**Examination Procedure Outline for**

**Vehicle and Axle‑Load Scales**

## Electronic-Digital Indicating

It is recommended that this outline be followed for vehicle and
axle‑load scales equipped with electronic digital indicators. 
Requirements that apply only to scales marked with an accuracy class are
indicated with an asterisk. Nonretroactive requirements are followed by
the applicable date in parentheses.

**SAFETY NOTES**

***Inspection:***

# Safety First

> **H‑44 General Code and**
>
> **Scales Code References**

1\. Position of equipment G-UR.3.3.

2\. Zero‑load balance as found. S.1.1., UR.4.1.

If the device is not in balance, the user should be made aware of
paragraph UR.4.1. and a warning issued if necessary.

Digital zero G-S.5.2.2.(d) (1/1/86)

Digital indicating elements S.1.1.1.

Zero-load adjustment S.2.1.1., S.2.1.2., S.2.1.3.,

(1/1/81), S.2.1.3.1. (1/1/01)

3\. Indicating, and recording elements.

> Appropriateness G-S.5.1.
>
> Graduations, indications, and recorded representations G-S.5.1.
>
> Values of graduated intervals or increments G-S.5.3., S.1.2.\*,,
> S.1.2.1.
>
> Repeatability G-S.5.4.
>
> Money values, mathematical agreement G-S.5.5.
>
> Recorded representations G-S.5.6., UR.1.3. (1/1/86)
>
> Magnified graduations and indications G-S.5.7.
>
> Rounding......................................................................................G-S.5.2.2.(c)
>
> Manual Gross Weight
> Entries..............................................................S.1.12.(1/1/93),UR.3.9.
>
> Tare S.2.3.(1/1/83)
>
> Damping and motion detection S.2.5., S.2.5.1.(a)

4\. Design of weighing devices, accuracy class S.5.\*, S.5.4. (1/1/94),

S.1.10., G-S.8. (1/1/90)

G-UR.4.5.,

S.1.11.(a) (1/1/79)

S.1.11.(b) (1/1/90)

S.1.11.(c) (1/1/95)

***Inspection (cont.)***

5\. Suitability G-UR.1.1., G-UR.1.2.,

UR.1., UR.1.1.(a),

UR.1.1.(b), UR.3.1.,

UR.3.5., UR.3.7.

6.  Marking S.6.3., S.6.2.

Nominal capacity S.6.1. (1/1/86)

Nominal capacity must satisfy the relationship of:

nominal capacity ≤ CLC x (N - 0.5), where N = the number of sections in
the scale

a\. Marking requirements - all devices

Identification G-S.1.

Name or ID of manufacture Retroactive

Model designation Retroactive

Model prefix (1/1/03)

Nonrepetitive serial number (1/1/68)

Serial number prefix (1/1/86)

Serial number -- appropriate abbreviations (1/1/01)

NTEP CC prefix and number (1/1/03)

(for devices that have an NTEP CC)

Remanufacturer information, as appropriate:

name and ID of remanufacturer (1/1/02)

model number if different from original model number (1/1/02)

Lettering G-S.7.

Operational controls, indications, and features G-S.6. (1/1/77)

Visibility of identification G-UR.2.1.1.

Interchange or reversal of parts G-S.4.

b\. Marking requirements - weighing and indicating elements in same
housing or covered on the same CC

(in addition to marking for all devices) S.6.3.

Accuracy class (1/1/86)

Nominal capacity Retroactive

Value of scale division with nominal capacity, if not apparent (1/1/83)

Value of \"e\" (if different from \"d\") (1/1/86)

Temperature limits if other than -10 ^0^C to 40 ^0^C (14^0^F to 104
^0^F) (1/1/86)

Scales designed for special purposes (1/1/86)

c\. Marking requirements - indicating element not permanently attached
or covered on separate CC

(in addition to marking for all device) S.6.3.

Accuracy class (1/1/86)

Nominal capacity Retroactive

Value of scale division with nominal capacity, if not apparent (1/1/83)

Value of \"e\" (if different from \"d\") (1/1/86)

Temperature limits if other than -10 ^0^C to 40 ^0^C (14 ^0^F to 104
^0^F) (1/1/86)

Concentrated load capacity (CLC) (1/1/89)

Section capacity (see note below) Retroactive

Scales designed for special purposes (1/1/86)

Maximum number of scale divisions (n~max~) (1/1/88)

***Inspection (cont.)***

d\. Marking requirements - weighing and load receiving element not
permanently attached or covered on separate CC (in addition to marking
for all devices) S.6.3.

