use the back-up grain sample tocomplete the testing.

Field Inspection and Test Method
Field inspection of NTEP grain moisture meters or meters manufactured orplaced into service after January 1, 1998, must be conducted in accordance with
NIST Handbook 44, Section 5.56.(a). This manual provides guidelines for using
the air-oven reference method transfer standards to test GMM and multiconstituent grain analyzers that measure moisture in accordance with NIST
Handbook 44, Section 5.56.(a), N.1.1.

Documentation
In addition to NIST Handbook 44, other documents are needed and useful inperforming the inspection of GMMs. These documents provide information on
jurisdictional policy, device operation, accessing audit trail information,verifying NTEP identification information, and the location of businesses withgrain moisture meters.
a. Departmental Policy and Inspection Procedures
Many weights and measures jurisdictions have state and/or local policies
and inspection procedures that are followed during an inspection. These
procedures should be provided to the inspector for reference.
b. Moisture Meter Operating Instructions and Current Certificates ofConformance (CC) for Moisture Meters
GMM operating instructions from the manufacturer will provide theinspector with detailed information on how to operate the meter and will
be useful to the inspector if the meter is new or if it is the first time an
inspector has tested a specific type of meter. CCs are available for all
NTEP GMMs and may be obtained from the NCWM, Inc. website atwww.ncwm.net. A CC for grain moisture meters includes the most current
calibration constants, sealing requirements, and other useful informationthat the inspector will need to perform an inspection.

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c. List of Moisture Meters and Locations, Type of Meters(s), and Types(s)of Grain Purchased
Many weights and measures jurisdictions maintain a database or otherlisting of moisture meters with the location, type of meters, and grains
purchased. This information will be helpful for the inspectors to prepare
for testing.

Official Grain Samples (Transfer Standards), Minimum Test, Minimum
Sample Size.
[Code References: NIST Handbook 44, Section 5.56.(a) GMM, N.1.1., N.1.2., UR.3.3.,
S.2.1.]
a. Official grain samples shall be used as the official transfer standards with moisture
content and test weight per bushel values assigned by the reference methods. The
reference methods for moisture shall be the oven drying methods as specified by the
USDA GIPSA. The test weight per bushel value assigned to a test weight transfer
standard shall be the average of 10 test weight per bushel determinations using thequart kettle test weight per bushel apparatus as specified by the USDA GIPSA.
Tolerances shall be applied to the average of at least three measurements on each
official grain sample. Official grain samples shall be clean and naturally moist, but
not tempered (i.e., water not added). ............................................................. N.1.1.
b. A means to prevent condensation of moisture or loss of moisture from grain
samples must be used. For example, a cold grain sample should be kept in a closed
container in order to permit the cold grain to come to within the operating
temperature range of the meter before the grain moisture measurements are
made. ........................................................................................................UR.3.3.
c. Meters shall be designed to measure the moisture content of representative-size
grain samples. The minimum allowable sample size used in analysis shall be 100 g
or 400 kernels or seeds, whichever is smaller................................................ S.2.1.
d. A minimum test of a grain moisture meter consists of test with samples (need notexceed three) of each grain or seed for which the device is used and for each grain
or seed type shall include the following: ..................................................... N.1.2.
-

tests of moisture indications, using samples having at least two different moisture
content values within the operating range of the device. ........................... N.1.2.(a)-if applicable, tests of test weight per bushel indications with at least the lowest
moisture samples used in (a) above. .......................................................... N.1.2.(b)49Part 2: Field Inspection and Evaluation_______________________________________________________________________________________________
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Safety Reminders
Lifting.
•

Be familiar with and use proper lifting techniques when lifting grain samples or heavyequipment to prevent personal injury.
ooTo reduce the possibility of back injury, use equipment which would decrease theamount of lifting required whenever possible (e.g., an extended height funnel, or
carts for transporting grain samples)
Periodic training in proper lifting techniques is encouraged.

Grain Sample Container.
•••

Use a lid opener if a grain sample container lid is too tight to be removed comfortably byhand. Do not strain. When opening samples, grasp the containers firmly with good hand
and wrist positioning and grip.
Dry condensation from the outside of a grain sample container to prevent slippage andpossible breakage of container and/or injury to feet.
Watch for chips, cracks, or breakage of glass containers. If found, dispose of the container
properly to prevent injury to the inspector or damage to the GMM. A damaged container
may also affect the integrity of the grain sample moisture.

