photoeye and relay selction

[bucks7756]

I have a photoeye with a DC control output (PNP) of 100ma (26.4V) max. I need to interface it to a micrologix 1200 with a 120VAC input card. What kind of relay do I need to do this?

 

[itsmoked]

What power are you running the "photoeye" with?

 

[bucks7756]

24VDC

 

[itsmoked]

OMRON MK2P-S-DC24
OMRON PL08 (OCTAL SOCKET)

 

[bucks7756]

Thank you. Would you be able to briefly explain how a relay switches DC to AC?

 

[itsmoked]

ummm.. you're making me nervous...

The relay doesn't change DC to AC.. It allows the 24VDC running your electric eye to make the relay activate(close a pair of contacts). You then provide AC power from your micrologix to one side of the relay contact and the other side of the relay contact goes back to the micrologix AC input.

Let me say, there are a whole Cr@p-load of problems you can get yourself into doing this. Your last question tells me you really need some skilled assistance even if it is just someone looking at the whole scheme and approving it.

 

[bucks7756]

Sorry about that. I worded the question wrong. I understand how a relay works. What I had a question about was when the DC circuit energizes the coil, what is the correct contact rating. Why did you choose 10 amps? Just to make sure the rating is a couple hundred times bigger than the current going through the relay which is around 30mA. Wouldn't 5 amps be okay? Also, what sort of issues could I run into with this configuration

 

[Barry1961]

Most of the 5 amp relays I have used have blade type pins which tend to come loose under vibration. Of course there are snap clips you can get to hold them in socket.

I like the octal relay socket with round pins myself.

What frequency do you expect the photoeye to operate at?

Barry1961

 

[bucks7756]

25HZ

 

[itsmoked]

25Hz!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Forget the relay.

Get a proper photoeye instead.

 

[ScottyUK]

25Hz... consider a pulse counter card for the PLC. Or use a freq/voltage or freq/current converter and a standard analog input channel.





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One day my ship will come in.
But with my luck, I'll be at the airport!

 

[DReimer]

Or you could pony up for a 24VDC input card for the ML1200, provided you have the space.

AC sensors typically have poor switching frequency due to the 60Hz source. 25Hz will likely be at or near the max switching frequency for most AC sensors. I wouldn't want to rely on a sensor operating at its limits.

You could also look at a solid state relay, like the Omron G3NA. The G3NA-205B will switch a 5A load with a 24VDC input. (That's the lowest current rating). Looking at the specs it appears that it would take about 9ms to energize the output.

D

 

[itsmoked]

DReimer won't there be problems with the SSR's snubber network easily driving the PLCs AC input? I have an 128 LED flood light that only gets mildly dimmer when the SSR is off.