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Strange timer issue - PLC2

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I am having a problem with a TOF in one of my programs that has been working fine for years. Ther PR value of the timer has suddenly changed from 012 to FDC. Reloading the program corrects the issue for a day or two, but then it reverts to FDC. I cannot find any info on this and will not pay Rockwell $600 to answer my question. Only one TOF is affected. Thanks for any input.

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That is a strange one. Don't have much of an idea , but a few questions to rule out things. 1. What has chaged about this system recently - besides the problem? 2. What is the Address of the TOF T4:0 , T4:32 etc? 3. If the TOF is T4:X how many total T4:Y timers exist? 4. What is the file ?3:Z and ?5:W of type.? assuming your Timers are T4. OFDC is a valid hex number and could have been written there by an icorrect size or offset variable. A wild shot, but hey you asked for ideas.

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What address is your TOF using. It looks like you may be using the same PR address somewhere else. So you also need to find out what has changed in your program (or maybe your HMI).

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Its been ages and ages since I touched a PLC-2 and I’m shooting from the hip here and I may be up in the night about this. PLC2 timer presets are in BCD format. FDC look like a hex number. BCD and Hex look exactly the same when each digit is less than 9. 012 = 0000 0001 0010. The bit pattern is the same for both Hex and BCD. FDC = 1111 1011 1100. The bit pattern is a valid Hex number but not a valid BCD number because each of the digits is greater than 9. FDC is 4060 in decimal. The HEX display is what has me a little concerned here. Where are you seeing the HEX number FDC at? Usually when you see a HEX number on a rung it is an error code and it will be preceded by ERR. Can you post what you are seeing on the programming terminal?

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I am seeing the Value at the TOF preset value. All other timers are working normally. More background. This happened when I was online troubleshooting. I was watching an output that is in no way assocoiated with this element. I ended up replacing an output card. UPDOC is the program I use. I can't see how an output card change would affect an internal timer.

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Try using another timer address. I've seen troublesome 1771 racks do wierd things to a 2's memory too. These 2s are getting so long in the tooth that there is hardly anyone at A-B that knows anything about them. Say PLC-4 (I know, not fair) and sometimes PLC-3 and you get the deer blinded by the headlights look. You might want to consider getting ready for a PLC5 or ControlLogix replacement as a long term maintenance item.

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I've seen several applications where multiple PLC5 and PLC2's were replaced by 1771-ACN15 modules and ten connected to a ControlLogix Rack with a CPU and ControNet scanner. The systems were programmed one Task per old PLC 5 or PLC2.

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many thanks to all who replied to my dilema. I will try the several suggestions made. As my boss is inherently cheap, I think this is an ideal time to push for PLC5.

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I'll say it one last time. If your boss is cheap look at the following comparison. PLC 5 Repalces PLC 2 Two PLC 5/20E processors with only 16K memory would replace 2 PLC 2's one for one 1. 1785-L20E list cost of $8245.00 each or $16,490.00 2. RSLogix 5 Standard Software 9324-RL5300ENE $3,790.00 Option Total Aui's for 15 pin to Cat5 Ethernet Conversion $20,280.00 ControlLogix replaces PLC 2 A ControlLogix System configured with the following: 1. 1756-PA72 Power Supply $805.00 2. 1756-A4 ControlLogix Backplane $291.00 3. 1756-L55M12 ControlLogx CPU with 750K Memory $5,200.00 4. 1756-ENBT 10/100 Ethernet Card for $1760.00 5. 1756-CNB ControlNet Scanner/Bridge Card $1312.00 6. 1771-ACN15 ControlNet Adapter Card $1575 each or $3150.00 7. RSLogix 5000 Standard Software 9324-RLD300ENE $2,680.00 8. RSNetworx for ControlNet Software 9357-CNETL3 $1089.00 Option Total Minus Coax for Controlnet. $16,287 P.S. - I used the Rockwell Website List and avoided choosing software bundles or any distributor special deal pricing options. Just food for thought. You'll have sofware conversion expnses and time no matter what you do and ControlLogix can replace several PLC 2's if designed correctly. Each new PLC 2 added will mean anotehr 1771-ACN15 abd more coax. Edited by BobLfoot

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I've never worked with UpDoc, but I know that even the legendary -T3 terminal would display hex digits if a preset or other data table value was not valid BCD.. I think Taylor and ICOM s/w did the same.

