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How can I make a 1 second on, 1 second off circuit using PLC logic. I should have two timers in the circuit.?
I’m not using AB PLC’s. I know they have a system 1 second bit that will do this for me. But I have to make this happen using ladder logic.
The simplest way is to use the system’s free-running clock using one of the bits in register S4. It will one on for one second and off for one second. That is how a professional would do it.
Here is how to do it with A-B logic. The logic is 4 rungs but it is hard to describe logic here because there is no graphic capability. [If you click on the left margin to highlight it, you can type in the rungs exactly as listed here using a space between instructions and ending the rung with the enter key. Then just clean them up with the graphics editor of your programming package.]
You need two TON timers and an output bit that you can latch/unlatch. You could use one-second timers with the preset at 1 but will get better accuracy if you use a .01 second timer with a preset of 100.
RUNG 1 Take the DN bit from timer T4:0 (XIC T4:1/DN) and parallel it with the first pass bit (XIC S:1/15) to latch on an output bit (OTL O:0/0) and to reset a second timer T4:1 (RES T4:1). That will initialize the output to be on.
RUNG 2: Take the inverted output bit (XIO O:0/0) and use it to run the timer T4:1 (TON T4:1) which runs for 1 second so the bit is on for that one second.
RUNG 3: Take the DN bit of timer 1 (XIC T4:0/1) and use it to unlatch the output (OTU O:0/0). Now the output will go off.
RUNG 4: Take the inverted output (XIO O:0/0) and use it to turn on the timer T4:0 (TON T4:0) which will run for 1 second keeping the output off for that time. After the second its DN bit will come on and the cycle will repeat from the action of the first rung.