Test
Minimum Test
Carefully review Section 7.1. “Official Grain Sample Maintenance, Test Methods andDocumentation,” before beginning the minimum test procedures and follow the guidelines
in this section.
a. Determine the official grain sample temperature and the ambient temperature. Do notremove the grain from the container until the grain is within 10 °F of the ambient
temperature.
b. When the grain comes to within the desired temperature, pour the entire contents of theofficial grain sample into a larger, clean glass container. Rotate the container about
10 times to further homogenize the contents and equilibrate the temperature.
c. Following the GMM operating instructions, select the grain type to be tested on the
GMM.
d. Fill the grain hopper with the official grain sample, starting with the high moisturesample first.
e. Following the GMM operating instructions drop the official grain sample through themeter and record the moisture results. Repeat the test for a total of three measurements.

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f.

If there are other GMMs at the inspection site, repeat steps (a.) through (e.) with the sameofficial grain sample, working in assembly-line fashion as quickly as possible.

g. Return the official grain sample to its original, clean jar; seal the jar with its lid; mark thejar with the number of drops; and return the jar to the cooler.
h. Analyze the test results by averaging the three-meter moisture measurements for eachmeter and comparing the average meter moisture to the known moisture value of theofficial grain sample and record the error.
i.

If the meter is not in tolerance and you suspect that the sample has changed, is damaged,
or contaminated, repeat steps (a.) through (h.) with the back-up sample. If the resultsfrom the back-up sample agree with the results from the primary sample, record theresults; return the back-up sample to the cooler; and continue to use the primary sample
as the standard.

j.

Proceed to the next lower moisture level of that grain and repeat steps (a.) through (h.)

k. If the results from the back-up sample are different, return the primary sample to theportable refrigerator for return to the laboratory. Use the back-up sample as the primaryfrom this point.
l.

Repeat steps (a.) through (h.) for each grain and each moisture level.

m. If appropriate, test the test weight per volume (e.g., test weight per bushel) indications
with at least the lowest moisture sample. Drop the official grain sample with the lowest
moisture through the meter three times and record the results. Analyze the test resultsby averaging the three-meter test weight measurements for each meter and comparing
the average meter test weight to the known test weight value of the official grain sample
and record the error. Evaluation of the test weight per bushel indications can be
performed while testing the moisture indications or a weights and measures jurisdiction
may choose to use a separate, low-moisture sample to test the accuracy of the test weightindications.
n. Remember to mark each sample label with the number of times that sample is dropped
and the number of times that sample was warmed.
o. Verify that the seals of the jars are tight and return the samples to the portable refrigerator
as soon as testing is completed for the day.
p. When samples exceed a specified number of drops, 18 drops for corn and soybeans above
18 % or 24 drops for all other grain types, the sample must be returned to the laboratory
and retested. A jurisdiction may determine that the maximum number of drops can beincreased with supporting historical data.

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Post Test Tasks
Provisions for Sealing[Code References: NIST Handbook 44, Section 5.56.(a) GMM, S.2.5.]
Provision shall be made for applying a security seal in a manner that requires the security
seal to be broken, or for using other approved means of providing security (e.g., audit trail
available at the time of inspection as defined in Table S.2.5. “Categories of Device andMethods of Sealing,” NIST Handbook 44, Section 5.56.(a) before any change that affects
the metrological integrity of the device can be made to any mechanism. ................... S.2.5.
Guidance:
As appropriate, follow the instructions for accessing audit trail information in the NTEP
certificate “Field Inspection Notes” and review the audit trail of the GMM device forcompliance with NIST Handbook 44. As appropriate, check for the presence of a physicalsecurity seal on the meter. Document missing physical seals on the official report andapply new ones as needed. Attach a copy of the printed event logger or event counter tothe test report and record any concerns on the test report.

Record Results
Record the test results on an official test report. See Appendix A for a sample test report.
A test report form for grain moisture meters should contain as a minimum:

a. name or initials of person performing the evaluation;b. date;c. description of the device, model, and serial number;d. environmental readings such as temperature, where applicable;
e. identification of standard grain samples (i.e., sample ID);f. device owner, name, address and phone number;g. device CC number;
Safety Reminders••

Be sure all equipment being transported by the inspector or service technician is properly
secured in the vehicle.
Practice defensive driving when traveling between sites.

h. field evaluation data;i. calculations;52Part 2: Field Inspection and Evaluation_______________________________________________________________________________________________
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j. numerical checks on calculation;k. sealing/audit trail information; andl. additional information such as device condition and other comments.
Review Resultsa. Test Data
The test data are to be entered in the appropriate spaces on the report form
during and immediately following the test.
b. Reporting Error
To report the error of the meter under test, the moisture value of the grainstandard is subtracted from the average of three readings of the meter that isbeing tested
Error = Average meter reading − Grain Standard Moisture Valuec. Explain Results to Device Owner
Explain the results to the device owner including any corrective action needed
and the disposition of the device

