Plc question

Hi Team.
I have a question about programing a slc 500 using rs logixs software. I'm using a simulator to learn how to program and I'm programing a batch mixer. It is getting pretty complex with timers and counters. My question is, I have noticed if I switch from run to program in the middle of operation, then go back to run sometimes the timers and counters don't reset. Is this just the simulator program doing that or do I need a special reset like a MCR or something else to tell the program to reset itself. They will reset if I download to the plc . I was wondering this because we had a power outage at work and some of the plc's were in fault condition when power was restored and had to be reset manually but some did not.
Thanks for your help...

I've never tested what you're seeing. Could it be that the rung conditions for your timers are still true when you switch the PLC to run mode? Try inserting a first-scan system bit into the rung conditions. What is that S1:15? I forget. I have to look the blasted thing up every time!

It's an interesting question. What should happen to timers on the first scan? Should they reset, or retain their last state and pick up from there? I imagine there are arguements for each case.

AK

you said:

I'm using a simulator ...

Click to expand...

if that “simulator” that you’re using is just a software program which “emulates” a PLC, then what you’re reporting could DEFINITELY be a function of the emulation software ... specifically, this thing is NOT a real hardware PLC and so you can’t count on it to act EXACTLY like a real hardware PLC in every single way ...

for an Allen-Bradley processor from the SLC-500 family, when the processor first goes into the Run mode, all TON (Timer On Delay) timers will automatically reset their accumulators back to zero ... if you want the timer’s accumulator to NOT reset back to zero at startup, then you should use an RTO (Retentive Timer On) instruction in your program ...

if the software emulator which (I assume) that you’re using does not precisely duplicate the PLC’s action at startup, then you might need to test your program (or at least the final draft of it) on a real hardware PLC in order to determine that what you’ve written will actually function exactly the way you intended ...

final note: the processor will “go into the Run mode” if it’s placed in the Program mode and then switched back to the Run mode ... or if the power to the processor is turned off and then back on again ... either of these actions will automatically reset the accumulator of any TON timer in an Allen-Bradley PLC-5 or SLC-500 family processor ... with a software emulator, well, ... maybe ... but maybe not ...

you also said:

we had a power outage at work and some of the plc's were in fault condition when power was restored and had to be reset manually but some did not.

Click to expand...

now that sounds like a totally unrelated problem ... but if you’ll give us some more details (fault codes, etc.) then we could discuss that issue too ...

hope this helps ...

Quote from the source!

When the processor changes from the REM Run or REM Test mode to the REM Program mode or user power is lost while the instruction is timing but has not
reached its preset value, the following occurs:
Timer Enable (EN) bit remains set.
Timer Timing (TT) bit remains set.
Accumulated value (ACC) remains the same.
On returning to the REM Run or REM Test mode, the following can happen:

If the rung is true:
EN bit remains set.
TT bit remains set.
ACC value is reset.

If the rung is false:
EN bit is reset.
TT bit is reset.
ACC value is reset.

excerpted from the AB SLC500 User manual

Counters are retentive so if the ACC has a value, that value is maintained for all situations until it is reset by a RES instruction or other means of changing the value. A MOV could be used to alter the ACC of either timers or counters.

Thank you for your answers. The Simulator is a complete software only program running on windows xp . The one fault I did see was a math function error. This plc controls an extruder for plastic. It has thermocuple modules and is using the PID instructions. It uses the outputs from the plc to control a asco soleniod valve to control the cooling of each barrel, and SCR's to control the heating. The soleniod valve is either open full or closed completely. The a/b panelview 900 series shows a percentage of cooling or heating, However they are either on or off physically. The machines which is almost all of them that we have, all have trouble maintaining setvalues during running, but when idle they maintain setvalues. Another issue is we have some Barber coleman temperature controls that control individual barrels on a older extruder and we don't have the deviation compared to the SLC 500 controlled extruders.

SLC500 with RS Logix 500

Hello

First posting here so here we go!

I have just started a major project at work using PLC's (I have just about remembered my college work from over 5 years ago!).

I have purchased an Allen Bradley SLC-500 PLC which will do the business and I have just started my ladder logic.

I have also noticed that when I turn the key from RUN to PROG and then back again, the program tries to return to the previous condition with the same outputs energised. I need to work through the program to try and see if any inputs are still energised causing the program to restart.

Does anyone know if there is a way to get the program to carry out an action when it has been switched from RUN to PROGRAM.

Actually, as I write this I'm thinking that if the controller is not in RUN, it cannot do anything!

or, is there a way to make something happen when the switch is first switched to RUN, something like unlatch outputs?

Anyway, back to the drawing board!

Cheers

Simon

S:1/15 should turn on for the very first scan only after a transfer to run. Use it to set up desired initial conditions.

Bloo~@y hell, that was a quick reply.

Thanks for the information. I will give it a try. I can see that I will be spending a lot of time on this forum.

Cheers

Simon