Automatic Bulk Weighing Systems 

EPO ABWS (Rev. 08/14) DRAFT Page 1

EPO No. 16

Appendix B (Supplement 1)

Applying the High-Level Steps of the Substitution and Alternative

Substitution Test Method

This supplement to Appendix B provides detailed instructions on how to apply each of 

the high level steps necessary to perform a proper increasing-load test on a scale with 

digital indication using the substitution or alternative substitution test method. The 

procedures contained in this supplement are intended to be applied in the order that they 

appear. 

Establishing a proper reference at no-load (high-level step 1)

a. At no load, apply error weights to the load-receiving element in increments equal 

to 0.1 d until the displayed indication just begins to flicker to the next higher 

increment. If the displayed indication is already flickering before adding any

error weights, it will be necessary to add enough error weights in increments 

equal to 0.1 d to go beyond the existing zone of uncertainty to a point just above 

the lower edge of the next higher one. 

b. Remove an error weight equal to 0.1 d from the load-receiving element to confirm 

that the indication returns to a constant display of the lower increment. If the 

indication returns to a constant display of the lower increment when the 0.1 d is 

removed, add back 0.1 d to cause the indication to once again flicker to the next 

higher increment. A proper reference is established when the indication is 

flickering between two consecutive increments and removal of an error 

weight equal to 0.1 d from the load-receiving element causes the constant 

display of the lower increment. Thus, the proper reference to establish is a point 

just above the lower edge of the zone of uncertainty between two consecutive 

scale increments. The illustration on the next page depicts the area within the 

zone of uncertainty where the proper reference should be established. 

c. Once a proper reference at no-load has been established, record the values of the 

two increments that are flickering and the total value of error weights on the 

load-receiving element of the scale; then remove the error weights.
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Illustration Depicting Proper Reference

Applying the test weight and establishing proper reference (high-level step 2)

d. Apply the first test load consisting entirely of test weight to the load-receiving 

element and observe the displayed indication.

e. Add error weights to the load-receiving element in increments equal to 0.1 d to 

establish a proper reference with the test load applied. For example, if the scale is 

indicating a constant 3 000 lb after the test weight has been applied, add error 

weights in increments equal to 0.1 d to establish proper reference at a point just 

above the lower edge of the zone of uncertainty between 3 000 lb and the next 

higher increment. Record the total value of the error weights on the scale; then 

remove the error weights.

Determining the amount of error in the scale at first test load (high-level step 3)

f. Determine the amount of “step” error in the scale at the first test load by inserting 

the appropriate corresponding values obtained from testing into the following 

error formula and solving the equation:

En = Ie – Is – L + Rs – Re 

Where:

“En” (Error) represents the amount of error in the scale relative to the applied test 

weight portion of the total applied test load;

Higher 

Increment 

Shaded area denotes

proper reference, i.e., 

just above the lower 

edge of the zone of 

uncertainty 

Upper edge of 

zone of uncertainty Lower edge of 

zone of uncertainty

Zone of uncertainty 

between two 

consecutive digital 

increments not 

permitted to be 

greater than 0.3 d 

Lower 

Increment
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“Ie” (Indication ending) represents the scale indication after the test weight has 

been applied and proper reference established;

“Is” (Indication start) represents the scale indication before the test weight was 

applied;

“L” (Load) represents the value of the applied test weight excluding any 

substituted load;

“Rs” (Reference start) represents the value of the error weights on the 

load-receiving element that established proper reference prior to the test weight 

being applied; and

“Re” (Reference ending) represents the value of the error weights on the 

load-receiving element that established proper reference after the test weight had 

been applied. 

Determining appropriate values for “Ie” and “Is” in the error formula: 

Because the scale indication flickers between two consecutive increments when 

proper reference has been established, an average of the two increments should be

inserted in the error formula for each of the two components “Ie” and“Is.” For 

example, if the scale indication at no load is flickering between 10 lb and 20 lb

after a proper reference has been established, the average of 10 lb and 20 lb 

should be determined and inserted in the error formula. The average of 10 and 20 

is calculated as follows: 

15

2

30

2

(10 20) = = +

Thus, the value to be applied in the formula for Is is 15 lb. 

If the scale indication, with a 3 000 lb test load applied, is flickering between 

3 010 lb and 3 020 lb after a proper reference has been established, the average of 

3 010 and 3 020 is calculated as follows:

3 015

2

6 030

2

(3 010 3 020) = = +

Thus, the value to be applied in the formula for “Ie” should be 3 015 lb. 

