Laboratory manual for the evaluation of non-automatic weighing devices
Part 2, section 18—Motion detection
Table of contents
- 18.0 Motion detection—Generalities
Sections 30, 31, 32 and 45 of the Specifications Relating to Non Automatic Weighing Devices (1998)
18.0 Motion detection—Generalities
Electronic devices must have motion detection capability to prevent the device from zeroing (semi-automatic zero) or taring (platter tare or keyboard tare) a part of the load when the semi-automatic zero or tare key is activated while a load is added, changed or removed from the platter.
Electronic devices equipped with a printer (or that have connections for a printer) must have motion detection capability to prevent the device from printing values before the weight display has stabilized. This reduces the possibility of recording incorrect weight values.
The following test procedure is used to assess the effectiveness of the motion detection feature.
LG-18.01 Motion detection test
Applicable to complete electronic scales, or to electronic indicators which are intended to be used as part of a non-automatic weighing electronic scale (tested by means of a load cell\dead load tester assembly or by means of a load cell simulator).
To determine if printing, zeroing or the entry of a tare is inhibited when motion is detected.
To evaluate the maximum range within which printing is possible in spite of motion.
- Place a load within the weighing range on the platter and allow time for the indication to stabilize.
- Induce a motion to the scale indications to a peak magnitude of at least 10 e (amplitude).
- While disturbing the weight indication, activate the SAZSM and allow the oscillations to settle out. The scale may eventually zero the load or may reject the command.
- While disturbing the load, attempt to activate the tare button (platter tare). The scale may eventually tare the load on the platter, or reject the command.
- While disturbing the load, attempt to print. The scale may print a weight or reject the command.
- Repeat the test at least five times for small loads (near zero) and loads near capacity.
Note: For larger capacity devices, it may not be convenient or practical to disturb the load by hand. A load of greater than 10 e may be applied or removed while activating the zero, tare, stored weight or print key. Under laboratory conditions, since this is primarily an instrument test, a low capacity load cell or a load cell simulator may be connected to the device or the indicating element to simulate motion.
Interpretation of results
The device complies with the requirements if zeroing, taring or printing the load on the platter is prevented, or is within 1 e (verification scale interval) for scales that have a maximum capacity of up to 2 000 kg (5 000 lb); or 3 e (verification scale intervals) for scales of more than 2 000 kg (5 000 lb). Printed and displayed weight values must be within the prescribed limits of error.
18.1 Push-button zero complies with the motion detection requirements
18.2 Push-button (platter) tare complies with motion detection requirements.
18.3 Stored weight key(s) comply with the motion detection requirements.
18.4 Printed weight values comply with motion detection requirements.
18.5 Printed values are within prescribed tolerances.
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