# Pots in series ~ can it be done?



## Introyble (Jul 10, 2010)

I've been industrial electronics, controls and electricity for a long time now. I want to wire 2 pots in series without one affecting the other. 

Simple 0-10 volt speed reference. Problem, I want to control a single VFD from two separate remote start points. Pots wired in series will act like a master/slave relationship. How do I put 2 pots on a single speed reference and let them behave independent from one another? 

Kudos to somebody ~ simple answer I know I'm missing.


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## MDShunk (Jan 7, 2007)

I'd probably use PLC i/o if I wanted the speed control from two places.


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## Introyble (Jul 10, 2010)

MDShunk said:


> I'd probably use PLC i/o if I wanted the speed control from two places.


I agree, thats the only solution I can come up with. Before PLC's this problem had to been dealt with ~ I just can not figure the solution in my limited brain.


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## JohnR (Apr 12, 2010)

Not quite sure what you mean about pots, (potentiometer?) but your question reminds me of the 4 light bulbs, 2 single poles in series trick using diodes

can't remember exactly how it was made but what you could see was a small lampholder with a A90 bulb in it and two single pole switches. mounted on a plexiglass box.
Clearly shown was the wires point to point. what was not shown was the diodes paralleling the switches and lamps. Every other diode was reversed. 


Failing this method, you could have one potentiometer with a higher rating than the next, say 10k, 100k and give a IF input =<10k then "X" ,else "Y", IF input =<100K Then "B" else "C"

I may have the greater, less than mixed, and you may have to add more parameters like if it is greater than 10 but less than 10K and more than 15K but less than 100K . for instance.


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## Jlarson (Jun 28, 2009)

Introyble said:


> I've been industrial electronics, controls and electricity for a long time now. I want to wire 2 pots in series without one affecting the other.
> 
> Simple 0-10 volt speed reference. Problem, I want to control a single VFD from two separate remote start points. Pots wired in series will act like a master/slave relationship. How do I put 2 pots on a single speed reference and let them behave independent from one another?
> 
> Kudos to somebody ~ simple answer I know I'm missing.


I have put pots in series but not for something like that. When I do it it is usually to provide a course and fine adjustment from one location. It could probably be done with some logic and comparator circuitry, but a PLC would be cleaner.


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## wildleg (Apr 12, 2009)

I don't know how you would get a zero reference doing that if you wanted to reset the motor to a known speed - is there another motor speed selector to do that ? what's the application ? if you just want analog bump up/bump down speed you could just use a momentary contact up/down for analog speed adjustment at multiple stations. (sorry, just rambling thoughts I guess, not really an answer to your question)


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## John Valdes (May 17, 2007)

Does the VFD not have this capability? Two remote reference signals sure sounds pretty elementary.
Is there not an expansion card for this? A logic card that attaches to the control board. What is the VFD brand and have you talked to them? That is what I would do first is call the manufacturer.
A small relay can be used for multiple reference signals. That would be what I would do after I talk to the VFD manufacturer or distributor.


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## Jlarson (Jun 28, 2009)

Introyble said:


> I've been industrial electronics, controls and electricity for a long time now. I want to wire 2 pots in series without one affecting the other.
> 
> Simple 0-10 volt speed reference. Problem, I want to control a single VFD from two separate remote start points. Pots wired in series will act like a master/slave relationship. How do I put 2 pots on a single speed reference and let them behave independent from one another?
> 
> Kudos to somebody ~ simple answer I know I'm missing.


Can you parallel the two pots?


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## miller_elex (Jan 25, 2008)

So the slave speed command will never go lower than the master pot, or higher than the master pot?

2 to 10V reference?

My gut says reprogram one of the empty AI's on the drive to add the slave pot's speed command. 10kohm.

I've never used a pot. If I want to change the speed, I do it in HAND.


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## Mr.C (Dec 20, 2009)

Use 2 three way switches and put a pot in line with each traveler. Then locate one switch and one pot in each location.


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## Introyble (Jul 10, 2010)

John Valdes said:


> Does the VFD not have this capability? Two remote reference signals sure sounds pretty elementary.
> Is there not an expansion card for this? A logic card that attaches to the control board. What is the VFD brand and have you talked to them? That is what I would do first is call the manufacturer.
> A small relay can be used for multiple reference signals. That would be what I would do after I talk to the VFD manufacturer or distributor.


Well I can't argue with that at all ~ knew I was missing something simple. Thank you.

Wildleg, I have used momentary switch's in series. And perhaps MR C's solution would work.

Thinking John nailed it down already.


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