limit switch: potentiometer to 4-20mA?

[NoHoCa]

Our client had a butterfly valve/actuator/limit switch assembly in storage for over 30 years. Now they want to use it. The limit switch is manufactured by Limitorque (who are not answering their phones at the moment). They gave me an old wiring diagram which shows a PAIR of potentiometers (rated 1300 Ohms each) used for position indication. Normally we'd expect to get a single 4-20mA analog output for position indication. Is there an easy way to convert? I found a couple converters online, but I'm unclear as to the typical use of a dual-pot interface. Thanks for any help...

 

[Skogsgurra]

The dual pot system was (probably) used in two separate systems. One for indication and one for the position feed-back. That is how things were done a long time ago. There was some concern about having the indicator wire shorted or something and one tried to keep such happenings away from the control system.
You can safely use just one of the pots and use it as a voltage divider to get an input signal to a 0-5V/4-20 mA converter. You can, of course also use a 0-10V/4-20 mA converter.

Gunnar Englund

http://www.gke.org

 

[ScottyUK]

I've had some great results from a product by PR Electronics, the PR5111, for converting a pot signal to a voltage or current output. The PR5111 gives you the choice, and has an amazingly wide input voltage range. Nice bit of kit.

There's also the AP4003 and maybe one or two types - the Q436 or Q438 perhaps? - made by Action Instruments.

Happy Googling.



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I don't suffer from insanity. I enjoy it...

 

[JimCasey]

Limitorque may have moved since the nameplate was riveted to your actuator. They are now in Lynchburg, VA.
try 434 522 4107. Earnie Carey will be able to help, or put you in touch with someone who can. When you call be sure to have the complete model number and serial number information so the factory can ID what you have.

Usually a Limitorque has a stack of sixteen or so limit switches inside the housing, most of which are assignable to customer usage.

Other comments are also valid: the electronic hockey puck manufacturers have ohm-to-milliamp convertors that work nicely. Transmation, M-System, Action Instrument, Moore Industries, are a few names.