Pot fault detection [tour 24]

If a wire to the pot breaks various things can happen. If the full speed wire breaks, then the pot cannot select full speed so this is generally safe. If the output (wiper|) from the pot breaks – the controller sees zero speed. However if the zero speed wire breaks, then the pot will return full speed to the controller.

In some applications this is undesirable, in others it really doesn’t matter and is not worth protecting against.

So some controllers have a pot fault detection feature, others (the simpler ones) do not.


This system measures the resistance of the pot and, if it goes too high, turns the controller speed down to zero. So for a 10K pot, a ‘fault’ condition might be detected at about 25k.

The following controllers use resistance detection

  • 4QD series
  • DNO series
  • Pro-120
  • Pro-150 – this uses a microcontroller to measure.


This method measures the ‘speed’ line returned from the pot and assumes a fault if this rises too high. So if full speed is 4v, then a level of 6v could only be obtained under fault condition.

The following controllers use voltage detection

  • Uni (see manual for how to engage it)
  • 1QD series
  • Porter

The following controllers have no Pot fault detection:

  • 2QD series

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