Accuracy class (1/1/86)

Nominal capacity on load receiving element (1/1/89)

Concentrated Load Capacity (CLC) or Section Capacity (see note below)
(1/1/89)

Temperature limits if other than -10 ^0^C to 40 ^0^C (14 ^0^F to 104
^0^F) (1/1/86) Scales designed for special purposes (1/1/86) Maximum
number of scale divisions (n~max~) (1/1/88)

Minimum verification scale division (e~min~ or d) (1/1/88)

e.  Marking requirements - load cell with Certificate of Conformance

> (in addition to marking for all devices) S.6.3., S.5.4. (1/1/94)

Accuracy class (1/1/86)

Temperature limits if other than -10 ^0^C to 40 ^0^C (14 ^0^F to 104
^0^F) (1/1/86)

Maximum number of divisions (1/1/88)

> "S" or "M" for single or multiple cell applications (1/1/88)

Direction of loading, if not obvious (1/1/88)

Minimum dead load, maximum capacity, safe load limit, and load cell

Verification interval, v~min~ (1/1/88)

> Note**:** Requires information on a data plate attached to the load
> cell or in accompanying document. If a document is provided, the
> serial number shall appear on the load cell and in the document
> (1/1/88).
>
> Note: Manufacturer's name or trademark, model designation, model
> prefix and serial number and prefix shall also be marked on both the
> load cell and in any accompanying documents (1/1/91).

Note: Indicating and weighing elements manufactured prior to 1/1/89 are
required to be marked with a section capacity rating. However, it is
acceptable for these devices to be marked with a CLC instead. It is not
permissible, however, to substitute a section rating for a CLC on
devices manufactured or placed into service on or after 1/1/89.

7\. Design of weighing elements S.4.

8\. Load cell installation

Full elec­tronic scale T.N.8.1.3., S.5.4. (1/1/94) Appendix to EPO 13-E

Number of scale divi­sions, n, [\<]{.underline} n~max~ of the in­dicator
or load cells, which­ever is less.

> Verification scale division, v~min~, for the load cells must be less
> than or equal to the scale divi­sion, d, divided by the square root of
> the number of load cells, N, used in the scale:

v~min~ [\<]{.underline} [d]{.underline}

> N
>
> **[Note:]{.underline}** Compliance with T.N.8.1.3. cannot be
> determined in the field. The v~min~ value on the load cell is used to
> determine compliance with T.N.8.1.3. The v~min~ value marked on the
> load cell must be less than or equal to the v~min~ value in the table
> of Appendix A of this EPO based upon the d and N for the scale; if it
> is not, the scale does not comply with T.N.8.1.3. (See also 1988 OWM
> paper on \"Device Regulation Under the New Scales Code.\")

Mechani­cal lever systems with a single load cell:

v~min~ [\<]{.underline} [d]{.underline}

scale multiple

> **[Note:]{.underline}** Maximum values of v~min~ for commonly
> en­coun­tered multiple load cell scales are listed in the Appendix to
> EPO 13E.

9\. Installation G-UR.2., UR.2.3., UR.2.4.,

UR.2.5., UR.2.6., UR.2.8.

10\. Maintenance, use, and environmental factors.

Facilitation of fraud G-S.2.

Environment G-UR.1.2.

Operation G-UR.3.1.

Maintenance G-UR.4.

Maximum load UR.3.2.

Single draft vehicle weighing UR.3.3.

Manual gross weight entries UR.3.9

Minimum load UR.3.7.

Scale modification UR.4.3.

11\. Assistance G‑UR.4.4.

***Pretest Determinations:***

1\. Tolerances:

Acceptance/maintenance G‑T.1., G‑T.2.

Application:

Scales marked with an accuracy class T.N.2.1., T.N.2.3., T.N.2.4.

Tolerance values:

Scales marked with an accuracy class T.N.3.1./Table 6 (Accuracy Class
III L), T.N.3.2.

> Scales not marked with an accuracy class T.1.1., T.N.3.1./Table 6
> (Class III L), T.N.3.2.,
>
> Other applicable requirements T.N.4.1., T.N.4.2., T.N.4.3., T.N.4.4.,
> T.N.5.
>
> T.N.7.2.

