Inside this Issue

Tightening the Belt 2

Calendar 3

Weights and Measures in the News 6

Weights 

and 

Measures 

Historical Moment 

Weights and Measures Week was first reported in the 1916 National Conference on

Weights and Measures Annual Report. There

was a resolution for the observance to be

scheduled for Sunday, June 18, and ending

Saturday, June 24. The resolution originated

in New York City. The report states:

“It is further recommended that weights and

measures officials who intend to promote

weights and measures week obtain support

of supervisors, the mayors, and governors of

their respective communities, as well as the

cooperation of consumers, organizations,

women’s clubs and societies, trade, commerce, and industrial associations. It is further recommended that weight and measure

week shall not be celebrated as a fete or a

ceremony, but shall be used for the general

purpose of stimulating interest in and support of weights and measures laws and subjects with the ultimate view of educating

both the buying and selling public.” 

1

Volume 5 Issue 1

March 3, 2014

Will Spring Ever

Come?

What an interesting winter we have been experience here in the Washington, D.C., Metropolitan Area. The groundhog definitely saw his

shadow on Ground Hogs Day! It has been unseasonably snowy and cold this year. While our

areas does not see the huge snowfalls that some

of you experience each year, here snow and ice become crippling because

we are not customarily treated to so many of these events. 

The school kids are delighted, at least for now, because they have had many

days off of school or with delayed start times. Of course, if they are forced

to make-up days, there will be frowns later! The disruptions have also been

experienced at work too. While our worksite has been closed on several

occasions and there have been days of late arrivals, many of us are continuing to try to service our customers through telework options. This is not a

perfect solution to being away from the office, but it does afford us the opportunity to stay in touch and forward electronic information to our customers via e-mail. So, while we are not at the office, we are camping out in

our home offices, kitchens, or handy nooks waiting to help our customers

in the best way we can. Take notice Mr. Groundhog, while we are not happy

with the six weeks of extended winter you granted us, we know that soon

spring will come, the days will warm up, the flowers will bloom, and disruptions will be a past memory. Thank you to the Weights and Measures Community for bearing with us.

The Editor

Weights and Measures Week

March 1 - 7, 2014

Celebrate all that you do to assure equity in the marketplace!
W&M Connection 2 Volume 5 Issue 1

Tightening the Belt 

(ON BELT-CONVEYOR SCALE SYSTEMS)

By John Barton

The NIST Office of Weights and Measures (OWM) periodically receives questions about the installation and operation of

belt-conveyor scales. More recently, OWM has been asked for information and guidance pertaining to requirements regarding the method(s) of applying tension to the conveyor belt. The objective of this article is to answer those questions

and provide guidance for those responsible for the inspection and testing of belt-conveyor scale systems.

Consider the diagram of a simple conveyor belt in Figure 1 below. As one would likely expect, an appropriate amount of

friction must be maintained between the conveyor belt and the drive pulley to transfer the motion from the drive pulley

to the belt. In other words, the belt must maintain a “grip” on the drive pulley in order for the belt to be set in motion. In

many of these systems, specially designed components are needed to ensure that proper belt tension is achieved.

Figure 1. Conveyor Belt 

In addition to being a critical factor in facilitating the movement of the conveyor belt, appropriate belt tension is crucial for

other reasons such as preserving the condition of the belt. Too little or too much belt tension can lead to shortened belt

life, uneven belt wear, excessive friction (a potential fire hazard), and mechanical (bearing) failure of the conveyor structure. 

Belt-conveyor scale manufacturers will generally specify that belt tension should be consistent for optimal performance of

their weighing devices and the belt-conveyor scales should be installed in an area along the conveyor where belt tension

is minimal. 

The consistency of the belt itself is subject to changes under normal operating conditions. Variations in the ambient temperature at the location site of the belt-conveyor as well as variations in the temperature of the belt imparted through the

operation of the conveyor can result in changes in the elasticity of the belt. This change in the elasticity will cause the belt

to stretch and contract with those fluctuations in temperature. The magnitude of change in the elasticity of the belt will

correspond to the amount of temperature change. These physical characteristics of the belt are also directly related to the

type of material and manufacturing process used when the belt is produced.

The potential for significant development of “slack” in the belt due to temperature-related changes will increase as the

initial size of the belt increases. In other words, a longer conveyor belt will typically exhibit greater changes in size due to

temperature variation than will a shorter conveyor belt. Of course, any substantial amount of slack in the belt will result

in a loss of friction between the belt and the drive pulley.

HAVE YOU CHECKED OUT THE TRAINING CALENDAR?

