# 4-20ma Relay



## John Valdes (May 17, 2007)

A 4-20ma reference signal needs a source. What is the source?


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## erics37 (May 7, 2009)

MasterE said:


> I don't really want a PLC just to read an analog input and turn on a relay.


Getting a really tiny little dinky PLC would be pretty quick 'n cheap.


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## sparky970 (Mar 19, 2008)

google


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## MechanicalDVR (Dec 29, 2007)

We used to use these. http://www.ap-c.com/products/relays_n_accessories/PAM.asp


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## Jlarson (Jun 28, 2009)

I've been using a signal conditioner like this to do the same thing for a long time, commonly to replace mechanical pressure switches in relay controls with a transmitter. 

http://www.automationdirect.com/adc/Shopping/Catalog/Process_Controls/Signal_Conditioners/884116


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## erics37 (May 7, 2009)

MechanicalDVR said:


> We used to use these. http://www.ap-c.com/products/relays_n_accessories/PAM.asp


We use those in some HVAC controls jobs to turn s**t on and off.


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## oliquir (Jan 13, 2011)

here one unit form turck
MK43-111-R


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## bill39 (Sep 4, 2009)

MasterE said:


> I've got a few applications that need a simple relay closure based off of a setpoint on a 4-20mA input. I don't really want a PLC just to read an analog input and turn on a relay.
> Any suggestions ?


Phoenix & Action Instruments are the first two that come to mind.


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## JRaef (Mar 23, 2009)

What you are looking for is called a "Setpoint Relay" or "Limit Alarm Relay", Action Instruments is a good suggestion as already mentioned, Acromag is another big name in that. They will set you back around $200 - $250. The others like the Automation Direct shown above are capable of that function too, but you are also buying a lot of signal conversion hardware that you would not necessarily need and you will pay for that, usually about another $100 more.

That said, what erics37 said is also true that a small micro PLC or "smart relay" like an A-B Pico is now capable of that and you can get those (stripped down) for around $100, which is often less than those setpoint relays and definitely less than those signal conditioners, plus you get the ability to do more later if you need to. I go that way now.


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## MasterE (Dec 31, 2011)

John Valdes said:


> A 4-20ma reference signal needs a source. What is the source?


The source rely doesn't mater when the signal reaches the set point, close a relay contact or open a relay contact.
Its a Sonar unit for a Manure Pump Pit


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## Lone Crapshooter (Nov 8, 2008)

http://www.miinet.com/products/sg_alarm.shtml 
Mooer Industries makes relays that respond to 4-20 mA signals.


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