Applying the Error Formula:

The following example test results, which include references to the different 

variables in the error formula, are provided to show how error is to be calculated 

from results of having applied an initial test weight load of 3000 lb to an ABWS 

equipped with a scale division value equal to 10 lb: 
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Scale indication at start of the test with no load applied: 10 lb (this value is not 

used in the error formula but represents the no-load indication of the scale at the 

start of the test)

Amount of error weight added at no load to achieve proper reference: 6 lb (Rs)

Scale indication at no load and proper reference established: 10 lb flickering 20 

lb (Is = 15 lb and is determined by averaging the two alternating values as 

explained above in “Determining appropriate values for “Ie” and “Is” in the error 

formula”)

Amount of test weight applied: 3 000 lb (L)

Scale indication with test load applied: 3 010 lb (this value also is not used in the 

formula and represents the scale indication after the test weight has first been 

applied)

Amount of error weight added with test weight applied to achieve proper 

reference: 9 lb (Re)

Scale indication with first test load applied and proper reference established: 

3 010 lb flickering 3 020 lb (Ie = 3 015 lb and is also determined by averaging the 

two alternating values as explained above in “Determining appropriate values for 

“Ie” and “Is” in the error formula”)

To determine the amount of error in the scale at the first test weight load insert the 

appropriate values from the example steps above into their proper position in the 

formula and solve as follows:

Error formula: En = Ie – Is – L + Rs – Re

Corresponding values inserted from the example steps: 

En = 3 015 – 15 lb – 3 000 lb + 6 lb – 9 lb 

Solve equation to determine amount and direction of scale error at the first test 

weight load:

En = - 3 lb

Note: The first two tables included in Appendix B (Supplements 2 and 3) provide 

indication of how an official might record each of these steps. 

Sum the cumulative errors (ΣEn) for all steps of the substitutions.

Verifying return to no-load reference (high-level step 4)
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g. Remove the first test load and add error weights on the load-receiving element to 

reach the no-load reference between the same two consecutive increments made 

note of in step b. Then subtract the total value of error weights needed to reach 

the no-load reference from the total value required to establish the initial no-load 

reference (i.e., the amount made note of in step b.). The result provides the 

direction and the amount of change in the return to no-load condition. If the 

amount of change exceeds applicable tolerance, testing should not proceed until 

the cause of the change has been determined and corrected. 

If no change has occurred or the amount of change does not exceed applicable 

tolerance, testing may continue. However, in the latter case it will be necessary to 

make note of the value of the error weights needed to re-establish proper no-load 

reference. If no change has occurred, the value of the error weights made note of 

in step b. establishes the no-load reference. Once you’ve recorded the total value 

of the error weights that establishes the no-load reference, remove the error 

weights from the scale.

Creating the first substitution test load (high-level step 5)

h.

Substitution Test

Instruct the system operator to load bulk material onto the load-receiving element 

in an amount to cause the indicator to display as nearly as possible, but not to 

exceed, the value that was displayed after the first test load was applied in step d. 

At a location on the load-receiving element separate from the error weights, apply 

trim weights as needed, and in whatever amount necessary, to increase the 

displayed indication to that which was first indicated when the test weight was 

applied in step d. Then add error weights to the load-receiving element in 

increments equal to 0.1 d to establish proper reference between the same two 

increments as was established in step e. (i.e., the indication flickering between 

the same two consecutive increments and the removal of 0.1 d causing a constant 

display of the lower increment). Once proper reference has been established 

between the same two consecutive increments, it can be assumed that the weight 

of the applied load (i.e., the first substitution test load) is the same as that of the 

field standard test weight for which it now substitutes. Thus, it can also be 

assumed that the error in the scale with either load (i.e., the test weight or first 

substitution load) applied is also the same. 

Record the total value of the error weights on the scale; then remove them. 

Alternative Substitution Test

Instruct the system operator to load bulk material onto the load-receiving element 
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in the amount necessary to cause the scale to indicate a value that is within five 

scale divisions of the value that was displayed after the first test load was applied 

in step d. To qualify as a substitution test load, the weight of the bulk 

material must provide a displayed indication that is slightly less, but in no 

case more than five divisions less, than the indicated weight of the test load 

for which it is intended to substitute (i.e., the value indicated in step d.). 

Note: Depending upon how close an operator is able to stop the flow of material 

onto the load-receiving element relative to the weight targeted (i.e., the value 

indicated in step d), it may be necessary to add trim weights to increase the weight 

of the bulk material so that its displayed indication is within five divisions of the 

target weight.

Add error weights in increments equal to 0.1 d to establish a proper reference (i.e., 

the indication flickering between two consecutive increments and the removal of 

0.1 d causing a constant display of the lower increment). Once proper reference 

has been established, record the values of the two increments that are flickering, as 

well as the total value of the error weights on the scale; then remove the error 

weights. 