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APPENDIX A. Grain Moisture Meter Sample Test Report Form

Grain Moisture Meter Examination Report

Firm
Name: ________________________________________________

Telephone: ____________________________________

Report Number: __________________________ Page _________of__________

Address:_______________________________________________________

Company representative: __________________________

Date:_____________________ Date of last inspection:_____________________

City/Town: _____________________________________________ Zip:_______________

Title:__________________________________________

Inspector:____________________________________

Time In: _____________
Time

out:_____________

Meter Description ____________________________________________________________________ Manufacturer ____________________________________________ User ID_______________________________
Model _______________________________________
Serial Number_______________________ NTEP CC number ________________________________________
Printer: _______________________________
Calibration Version_______________________________________
Audit Trail Information Printed and Attached Y_____ N_____

I.D:
Type:
I.D:
Type:
I.D:
Type:
I.D:
Type:
I.D:
Type:
I.D:

Meter
Weight Per
BushelIndications

Moisture Error =(Average Meter %Moisture − Standard %Moisture)

Average Meter
Weight Per
Bushel (Test
Weight)Indications
Drop 3

Grain
Standard% Moisture
Value

Drop 1

Avg.
Meter %
Moisture

Drop 3Meter% Moisture
Indications

Drop 2

Grain
temp
°C

Grain Standard
Weight Per
Bushel(Test Weight)

Wt. Per Bushel(Test Weight)
Error =
(Avg. Meter Wt.
Per Bushel − Std.
Wt. Per Bushel

Appendix A. Grain Moisture Meter Test Report

Type:

Air
temp
°C

Drop 1Grain
Standard

Signature for firm: _____________________________________________________________

Drop 2

I acknowledge receipt of this report and certify that I understand the information and/or instructions described herein.

Telephone: ____________________________________

Report Number: __________________________ Page _________of__________

Type:
I.D:
Type
I.D:
Type:
I.D:
Type:
I.D:

This device has been examined for compliance with the specifications, tolerances, and technical requirements set forth in the latest edition of the National Institute of Standards and Technology Handbook 44 and the______________________ weights and measures law.
Action Taken: approved, rejected, condemned. Any violations must be corrected by ___________________________.

Violations:Remarks/Instructions:

Accessory equipment:

Appendix A. Grain Moisture Meter Test Report_____________________________________________________________________________________________
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Firm
Name: ________________________________________________

Grain Moisture Meter Examination Report

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Appendix B.
Grain Moisture Air-Oven Reference Methods in the United States1
Byline: G. Diane Lee

Grain moisture air-oven reference methods are used by many stakeholders in the United States and thesereference methods play an important role in measurement accuracy and uniformity of commercial grainmoisture meter measurements in the country. This article will provide a basic description of the air-ovenreference methods and their use; discuss the importance of grain moisture measurements in legal-for-tradeapplications; identify the key users of the air-oven reference methods for commercial use; review the originsof these air-oven reference methods; and outline the specific air-oven reference methods used for the major
U.S. grains.
What are the grain moisture air-oven reference methods in the United States and how are they used?
The grain moisture air-oven reference methods are procedures used to determine the percent moisture content in grain.
Basically, a small sample of grain (ground or unground) that represents a larger sample set of that grain is placed in asmall metal dish and the weight of the sample is recorded. The sample is then placed in an oven at a specifictemperature and heated for a specific amount of time. The sample is removed from the oven and cooled in a containerthat prevents loss or gain of moisture during the cooling process. Then the sample is reweighed. The loss in thesample mass is calculated as the percent moisture content of the grain.
Commercial grain moisture meters are devices that provide a rapid prediction of moisture in grain and are used to test
the moisture of grains that are bought and sold in the United States. Calibrations for commercial grain moisture meters
are developed by comparing the grain moisture meter reading to grain moisture air-oven reference values. Also, airoven reference methods determine the reference moisture values of grain samples that verify the accuracy andoperation of commercial grain moisture meters.
Why are grain moisture measurements important in commercial (legal-for-trade) applications?
Moisture is a critical commercial measurement in grain because “discounts” to the price per bushel of grain are madeat the time of sale, based on the moisture content of the grain. “Discounts” are reductions to the price per bushel ofgrain. Two examples of discounts are drying and shrinkage discounts. A grain buyer must dry grain that is too highin moisture to prevent molding during storage. The cost associated with drying the grain or a “drying discount” isdetermined based on the grain moisture measurement at the time of sale. This discount reduces the amount of money
the seller receives for the grain. For example, a buyer may be purchasing corn from a seller at $4.00 per bushel ofcorn at a target or desired 15 % moisture content. If the seller’s corn is higher in moisture content at the time of salethan is targeted or desired, the buyer will reduce the unit price per bushel he will give the seller for the grain. Grainsthat are too high in moisture may be placed into storage with aeration causing shrinkage. The cost associated withshrinkage or a “shrinkage discount” is also based on the moisture of the grain at the time of sale. Errors in the moisturemeasurements may result in large losses to either the seller or buyer of grain. See article number C-006, March 2007
“The Economic Impact of Errors in Moisture Measurements, Part 2, Grain Moisture Meter Series,” located at:www.nist.gov/pml/wmd/pubs/archives-grain-moisture.cfm, for additional information on discounts.
Who uses air-oven reference methods?
Stakeholders in the United States that use air-oven reference methods as the basis for commercial measurements ofmoisture in grain include:

