Analog output failure 1762-IF2OF2

snordvikqplas

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just re-uped membership so thanks for help previous and future.

Bear with me on typing or responses back, pinky finger is broken and typing has become an adventure! Also this is a long post so thanks in advance to anyone taking the time to read it.

Components Used:
Micrologix 1200 L24BWA Ser C Rev A FRN 4
1762-IF2OF2
1762-IT4
Logix 500 8.20

Program has been working for 5 years without issue.

Both analog outputs are used to control ITT proportional air valves that have an input resistance of 200-300 ohms and are driven by 4-20mA with output 3-15 Psi.

Analog outputs are configured to 4-20ma and PID (0-16383)


Initial problem:
Told that proportional valves were not working properly (ie would not close on heat and open on cool, stayed in one position). Using a process meter I was not reading an output on either current output on IF2-OF2 card. Program had a decimal number of around 3120 so I should have had a reading of about 4mA,increased decimal output to 12000 and still 0 mA on each output. Common node inputs on card read open therefore they were no longer common.

Unwired card and drove valves no problem with process meter, ie sourced 4-20mA took each controller from open to close respectfully. Input resistance of each controller was read at 200 – 300 ohms so well within range of output card.

Determined at this point card was bad. Also, and this to me is important for later, 1200 showed no fault and all inputs and outputs were working properly. IT4 was reading all four J-type inputs properly.

Input power to processor was 123-125 VAC and DC output of processor was read at 23-23.2 DC.


Decided to replace IF2-OF2 card with another card. After doing a bench test on the replacement card, the replacement card had been on a shelf so wanted to make sure that it was functioning properly. Using a separate Micro 1200 (L24BWAR Ser C FRN 12) and IT4 determined that replacement card was outputting 4-20mA correctly.

Placed card and booted power, analog outputs would not work and once again read open on the two common node inputs.
At this point I though that I had gone to fast and had not read my meter correctly and since this card had not come out of the box brand new it had been somewhat defective without someone placing a label on it.

Bought new card and took extreme car and thought before using. By this I mean I read doc on card and also section in 1200 user manual about analog outputs. Again this particular program has been working correctly for 5 years. Also no faults on 1200 and also no faults registered in the I/O Status file (0h). I then took input resistance readings of the voltage inputs and both current and voltage outputs, numbers jived with spec sheet. Common node inputs range through. Connected card at bench, card worked as it should. Connected at the press without connecting up prop controllers only connected the ribbons, and outputs fried, by this I mean both channel 1 and 0 read open and common node reads open. These reading were taken with card separate of bus powered down.

Neither card works with my 1200 test processor either. The are DOA.

Called Rockwell Tech and worked the way up the ladder for 2 hours, both techs and some other person they were talking to could not figure what would have happened. I posed to them that I felt that the internal power supply used for analog outputs in the processor must be the cause. I asked for pinout readings for proc bus and they do not have that info. I asked for what value the power supply (internal of the 1200) for analog output should read and no answer. Please understand that these guys were as helpful as they could be they just could not provide an answer. Of course I am going to replace the 1200 and Rockwell to their credit is going to warranty the IF2OF2 after a little discussion. I just do not like it when I do not have an answer as to why this would happen. Little side note, the inputs of the analog cards continued to work so only the output section was killed, and on the second replacement card no field wiring was connected.

Maybe there is no answer but I thought to throw this to you guys and maybe someone else had this issue and had a bench test done or knows what pins on the 1200 bus I could check. I hate just plugging and saying oh well guess it was bad.


Thanks
Stuart
 
quick question, think of it this way.

Can a Micro 1200 have an internal problem (power supply) that would not come up as a hardware or software error (fault) that would destroy outputs on an analog card?
 
First I don't have an answer for you and I don't think you will get that secret stuff .

I will say though, that is one of best description I have seen here in a long time with all the info anyone would need to help.

Let us know how it all works out.
 
If both replacement analog modules failed when connected to the press ML1200 without any field wiring attached (while the first replacement was functional on the tester ML1200) it could very well be a supply power/bus issue with the production PLC.
Too bad that the CPU doesn't have the "tools" to identify the power issues capable to generate such major hardware failures...
 
First, thanks for the replies.

dmargineau, agreed and that is why I have contacted AB again. I have an issue with this in that if the only way for me to know that a 1200 can fry the outputs of an IF2OF2 card is by having another card get fried that is not good. Especially if I am pulling a card off my shelf that I have not used in two years yet worked before, how do you warranty that?

Sure I can assume that this is the problem and purchase another card and another processor but what if there is someting else and I loose another card.

I have requested a pinout of the field buss connector on the 1200. I will update as to the outcome.

Any other ideas or thoughts on testing are greatly appreciated, controls is a humbling ocupation if you are any good! just when you think you have it all figured out.....you don't. I find that it pays to listen.

Thanks guys
 
The following is what I have gotten back so far as a pin out of the bus goes:


Stuart


This is the only information that I got back so far from engineering.

Looking straight at the controller connector, the power pins are as follows:

Pin 1 (top left) - 5VDC
Pin 2 (top right) - ground
Pin 7 (4th row, left) - 24VDC
Pin 10 (bottom right) - 5VDC

I will research your other question. Please note that Tech Support has no access to product schematics.

Kathy, SLC Tech Support

So I checked what I think is a faulty 1200 and all of those voltages check out, so my next question is; if these check out what would it be in the 1200 that would cause this issue or is it even the 1200 at all?
anyways will continue to update, pin out may be helpfull for other diagnostics.

Stuart
 

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