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Small typo just in case you use this for your justification, item 2s part number is correct but it should be RsLogix 5

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9324 part number was right , description was wrong. it is correct now

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Thanks for the reminder Gerry, I think you are right. Actually, I suspect its the same display routine in the software for both since a valid BCD looks exactly like its Hex equivalent in binary. As I said, its been ages and ages since I touched a PLC/2, although I do still have just one cranking away and dreading the day I have to replace it. I think Bob is on the right track. it may very well be time to replace that PLC2 with a CLX and a C-Net scanner. In fact, IIRC AB even packs around a trainer case to their tradeshows showing just such a set up.

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Two other notes about converting PLC2 or PLC 5 to CLGX. 1. Pay attention to Analog I/O some situations I've used the 1756-DHRIO and 1771-ASB rather than ControlNet due to compatability issues between Analog and ControlNet. 2. If you can rummage a spare "keep alive" rack or two for your old processors you can swap between adapter and processor while commissioning. We spent 4 weekends debugging a CLGX system on Saturday and Sunday only to put the PLC 5's back in each Monday until we got things fully right. Pretty cool way to convert.

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Back to the problem. Take a look at the memory address of the Timer Preset. which is different than the ACC & control word addresses.

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I would not go to a PLC-5, it is a short timer in the PLC world. I would go with the Control Logix first and a SLC-5 series next. The SLC's seem to be a current staple and the Control Logix family is the long term replacement. I just recently priced out a PLC-5-40 replacement spreadsheet. The processor alone cost more than adding the components to an existing SLC-5/04, not to mention the time and materials for installing the new hardware for the remote chassis. IIRC the timers in the PLC-2 were addressed as 200-277 (?) with the offset being 300-377. I think you could go to the 400-477 as well and use the 500-577 for the offset. Offset being either the preset value or the elapsed time, I don't honestly remember, it's been too long. - - 1987 since I used a PLC-2 family Processor. Are you sure that 100 can be used? I only ask because I thought the first two numbering groups: 000 and 100 were reserved for real inputs. 01100 would be 0 - Output 01 - Rack 011 - Slot 01100-17 - Input point in Octal format.

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Your memory's working pretty well. The timer address (in program) used the accumulator address. Accumulator (timer or counter) addresses always started with an even number (0,2,4,etc.). The preset was always 100 higher. All addresses in octal. The first available address for timers and counters was determined by the number of I/O racks in the system but was never below 030. If the full complement of 7 racks was used, then the first available address was 200. If the system contained block transfer modules, then the first available timer/counter addresses had to be reserved for the block transfer instructions.

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Short timer? Say what? With over one million installed units, AB has publically announced that they are comitted to the 1771 line for 40 more years. I would wager that the SLC will be long gone before the PLC5 is - the SLC is a sick dog compared to the PLC5, it has an grossly inferior instruction set and is much more limited in capability. I would choose a PLC5 upgrade for a PLC2 over a SLC any day. That said, the CLX family represents the future. Everything new we do (if its AB) is with the CLX family unless we need a brick and for that we use MicroLogixs. If upgraded, go with the CLX, not because the PLC5 wont be around (it will be) but because the CLX costs a lot less money and the CLX can be integrated very smoothly with 1771 IO.

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I don't know a thing about a PLC2 but I will have to agree with Alaric. It doesn't look like the PLC5 is going anywhere. I see the Compactlogix replacing the SLC long before then. Mainly the instruction set of the SLC is dated and the Compactlogix has integrated motion control and much better support for I/O networking. Unless someone tells me I have to I'll probably use the Compaclogix in place of SLC applications from now on. Or atleast I have been

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The compact logix is cheaper than the SLC as well. There is a control net compact logix processor. That might just be the cheapest way to upgrade, one CNET compact logix, a power supply, and a scanner card for the 1771 IO rack.

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I believe the PLC2 only talked remote I/O - not ControlNet. I would upgrade with PLC5 because the addressing is closer than ControlLogix. But ControlLogix is cheaper. Just watch out for the weak 1756-DHRIO module, but if upgrading a PLC2, you probably don't need to worry (unless you have complementary I/O which the 1756-DHRIO doesn't support). Edited by newpageboba

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Also the 1771 I/O will communicate over Controlnet. As Boblfoot stated earlier there could be issues with some analog modules. Perhaps Boblfoot or someone else could elaborate

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