Laboratory manual for the evaluation of non-automatic weighing devices

Part 2, section 14—Limits of indication

Table of contents


Reference

Sections 30 to 33 and 40 of the Specifications Relating to Non Automatic Weighing Devices (1998)

14.0 Limits of indication—Generalities

Weighing devices shall neither indicate nor print weight values in excess of their maximum rated capacities (Max). Perform the following test.

LG-14.01 Overload tests

Application

Applicable to complete electronic weighing devices and to separate electronic weight indicators. If the units of registration can be changed without having to perform a re-calibration of the device, then perform individual tests for each and every unit which the device is capable of registering.

Note: For the purposes of the Display Blanking Test, a POS (Point of Sale System) is considered a computing scale and is subject to a maximum of 9 d.

Test procedure
Span
  1. Stabilize and zero the device at nominal conditions.
  2. Load the device to its maximum rated capacity.
  3. Add loads until the device ceases to display weight values.
  4. Record the last weight value indicated (WI); attempt to print or transmit data to external ports at overload condition.

    Note: On some devices, under overload conditions, data is not transmitted through the printer port; however, it may be transmitted through another port.

  5. Repeat the test for other units of measurement that the device can display.

    WI ≤ Max + (5% Max or 9 e)

Tare features
  1. Remove the load and set the device to zero.
  2. Enter a keyboard or a platter tare (T) equal to approximately 20% of Max.
  3. Add loads until the device ceases to indicate/print weight values.
  4. Record the last value indicated (WI).

    WI + T ≤ Max + (5% Max or 9 e)

    Note: Certain approved devices may incorporate a full or partial additive tare feature. An additive tare feature extends the weighing capacity of the scale. This must be taken into consideration when performing the blanking display test.

Zero (to be performed if the scale can zero loads in excess of 4%)
Positive portion
  1. Remove the load and set the device to zero.
  2. Add a load equal to 4% of Max; zero that load using the SAZSM.
  3. Apply any load the can be re-zeroed using the AZSM and re-zero the load. Record this value as (ZI)
  4. Add loads until the device ceases to display/ print weight values; Record the last value indicated (WI).
  5. If the scale limits the amount that can be zeroed with a semi-automatic zero setting mechanism but the operation can be repeated several times, zero the maximum weight possible equal to or under 5% of Max.

    WI + Zl ≤ Max + (5% Max or 9 e)

Negative portion
  1. Place a small weight that is within both IZSM and SAZSM range of the device, on the platter and re-zero the device using the IZSM (device must have an IZSM to continue with test)
  2. Once the scale has reached a zero condition remove the small weight and re-zero the device using the SAZSM.
  3. Add loads until the device ceases to display/ print weight values; Record the last value indicated (WI)

    WI ≤ Max + (5% Max or 9 e)

Interpretation of results

14.1 The device is deemed to comply with the requirement if the device can not display or print weight values in excess of:

14.2 When over capacity, the device registration must blank within prescribed limits, or display a clear message that cannot be confounded with a weight value.

Acceptable solutions

Amongst others, the following means of indicating overcapacity are acceptable:

Among others, the following means of indicating overcapacity are not acceptable:

The same rules apply to printed information.

Revision

Rev.1 (March 2010)
  • Test for zeroing a negative quantity included
  • altered procedure for devices that can zero over 4%
Date modified: