1. Weighbridge Training Course Beijing - September 2017
Zero Setting Devices

2. Zero setting devices
A zero setting device is a device for setting the indication to zero when there is no load on the load receptor
The following are zero setting devices found on NAWI:
Semi automatic zero-setting device
Non-automatic zero setting device
Zero tracking
Automatic Zero setting device

3. Zero setting devices
Semi automatic zero setting device Device for setting the indication to zero automatically following a manual command ( zero button) Non automatic zero setting device Device for setting the indication to zero by the operator Zero tracking device Device for maintaining the Zero indication within certain limits automatically Automatic zero setting device Device for setting the indication to zero automatically without the intervention of the operator
Equilibrium is stable means = it can maintain the reading / maintain the accuracy requirement

4. Zero setting devices Zero setting requirements
The effect does not alter maximum capacity
The accuracy is ± 0.25e
The range is 4% of max for zero setting and zero tracking
Equilibrium is stable means = it can maintain the reading / maintain the accuracy requirement

5. Zero setting devices Zero tracking device To test zero tracking:
Reset the instrument to zero using the zero setting device
Apply a load of 1e to the load receptor
If after 5 seconds the indicator
changes and stabilises at 1e :Pass
remains on zero : Fail

6. Zero setting device accuracy
Non-Automatic and Semi-automatic zero -setting device
To test non-automatic and Semi-automatic zero setting:
Apply a load that is within the range of the instrument. This range varies between 0 to 4% of maximum capacity , in most cases it will be ± 2% around zero
Add small additional loads of 0.1e to take the load just below the next change over point
Zero the instrument using the zero setting device ( zero button)
Ensure that:
The numerical indicator displays zero

7. Zero setting device accuracy
The zero indication lamp or enunciator is illuminated
Apply a load of 10e
Lightly apply an additional 0.25e
If the instrument changes and stabilises at +1e from the original indication the instrument fails
If the indication remains unchanged firmly apply an additional 0.5e
If the indication changes and stabilises at +1e from the original indication the instrument passes
If the indication remains unchanged the instrument fails

8. Zero setting device accuracy (cont’d)

9. Zero setting device accuracy
Automatic Zero setting
To test automatic zero setting:
Initiate the automatic zero setting device by:
Applying a load of 5e
Zero the instrument using the zero setting device and remove the load
Wait for the automatic zero setting to occur and the indication displays zero , this should take a minimum of 5 seconds
Note: if the indication does not change after 15 seconds , the instrument does not have automatic zero setting and should be tested as semi-automatic zero setting
Quickly apply a load of 10e to the load receptor
Lightly apply an additional 0.25e

10. Zero setting device accuracy
Automatic zero setting continued
If the indication changes and stabilises at +1e from the original indication
then the instrument fails
If the indication remains unchanged firmly apply an additional 0.5e
If the indication changes and stabilises at +1e from the original indication the instrument passes
If the indication remains unchanged the instrument fails

11. Zero setting device accuracy
Non-self indicating Instrument ( eg. Steelyard weighing instrument)
It is essential that the instrument is set on zero before any tests are performed
After completing any test , remove the load and visually check that the instrument has returned within ± 0.25e of its equilibrium position.
If it has not returned to its equilibrium position apply 0.25e to the load receptor. Then:
If the indicator moves through its equilibrium point , the instrument passes
If the indicator does not move through its equilibrium point , the instrument fails

12. Zero setting device accuracy
Analogue indicating instrument
It is essential that the instrument is set on zero before any tests are performed
After completing any test , remove the load and visually confirm that the instrument has returned to within ± 0.25e of zero

13. Zero Setting Devices That’s the End of the presentation
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