PLC Clock Timing Problem

[Romeo 0]

Hi, I hope someone can help me with my Problem regarding Series 6 PLC which is programed to control "ALS" or Airfield Lighting System in an airport which i work at, the ALS has timer dependent lights which is programed to automaticaly turn on after 60 seconds whenever the operator or user switches it off, the problem is that the lights turns on in less than 60 seconds usualy 20+ secs, i have checked the ladder and all the values are correct and i am using as built and un-edited ladder, Timer is set to TS or to count in seconds and it is set to count 60 seconds. what i have noticed how ever is when i monitored the timer on the workmaster computer is that the counter is counting faster than it should be thats why even i have have the correct value for the timer which is 60 secs for the timer dependent lights it still turns on within 20+ secs. Could it be a hardware problem? Could a bad power supply cause Clock or timing problem? These are the module boards on the PLC IC600CB500K ARITHMETIC CONTROL MODULE IC600CB502L ADV. LOGIC CONTROL MODULE IC600LR616K 8K/8K MEMORY IC600BF830K ADV I/O RCVR IC600PM501A CPU/DPU POWER SUPPLY MODULE

[Steve Bailey 118]

The first thing I would do is to make sure the register assigned to the timer function isn't being used anywhere else in the program. That's the address at the ACCRG location in the function. Be aware that Rxxxx addresses in a Series Six share the same memory space as AI and AO bits, so it's possible that ladder elements in the program could be altering the register value. Be sure to perform an implicit search rather than an explicit search when looking for other usage. Explicit search will locate all usage of the Rxxxx address. Implicit search will locate 'hidden' usage such as the second address of a 32-bit instruction. If possible, post a copy of the program file and I'll look at it for you. I have a Series Six that I can download it to and see if I get the same results. Edited 25 Nov 2012 by Steve Bailey

[Romeo 0]

Thank you Mr. Steve, ill post the ladder as soon as i can.

[Romeo 0]

Hello Mr. Steve, i have attached the ladder for the ALS, thanks. KFIA_ALS.rar

[Steve Bailey 118]

The program you posted has sixty instances of the TS instruction. Which is the one with the problem? Furthermore, the presets for most of the timers are either registers R00271, R00258, or R00259. R00258 gets loaded with a value of 15 on rung 3. R00259 gets loaded with a value of 30 on rung 4. R00271 gets loaded witrh a value of 5 on rung 5. The only TS instruction that does not use one of theses three registers for a preset is the one on rung 1047 which uses a constant of 2. The bottom line is that I could not find any TS instruction that has a preset of 60 seconds. Edited 25 Nov 2012 by Steve Bailey

[Romeo 0]

Hello Mr. Steve, i may have posted a wrong ladder, il try to get the one that is loaded on the PLC. Thank You for your effort.

[Romeo 0]

Hello Mr. Steve, im having dificulty copying the ladder wich is loaded on the PLC bec it is saved on a 1mb floppy disk wich cannot be read on a desktop floppy drive, it can only be read on the workmaster floppy drive, any way im going out for my 30 day vacation, we will pick this up after i get back ok Mr. Steve? Thanks again for your effort.

[rootboy 1]

We had this exact same problem with our S6's. Random timers would time out in a fraction of their preset time. The PLC code was stable enough that no one really bothered to look to see if something had ended up being used twice (and we would have caught that sort of mistake in Ladders). What it ended up being was leaky CPUs on the Arithmetic Control Module (according to ATS, who fixed the boards for us). What they did to fix the problem was to replace the four 4-bit CPUs on the board. This did the trick, no more problems. Here is one for sale (I really wanted the link for the photo), the CPUs in question are the four gold-plated ones: http://www.ebay.com/itm/GE-FANUC-IC600CB500A-CONTROL-MODULE-ARITHMETIC-ALU2-SERIES-6-/221045324299 Before you drop $65 bucks on an iffy ACM :) We had a way of determining if the problem was with the CPUs or not. We would cycle power on the PLC and if that cleared up the problem (even temporarily) then the CPUs needed to be replaced. And a further bit of tribal knowledge, never grab the ribbon cable that connects the Arithmetic Control Module to the Logic Control Module by the ribbon to pop it off. They break easily. Always use the pull tab on the connectors.