Calculation of process data
Calculation of process data
The concept “calibration”, which has historical roots at Beckhoff, is used here even if it has nothing to do with the deviation statements of a calibration certificate. Actually, this is a description of the vendor or customer calibration data/adjustment data used by the device during operation in order to maintain the assured measuring accuracy.
The terminal constantly records measured values and saves the raw values from its A/D converter in the ADC raw value object 0x80nE:01. After each recording of the analog signal, the correction calculation takes place with the vendor and user calibration data as well as the user scaling, if these are activated (see following picture).
Calculation | Designation |
|---|---|
XADC | Output of the A/D converter |
XF | Output value after the filter |
YH = (XADC – BH) x AH x 2-14 | Measured value after vendor calibration, |
YA = (YH – BA) x AA x 2 -14 | Measured value after vendor and user calibration |
YS= YA x AS x 2-16 + BS | Measured value following user scaling |
Name | Designation | Index |
|---|---|---|
XADC | Output value of the A/D converter | |
XF | Output value after the filter | - |
BH | Vendor calibration offset (not changeable) | |
AH | Vendor calibration gain (not changeable) | |
BA | User calibration offset (can be activated via index 0x80n0:0A) | |
AA | User calibration gain (can be activated via index 0x80n0:0A) | |
BS | User scaling offset (can be activated via index 0x80n0:01) | |
AS | User scaling gain (can be activated via index 0x80n0:01) | |
YS | Process data for controller | - |
 | Measurement result The accuracy of the result may be reduced if the measured value is smaller than 32767 / 4 due to one or more multiplications. |