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Registered Member #2628
Joined: Fri Jan 15 2010, 12:23AM
Location:
Posts: 627
I was cleaning a plc today (and found alot of brown dust inside) and now that It is cleaned up, there is board, there are the PLC's relays on one side, then these rows of yellow components...I have no idea what these components are or what they do... does anyone know?
the last picture shows the underside of the board. (click to enlarge)
Registered Member #2028
Joined: Mon Mar 16 2009, 08:13PM
Location: Norway
Posts: 319
Most likely some kind of galvanic separation to protect the internals from short circuits, voltage spikes, revesed voltages, those things. Also, the PLC's guts probably operate at a voltage of 5V, while the inputs are of a higher voltage (usually 24V ac or dc, but sometimes 12V and even mains in some cases)
Registered Member #2628
Joined: Fri Jan 15 2010, 12:23AM
Location:
Posts: 627
hm... also, I forgot to add, the input voltage is 120VAC, and this board is the middle layer of 3 boards, the top board is the PLC's logic circuits(you can see a the cover in the pic), the middle one is in the picture, and the bottom board is an SMPS with 5VDC to 24VDC output, one side of those bolt terminals is X (input) and the other is Y(output). the SMPS poweres the main board and the logic controller
Registered Member #2390
Joined: Sat Sept 26 2009, 02:04PM
Location: Milwaukee Wisconsin
Posts: 381
Radio tech is correct! Those are optocouplers, also known as optoisolators. To me it looks like the ones in your case also have a diode (aside from the led used in the opto). Thats pretty common in what looks to me like a micrologix, or compactlogix plc. They simply keep you from blowing up the input card (input portion) of the unit. It is still possible to blow out one of the optos (hence one input), but you wont wipe out the whole input side of the controller. The reason they are set up like that is for safety. If something fails on the machine its controlling you may loose one input not the whole thing which could cause loss of process control.
Registered Member #2628
Joined: Fri Jan 15 2010, 12:23AM
Location:
Posts: 627
I wouldn't bet on it 101111, there are more then 2 pins under those squares (I dont know why there is C-# on the silkscreen) and I read it with a multimeter, and they display some resistance and others an open circuit, so I would guess its an optoisolator but I would have to guess radiotech is right and doctor electrons explained it quite nicely, still, I do not plan on taking this thing apart for parts... I just wondered what those parts do.... also, I like this PLC, as it is simple to program, and easy to disesamble and reasamble. here is some more pictures
one is fully assembled and one fully dissasembled.
due to the fact that this thing has about 10 screws, only 4 connectors and press fit connection rods, it can be taken apart in about 30 seconds or so (note that troubleshooting a hardware failiure will take a week lol...)
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PLC guts - whats this?