Tail Pulley

Carrying rollers

Return rollers

Snub pulley

Head pulley

Drive pulley 
W&M Connection 3 Volume 5 Issue 1

TYPES OF BELT TENSION DEVICES

To account for the changes in belt length that may occur during operation,

many conveyor systems are equipped with a means to adjust the tension of

the conveyor belt. Some tension devices will make this adjustment by increasing or decreasing the distance between the terminal pulleys (i.e., head

and tail pulleys in Figure 1) on the conveyor. Other systems will employ additional pulleys along the conveyor line that are designed to take-up excess

slack in the belt.

A significant distinction in belt tension devices is whether they function automatically or, conversely, must be adjusted manually. Considering the previous discussion regarding the effect of temperature on belt elasticity, one

might expect that belt tension devices designed to be adjusted manually

would require continuous monitoring by an operator and adjustment during

operation on systems where changes in belt elasticity and temperature stability are issues. This is the primary reason why leading belt-conveyor scale

manufacturers will not recommend the use of manually-adjusted tension devices in “legal for trade” applications.

Automatic belt tension devices are capable of maintaining a more consistent

belt tension by making prompt adjustments in direct response to the changes

in the belt elasticity. These devices utilize various methods to maintain relatively consistent belt tension. Some examples of these methods include:

gravity type take-ups, spring tension, and pneumatic/hydraulic controlled tension.

Currently, the NIST Handbook 44, Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices, Belt-Conveyor Scale

Systems Code only permits the “counter weighted” (or gravity type) take-ups

to be used on commercial belt-conveyor scale systems. Of the various methods listed, gravity take-ups are arguably one of the simplest and most commonly used means for automatically controlling tension in

belt-conveyor scale systems, particularly on larger systems. As illustrated in

figure 2, these devices incorporate a weighted roller suspended from the underside (return side) of the belt. The effect of gravity on the roller effectively

pulls that portion of the belt downward, thus, providing a constant tension

to automatically account for slack in the conveyor belt.

Calendar 2014

Registration for training in the NIST Office of

Weights and Measures is handled by Yvonne

Branden at yvonne.branden@nist.gov.

Course descriptions can be viewed on the Office of Weights and Measures website at

http://www.nist.gov/pml/wmd/calendar.cfm

and clicking on the name of the course. 

March 10 - 14 (5 day)

HB 130, Packaging and Labeling

Class No. 5307

Frankfort, KY

March 26 - 28 (3 day)

HB 130 Packaging and Labeling

Class No. 5303

White Plains, NY

March 31 - April 4 (5 days)

Fundamental of Metrology

Class No. 5275

NIST/Gaithersburg, MD

April 7 - 11 (5 day)

HB 130 Packaging and Labeling

Class No. 5300

Arcadia, CA

April 8 - 10 (3 days)

Train the Trainer

Class No. 5305

NIST/Gaithersburg, MD

April 17

Webinar - Proficiency Testing Follow-up Actions and

Root Cause Analysis

2:00 p.m. - 4 p.m.

Class No. 5306

April 28 - May 9 (2 weeks)

Mass Metrology Seminar

Class No. 5290

NIST/Gaithersburg, MD

May 5 - 8 (4 days)

Northeastern Weights and Measures Association

(NEWMA) - Annual Meeting

Manchester, NH

Contact: James Cassidy at

jcassidy@cambridgema.gov

May 19 - 22 (4 days)

Central Weights and Measures Association

(CWMA) Annual Meeting

St. Louis, MO

Contact: Sherry Turvey at 

sherry.turvey@kda.ks.gov

June 2 - 6 (5 days)

LiquefiedPetroleum Gas Liquid-Measuring Devices

Class No. 5314

Las Cruces, NM

(con’d on pg 4)

Gravity Take-Up

Figure 2. Counter-weighted or Gravity Take-up Device
W&M Connection 4 Volume 5 Issue 1

June 9 - 13 (5 days)

HB 133, Basic - Checking the Net Contents of Packaged Goods

Class No. 5304

Williamston, MI

June 19 - 23 (5 days)

Laboratory Administration

Class No. 5291

NIST/Gaithersburg, MD

July 13 - 17 (5 days)

National Conference on Weights and Measures -

Annual Meeting

Detroit, MI

Contact: info@ncwm.net

August 11 - 15 (5 days)

HB 133, - Basic - Checking the Net Contents of

Packaged Goods

Class No. 5313

Little Rock, AR

August 14

Webinar - Calibration Certificate Evaluation

2:00 p.m. - 4 p.m.

Class No. 5292

August 18 - 22 (5 days)

Volume Metrology Seminar

Class No. 5293

NIST/Gaithersburg, MD

August 20 - 21 (2 days)

NTEP Grain Analyzer Sector Meeting

Kansas City, MO

Contact: info@ncwm.net

August 21

Webinar - Contract Review

2:00 p.m. - 4 p.m.

