Greetings, 

I am trying to retrofit an existing piece of industrial machinery to include a 2nd (remote) operator's console. The existing console features a rotary knob type operator interface for speed control (potentiometer wired to DC motor speed controller). This rotary type of input is preferred by the end user. Ideally, the operator will be able to adjust motor speed from either of the two consoles via a simple pointer-less dial (machine run rate is measured and displayed independently of the control circuit).

So, one speed controller, two rotary input devices... I would have thought there would be an off-the-shelf solution to this problem, but hours of searching have produced nothing. Closest thing I've seen are 3-way ceiling fan speed controls, but these would not integrate well with the DC speed controller, nor would they survive the industrial setting.

I suspect the solution is to use a pair of rotary encoders in place of potentiometers? My experience with encoders is limited, but I understand some have a directional output in addition to the usual pulses. This would allow for two pointer-less input devices. The operator could dial the machine speed up from one console and down from the other regardless of where either knob was left. An intermediary device would be required to decode the signals from the two encoders, and convert them to something the motor speed controller can use (4-20mA or 0-5vdc signal).

So, where do I find this mysterious device?

 Any ideas?
 

The current components are: 

1/2 HP, 180VDC geared motor

DART Controls 250-series analog controller, with a single potentiometer input for speed control.

Your comments are appreciated!

-Tom