Rung # 2

[panel1]

Attached is an RSlogix 500 program Im working on. Im having trouble with rung two. I have been learning PLC's off and on for the past year. Thanks for the help.

 

[93lt1]

First things first

I see you are reseting the timer on the same rung as the timer, based on the status of the .DN bit.
This will prevent logic in rungs lower to see the .DN bit on, because you are shutting it off immediately. In other words, the timer .DN bit will come on when the timer's preset equals it's accumulated. You will then immediately reset the timer; clear the pre, acc and the .dn bit upon execution of the RES instruction, before the next rung is scanned. Think about doing it another way. It would be easiest to do it without a RES instruction.


If there are only 2 possible values that can be in N7:1 and N:2, think about doing some EQU MOV of these values upon timer.DN. See my example below. The one-shot is not required if the timer's .DN bit is only true for one scan, but I put it in there just in case. I would consider putting a first scan rung that sets up the proper values in N7:1 and N7:2 just in case someone comes along some day and accidentally changes the value of either.

Keep in mind, there are several different ways to do this. I am going on what you started.

 

[93lt1]

One more thing...

Here's a before and after of what I would do with that timer:

 

[Ken Moore]

I've attached an alternate method, instead of moving a value into N7:1, I use a self resetting timer done bit and flip flop logic to toggle a bit every 60 seconds. Then used bit true and false conditions to alternate "main" and "standby" solenoids.
Didn't give it a whole lot of thought, but I believe it will work, let me know if you try it.

Ken

edit: This program was written using ver 6.0, I can save differently if needed.

 

[Ken Moore]

screen shot 1

timer and flip flop logic

 

[Ken Moore]

screen shot 2

fire solenoid based on condition of flip flop bit