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Old October 18th, 2017, 10:55 AM   #1
sumPLC
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Getting a DC input from an AC circuit

I am automating a COP tank. If you're not familiar with the term, it's basically a big dishwashing sink. I am using a level sensor to know when to stop filling the tank. The sensor is in a 120vac circuit. When the water gets to the level, it completes the circuit and triggers a relay that controls another 120vac circuit. I would like to use the second circuit as a digital input to the PLC. The best idea I've had is to use a transformer to transform the ac to dc. Is there a better, simpler, cheaper way to do this?
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Old October 18th, 2017, 10:57 AM   #2
g.mccormick
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Relay switching dc back to your plc.
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Old October 18th, 2017, 11:04 AM   #3
damica1
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Is your PLC inputs 120vac or 24vdc? If they are 24vdc then just like "g.mccormick" has mentioned. A small 24vdc power supply ($20.00) then if your existing second circuit relay has a spare set of contacts.(Make and Break a 24vdc line through those contacts to an input on the PLC.)

That's about all it should take.
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Old October 18th, 2017, 11:22 AM   #4
Bit_Bucket_07
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Quote:
Originally Posted by sumPLC View Post
I am automating a COP tank. If you're not familiar with the term, it's basically a big dishwashing sink. I am using a level sensor to know when to stop filling the tank. The sensor is in a 120vac circuit. When the water gets to the level, it completes the circuit and triggers a relay that controls another 120vac circuit. I would like to use the second circuit as a digital input to the PLC. The best idea I've had is to use a transformer to transform the ac to dc. Is there a better, simpler, cheaper way to do this?
A transformer will not convert AC voltage to DC. You'd need a rectifier to accomplish that.

Two words... Interposing relay.
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Old October 18th, 2017, 11:52 AM   #5
sumPLC
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Thaks guys. Relay it is.
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