Note: Some TN tolerances apply to unmarked vehicle scales, see NIST HB
44 Table T.1.1.

Discrimination T.N.7.2.

2.  Determine maximum test load to be applied during test: A test load
    not to exceed marked concentrated load capacity (or for scales
    manufactured prior to January 1, 1989, the marked section capacity)
    may be applied to any section or between any two sections. A test
    load of 100 percent of capacity may be distributed over the entire
    platform.

3\. Minimum test weights and test loads N.3., Table 4

***Test Notes:***

1\. Check repeatability of, and agreement between, indications
throughout test. T.N.5., G‑S.5.2.2.(a),

> G-S.5.2.2.(c)

2\. Recheck zero‑load balance each time test load is removed N.1.9.,
G‑UR.4.2.

3\. If the scale is equipped with a printer, print ticket at each test
load.

If the device will print only one load without returning to \"zero,"
check

printer with at least four different loads at convenient times during
test.

Check effectiveness of motion detection. G‑S.5.6., S-2.5.1.(a),

> UR.1.3. (1/1/86)\*

4\. If, during the conduct of the test, the performance of the device is

questionable with respect to the zone of uncertainty and the width of
zero,

additional tests may be conducted to determine compliance. N.1.5.
(1/1/86)\*, N.1.5.1.\*,

> S.1.1.1.

5\. If the device is equipped with operational features such as manual
weight entries, programmable tare,

multiple tare memory, weigh‑in/weigh‑out, or multiple weighing elements,
check

proper operation and appropriateness. G-UR.4.1,G-UR.4.2, S.4.3.,
S.1.12., (1/1/93), UR.3.9., See also - Type Evaluation Handbook

***Test:***

1.  Discrimination test at or near zero load, if deemed necessary and if
    environmental

conditions can be controlled N.1.5. (1/1/86)\*, N.1.5.1.\*

2.  Test for proper configuration of automatic zero-setting mechanism,
    if device is

so equipped. S.2.1.3.(b) (1/1/81)

> S.2.1.3.1. (1/1/01)

3\. If equipped with a semi‑automatic zero-setting mechanism (push
button), test

effectiveness of motion detection Type Evaluation Handbook;

> S.2.1.2.(a)

4\. Check proper design of tare auto-clear, if device is so equipped.
S.2.3. (including note for auto clear 1/1/83)

5\. Establish correct zero‑load balance.

6\. Increasing‑load and shift (section) test .N.1.1., N.1.3.4.,
N.1.3.4.1.,

N.1.3.4.2.

Minimum shift test. Conduct at least one shift test with a minimum test
load of 12.5 percent of scale capacity anywhere on the load receiv­ing
element using the pre­scribed test patterns and maximum test loads
specified below.

Prescribed test pattern: An area of 1.2 meters (4 feet) in length and
3.0 meters (10 feet) in width or the width of the scale platform,
whichever is less. When loading the scale for testing, one side of the
test pattern shall be loaded to no more than one-half of the
con­centrated load capacity before loading the other side.

For test patterns less than 1.2 meters (4 feet) in length, determine the
maximum loading by the formula:

> \[(wheelbase of test cart or length of test load ÷ 48 in) x 0.9 x
> CLC\]

For test patterns that exceed 1.2 meters (4 feet), the maximum test load
applied shall not exceed CLC x the largest r factor in Table UR.3.2. for
the length of the area covered by the test load.

Multiple pattern loading: To test to the nominal capacity, multiple
pat­terns may be simultaneously loaded in a manner consistent with the
method of use.

Other designs: Special design scales and those that are wider than 3.7
meters (12 feet) shall be tested in a manner con­sistent with the method
of use but following the principles described abo­ve.

Number range CHAPTER 1.2 m 1.2 m 1.2 m 1.2 m 1.2 m

(4 ft) (4 ft) (4 ft) (4 ft) (4 ft)

  --------- ---------- ----- ------------ ----- ------------ ----- --------- -----
  Number                                                                     
  range                                                                      
  CHAPTER                                                                    

  --------- ---------- ----- ------------ ----- ------------ ----- --------- -----

Section Midway Section Midway Section

1 between 2 between 3

sections sections

1 and 2 2 and 3

Test load: The maximum test load applied to the prescribed test pattern
shall not exceed the con­centrated load capacity (or for scales
manufac­tured prior to January 1, 1989, the rated section capacity).

