Lookup table for a resistive AI (Analogue Input) device.

Issue

How do I calculate the input value for a Lookup table for a resistive AI device.

Product Line

Satchwell Sigma

Environment

BAS, Sigma

Cause

A new lookup table needs to be created for the resistive AI device.

Resolution

The following parameters will be needed.

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.