Class No. 5301

August 26 - 28

NTEP Joint Meeting of:

Weighing Sector (Aug. 26 - 27) (2 days)

& Software Sector (Aug. 27 - 28) (2 days)

College Park, GA

Contact: info@ncwm.net

Webinar - Document Control and Record Keeping

2:00 p.m. - 4 00 p.m.

Class No. 5299

September 8 - 19 (2 weeks)

Mass Metrology Seminar

Class No. 5297

NIST/Gaithersburg, MD

September 11

Webinar - Conducting an Effective Management

Review

2:00 p.m. - 4:00 p.m.

Class No. 5295

September 14 - 18

Western Weights and Measures Association 

(con’d on pg 5)

If slack in the belt increases, belt tension is maintained due to the counter

weighted take-up device being drawn further downward. If the slack in the

belt decreases, the counter-weighted design allows the belt to return towards

its original profile.

There are other more sophisticated methods that are reportedly at least as

effective as the gravity take-ups. Other automatic types of devices use pneumatic or hydraulic pistons to adjust the position of an attached pulley which

in turn will apply more or less tension on the conveyor belt. As to why these

methods are not recognized in Handbook 44, it is likely that they may not

have existed when the Handbook 44 Belt-Conveyor Scale Code was drafted.

These alternatives, therefore, may not have even been considered when the

counter weighted take-ups were recognized as being the only type of tension

devices appropriate for use in commercial applications.

HANDBOOK 44 REQUIREMENTS FOR MAINTAINING BELT TENSION

While improper belt tension is certainly problematic for the owner or operators of conveyor systems by causing belt slippage and poor belt tracking, it

must also be of considerable concern to officials conducting inspections of

belt-conveyor scale systems due to the impact it can have on the accuracy of

these weighing devices. 

There are requirements in HB44 that can be cited to require a device owner

or operator to take corrective action on a conveyor belt operating when the

belt tension is not properly maintained; however, those requirements have

somewhat limited applications.

General Code paragraph G-UR.2.1. Installation and Belt-Conveyor Scale Systems Code paragraph UR.1.2. Conveyor Installation shown in Figure 3, both

relate to the installation of equipment and state that the systems must be

installed in accordance with the manufacturer’s instructions. 

G-UR.2.1. Installation. – A device shall be installed in accordance

with the manufacturer’s instructions, including any instructions

marked on the device. A device installed in a fixed location shall be

installed so that neither its operation nor its performance will be adversely affected by any characteristic of the foundation, supports, or

any other detail of the installation.

UR.1.2. Conveyor Installation. – The design and installation of the

conveyor leading to and from the belt-conveyor scale is critical with

respect to scale performance. The conveyor can be horizontal or inclined, but if inclined, the angle shall be such that slippage of material

along the belt does not occur. Installation shall be in accordance with

the scale manufacturer’s instructions and the following:

•

•

•

(d) Take-up Device. – If the belt length is such that a take-up device is required, this device shall be of the counter-weighted

type for either vertical or horizontal travel.

Figure 3. Handbook 44 Requirements G-UR.2.1. and UR.1.2.
W&M Connection 5 Volume 5 Issue 1

The application of these two requirements to address concerns about proper

belt tension is somewhat dependent upon whether or not the belt-conveyor

scale manufacturer’s installation instructions specify that a tension device

must be installed and how it must be used. 

It should be noted that the subparagraph UR.1.2.(d) also shown in Figure 3 is

the only requirement in Handbook 44 that specifically addresses belt tension.

This requirement also has limited application, in that it only specifies that a

take-up device must be the counter-weighted type for either vertical or horizontal travel. It does not require a belt tension device to be incorporated in

the system unless the belt is long enough that one is needed. 

The central issues of inquiries received by NIST OWM regarding conveyor belt

tension have been that: (1) HB44 requirements do not mandate that a takeup device be used unless the belt is of such a length that one is needed, yet

the specific length is not defined; and (2) if a tension device is used, it shall

only be the “counter-weighted type.” A number of field officials believe that

the language in Subparagraph UR.1.2.(d) is subjective and that it does not

provide clearly defined parameters (for conveyor length) to indicate when a

belt tension device is needed. This requirement is also considered by some

as being excessively prescriptive because only one particular design type of

belt tension device is permitted.

