OkiePC
Lifetime Supporting Member
If you're only talking about two digital inputs per machine, (power, running) then having them all networked might be overkill for your basic purposes.
Having them all networked is a good thing, don't get me wrong, but if the existing PLCs don't support Ethernet, you may end up with a kludge by adding separate PLCs.
Another thing to consider is using radio modems with I/O for your data collection. The hardware can be expensive but often a whole lot cheaper than running conduit for all the wiring you might need. Radios make moving the equipment (or just the radio and I/O wiring) much easier.
We use Phoenix contact TWE models with add on I/O for monitoring and controlling simple systems up to 12 miles apart with one PLC doing the Modbus polling to collect all the data. They have a simpler system called Radio Line that might cost less money and give you similar functionality.
One drawback to using radios are that your data may not be as precise since polling 20 radios could take up to a minute or so (if some of the nodes are missing and generate errors, that can take a couple of seconds). This drawback is also going to exist if you are polling 20 PLCs over copper.
Another way you could do this would be to pull 2 inputs from all twenty machines back to one central PLC and let it do the math and connect to an HMI.
I like the idea of networking ethernet capable machines for all the other advantages it will give you but wanted to point out some of the other possibilities.
Having them all networked is a good thing, don't get me wrong, but if the existing PLCs don't support Ethernet, you may end up with a kludge by adding separate PLCs.
Another thing to consider is using radio modems with I/O for your data collection. The hardware can be expensive but often a whole lot cheaper than running conduit for all the wiring you might need. Radios make moving the equipment (or just the radio and I/O wiring) much easier.
We use Phoenix contact TWE models with add on I/O for monitoring and controlling simple systems up to 12 miles apart with one PLC doing the Modbus polling to collect all the data. They have a simpler system called Radio Line that might cost less money and give you similar functionality.
One drawback to using radios are that your data may not be as precise since polling 20 radios could take up to a minute or so (if some of the nodes are missing and generate errors, that can take a couple of seconds). This drawback is also going to exist if you are polling 20 PLCs over copper.
Another way you could do this would be to pull 2 inputs from all twenty machines back to one central PLC and let it do the math and connect to an HMI.
I like the idea of networking ethernet capable machines for all the other advantages it will give you but wanted to point out some of the other possibilities.