Potentiometer Position Sensor Loading Error Calculator
A potentiometer used as a position sensor is only linear when the input reading it draws no current. This calculator finds the real output and the loading error for a given input resistance.
- Vout = Vs × x ÷ [1 + (Rp/RL) × x × (1 − x)] = 4.878 V
- Error = (Vsx − Vout) ÷ Vs × 100 = 1.22 %
Potentiometer Loading Formula
Error = (Vs × x − Vout) ÷ Vs
x is the wiper position as a fraction of travel, Rp the total potentiometer resistance and RL the resistance of the input reading the wiper. The error is zero at both ends and largest at about two thirds of travel.
Worked example
A 10 kΩ potentiometer at mid travel read by a 100 kΩ input gives 4.878 V instead of 5 V, a 1.22 % error. The maximum error is about 1.45 % near 67 % travel.
Frequently Asked Questions
Why does loading cause error?
The input resistance is in parallel with part of the potentiometer, pulling the wiper voltage down, most in the upper middle of travel.
How large should the input resistance be?
At least 10 times the potentiometer resistance for about 1.5 % error, 100 times for about 0.15 %.
Do PLC voltage inputs load the potentiometer?
Yes. Many 0 to 10 V inputs are only 100 kΩ or less; check the module input impedance.
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