1 Source:

Weights and Measures Connection, Volume 3, Issue 6, November 19, 2012.

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The U.S. Department of Agriculture, Grain Inspection, Packers, and Stockyards Administration (USDA, GIPSA);•The National Type Evaluation Program (NTEP) Laboratory for Grain Moisture Meters;•

Grain Moisture Meter (GMM) Manufacturers; and•State Weights and Measures and other state officials.

These organizations work together to ensure equity in the commercial grain market as illustrated in Figure 1. The
System of Commercial Grain Moisture Measurements in the United States, and Figure 2., The Movement of Grain in
The United States and Inspection Points.
The USDA, GIPSA uses air-oven reference methods to develop the calibrations for the official grain moisture
meter(s). These official grain moisture meters are used to measure the moisture of grains at export locations and uponrequest at interior grain facilities in the United States.
The National Type Evaluation Program (NTEP) Laboratory at the USDA, GIPSA uses these air-oven reference
methods when analyzing a national grain sample set and providing manufacturers with data to develop the calibrations
for all grain moisture meters used in commercial service in the United States. These reference methods are also used
to evaluate commercial (i.e., legal for trade) grain moisture meters in the NTEP laboratory to determine if prototypesof the device meet the requirements of the National Institute of Standards and Technology (NIST) Handbook 44
Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices, prior to being
used commercially in the United States. See Figure 1., the system of commercial grain moisture measurements in the
United States.
State Weights and Measures Officials and other State Officials use these reference methods to determine the moisturein grain samples that are used to test commercial grain moisture meters. Typically, the grain moisture meters tested
by State Weights and Measures or other state officials are at local elevators that purchase grain from farmers in theirjurisdictions. See Figure 1., the system of commercial grain moisture measurements in the United States and Figure 2.,
the movement of grain in the United States and inspection points.
Manufacturers of grain moisture meters use these reference air-oven moisture methods when developing thecalibrations for grain moisture meters that they sell for use in legal-for-trade applications. (See Figure 1. The systemof commercial grain moisture measurements in the United States.)

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NTEP and Manufacturing
SystemOfficial System

State Weights andMeasures System

USDA
GIPSA
Air-Oven
Moistures

Manufacturers
Air-Oven
Moistures
GIPSA
Master
Meter

Manufacturer'sLaboratory
Standard Meters

NTEP Lab
MetersStates AirOven
Moistures

Field Meter
Field Meter

Manufacturers
Production
Master Meters

GIPSA Field
Meter
GIPSA Field
Meter

Field Meter

Meters to be
Shipped(These Become
Field Meters)

GIPSA Field
Meter

Industry Expectation

Figure 1. The System of Commercial Grain Moisture Measurements in the United States.

Farm

Via Trucks

Local Elevator

State Weights and Measures Field Inspection
Test of commercial meters, typically at local elevators.

Usually Via Railway,
Barges or Ships)

Terminal
Elevator(Grain May be
exported from thislocation)

GIPSA Official Inspections
The official meter is used to test grainmoisture at Interior facilities and at export
locations.

ExportElevators

Usually Via Railway,
Barges or Ships)

Figure 2. The Movement of Grain in the United States and Inspection Points.

