You need two voltage readings and two corresponding data points in order to calibrate an input to a sensor. You can usually get sufficient data from the specifications published by the manufacturer of the sensor. You can also derive the data by taking calibration readings. Most of the time, zero volts represents zero data units. If this is the case, you can enter 0 and 0 for reading #1. Next, look for the full scale reading of the sensor. It may be specified as 100psi @ 10VDC for example. If this is the case, your voltage reading #2 would be 10 and data reading #2 would be 100.

Signal type should be selected as volts or milliamps. If milliamps is selected, you must also enter the value of the external resistor you will use to convert milliamps to volts. When calibrating milliamps, enter 4mA as 4, enter 20mA as 20, etc. When calibrating volts, enter 10V as 10, etc.

Once you have calculated a slope and intercept, you should enter those values in the approprate boxes back in the Analog Inputs setup page. The input should now produce scaled data units in the input's floating point registers. Note that the integer registers will always reflect raw A/D counts.

During the calculation process, you can test hypothetical input values by entering numbers for input signal and/or A/D counts at the bottom of the above table. Click calculate again to see the results using your calculated slope and intercept.