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Field Inspection Manual — Non-Automatic Weighing Devices

Part 2, Section 10: IPO-10: On-board Weighing Systems


On-board weighing systems (OBWS), including: Anhydrous ammonia (NH3) truck mounted weighing systems, weighing systems mounted on lift trucks, weighing systems mounted on front end loaders, on-board waste weighing systems, and other on-board systems.


Inspector's weight kit, local standards in sufficient number and capacity, and suitable material for strain and/or product tests. A reference scale may also be required in some cases.


Device is approved for trade use (NOA, W&M Act, section 8)

Device is suitable for the actual use (STP-1)

Device has been initially inspected (if applicable) and bears the initial verification marks (R.29)

Device is sealed (NOA, STP-4)

Visual Examination

Installation and Location (STP-7)

Device is installed in accordance with restrictions and conditions listed in the notice of approval and in accordance with manufacturer's instructions.

Weighing element is adequately supported and load cell mounting is adequate.

Device indicating and weighing elements are positioned in customer's view (if applicable), or a secondary indicator is provided.

Load receiving element can be observed from indicator's reading position.

Clearance around load receptor.

Device is adequately protected.

Means are provided to apply standards and testing material.

Marking (STP-3)

Device is marked with the required information.

Marking is located as required.

Marking is permanent (if applicable).

Marking plate is permanently attached to the device.

Indicating Element (STP-5)


Display Test (segment).

Indicated and recorded values are adequately defined.

Defining words and symbols for annunciators (tare entered, gross and net weight, center-of-zero) are readable.

Recording Element (printer) (STP-6)

Device prints the required values.

Printed values are adequately defined.

Device Configuration (Electronic)

Device configured as prescribed by the NOA (STP-2)

Zero Setting Mechanism Range (4% of Max or more) (STP-8)

Initial Zero Setting Mechanism Range (20% of Max or more) Footnote 1

AZTM Maximum Range (0.6 e)

Manual Entries of Gross Weights (prohibited on OBWS) (STP-9)

Sleep Mode Test (STP-10) Footnote 1

Tare (platter and pre-programmed tare entry) (STP-11)

(Keyboard tare prohibited on OBWS)

Free Floating Weight Signal (STP-12)


Load Discrimination Test (no load) (STP-14)

Increasing Load Test (strain test) (STP-13)

Eccentricity Test (STP-15)

Load Discrimination Test (Max) (STP-14)

Agreement of Registration (STP-17)

Display Blanking Tests (zero, tare) (STP-18)

Decreasing Load Test (STP-13)

Return-to-Zero Test (STP-13)

Repeatability Test (STP-16)

Motion Detection Test (STP-19)

Accuracy of Price Computation (if applicable) (STP-20)

Mathematical Agreement of Tare, Net and Gross Weight (STP-21)

Disturbance Tests (electromagnetic interference and radio frequency interference, vibrations) (STP-23)

Level Effect on Accuracy / Display Interlock / off Level Condition (STP-22)

NH3 On-Board Weighing Systems — Product Test (STP-27)

Other OBWS Specialized Tests (STP-31)

Note: Test the performance of the device in a manner approximating its intended use. Use different loads; test with vehicle in motion (if intended to be used while in motion); test when the engine is running (increasing/decreasing load tests), etc.

Note: Off level tests are performed at initial and subsequent inspections.


The purpose of revision 2 is to:

  • add other OBWS device types (previously anhydrous ammonia only).
  • add a reference to new OBWS STP-31.
  • add manual weight entry and keyboard tare prohibition statement.

The purpose of revision 1 was to remove the reference to static weighing.


Footnote 1

Test performed at the initial inspection only.

Return to footnote 1 referrer

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