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History of Air-oven Reference Methods in the United States
The most widely recognized reference methods for determining moisture content in grain are based on drying known
weights of grain in various types of ovens and calculating moisture content from the weight lost in the drying
operation. 2 The USDA, GIPSA, identifies the “air-oven methods” as its official reference methods for determining
moisture in grain and oil seeds. According to the history of changes to USDA, GIPSA grain standards, these air-ovenreference methods have been in use since July 1, 1935. The USDA, GIPSA air-oven reference methods were acceptedby the American Association of Cereal Chemists (AACC, currently known as AACC International), Method 44-15A.
Although oven methods are subject to error due to the loss of substances other than water during the drying process,Hart and Neustadt adapted the use of Karl Fisher (KF) Titration in 1957 to test the accuracy of the USDA air-ovenmoisture methods. i The USDA air-oven methods were designed to give results which agree with those obtained by
KF Titration. KF Titration provides moisture values by extracting water from grain with the use of a solvent, such as
methanol, and is more specific for grain moisture. Historical records have noted that KF Titration required more time
for testing than was practical and, due to the test process at that time, there were repeatability issues from operator tooperator due to portions of the test that were not automated. Frank E. Jones and Carroll S. Brickenkamp, National
Bureau of Standards (NBS, now known as the National Institute of Standards and Technology), National Engineering
Laboratory, noted that techniques were developed to automate KF Titration to address some of the earlier
disadvantages of this method. Jones and Brickenkamp also noted that, although the KF Titration is more specific formoisture, additional tests are needed to determine if other substances react with the solvent used to extract water.3
The air-oven reference methods remains the reference methods for moisture in the United States; this is likely because
these methods have been compared to KF Titration and/or other more definitive tests and have proven to provide very
repeatable measurements.
Air-oven Reference Methods for Major U.S. Grains
There are currently eight air-oven moisture reference methods used to determine moisture in the major U.S. grains
and these methods are recognized internationally. These reference methods vary per grain type, moisture, andcommodity and are maintained at the USDA, GIPSA in the Technology and Science Division’s Laboratory Work
Instructions. These work instructions include specific procedures, guidance on test sample size, equipment andmaterial, and acceptance criteria needed for each test. Because these air-oven reference methods vary per grain type,the following tables are provided to summarize the different air-oven reference methods used in the United States.
AO_1
Single-Stage Air-Oven Reference Method for Moisture in Grains, Oilseeds, and Commodities: is thedifference in weight after drying a ground sample of grain for one hour at 130 ºC ± 1 ºC (drying timeis two hours for soybean meal). The following grains and commodities are tested using this method:
Grains and Oilseeds

Commodities

Description

Moisture
Restriction

Description

Barley≤ 16 %

Barley - submitted

Lentils≤ 16 %

BulgurOats≤ 16 %

Corn Soy BlendPea≤ 16 %

Corn Soya Flour

Rice, brown≤ 16 %

Corn Soy Milk

Rice, milled≤ 16 %

Corn - submitted

Rice, rough≤ 13 %

Corn Meal

Rye≤ 16 %

Dessert Powder

2 Storage of Cereal Grains and Their Products, Chapter 1:

Moisture–Its Significance, Beahavior, and Measurement, W. Harward
Hung and S.W. Pixton.
3 Journal of AOAC, Volume 64, Number 6, 1981, Frank E. Jones and Carroll S. Brickenkamp.

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AO_1
Single-Stage Air-Oven Reference Method for Moisture in Grains, Oilseeds, and Commodities: is thedifference in weight after drying a ground sample of grain for one hour at 130 ºC ± 1 ºC (drying timeis two hours for soybean meal). The following grains and commodities are tested using this method:
Grains and Oilseeds

Commodities

Description

Moisture
Restriction

Description

Sorghum≤ 16 %

Egg Noodles

Soybeans≤ 10 %

Hominy Grits

Sunflower ground 50/50 with celiteNon (formoisture
correctionof crude oil
results

Icing Mix Powder

Triticale≤ 16 %

LasagnaWheat≤ 16 %

Macaroni
Macaroni and Cheese
Rotini
Rolled Wheat
Sorghum Grits
Soybean Meal
Spaghetti
Wheat Flour
Wheat Soy Blend
Wheat Soy Milk
Wheat – submitted

Cited References: AOCS Method Ba 2a-38; AACC Method 44-15A; AOAC Method 925.10;
ASTM; NIST; Kenyon, A.S., Black, J.C., & Layloff, T.P. (1995); J. Assoc. Off. Anal. Chem. 78,
1109-1111

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AO_2
Two-Stage Air-Oven Reference Method for Moisture in Grains and Oilseeds is the differencein weight after air-drying a unground sample of grain until its moisture content is≤ 16 % (≤ 10 % for soybeans and ≤ 13 % for rough rice), then drying the ground, air-driedsample for one hour at 130 ºC ± 1 ºC (two hours for soybean meal). The following grains aretested using this method:
Grains and Oilseeds
Description

Moisture
Restriction

Barley˃ 16 %

Lentils˃ 16 %Oats˃ 16 %

Peas

˃ 16 %

Rice, brown˃ 16 %

Rice, milled˃ 16 %

Rice, Rough˃ 13 %

Rye˃ 16 %

Sorghum˃ 16 %

Soybeans

˃ 10 %

Triticale˃ 16 %wheat˃ 16 %

Cited References: AACC Method 44-15A;, ASTM; NIST; Kenyon, A.S., Black, J.C., & Layloff, T.P.
(1995); J. Assoc. Off. Anal. Chem. 78, 1109-1111.

