Laboratory manual for the evaluation of non-automatic weighing devices
LG-3.01 Linearity, hysteresis and repeatability at ambient temperature
Table of contents
- Multiple range weighing devices
- Interpretation of results
Sections 9, 10, 11, 12, 13, and 17 of the Specifications Relating to Non Automatic Weighing Devices (1998)
This test is intended for complete mechanical or electronic weighing devices, indicating and load receiving/weighing elements tested separately.
- AZTM may be in operation during the tests. It must be set to the lowest value; if zero is the lowest selectable value, it will be set to zero. However, the amount that the AZTM may track at once may not be set to a value larger than 0.6e which is the maximum value allowed by the Non Automatic Weighing Devices Specifications.
- If the IZSM range does not exceed 20% of the device capacity, tests will be performed with the IZSM set at the upper limit of its range. The IZSM range of an indicating element tested separately may not exceed 20%.
- If the IZSM range exceeds 20%, tests will be performed twice. A first series of tests using the lighter platter provided by the applicant, and the second series with the IZSM set to the upper limit of its range.
Note: In the case of a multi-range device, it is 20% of Max of the lowest range; in the case of a multi-interval device, it is 20% of max of the first range.
- The weighing device must be leveled, adjusted as to zero error as possible and pre-loaded (exercised) 3 times up to at least 90% Max.
- The device must be configured for the maximum capacity and smallest verification scale interval for which the approval is sought.
- If so equipped, the "enhance resolution feature" of the device will be used during the tests. If this feature is not available, use the small weight method to determine the device errors before rounding (internal errors). This is not necessary if the errors are marginal.
- This test is performed at ambient temperature (≈ 20°C, or at the mid point of the temperature range if significantly different from 20°C, and at relative humidity of ≈ 50%).
- Pre-condition the device: the DUT must have reached a stable temperature at ambient condition.
- Set the device to zero.
- Perform a minimum of three increasing and decreasing load tests to capacity using at least 5 known test weights. Loads must be centered on the load receiving element. Loads must be selected in relation to the device capacity, the value of the verification scale interval and the turning points of the tolerances. Determine the true error before rounding (internal or true errors). Record the results.
Multiple range weighing devices
- Perform a minimum of three increasing and decreasing load tests using at least 5 known test weights in each individual range. Record the results.
- Load the scale to the maximum capacity of the highest range (or manually select the highest range and then load the device to capacity); Remove the load: the indications should return to zero immediately. Switch the device to the lowest range immediately (If the switch over is automatic, the device should have returned to the lowest range automatically). Note the indication near zero at the time the device switches to the lowest range. Observe the weight indication for 5 minutes. Record any changes.
Interpretation of results
All functions must operate as designed and as intended.
Linearity and hysteresis
Each individual result must be within the tolerance envelope as prescribed by the Non Automatic Weighing Devices Specifications.
Return to zero
The device must return to zero from Max within 0.5e for a complete device, and within 0.35e for an indicating or load receiving/weighing element tested separately.
A multiple range device must return to zero from Max I within 0.5eI. After returning to zero from any load greater than Max1 and immediately after switching to the lowest weighing range, the indication near zero shall not vary by more than 0.5e1 during the following five minutes.
Compare the results for each individual load of increasing and decreasing tests. The maximum difference between the results for the same load must not exceed the in-service
Note 1: The error of any single weighing result must not exceed the maximum limit of error for the given load.
Note 2: A major element (module) tested separately and that is the only component of the weighing system subject to measurement errors due to disturbance or influence factors is allowed entire applicable limits of error (i.e. a weighing element which produces an output digital signal readable by a computer).
- Rev. 1 (March 2010)
- AZSM renamed to AZTM
- Formatting changes
- Date modified: