billyboot Posted January 16, 2006 Report Posted January 16, 2006 Hi, the controller of our water pump was damage and we have to turn them ON/OFF manually. We have a FX0 plc and I am planning to use it to replace the controller. The water pumps works alternate/parallel and I think first-in first-out. Can somebody share an Idea how to make work first-in first-out. regards, billy Quote
Walden Posted January 16, 2006 Report Posted January 16, 2006 No problem! This requirement is one of the joys of PLCs! You need to set up two ring counters with latching relays. The first ring counter loads, and sets the latching relays which in turn switch on the outputs to the pumps. The second ring counter responds to the unloading signal and resets the latching relays and hence the pumps. I’ve used this system on fifty or sixty sites, regulating compressors, pumps and general motors to obtain a degree of equal wear. Quote
billyboot Posted January 16, 2006 Author Report Posted January 16, 2006 walden, thanks for your knowledge, just confused with your term, sorry, what do you mean by ring counter? did you mean just an ordinary counter or it is a special counter? Sorry because my knowledge with plcs is not that deep. thanks Quote
Walden Posted January 16, 2006 Report Posted January 16, 2006 OK, here goes! For two pumps, program two latch relays. The lower latch relay in the ladder will enable the first motor. The second latch relay above the first, will enable the second motor. The first loading pulse signal will set the first latch relay which will enable the motor output and, when the loading pulse hits it, switch on the first motor. The first latch relay will enable the second latch relay and the second latch relay will disable the first latch relay when it is set. The second loading pulse will set the second latch relay and enable the output circuit for the second motor and when the second loading signal hits it, switch on the output. You will need a relay at the top of the ladder to accept the thrid loading pulse and reset the second latch relay. Do the same thing with two more latch relays which will switch off the motor outputs as they receive an unloading pulse. You will have to stop the loading signal when both motors are running and stop the unloading signal when both motors have stopped. This can be expanded to any number of motors, within the limits of the PLC. Sketch it out in ladder format and remember that the scan goes from top to bottom. Quote
billyboot Posted January 17, 2006 Author Report Posted January 17, 2006 walden, thanks for the info, appreciate it much. regards Quote
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