Field Inspection Manual — Non-Automatic Weighing Devices

Part 3, Section 18: STP-18: Blanking Display Test

Reference

Sections 39 of the Specifications Relating to Non-automatic Weighing Devices (1998).

Purpose

Weighing devices shall not indicate or print weight values that exceed their maximum capacity (Max or Max + additive tare). If the units of registration can be changed without having to perform a re-calibration of the device (lb/kg switch), 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 Max + 9 e.

Procedure

Span

  • Stabilize and zero the device at nominal conditions;
  • Load the device to its maximum rated capacity;
  • Add loads until the device ceases to display weight values;
  • Record the last weight value indicated (WI); attempt to print.
  • Repeat the test for other units of measurement that the device can display.

WI ≤ Max + (5% Max or 9 e)

Tare

  • Remove the load and set the device to zero.
  • Enter a keyboard or a platter tare (T) equal to approximately 20% of Max.
  • Add loads until the device ceases to indicate/print weight values
  • 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. Additive tare extends the weighing capacity of the scale. This must be taken into consideration when performing the blanking display test. (Consult the applicable Notice of Approval)

Zero — (To be performed if the scale can zero loads in excess of 4%)

  • Remove the load and set the device to zero.
  • Add a load in excess of 5% of Max (e.g. 20%); zero that load (Zl).
  • Add loads until the device ceases to display/print weight values.
  • Record the last value indicated (WI)
  • If the scale limits the amount that can be zeroed by the 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)

Interpretation of Results

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

  • 9 verification scale intervals e, for Point of Sale Weighing Systems (POS) and computing scales other than weight classifiers and postal scales and is the preferred option for all non-automatic weighing devices; or
  • 105% of Max, for other non-automatic weighing devices.
    When over capacity, the device registration must blank within prescribed limits, or display a clear message that cannot be mistaken for a weight value.

Acceptable Solutions

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

  • a row of "EEEEEEE"
  • a blank registration
  • the word "OVERCAPACITY"

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

  • displaying a flashing eight
  • displaying a row of zeros or eights
  • any other indication which may possibly be mistaken for a weight value.

The same rules apply to printed information.

Revision

Rev 1.

  • reference to +9 e being preferred blanking point for all Non-Automatic Weighing Devices (OIML R76 4.2.3)
  • clarify reason for some unacceptable display options.
  • change reference from "scale" to "non automatic weighing device".
  • change various references to d and/or scale division to verification scale interval or e.
  • correct references to Specifications Relating to Non-automatic Weighing Devices (1998).
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