PLC logic

Hi

I want to know about the logic level specs used by PLCs just as we specify the TTL logic as Voh, Vil, Vih ....etc

Plz reply me quickly...
i need it badly rightnow...

regards

This looks suspiciously like an earlier post that Steve Bailey attempted to field.....but why not.

First, each type of PLC digital input card is specific to itself and then to the manufacturer. Some are 24VDC, some are 120VAC, and so on.

In turn, each has its own "minimum" voltage level where the PLC says "Gee, this input is ON." By the same token, each has a "maximum" threashold where it says "OK, now it is OFF."

When we wire up and plan to use these inputs, we simply make sure that our "high" voltage when we want to send an "ON" signal to the PLC is above that "minimum". Similarly, for an "OFF" signal, we make sure the voltage drops below the "maximum."

If absolutely MUST have the values for a specific input, you will HAVE to go the manufacturer's data sheets for your specific card to get it. These values vary from card to card.

Is this what you are looking for?

Steve

gns,

If you could tell us what brand and model PLC you plan to use, someone might be able to post a url where you can download the data sheets with the information you need. If you're evaluating different brands, tell us what you're considering.

I am not aware of any standard within the PLC industry for on-state and off-state threshold voltage levels for a 24 VDC input. There is pretty wide range of off-state leakage current for 24 VDC outputs among the different manufacturers. It is just not possible to give you a simple (and accurate) answer to your question as you've phrased it.

On one project I needed to use an A-B input card, 120vac but the cycle was 25hz and A-B was concerned that the PLC may not see it as being "ON" due to the low hz.
I installed it and it worked fine.
So now you know A-B ac cards will work on 25hz.


Roger

25HZ, really?

Roger,
Was that by any chance a paper mill application? I have only encountered 25hz one time in my career and it was in a paper mill. Just curious is all.
Thanks

No it wasn't, it was a steel mill.

They used waste gas, from the blast furnace, to make steam to turn a turbine and generate 6600 volts 25hz which was then sent through a frequency changer changing it to 60hz then they sold it to the power company which then deducted that amount from the monthly bill.
I had the honor of putting the process on A-B Processors.

Roger