Field Inspection Manual — Automatic Weighing Devices
Part 2, Section 1 b: Type 3-12: Automatic catch weighing device—Static weighing
Table of contents
Weights and Measures Regulations—limits of error from section 176, 177 or 185, as appropriate.
Static weighing of discrete loads on a scale incorporated into a fully automated production system. Typical applications include scales equipped with motorized belts or roller systems used in manufacturing facilities and other industrial establishments where the products being weighed must come to a complete stop before their weight can be recorded or printed.
The device under test (DUT) must be tested for performance in the static mode (including motion detection), using the standard test procedures (STPs) / inspection procedure outlines (IPOs) from the Specifications Relating to Non-automatic Weighing Devices, applying limits of error applicable to automatic scales. The following requirements are in addition to static testing.
Automatic catch weighing devices (ACWDs) that weigh statically must also be tested to ensure that the automated production system in which they are installed does not adversely affect their ability to record or print accurate weights. Additional testing must be conducted using test loads representative of the types of products intended to be weighed by the system.
Determining the speed of the weighing system in automatic mode
Although the number of loads weighed by an automatic catch weighing device that weighs statically is typically not very high, the speed of the operation of the weighing system must be recorded in the comments section of the device examination certificate. If the speed of the weighing system is intended to be operator controlled or the speed control cannot be sealed, the range of possible operating speeds must be determined and recorded on the device examination certificate and the DUT must be tested in automatic mode at both the lowest and highest possible speeds.
The operating speed of the weighing system can be determined by counting the number of loads weighed in a one-minute period.
Selecting test loads and testing in automatic mode
Once the device has been tested and it has been determined that the motion detection feature operates correctly in static mode, the device must then be tested to ensure that the motion detection feature also operates correctly when used in automatic mode.
Selecting appropriate test loads
- Select suitable test loads representative of the product typically weighed on the device. The minimum number of test loads and test runs required must be representative of the range of weights intended to be weighed by the system. The total number of individual test loads may be increased in order to facilitate testing, but the minimum number of runs must be respected at all times. Test loads must be stable and should be representative of the actual product to be weighed.
- The weight of each test load must first be determined and recorded using the DUT in static mode.
- A minimum of three test runs must be conducted to confirm the correct operation of the motion detection feature when the DUT is used in automatic mode.
- If the DUT is used to weigh loads which are similar in size and do not vary in weight by more than 10%, one test load may be used provided that it can be run across the device several times, otherwise separate test loads can be used to obtain the minimum of three test runs required. If the DUT is used to weigh loads that vary in size or have a range of weights which vary by more than 10%, then a minimum of three test loads must be selected so that they span the intended usage range of the device (small to large, light to heavy).
Interpretation of results
For each test run, the weight of the test load(s) obtained in automatic mode must be recorded or printed by the DUT in accordance with the requirements for motion detection when compared to the weight of the test load(s) obtained in static mode.
Power failure test (initial inspection only)
Systems which store cumulative totals for subsequent trade transactions must have power failure safeguards in place. Prior to proceeding with the power failure test, the inspector must ensure that a loss of power will not adversely affect any other ancillary equipment associated with the DUT.
While the system is in operational mode, interrupt the power to the DUT or, if so equipped, to the uninterruptible power supply. If an uninterruptible power supply is used, do not disconnect the DUT from the UPS to conduct the power failure test.
After a sufficient length of time (i.e. 1-2 min) has elapsed, return power to the system and complete the transaction. All items which have passed over the load receiving element must be accounted for in the system memory or on a printed ticket.
Interpretation of results
The DUT is deemed to comply if items previously weighed are accounted for in the system memory or on a printed ticket.
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