AO_3
Air-Oven Reference Method for Moisture in Corn and Beans is the difference inweight after drying an unground sample of grain for 72 hours at 103 ºC ±1 ºC. The
following grains are tested using this method:
GrainsDescription

Moisture

Corn

Any

Beans

Any

Cited References: AACC Method 44-15A; ASTM; NIST; Kenyon, A.S., Black,
J.C., & Layloff, T.P. (1995); J. Assoc. Off. Anal. Chem. 78, 1109-1111.

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AO_4
Air-Oven Reference Method for Moisture in Mustard, Canola and Rapeseed is thedifference in weight after drying an unground sample of grain for one hour at 103 ºC±1 ºC (two hours for soybean meal), repeat the drying and if the difference between
the 1st and 2nd weight after each drying is greater than 0.01 g the sample is dried foran additional hour. The following grains are tested using this method:
GrainsDescription
Moisture
MustardAny
CanolaAny
Rapeseed
Any
Cited References: ISO 665; ASTM; NIST; Kenyon, A.S., Black, J.C., & Layloff,
T.P. (1995); J. Assoc. Off. Anal. Chem. 78, 1109-1111.

AO_5
Air-Oven Reference Method for Moisture in Flaxseed is the difference in weight after
drying an unground sample of seed for four hours at 103 ºC ±1 ºC. The following
grains are tested using this method:
Grain

Description

Moisture

Flaxseed

Any

Cited References: AACC Method 44-15A; ASAE Method S352.2; ASTM; NIST;
Kenyon, A.S., Black, J.C., & Layloff, T.P. (1995); J. Assoc. Off. Anal. Chem. 78,
1109-1111.

AO_6
Air-Oven Reference Method for Moisture in Safflower seeds is the difference inweight after drying an unground sample of seed for one hour at 130 ºC ±1 ºC. The
following grain is tested using this method:
Grain

Description

Moisture

Safflower seeds

Any

Cited References: ASAE Method S352.2; ASTM; NIST; Kenyon, A.S., Black,
J.C., & Layloff, T.P. (1995); J. Assoc. Off. Anal. Chem. 78, 1109-1111.

AO_7
Air-Oven Reference Method for Moisture in Sunflower seeds is the difference in weightafter drying an unground sample of seed for three hours at 130 ºC ±1 ºC. The following
grain is tested using this method:
Grain

Description

Moisture

Sunflower seeds

Any

Cited References: AOAC Method Ac 2-41; AOAC Method Ai 2-75; ASTM; NIST;
Kenyon, A.S., Black, J.C., & Layloff, T.P. (1995); J. Assoc. Off. Anal. Chem. 78, 11091111.

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AO_8
Air-Oven Reference Method for Moisture in Corn Gluten Feed is the difference in weightafter drying the ground sample for four hours at 103 ºC ±1 ºC. The following sample istested using this method:
Grain

Description

Moisture

Corn Gluten Feed

Any

Cited References: Method of the Corn Refiners Association; ASTM; NIST; Kenyon,
A.S., Black, J.C., & Layloff, T.P. (1995); J. Assoc. Off. Anal. Chem. 78, 1109-1111.

AO_10 through AO_15 are reference methods for other commodities and processes forlaboratory check samples and equipment maintenance:
AO_10

100 º C Vacuum Oven Reference Method for moisture in Commodity Samples

AO_11

Processing the Air-Oven Laboratory Wheat Check Sample

AO_12

Processing the Air-Oven Laboratory Corn Check Sample

AO_13

Air-Oven Uniformity Check

AO_14

Calibrating the Thermometers Used in the Air-Oven Laboratory

AO_15

Moisture Dish Maintenance and Tare Weight Check Schedule

Many studies of air-oven reference methods have been conducted over the years since the first use of these reference
methods. These studies resulted in changes to the air-oven reference methods that improved the accuracy of grainmoisture meter measurements. The air-oven reference methods are well established in the United States. Stakeholders
use these reference methods to develop the calibrations for all commercial grain moisture meters and to test thesedevices to provide uniformity in the market place.
NIST, OWM greatly appreciates the review and comments of Dr. Richard Pierce, USDA, GIPSA during thedevelopment of this article.
For additional information concerning this article, please contact Diane Lee by e-mail at diane.lee@nist.gov or the
Office of Weights and Measures at (301) 975-4004, e-mail at owm@nist.gov.

