Hello chaps i wonder if someone could have a look at the attached file and try to guide me in the right direction as to a problem I have with the functionality of the program. In Ladder 7 there are 3 timers that should shut the plant down after 40 hours. What is happening is the plant shuts down immediatley when the input that triggers the timers is activated. Any help would be greatly appreciated. Thanks in advance. Mike.
Allen Bradley SLC5/02 timer problems?
- Thread starter welshman1
- Start date
OkiePC
Lifetime Supporting Member
The thing about TOF timers, is that the DN bit will be true when the rung conditions are true, and the DN bit will stay true for the preset amount of time after the rung goes false.
You could get around the problem you face by switching to TON style timers.
Also, the timers are 1 hour timers, not forty hours. If you want a forty hour delay, then you should be using the counter done bits from C5:3, 4, and 5
You could get around the problem you face by switching to TON style timers.
Also, the timers are 1 hour timers, not forty hours. If you want a forty hour delay, then you should be using the counter done bits from C5:3, 4, and 5
Eventaully had the time to try changing timers and using the accumalator bits, but alas when the the reset is pressed the timers reset and the shutdown bit resets. Am i right in assuming that if I remove the timer resets in ladder 2 it will work? Thanks in advance Mike
OkiePC
Lifetime Supporting Member
Can you post the latest program you're working with?
Paul
Paul
OkiePC
Lifetime Supporting Member
It looks to me like the shutdown rung dropped out because I:12.2 is greater than 310, which causes T4:4 to timeout, then C5:5 gets done.
Note that C5:5. with a preset of 1, and being driven by T4:4 is not a 40 hour timer, rather a 100 second timer.
I don't see any reason why pressing the reset button would cause the shutdown to occur. Of course, I am only able to see the logic, not the wiring of the machine. Are there multiple contacts on that button?
Note that C5:5. with a preset of 1, and being driven by T4:4 is not a 40 hour timer, rather a 100 second timer.
I don't see any reason why pressing the reset button would cause the shutdown to occur. Of course, I am only able to see the logic, not the wiring of the machine. Are there multiple contacts on that button?
Last edited:
Morning, the reset pushbutton I:3 resets the timers and accumalators in Ladder 5 rungs 15 to 20. It then in turn resets the shutdown bit in ladder 7 rung 0. It doesnt actually cause the shutdown until the timer and accumalators had done their bit, but during the timing sequence they can be reset back to zero. So there could be the possibility that it would have counted 39hours then an operator would press reset and the timers would start again. The way it should operate is that until the TE's in Ladder 5 rungs 15,17 and 19 are operational again the timers should carry on until shutdown after 40 hours. The presets in the timers have been adjusted for testing purposes to alleviate the need for waiting the 40 hours. I appreciate your help very much. Thanks in advance Mike.
OkiePC
Lifetime Supporting Member
Okay, I understand better now.
In order to fix this, you can't just remove the resets from the reset oneshot rung or you'll be stuck in shutdown mode.
You could only reset those that are done (counters), or reset them all if a shutdown occurs. It depends on what you want. For example, suppose one counter gets done and shuts the system down, while another one is at 38 hours and still in an alarm condition. Do you want to be able to reset both of them, or do you want to only reset the one that is done, and then have another shutdown two hours later when the other fault timer/counter gets done?
Also, do you want to be able to reset a counter if the fault condition still exists?
In order to fix this, you can't just remove the resets from the reset oneshot rung or you'll be stuck in shutdown mode.
You could only reset those that are done (counters), or reset them all if a shutdown occurs. It depends on what you want. For example, suppose one counter gets done and shuts the system down, while another one is at 38 hours and still in an alarm condition. Do you want to be able to reset both of them, or do you want to only reset the one that is done, and then have another shutdown two hours later when the other fault timer/counter gets done?
Also, do you want to be able to reset a counter if the fault condition still exists?
Thanks for the response, the scenario we need is if any of the temperature elements in ladder 5, rungs 15-20 fail, after 40 hours if the fault is not rectified the plant would shutdown. If in that time the element is repaired and therefore not in alarm then we will need to be able to reset it and the plant not shutdown after the 40 hours. The alarm for the elements failing stay in alarm until the fault is rectified and in essence this is what we need for the timers and shutdown. Thanks in advance Mike
OkiePC
Lifetime Supporting Member
aLRIGHTY tHEN...
Here's what I think you need...
I believe you would want the counters to reset when the fault condition is no longer true?
So, I would add a rung below each affected CTU instruction, and remove the counter and timer reset instructions from the reset oneshot rung. The TON timers will automatically reset when the fault condition goes away, but the counters would be retentive unless you reset them seperately something like this:
Here's what I think you need...
I believe you would want the counters to reset when the fault condition is no longer true?
So, I would add a rung below each affected CTU instruction, and remove the counter and timer reset instructions from the reset oneshot rung. The TON timers will automatically reset when the fault condition goes away, but the counters would be retentive unless you reset them seperately something like this:
Okay some progress but what is happening now is the counter does not count up. I wasnt sure whether it was anything to do with the RES instruction across the CTU instruction so i removed this and tried. The counter did increment but the timer did not reset. Any ideas?
OkiePC
Lifetime Supporting Member
You need the reset for the timer or you'll only get one count.
Did you use code like my example? Did you use the EN bit of the timer (not the DN bit!)?
Did you use code like my example? Did you use the EN bit of the timer (not the DN bit!)?
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