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How do PLCs get data

A simple question (I've had very little PLC experience, forgive my ignorance)

Say I have a device, like a thermocouple, does the PLC fetch the current value from that device every execution interval, or does that device write its current value into the PLC?

The first option seems more realistic to me. Can some please explain.

Related to this question is that we have a smart camera device (basically a digital camera with processor and ethernet connection). If I wanted to get some numbers out of the camera and into the PLC, would a workable approach be that one tells the PLC to go fetch the value from the device? (The device has a known IP number on the network)

Thanks for any help, Kevin

Reply to
K Dunn
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It depends upon whether the device is "passive" or "active" - passive meaning that the PLC will need to read from it to get any data; active meaning that you could go either way.

As the camera is an "active" device on the network you could go either way - but convention and available software would likely dictate that the PLC reads the data from the Camera and not the other way around.

I hope this helps, Cameron:-)

Reply to
Cameron Dorrough

Reply to
Francis

Basically the PLC scans the devices instead of waiting their inputs.

If you want to know about PLC basics, visit this site:

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About the camera integration, generally PLC uses Modbus protocol to talk over the Ethernet. So the first thing to do is check if this camera talks Modbus. I have never seen a camera that communicates via Modbus, anyway, if this one does, you will be able to talk to most of the PLC brands in the market. Another point is to check who is going to be the master/slave of the communication.

Check out this PLC brand:

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this can help.

Fl=E1vio.

Reply to
flaviostz

you are talking from the other side of that ocean ... well ... uhmmm ... atlantic ocean ? ^^

modbus - what a laugh ^^

Mike

Reply to
Michael Marx

Michal,

Express your opinion. Make your point, but dont put trash in this group.

You make me laugh when I think how many people waste their time in internet writing something that does not even make sense.

Flavio

Michael Marx wrote:

Reply to
flaviostz

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