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Appendix C. Reference Test Weight Value of per Bushel Value of Grains_______________________________________________________________________________________________
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Appendix C.
Determining Reference Test Weight per Bushel Value of Grains1
By G. Diane Lee“Test weight per bushel” is a measurement of the weight of a volume of grain required to fill level a Winchester bushel
measure of 2 150.42 cubic inches (equivalent to 32 quarts) in capacity 2. Test weight per bushel is one of themeasurements used by the U.S. Department of Agriculture (USDA), Grain Inspection Packers and Stockyards
Administration (GIPSA) in grain grading. For example, USDA No. 1 hard red spring wheat has a minimum limit fortest weight per bushel of 58.0 pounds per bushel. In the market place, test weight per bushel is a commercial
measurement because it affects the market value of grain. When a farmer sells grain, the grain price may be“discounted.” If “discounted” for test weight, the farmer receives less money for the grain if the test weight per bushel
measurement is under a certain specified target weight per bushel, such as 58.0 pounds per bushel. Many grainmoisture meters, currently in commercial use, that are covered by a National Type Evaluation Program (NTEP)
Certificate of Conformance, provide grain test weight per bushel measurements that are used to assess the amount ofmoney a farmer will receive for grain. As such, the “test weight per bushel” measurement must be verified for
accuracy. The process used to verify the accuracy of a meter’s test weight per bushel measurement begins in thelaboratory. Both the NTEP laboratory and state weights and measures laboratories use a reference test weight per
bushel measurement procedure, and specific equipment to determine the reference test weight per bushel values ofvarious grains. Once a reference test weight per bushel value is determined for the grains, the grains are used to verify
the accuracy of the test weight per bushel feature on meters. Both the NTEP laboratory and State Weights andMeasures field inspectors verify the accuracy of the weight per bushel measurement of meters by comparing the resultsof the weight per bushel measurement on the meter to the reference “test weight per bushel” value of the grain samples
that are placed in the meter for measurement. This article addresses the laboratory equipment, equipment maintenance,and reference procedures for test weight per bushel because of its importance in determining the accuracy of the test
weight per bushel measurement of meters.

Equipment
To determine reference test weight per bushel
measurements of grain, use test weight per
bushel equipment approved by USDA, GIPSA.
The USDA, GIPSA Equipment Handbook
includes two lists of GIPSA approved
equipment: active and inactive. The active
equipment list includes GIPSA approved
equipment that is commercially available. The
inactive equipment list contains GIPSA
approved equipment no longer manufactured
or widely marketed, but is still approved foruse.
The equipment used to determinereference test weight per bushel values forgrain are:•

1 Source:a quart kettle,

Weights and Measures Connection, Volume 4, Issue 6, September 26, 2013

2 Circular No. 921 U.S. Department of Agriculture, June 1953

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a scale specifically designed to measure test weight per bushel,•a filling hopper,•

an over flow pan, and•a stroker.

Figure 1. Test Weight per Bushel Equipment – Active Approved Equipment includes test weight per bushel equipmentfrom GIPSA’s active approved equipment list and currently in use at the USDA, GIPSA in Kansas City, Missouri.

Equipment Maintenance
The test weight per bushel equipment must be checked and adjusted prior to initial use; and periodically, thereafter,
as needed. A maintenance schedule of the checks and adjustments made to the equipment must be documented. The
specifications and maintenance for test weight per bushel equipment are included in GIPSA’s Equipment Handbook,which can be downloaded from the USDA, GIPSA Website at:
http://www.gipsa.usda.gov/fgis/handbook/equip_inspec.aspx

Procedure for Determining the Reference Test Weight per Bushel Value ofGrainsIn general, the procedure used to determine the reference test weight per bushel of grain
is to weigh one dry quart of the grain on a suitable scale that is designed to multiply theweight by 32, since there are exactly 32 quarts to a dry bushel. These specially designed
scales provide a direct reading of test weight per bushel. Since these scales indicate 32
times the weight of the content in the dry quart, it is very important to follow proceduresfor determining the reference test weight per bushel values of grain.
The following is a step-by-step procedure to determine the reference test weight per bushel
values of grain samples that are used to test meters or other equipment used to provide test
weight per bushel measurements to customers in the marketplace.

