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General => Technical support => Topic started by: cdenk on December 19, 2005, 07:49:10 AM

Title: Sensing 120 VAC input
Post by: cdenk on December 19, 2005, 07:49:10 AM

I have a TRI-PLC T00MD-888+, and would like to sense the 120VAC as being on/off only. Know I could do it with a 9 transformer, rectifier bridge , capacitor resistor divider and opto-isolator. Thinking there is a simpler way to do it, like a 120vac input, TTL output Opto-isolator chip.

Title: Re:Sensing 120 VAC input
Post by: support on December 19, 2005, 04:02:43 PM

I think the easiest and cheapest way is to get a small relay with 120VAC coil, and then the contact of the relay is used to connect the PLC's input to 0V. That way it provides complete isolation from the AC. When 120V is present the contact of the relays will turn on the PLC's input and when 120V is removed, the PLC's input is turned OFF.