Hello everybody!

First of all, I'm not an experienced PLC Programmer.

At my current company, I just checked some programs from the past to get an idea of my current project.

Somebody who is not working here anymore, for valve controlling (on/off) used 1Hz Clock Memory. With edge triggering he made a counter, so adding +1 to a variable each second to measure the time.

As I said I don't have so much experience in that profession and I cannot decide that, is a good solution or not? It can really work as stable as a TON Timer for example? Maybe I could save some memory too, instead of using a Timer?

Another question is when I would like to control for example 40-50 valves, is that a still stable?

Sometimes Timers can behave "strange" and for a beginner and more difficult to handle, like an easy Edge-Trigger and ADD process, and could be a good alternative...?

Thanks for your answers!

Have a nice day!

 Hello,

deadandan

Hello everybody!

First of all, I'm not an experienced PLC Programmer.

At my current company, I just checked some programs from the past to get an idea of my current project.

Somebody who is not working here anymore, for valve controlling (on/off) used 1Hz Clock Memory. With edge triggering he made a counter, so adding +1 to a variable each second to measure the time.

As I said I don't have so much experience in that profession and I cannot decide that, is a good solution or not? It can really work as stable as a TON Timer for example? Maybe I could save some memory too, instead of using a Timer?

Another question is when I would like to control for example 40-50 valves, is that a still stable?

Sometimes Timers can behave "strange" and for a beginner and more difficult to handle, like an easy Edge-Trigger and ADD process, and could be a good alternative...?

Thanks for your answers!

Have a nice day!

 hope I'm not that one  or? Check that FB/FC property where I have my name as creator. I've prepared many years ago some useful Timer with your described idea, very simple and durable. It's prepared af VOID with input parameters and also output parameters, logically you need save many different Timers state and timer value. It's very useful timer with logical 1s time only, it's enough for many situations and is limitted (really had also in my prj 50 timers like this) only with memory for save state and generally INT data type to save time. Then you can ask, set, and change memory, start/stop bit as parameter as you wish.

Using the clock memory pulses seems like a good solution in the program in question.

But there are some pitfalls that you might fall if you don't know them, so here are few of them:

- The PLC program does not actually know if the hardware configuration has activated the clock memory pulses or not. If HW config is updated (for example with Replace device when you are updating your PLC hardware) the setting to enable the clock memory might not be active any more, and then the approach does not work.

- Since you are checking the rising edge of clock memory pulses, the program must be run at least twice / second. Usually this won't be a problem, but depending on your program architecture you might skip the program now and then.

- The clock memory pulse is asynchronous. If you check the signal at the beginning of the program and then you check the signal at the end of the program, you might get different results. This can lead to situations where some of the valves are controlled in program cycle X and some are controlled with program cycle X+1.
-- Edit: This is actually also partially true to the output of any timer. Whenever the actual timer output is accessed, it again processes the timer. That's why you should read the results of timer only once and write the result to a Datablock, instead of checking the instance DB output multiple times.

I would recommend creating the pulsing bit yourself with a few timers. Generate a signal that is 500ms True and then 500ms False and repeats this pattern. (Maybe set the times to 490ms or 495ms actually to account for program cycle times). Then once you have created the pulsing bit yourself, you can use that in place of the system clock memory bit.

That way you don't need to worry about HW configuration accidentally setting the bit to False or the asynchronous nature of the clock memory bits.