The calibration interface features a "TRACEABLE ACCESS CODE" (TAC), as is required for use in “approved” applications. This feature also ensures that access to the calibration functions is protected from inadvertent or unauthorised change. The following parameters are considered as CALIBRATION commands:
|CE||Calibration Enable - returns the current TAC value.|
|CZ||Calibrate zero - sets the system zero point.|
|CG||Calibrate gain - sets the system gain.|
|CM||Calibrate maximum - sets the maximum allowable display value.|
||Calibrate maximum - same as CM when CM2=0 and CM3=0.
CM1 defines the limit between range 1 and 2.
||Calibrate maximum - sets the maximum allowable value for range 2.
CM2 defines the limit between range 2 and 3.
||Calibrate maximum - sets the maximum allowable value for range 3.
When the weight becomes greater than the highest CMn then Overrange is indicated.
|DS||Display step size - sets the output incremental step size.|
|DP||Display decimal point - sets the position of the output decimal point.|
|ZT||Zero track enable.|
|FD||Factory default setting (return to).|
To make an enquiry as to the setting of any of these commands requires the issue of the command with no parameters attached.
To make a change to the settings of any of these commands REQUIRES THE ISSUE OF THE CE COMMAND FOLLOWED BY THE CURRENT TAC VALUE (CE XXXXX).
For example, if the output step value needs to be changed from 1 to 5, the following steps would be required:
|Master sends||CE 16|
|Master sends||DS 5|
The output will now increment in steps of 5 divisions. It will then be necessary to SAVE the calibration parameters to non-volatile memory, by issuing the CS command. The CS command, which has no parameters and must be preceded by the CE XXXXX command, will return OK to signify successful update. The TAC is then incremented by 1.
An example of the recommended calibration procedure follows:
With the device selected, a suitable load cell in place, with known test weights available, (the example uses 5000 as a test weight value):
|Step 1||Master sends:||CE||Query the current TAC value|
|Step 2||Master sends:||CE 17||Enable the calibration sequence|
|Step 3||Master sends:||CZ||Ensure that the weigher is unloaded|
|Step 4||Master sends:||CE 17||Enable the calibration sequence|
|Step 5||Master sends:||CG 5000||Where 5000 is the weight value added|
|Step 6||Master sends:||GG||To confirm the calibration is correct|
|Step 7||Master sends:||CE 17||Enable the calibration sequence|
|Step 8||Master sends:||CS||Writes the calibration data to memory|
The system zero and system gain value will have been updated and written to EEPROM, and the TAC will have been incremented.