How To Simulate a Potentiometer?

[brianafischer 2]

I have an application in which the operator currently turns a dial on the front of a clutch controller to set the maximum torque. I would like to control this with a PLC instead. The clutch controller is a Warner CBC-300 and the manual is located here. After speaking with technical support, the potentiometer on the front of the unit has 3 terminals as displayed in the attachment. I was told that the potentiometer feeds a -4.5V to -10.5V voltage to the terminals of an op-amp. How can I use a PLC to "simulate" the operator from using the dial? Is it safe to reverse the polarity of a 4.5 to 10.5V analog output signal from a PLC card? Thanks! Edited 19 Jul 2006 by brianafischer

[TConnolly 13]

Remember that voltage is only positive or negative with respect to some reference point. In this case you will have to tie your PLC analog output common to common on the pot input. How about using a -10 to +10 output card? Or use a signal conditioner to isolate the two.

[Mickey 71]

Be careful here: It looks to me like the external pot is being powered by the Warner CBC-300. You cannot bring power from your PLC to these terminals. There are such devices as Motor Operated Pots http://www.precisionsales.com/motrpts.html Edited 19 Jul 2006 by Mickey

[brianafischer 2]

So assuming that pin#1 BLK is -10.5V, I would tie that to the common on the analog out channel. If I then had a 0-10V signal output attached to pin#2 WHT, this would allow me to adjust from -10.5V to -0.5V. Pin #3 would have no connection. If so, that was along the lines of what I was thinking. Is this correct? Also, when you refer to signal conditioning, are you suggesting a DC-DC converter like the the ADAM-3014 Isolated DC Input/Output Module? Thanks for the help! Edited 19 Jul 2006 by brianafischer

[brianafischer 2]

It looks like pin#1 is providing -10.5VDC, and the voltage divider formed by the potentiometer is creating an input voltage to pin#2. This would leave me to believe that pin #2 is floating. Could you be a little more specific why pin #2, cannot be powered from the PLC output? Are you saying that this is grounded on the Warner CBC-300 board? Edited 19 Jul 2006 by brianafischer

[Mickey 71]

I have no experience with this device. I was just offering a word of caution. Take some measurements before connecting. (common to what you think is a floating terminal, common to common etc.). Better to be sure then smoke it.

[TConnolly 13]

I would assume that pin 3 is probably your common and you apply a -4.5 to -10.5V signal at pin 2. But then I'm not standing in front of the equipment with a DVM. IF that is the case then pin 3 would connect to the AO common and pin 2 would connect to the AO if you used a -10 to +10 DC output. Its best to take some measurements. I'm going to assume that because you are in the AB forum you are using an AB IO module. Be advised that if you attempt to wire the module with the common attached to a -10.5 reference point that all the other analog channels on that card may be unusable, even if it works. The channel to channel isolation may not be sufficient. I wouldn't do it myself, I would use an isolator. Edit: Just a thought... How often do you need to adjust the setting and do you need infinite adjustment or a finite number of discrete settings? For example if you only need three or four discrete clutch torque settings then determine what these are and use relays to switch a resistor network. Edited 19 Jul 2006 by Alaric

[Snerkel 0]

Be careful with this one as the instructions state it isn't isolated, eg in a fault condition you could get an high voltage at the pins. We used to use an interface card that provided an isolated circuit in situations such as this.

[brianafischer 2]

I need to have a pretty high resolution. I am looking for around 70 points in that voltage range or 0.0857V/div. What type of "isolator" do you reccomend?

[panic mode 246]

i've been using a lot weidmuller lately: http://forums.mrplc.com/index.php?showtopic=8209 it does everything so only one part to stock.