Sensor calibration

The EL3356 is matched to the characteristic curve of the sensor element by means of the calibration. Two values are required for this procedure: the initial value without a load (“zero balance”) and fully loaded (“rated output”). These values can be determined by a calibration protocol or by a calibration using calibration weights.

Sensor calibration 1:
Adaptation to the sensor curve

Calibration by means of compensation in the system

In the “practical” calibration, measurement takes place first with the scales unloaded, then with a defined load on the scales. The EL3356 automatically calculates the existing sensor characteristic values from the measured values.

Sequence:

  1. Perform a CoE reset with object 0x1011:01
    see Restoring the delivery state
  2. Activate mode 0 via the control word (EL3356-0010 only)
  3. Set scale factor to 1 (0x8000:27)
  4. Set gravity of earth (0x8000:26) if necessary (default: 9.806650)
  5. Set gain to (0x8000:21) = 1
  6. Set tare to 0 (0x8000:22)
  7. Set the filter (0x8000:11) to the strongest level: IIR8
  8. Specify the nominal load of the sensor in 0x8000:24 (“Nominal load”)
  9. Zero balance: Do not load the scales
    As soon as the measured value indicates a constant value for at least 10 seconds, execute the command “0x0101” (257dec) on CoE object 0xFB00:01.
    This command causes the current mV/V value (0x9000:11) to be entered in the “Zero balance” object.
    Check: CoE objects 0xFB00:02 and 0xFB00:03 must contain “0” after execution.
    10. Sensor calibration 2:
    Zero calibration with command 0x0101 in CoE object 0xFB00:01
  10. Load the scales with a reference load. This should be at least 20% of the rated load. The larger the reference load, the better the sensor values can be calculated.
    In object 0x8000:28 (“Reference load”), enter the load in the same unit as the rated load (0x8000:24).
    As soon as the measured value indicates a constant value for at least 10 seconds, execute the command “0x0102” (258dec) on CoE object 0xFB00:01.
    By means of this command the EL3356 determines the output value for the nominal weight (“Rated output”)
    Check: CoE objects 0xFB00:02 and 0xFB00:03 must contain “0” after execution.
    11. Sensor calibration 3:
    Loading with reference load, command 0x0102 in CoE object 0xFB00:01
  11. Reset: execute the command “0x0000” (0dec) on CoE object 0xFB00:01.
  12. Set the filter to a lower stage.

Calibration according to the sensor calibration protocol (theoretical calibration)

The sensor characteristic values according to the manufacturer's certificate are communicated here directly to the EL3356, so that it can calculate the load.

  1. Execute a CoE reset
  2. Set scale factor to 1 (0x8000:27)
  3. Set gravity of earth (0x8000:26) if necessary (default: 9.806650)
  4. Set gain to (0x8000:21) = 1
  5. Set tare to 0 (0x8000:22)
  6. Specify the nominal load of the sensor in 0x8000:24 (“Nominal load”)
  7. Adopt the “Rated output” (mV/V value 0x8000:23) from the calibration protocol
  8. Adopt the “Zero balance” (0x8000:25) from the calibration protocol
Sensor calibration 4:

Calibration

The calibration is of great importance for the accuracy of the system. In order to increase this, the filter should be set as strong as possible over the entire calibration phase. It may take several seconds before a static value is obtained.

Sensor calibration 5:

Local storage

The values modified during the theoretical and practical calibration are stored in a local EEPROM. This can be written to up to 1 million time. In order to prolong the life of the EEPROM, therefore, the commands should not be executed cyclically.