Applying the test weight to the first substitution test load, establishing proper reference, 

and determining scale error (high-level steps 6 and 7)

i. Reapply the test weight to the load-receiving element of the scale and observe the 

displayed indication. 

j. With the test weight and first substitution test load now applied, add error weights 

in increments equal to 0.1 d to re-establish a proper reference. 

k. Determine the amount of error in the scale with the test weight and first

substitution test load applied by inserting the appropriate corresponding values

obtained from testing into the following error formula and solving the equation: 

En = Ie – Is – L + Rs – Re 

Note: As per the instructions in step f., an average of the two increments that are 

flickering should be inserted in the error formula for each of the two components 

“Ie” and“Is.”

Once the total amount of error has been determined, remove from the 

load-receiving element the test weight portion of the test load, all error weights, 

and any trim weights that were previously added. 

Sum the cumulative errors (ΣEn) for all steps of the substitutions.

Creating the second substitution test load (high-level step 8)
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l.

Substitution Test

Instruct the system operator to load bulk material onto the load-receiving element 

in an amount to cause the indicator to display as nearly as possible, but not to 

exceed, the value that was displayed after the test weight was applied in step i. 

At a location on the load-receiving element separate from the error weights, apply 

trim weights as needed, and in whatever amount necessary, to increase the 

displayed indication to that which was first indicated when the test weight was 

applied in step i. Then add error weights to the load-receiving element in 

increments equal to 0.1 d to establish proper reference between the same two 

increments as was established in step j. (i.e., the indication flickering between the 

same two consecutive increments and the removal of 0.1 d causing a constant 

display of the lower increment). Once proper reference has been established 

between the same two consecutive increments, it can be assumed that the weight 

of the applied load (i.e., the second substitution test load) is the same as that of the 

combination of test weight and first substitution test load for which it now 

substitutes. Thus, it can also be assumed that the error in the scale with either test 

load (i.e., the second substitution test load or the combination of the first 

substitution test load and test weight) applied is also the same. 

Record the total value of the error weights on the scale; then remove them. 

Alternative Substitution Test

Instruct the system operator to load bulk material onto the load-receiving element 

in the amount necessary to cause the scale to indicate a value that is within five 

scale divisions of the value that was displayed after the first test load was applied 

in step i. To qualify as a substitution test load, the weight of the bulk material 

must provide a displayed indication that is slightly less, but in no case more 

than five divisions less, than the indicated weight of the test load for which it 

is intended to substitute (i.e., the value indicated in step i.). 

Note: Depending upon how close an operator is able to stop the flow of material 

onto the load-receiving element relative to the weight targeted (i.e., the value 

indicated in step i), it may be necessary to add trim weights to increase the weight 

of the bulk material so that its displayed indication is within five divisions of the 

target weight.

Add error weights in increments equal to 0.1 d to establish a proper reference (i.e., 

the indication flickering between two consecutive increments and the removal of 

0.1 d causing a constant display of the lower increment). Once proper reference 

has been established, record the values of the two increments that are flickering, as 

well as the total value of the error weights on the scale; then remove the error 

weights.
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Applying the test weight to the second substitution test load, establishing proper 

reference, and determining scale error (high-level steps 9 and 10)

n. Reapply the test weight to the load-receiving element of the scale and observe the 

displayed indication. 

o. With the test weight and second substitution test load now applied, add error 

weights in increments equal to 0.1 d to re-establish a proper reference.

p. Determine the amount of error in the scale with the test weight and second 

substitution test load applied by inserting the appropriate corresponding values 

obtained from testing into the same error formula provided in the previous steps 

and solving the equation. 

Sum the cumulative errors (ΣEn) for all steps of the substitutions.

Once the amount of error has been determined, remove from the load-receiving 

element the test weight portion of the test load, all error weights, and any trim 

weights that were previously added. 

Creating the third substitution test load (high-level step 11)

q. Apply the same procedures that were used to create the second substitution test 

load to create the third substitution test load except that the weight to be targeted 

for substitution is that which was first indicated when the test weight was applied 

in step n. 

Applying the test weight to the third substitution test load, establishing proper 

reference, and determining scale error (high-level steps 12 and 13)

r. Repeat steps n. through step p. replacing the term “second substitution test load” 

with the term “third substitution test load” to complete the third substitution test

and determine the amount of error in the scale using the error formula. 

Substitution Test

 Note: If after completion of three substitutions from the no-load reference, additional 

test loads are still needed to make possible a test to at least used capacity, it will be 

necessary to use a strain load to increase the loading of the scale to the appropriate area 

where additional testing is needed. Once the strain load has been created and proper 

reference established for the load, up to three substitution test loads can be created from 

that strain load using the same procedures outlined in this appendix. 

Alternative Substitution Test

Note: If after completion of three substitutions from the no-load reference, additional 
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test loads are still needed to make possible a test to at least used capacity, continue 

applying these same procedures, using as many additional substitution test loads as are 

needed, to complete the test.