***Test (cont.)***

> Note: When testing scales manufactured prior to January 1, 1989,
> caution should be exercised when loading test weights equi­valent to
> the rated section capacity onto areas between sections.
>
> Note: When loading the first section to be tested, it is recom­mended
> that obser­va­tions be made at each increment of test weight
> appli­ca­tion.
>
> Note: For weighing elements installed prior to 1/1/89, the rated
> section capacity may be substituted for concentrated load capacity to
> determine maximum loading.
>
> Prescribed test pattern and test loads for combination
> vehicle/livestock
>
> scales with more than two sections. N.1.3.4.2.

A minimum test load of 5000 kg (10,000 lb) or one-half of the rated
section capacity or CLC, whichever is less, shall be placed, as nearly
as possible, successively over each main load support as shown below.
Two section livestock scales shall also be tested consistent with
N.1.3.8.

  ------------------------ ------------------------ ---------------------
                                                    

                                                    
  ------------------------ ------------------------ ---------------------

= Load Bearing Point

7\. RFI/EMI Test.

To test for EMI, use procedures outlined in SMA Test Procedures[^1] . To
test for effects

of RFI, use equipment found at the site in a manner that is usual and
customary G‑N.2., G‑UR.3.2., G‑UR.4.2.,

> G‑UR.1.2., N.1.6., T.4., T.N.9.\*

8.  Decreasing‑load test, at one‑half of maximum test load N1.2.,
    N.1.2.2.

***Test (cont.)***

9.  Zero-load balance change N.1.9., G-UR.4.2

10. Strain‑load or substitution test on at least two sections; N.1.1.
    (See Appendix B)

at the end of this EPO)

For strain-load tests, position vehicle on one end of s­cale; Using error
weights, determine refer­ence point within the displayed divi­sion.

Dis­tribute test weights on other end of scale. Determine error-using
reference point noted above. The tolerances are

selected based upon the value of the test load only.

11. Discrimination test at maximum test load, if deemed necessary and if
    environmental

conditions are controlled N.1.5. (1/1/86)\*, N.1.5.1.\*

12. Over‑capacity test (if practical) S.1.7.

13\. Recheck zero‑load balance change N.1.9., G‑UR.4.2.

# Appendix A to EPO No. 13E

**Maximum Values of**

**Multiple Load Cell Scales**

**(Table values are in pounds.)**

  ------ -----------------------------------------------------------------
  Load   Scale Division

  ------ -----------------------------------------------------------------

  --------------------- -- ----------------- -- ----------------- -- ----------------- -- ----------------- -- ----------------- -- ----------------- -- -----------------
  [Cells]{.underline}      [1                   [2                   [5                   [10                  [20                  [50                  [100
                           lb]{.underline}      lb]{.underline}      lb]{.underline}      lb]{.underline}      lb]{.underline}      lb]{.underline}      lb]{.underline}

                                                                                                                                                         

  2                        0.71                 1.41                 3.54                 7.07                 14.1                 35                   70
  --------------------- -- ----------------- -- ----------------- -- ----------------- -- ----------------- -- ----------------- -- ----------------- -- -----------------

  ------ -- ------ -- ------ -- ------ -- ------ -- ------ -- ------ -- ------
  4         0.50      1.00      2.50      5.00      10.0      25        50

  ------ -- ------ -- ------ -- ------ -- ------ -- ------ -- ------ -- ------

  ------ -- ------ -- ------ -- ------ -- ------ -- ------ -- ------ -- ------
  6         0.41      0.82      2.04      4.08      8.2       20.4      41

  ------ -- ------ -- ------ -- ------ -- ------ -- ------ -- ------ -- ------

  ------ -- ------ -- ------ -- ------ -- ------ -- ------ -- ------ -- ------
  8         0.35      0.71      1.77      3.54      7.1       17.7      35

  ------ -- ------ -- ------ -- ------ -- ------ -- ------ -- ------ -- ------

  ------ -- ------ -- ------ -- ------ -- ------ -- ------ -- ------ -- ------
  10        0.32      0.63      1.58      3.16      6.3       15.8      32

  ------ -- ------ -- ------ -- ------ -- ------ -- ------ -- ------ -- ------

  ------ -- ------ -- ------ -- ------ -- ------ -- ------ -- ------ -- ------
  12        0.29      0.58      1.44      2.89      5.8       14.4      29

