connecting a directional valve to PLC

muzikant5

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Join Date
Mar 2009
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toronto
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17
Hi

I have two directional pneumatic valves that have some sort of coils on them, when energized they let the air out through a port. What i'm not sure is how to connect them to my dc output card?

If i have an output card with transistors can i use a solid state relay since these coils on my valves are operating at 115VAC. How to connect the relay is it just simple as connecting "+" side of solid state relay to one of the outputs, and "-" on solid state relay to COM of PLC.

Thanks
 
What make and model DC output card do you have?

When controlling a solid state device with a solid state output you need to consider leakage. Will the leakage of the solid state output be enough to keep the solid state relay energized?
 
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if you had a source card you would connect dc + to the card and then come from your outputs to the relay and then from the relay to DC -.

If it was a sinking card you would go from DC + to the relay and then from the relay to the Plc and you would have DC - connected to the PLC card.

Maybe you should look into a relay card or a 115 vac card.
 
Thanks for the reply guys

My coils are 4W, 115VAC, so the current the need to be energized is very small maybe 35-40mA. I dont know if the leakage current from dc output cards would be enough to false trigger the solid state relay. The reason why I don't want to go with relay card is because of longevity (life expectancy). If I'm going to be doing 12 000 clicks a day relay card won't last as long maybe. Another solution was to go with a TRIAC card but then I would be limited to using only AC for my outputs and I do need a dc output.

realolman would you be kind enough to post a simple diagram of what you just wrote above.

Thanks.
 
I think you may be missing the fact that if you are going to do 12000 "clicks" a day on this valve, the solenoids and valve itself are probably not going to last. I will bet on the relay lasting longer than the valve...

Russell
 
PLCMentor

I agree with you, but a solenoid is easier to replace than a relay output card and it's cheaper. Do you have any other solutions maybe?
 
muzikant5,

You will be fine with only 12,000 cycles a day on the solenoid valve.

At a previous job. We had two applications like you are proposing (DC output to solid state relay) that cycled 43,000 cycles a shift, two shifts a day, 3 shifts a week. About every two years a new solenoid valve was needed but a new air cylinder was needed every year.
 
You mentioned using a solid state relay, that should be OK. You just need to make sure when the PLC output turns off that the leakage current is not enough to keep the solid state relay turned on.
I assume your DC output is 24 VDC.
Please give us the model No of your output card and the solid state relay you have in mind.
Roy
 
Here you go... for what it's worth.

SOURCE-1.jpg
 
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Hi

Milldrone thanks for you input I really appreciate it. It's great when people use real life examples so I know that it will work fine. Do you remember what type of PLC you guys were using and was the output card just a transistor card? I guess that any solid state relay should have similar life expectancy (considering i buy a good brand).

Roy_Matson I still didn't decide what PLC to use I'm thinking that I don't need a powerful PLC like SLC 500 so I might go with MicroLogix 1000 it should do what I need. I'm not sure if mlogix 1000 has transistor outputs I think they are relay so I might go with a used SLC 500. I'm thinking that by choosing a solid state relay with a higher current rating on contacts should need more leakage current to trigger it so it should be on the safer side than a relay with low current rating.

Realolman thank you for the diagram I appreciate it.

Thanks to everyone for their help.
 
I would stay away from the micrologix line except for the 1100 and 1400. The others dont have online programming. That flexibility is worth any difference in price. Also the 1100 and 1400 have an ethernet I/P port that makes communicating with them simple.

Russell
 

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