WAGO-I/O-SYSTEM 750
Commissioning
87
750-451 8 AI RTD
Manual
Version 1.1.0
Table 68: “Calibration” Menu Item
Option
Description
Calibration settings
Manufacturer
calibration
Manufacturer calibration is enabled. Manufacturer-side
calibration is applied. The gain and offset values cannot be
entered individually.
Manufacturer calibration is disabled.
Gain
The gain value changes the slope factor of the A/D raw
value.
Offset
The offset value moves the zero point of the A/D raw
value (offset on the y axis).
User calibration
User calibration is enabled. By enabling user scaling, the gain
and offset values can be specified individually.
User calibration is disabled.
A/D raw value
Analog/digital converter raw value. This is a 24-bit value.
Resistance value
[Ohm]
This is the output value after calculating the gain and offset values and
conversion from A/D raw value. The output is in Ohm.
User calibration allows you to calibrate the I/O module individually. The
following calculation formulas apply when calculating both required factors:
•
Calibration gain: m = (y2
−
y1) / (x2
−
x1)
•
Calibration offset: b = y1
−
m × x1
The variables are assigned as follows:
•
m= Calibration gain
•
b= Calibration offset
•
x1= Actual value 1 (A/D raw value)
•
x2= Actual value 2 (A/D raw value)
•
y1= Setpoint 1
•
y2= Setpoint 2
7.2.1.3.7 Application Example of Calibration
For the calibration, a 2-point measurement with reference resistances is carried
out.
Example:
Measurement 1: y1= 100 Ohm
Measurement 2: y2= 4000 Ohm
Both values of the reference resistances are first converted into corresponding
A/D raw values. The following calculation formula is used:
A/D raw value = (Measure resistance × ((2^24)
−
1)) / 5050