1. Before starting the procedure, ensure that the equipment is positioned
correctly by placing a level on top of the quart kettle to ensure that it is in a level condition on thetest stand and position the filling hopper two inches above the top of the quart kettle. Procedures
for measuring this distance are included in Chapter 5 of the USDA GIPSA Equipment Handbook.
2. Place the empty quart kettle on the scale; then zero the scale (Figure 2. Zerio Weight of the Empty
Quart Kettle).
3. Close the bottom of the fill hopper; place about 11/8 quart of grain in the filling hopper, and place
the quart kettle on the test stand.
4. Position the fill hopper over the quart kettle by swiveling the fill hopperand fill the kettle from the hopper (Figure 3. Filling the Quart Kettle fromthe Filling Hopper). Do not move the kettle while it is being filled.
5. Once the quart kettle is full, move the fill hopper away from the quart kettle
being careful not to move the kettle.

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Appendix C. Reference Test Weight Value of per Bushel Value of Grains_______________________________________________________________________________________________
This publication is available free of charge from: https://doi.org.10.6028.NIST.HB.159-2017

6. Hold the stroker on each end with your fingers so that the sides are in a
vertical position and place it lightly on the edge of the kettle without moving
the kettle (Figure 3a. Remove Excess Grain).
7. Stroke the excess grain from the top of the quart kettle in a zigzag motion withthree full strokes. Each stroke should cover 1/ 3 of the top of the kettle (Figure 3b.
Stroke Pattern: Start with the Stroker at the Edige of the Quart Kettle and Follow a
ZigZag Pattern).
Important Note: Scales used to measure test weight
per bushel are specially designed to provide anindication that is 32 times the weight of the grain in
the quart kettle. So, if the quart kettle contains 1 pound, then the scale will show aweight per bushel indication of 32 pounds per bushel (1 to 32 ratio). It is extremely
important to follow the procedure for step 6, stroking excess grain from the quart
kettle because too much or too little grain removed, will impact the measurement by
a multiple of 32 (e.g., if 1 ounce of grain is removed that should have been part of themeasurement there will be a 2.0 pounds per bushel error in the test weight per bushel
measurement).

Example of calculation:
1 lb = 16 oz
1 oz/16 oz = 0.0625 lb,
so, 0.0625 lb × 32 = 2.0 lb
8.
Carefully remove the quart kettle from the stand and weigh the kettle and grainon the scale and record your results. (See Figure 4. Weighing the Quart Kettle and Grain)
In accordance with the National Institute of Standards and Technology (NIST)
Handbook 44, Specifications, Tolerances, and Other Technical Requirements for
Weighing and Measuring Devices, Section 5.56.(a) Grain Moisture Meters, paragraphN.1.1. Air-Oven Reference Method Transfer Standards, repeat steps 1 through 8, 10 times and average the results foreach grain type. The test weight per bushel value assigned to the grain samples is the average of 10 measurements.
When assigning this value, it must be noted that when a standard is used without correction, the combined error anduncertainty in your measurement must be less than one-third of the applicable tolerances, in accordance with NIST
Handbook 44, Appendix A. Fundamental Considerations, Section 3.2. “Tolerances for Standards.”
The consistent use of proper techniques and proper equipment is key to successfully determining the reference values
for test weight per bushel.
Using the prescribed test procedures and correct equipment, as provided in this article along with maintaining yourequipment in accordance with the USDA, GIPSA Equipment Handbook will reduce the variability and error in yourreference test weight per bushel measurements made in the laboratory. Practice removing the excess grain from thequart kettle will result in better measurement repeatability. Additionally, grain samples with accurate weight per
bushel values will help to ensure proper testing of meter weight per bushel measurements.

Resources for Test Weight per Bushel Reference Measurements•

USDA, GIPSA Equipment Handbook at:
http://www.gipsa.usda.gov/Publications/fgis/handbooks/equip_insphb.html.

•

Circular No. 921 “The Test Weight per Bushel of Grain: Methods of Use and Calibration of the Apparatus,”
June 1953, United States Department of Agriculture.

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Appendix C. Reference Test Weight Value of per Bushel Value of Grains_______________________________________________________________________________________________
This publication is available free of charge from: https://doi.org.10.6028.NIST.HB.159-2017

For additional information concerning this article you may contact Diane Lee of the NIST, Office of Weights andMeasures (OWM) by e-mail at diane.lee@nist.gov, or contact the office at owm@nist.gov, phone (301) 975-3998.

Note: It is policy of the National Institute of Standards and Technology to use metric units of measurement
in all of its publications. However, in this newsletter the references to inch-pound units are used as they
are commonly used in industry practice and in source documentation.

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