In order to require corrective action to be taken by the owner/operator of a

belt-conveyor scale system that is subject to problems related to belt tension,

officials would be advised to refer to any available installation instructions for

the device. If manufacturer instructions specify that a tension device must

be used, officials can require such in accordance with requirements noted

above. In the absence of the manufacturer’s installation instructions requiring

the use of a belt tension device, the owner may take the position that he or

she is not required to install a belt tension device and, therefore, cannot be

compelled to add one to comply with weights and measures regulations. 

PROPOSED CHANGES TO HANDBOOK 44

The NIST U.S. National Working Group (USNWG) on Belt Conveyor Scales is

working towards a resolution of this issue as part of a broader USNWG effort

to propose changes to a number of sections in the Handbook 44 Belt-Conveyor Scale Systems Code. The current requirements found in the existing

Belt-Conveyor Scale Systems Code apply primarily to belt-conveyor scales that

are installed in existing conveyor systems. The USNWG’s proposed changes

are intended to amend the requirements so that they are more applicable to

systems that are designed and manufactured as complete conveyor belt units

that include integral weighing devices. Some of these proposed changes involve specific requirements that refer to belt length and the required spacing

between the locations of different components in the system. During the

USNWG’s meeting in February 2013, members expressed their support for an

amendment to UR.1.2.(d) as shown below in Figure 4. Language to be deleted

is shown as strike through text and language to be added is shown as underlined text.

REMINDER

THE 99TH NCWM ANNUAL

MEETING

July 13 - 17, 2014

The 2014 Annual Meeting will take place in

Detroit, Michigan. Early Bird registration

closes June 20, 2014. Information can be obtained on the NCWM website at

http://www.ncwm.net. Register today and

share your valuable experience and knowlege with the membership. Federal, state,

county, and industry participation is welcome.

Contact: (402) 343-4880 or info@ncwm.net

S

P

R

I

N

G

WILL

C

O

M

E

(WWMA) Annual Meeting

Contact: Brett Saum at bsaum@co.slo.ca.us

October 15 - 16 (2 days)

Northeastern Weights and Measures Association

(NEWMA) Interim Meeting

TBD

Contact: info@ncwm.net

October 19 - 24 (6 days)

Combined Regional Measurement Assurance Program

Class No. 5157

St. Louis, MO

November 3 - 7 (5 days)

Fundamentals of Metrology

Class 5309

NIST/Gaithersburg, MD

*Invitation Only

**Limited to State Laboratory Program Participants
W&M Connection 6 Volume 5 Issue 1

WEIGHTS AND MEASURES

IN THE NEWS

ccj

Looming natural gas measurement proposal a setback for CNG/LNG adoption?

http://www.ccjdigital.com/looming-natural-gas-measurement-proposal-a-setback-for-cnglng-adoption/

Special Report: Retail Ripoff - Are You Getting What you Pay For?

http://www.wsaw.com/home/headlines/Retail-Rip-Off-246054341.html?ref=341

The Topeka Capital-Journal - cjonline.com

Agriculture budge panel OKs scale inspector money

http://cjonline.com/news/2014-02-10/agriculture-budget-panel-oks-scale-inspector-money

UR.2.2. Conveyor Installation. – The design and installation of the conveyor leading to and from the belt-conveyor

scale is critical with respect to scale performance. The conveyor can be horizontal or inclined, but if inclined, the

angle shall be such that slippage of material along the belt does not occur. Installation shall be in accordance with

the scale manufacturer’s instructions and the following:

•

•

•

(d) Take-up Device. – If the belt length is such that a take-up deice is required, this device shall be of the

counter-weighted type for either vertical or horizontal travel. Any take-up device shall provide constant

and consistent tension for the belt under all operating conditions.

The proposed amendment attempts to simplify the requirement and to clearly state that adequate belt tension shall be

automatically maintained in a constant and consistent manner. This wording is intended to provide clear requirements to

ensure that belt tension be maintained without the use of the prescriptive language that appears in the existing requirement. If the proposal is eventually adopted, it is expected to provide the field inspector with a more useful tool for the

regulation of belt-conveyor scale systems while also providing greater latitude in design specifications for belt tension devices.

As a critical aspect for the proper operation of a belt-conveyor scale system, belt tension should not be overlooked during

the inspection and test of these devices. At this time, field officials have somewhat limited options for requiring device

owner/operators to take corrective measures to resolve inappropriate belt tension. However, if the changes proposed by

the USNWG to the Belt-Conveyor Scale Systems Code are adopted, field officials will be provided with the means to help

ensure improved belt-conveyor scale performance.

Comments or questions about this article or related matters may be directed to:

John Barton

100 Bureau Dr., Mail Stop 2600

Gaithersburg, MD. 20899

(301) 975-4002

John.barton@nist.gov

Figure 4. Proposed HB44 Belt-Conveyor Scale Systems Code UR.2.2.