  ------ -- ------ -- ------ -- ------ -- ------ -- ------ -- ------ -- ------

  ------ -- ------ -- ------ -- ------ -- ------ -- ------ -- ------ -- ------
  14        0.27      0.53      1.34      2.67      5.4       13.4      27

  ------ -- ------ -- ------ -- ------ -- ------ -- ------ -- ------ -- ------

[Full electronic scales]{.underline}

Example: For a vehicle scale with four sections (eight load cells) and a
displayed scale division of 20 lb, the maximum value permitted for each
load cell is 7.1 lb. The calculation is shown below. If the value marked
on the load cell is less than or equal to the value computed for the
v~min~, then the load cell is considered to comply with T.N.8.1.3.

v~min~ ≤ [d]{.underline} = [20 lb]{.underline} = [20 lb]{.underline} =
7.07 lb \~ 7.1 lb

> N 8 2.83

[Mechanical Scales with single load cell]{.underline}

Example: Calculate the multiple of the lever system from the ratios
marked on the levers. Suppose the multiple for a vehicle scale is 400:1
and that the scale has a scale division of 20 lb. Then the maximum value
for the v~min~ of the load cell is 0.05 lb. The calculation is shown
below. If the load cell is marked with a v~min~ less than or equal to
the calculated value, then the load cell is considered to comply with
T.N.8.1.3.

v~min~ ≤ [d]{.underline} = [20 lb]{.underline} = 0.05 lb

scale multiple 400

**Appendix B to EPO No. 13E**

**Strain-Load Method of Testing**

(Excerpts from NBS Handbook 94)

**Description of Test.** When the supply of test weights is inadequate,
the principle involved in the use of strain loads is that the known test
load is first applied when the scale is carrying no other load (this is
frequently referred to as the \"light test\"), and is subsequently
applied one or more times when the scale is under some additional but
unknown load that stresses the parts as they are normally stressed under
ordinary operating conditions. Under this method, the actual values of
the strain loads - which may consist of miscellaneous material, loaded
vehicles, grain in a hopper, and the like - are immaterial and are not
determined, the strain loads being simply \"balanced out\" by any
convenient means. (The regular balancing means of the scale could be
utilized when arriving at the final balance for a strain load, but this
has the disadvantage that the scale cannot then be checked at the
conclusion of the test for a possible shift of its zero-load balance;
for this reason, use of the regular balancing means is not recommended
here.) Thus, after carrying the light test of a motor-truck scale, for
instance, as far as may be done with the test weights available, and
assuming that it is next desired to make a test in the region up to
one-half the nominal scale capacity, the test weights would be removed
and a vehicle would be driven onto the platform and the scale brought to
a balance; this vehicle would have been so selected that the sum of its
gross weight and the total value of the test weights would approximate
one-half the nominal capacity of the scale. The test weights would then
be added, in one or in several increments, and it would be observed
whether or not the scale properly indicated the value of each increment
of test weights added. Following this, another strain load would be
added, of such a value that the combined weight of the strain load and
test weights would approximate the value in the region of which it is
desired to make the next test; this strain load would then be balanced
out and the test weights subsequently added as in the earlier part of
the test. This operation may be repeated any desired number of times as
long as the gross load does not exceed the weighing capacity of the
scale; however, assuming that a reasonably satisfactory amount of test
weights is available, not more than two strain loads will ordinarily be
utilized, the scale being tested light and when loaded to approximately
one-half and full capacities.

**Tolerance Application on Strain-Load Tests.** In the strain-load
method, observed errors are errors on the \"test-weight load only,\"
since before each application of the test weight load the strain load of
unknown value has been balanced out; accordingly, the tolerances to be
applied are to be selected according to the value of the \"test-weight
load\" in each instance of an accuracy observation under the strain-load
method.

[^1]: ^?^These procedures, developed by the Scale Manufacturers
    Association, were adopted by the National Conference on Weights and
    Measures as part of the Final Report of the Committee on
    Specifications and Tolerances 63rd annual meeting, 1978 (copies of
    the 1978 procedures are available). Also reference SMA
    Recommendation on Electrical Disturbance -- SMA RED-0499 (copies of
    SMA RED-0499 are available at
    [www.scalemanufacturers.org](http://www.scalemanufacturers.org/))