The potentiometer provides an electrical signal that is then used for position display or as an actual value input device for a control loop. Users need to know, how many Volts per inch or foot of travel they get. The process to calculate a calibration factor is called calibration. The calibration factor is typically entered in application control software to add or subtract out the linearity error to meet specification. The calibration process also depends on the fraction of the full potentiometer range needed and calibration of the total travel would not necessarily provide the highest possible accuracy.

To calculate the calibration factor, it is essential to understand that the total mechanical travel of a potentiometer is larger than the electrical defined travel and that the potentiometer does not provide a proportional relationship between travel and electrical output on both ends of the travel, typically a couple percent of the total travel.

A common way to calibrate a potentiometer is to move the sensor between two positions and to read the change in mechanical movement and the corresponding change in output voltage at a given supply voltage, typically 5VDC or 10VDC. To provide the highest accuracy of calibration, the mechanical gauge (e.g. a gauge block) used for the relative movement has to be more precise than the precision the user needs and the two points of measurement need to be as far apart as possible, but still within the electrical defined range of the potentiometer. A gauge block is made of stainless steel and is available in standard sizes of 1" high 1/4" thick and 1.000" length, 1.010" length, etc.

A common misconception is to use both end stops, meaning the total mechanical travel, but - as mentioned earlier - these two points are outside the proportional range. Novotechnik recommends using the 10% and 90% point of the full travel of the potentiometer for this two point calibration.

The procedure is described in the following steps. It is basically the same for linear and rotary potentiometers. The example uses a linear potentiometer with an electrical defined travel of 100 mm. The potentiometer needs to be mounted to a flat surface. The tools needed are gauge blocks and a precision voltmeter.

Example: Novotechnik TR100 linear potentiometer 1. Apply  the supply voltage to the sensor  (10 Volts DC) by connecting Plus to pin 1 and Minus to pin 3.  pin 2 is the wiper output contact and can never be connected to either Plus or Minus - this would destroy the potentiometer.

2. Attach a Volt Meter to pins 2 and 3 of the sensor.

3. Move the shaft of  the potentiometer  to the position where the voltage meter reads exactly 50% of  the supply voltage
(10VDC / 2 = 5.000 Volts).

4. Leave the shaft in this position of the potentiometer. It is the center position.

5. Use multiple gauge blocks to add them up to 40 mm to create the 10% travel  point.

6. Align the gauge blocks with the tip of the shaft.

7. Provide a mechanical stop at the other end of the gauge block.

8. Take the gauge block out and extract  the shaft to the end stop.

9. Read the voltage and make a note.

10. Use multiple gauge blocks to add them up to 80 mm to create the 90% travel point.

11. Retract the shaft and fit the gauge block between the end stop and the tip of the shaft.

12. Read the voltage and make a note.

13. Subtract the lower voltage reading from the higher one.

14. The calibration factor (In this example ) = voltage difference divided by 80 mm.

The calibration factor is then added to the transfer function to take out linearity error that occurs over the range of travel leaving your output readings matching the length of travel to within the devices specifications.