ceedub
Member
Good evening everyone! This is my first post here, after extensive searching on the net I couldn't find an answer to my question so I thought I would register and post here hopefully you guys can help me with my question.
I work for a natural gas compression company and I operate a station in which I am working on converting the protection system and control to PLC's. I have installed a 24vdc MicroLogix1500 processor utilizing multiple input and output cards (thermocouple, analog in/out, digital in, and the embedded digital outs). I currently have 16 digital inputs all monitoring things such as engine oil level, coolant level etc etc etc. The inputs are normally closed sinking type sending 24vdc from my 24vdc source to the sinking input of the card for a normal run and opening the circuit in the event of a fault. For short to ground protection of these circuits I have used four 1 amp circuit breakers on the voltage source covering four DI circuits each.
What I'm wondering is since its cost prohibitive and takes up more room in my installation (which I cant spare) to fuse each individual DI's supply voltage, if I keep my existing 1A CB covering the 4 inputs but also place maybe a 100ohm resistor between the 1A protected supply and the wiring going out to each switch (oil level switch etc etc) so that in the event of a short to ground rather than tripping the CB and having to troubleshoot four individual circuits the resistor will limit current to the faulted circuit (but sized such to prevent too much current flow and tripping the breaker) thereby losing the sinking voltage coming back to the PLC ensuring that the faulted circuit is picked up by the PLC and not just the first circuit detected after tripping the breaker.
I hope this makes sense to everyone, I'm just starting to get familiarized with PLC's so please excuse me if I've left something out.
Thanks!
I work for a natural gas compression company and I operate a station in which I am working on converting the protection system and control to PLC's. I have installed a 24vdc MicroLogix1500 processor utilizing multiple input and output cards (thermocouple, analog in/out, digital in, and the embedded digital outs). I currently have 16 digital inputs all monitoring things such as engine oil level, coolant level etc etc etc. The inputs are normally closed sinking type sending 24vdc from my 24vdc source to the sinking input of the card for a normal run and opening the circuit in the event of a fault. For short to ground protection of these circuits I have used four 1 amp circuit breakers on the voltage source covering four DI circuits each.
What I'm wondering is since its cost prohibitive and takes up more room in my installation (which I cant spare) to fuse each individual DI's supply voltage, if I keep my existing 1A CB covering the 4 inputs but also place maybe a 100ohm resistor between the 1A protected supply and the wiring going out to each switch (oil level switch etc etc) so that in the event of a short to ground rather than tripping the CB and having to troubleshoot four individual circuits the resistor will limit current to the faulted circuit (but sized such to prevent too much current flow and tripping the breaker) thereby losing the sinking voltage coming back to the PLC ensuring that the faulted circuit is picked up by the PLC and not just the first circuit detected after tripping the breaker.
I hope this makes sense to everyone, I'm just starting to get familiarized with PLC's so please excuse me if I've left something out.
Thanks!
