Please help me about ladder diagram control conveyor

[drbitboy]

Nothing new under the sun:

• http://www.plctalk.net/qanda/showthread.php?p=362700#post362700
• http://www.plctalk.net/qanda/showthread.php?p=542984#post542984

 

[drbitboy]

@parky's approach:

​

also works if the Normally Closed contact on the timer-done bit is moved to the output rung, and the Run Latch bit is a simple one-time seal-in:

​

OP's problem description is a TOF (Timer OFf-delay) circuit.

Inverting the input and output of a TON (Timer ON-delay) instruction makes it a TOF, almost i.e. with the exception that it must not be running when the input is 0 at the time the PLC enters RUN mode: that exception is handled here by the Sealed-In Coil pattern (cf. here) driving the Run Latch bit.

Also, I had a typo in the STMR circuit; it should be this:

​

Finally, for brands of PLC with TOF timers that have more than 16 bits available in their preset value, the program may reduce to three instructions on as little as one rung:

​

 

[Puddle]

Finally, for brands of PLC with TOF timers that have more than 16 bits available in their preset value, the program may reduce to three instructions on as little as one rung:

View attachment 65338​

I hadn't realised that timers didn't generally go to an hour, as I only really use Siemens which go up to almost 25 days.

It seemed like an oversight at first, but how often do you genuinely need a timer for over an hour?

 

[parky]

Here it is on one rung, only downside is the timer will not start until the PE becomes clear but as it is only a second or two wouldn't matter over an hour.