Issue
How to calculate the input value for a Lookup table for a resistive AI device.
Product Line
Satchwell Sigma Software
Environment
Lookup Tables
Cause
A lookup table needs to be created for an additional resistive AI device. An existing lookup table does not exist.
Resolution
The following parameters are needed, the device's datasheet will normally provide this information.
The resistance of the device at a known value e.g temperature or a feedback potentiometer.
The following calculation is then used.
lookup table input value = R1*250 / R1+14700 (Where R1 is the resistance value)
The output value in the lookup table will be the known value (e.g temperature or a feedback potentiometer) for the resistance used in the calculation above.
Example:
Resistance = 5905 ohms at 17'C
Table input = 5905*250 / 5905+14700 = 71.6452
and
Table output = 17.0
The more samples taken, greater the accuracy.
Input values need to be entered with at least 3 decimal figures.
