How do you use one shots in PLC applications?įor more articles on PLCs and programming, see related articles below.
It is another good way to illustrate some of the uses of one shots.Ī few things to note about the accumulator: Users can count by numbers other than one, such as 10. It’s interesting to see when users realize that it’s not the signal that’s being counted, but the number of scans that occur while the button is pressed.įigure 4 is what the rung should look like if you want to count the number of signals (or pushbutton presses). Many of them will say "one," which is incorrect. It’s good to give this exercise to new programmers and ask them to enter it into the PLC and guess what the number will be after one press of a button (assuming Word 6 is at zero).
The problem with this rung is that it doesn’t count what you want it to count, which are activations of the count signal. It adds whatever is in "Word 6" (a memory location) to the number one and puts the result back in itself. This is important in some motor or actuator safety circuits to ensure that a device is initialized to the de-energized state.įigure 3 features an accumulator rung.
If a user holds down the "on" pushbutton, the device will still be turned off.