1771-OFE2 block transfer problems

I have a 1771-OFE analog output card that is controlling a VFD and a modulating gas valve on an AMU. The OFE-2 is in a remote rack that uses a 1771 ASB RIO and is controlled by a PLC-5. The problem that I am having is that when I put a value into the BTW, (for example lets say 2048) the BTR for that channel sometimes stays at zero, and sometimes will increase to approx. 1600, and if I am understanding this BTW/BTR thing correctly, they should be the same. The length of my BTW is 5, so I believe that means there is no scaling. In word 5 of the BTR, bits 1,2,and 3 = 1. I believe this means there the channels are recieving invalid data? If anyone has any ideas I would appreciate it, this is my first time dealing with an analog output card. We do have some spare parts in stock so I already tried to change the analog card, the 1771 asb and the power supply. I was told the system was previously working, but I have no way to verify this.

Rather than play 20 questions, can you post your RSLogix5 program file?

first of all, have you confirmed the actual current being output to the field - by using a milliammeter? ...

as you said, the data TO the module and the data back FROM the module should “match” ... but at this point, we don’t know whether the “data and signal” going out are OK - and maybe we’re just having a “feedback reporting” problem ... OR ... maybe something else again ...

next, I always recommend having the BTW send the "full-sized" amount of 13 words of data to that particular type card ...

NOTE: if you intend to increase the number of words (from 5 to 13) BE SURE that you don't inadvertently overlap any existing data ... that would be “bad” ...

most important: please follow the advice of my distinguished colleague Ken Moore and post your .RSP file (you’ll need to ZIP it first) ... we’ll do our best to help without the file, but this could be a long hard road ... the more we know, the more we can help ...

and welcome to the forum ...

Yes, I have verified the output with a milliameter. The output from the card is consistant with the the number in the BTR. I'll see what I can do about posting the file or at least some of it.

Yes, I have verified the output with a milliameter. The output from the card is consistant with the the number in the BTR.

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do you mean that the current output to the field matches the data reported BACK FROM the card - which is delivered BY the Block Transfer Read? ...



what we really want to know first of all is does the analog output in the field CHANGE when you alter the number stored in the memory location (on the data table) for that particular channel? ... it should ... if it DOES change, but not by the right amount, then you probably have a scaling problem ...



OR ...



another VERY COMMON error is to leave the “Data Format” set to the default of “BCD” ... for a PLC-5 system, the correct format is usually “Two’s Complement Binary” ...



survival tip: forget about the BTR operation for now ... it’s only used for “feedback” from the card - and many (most?) programmers don’t even use it ... instead, concentrate on getting the BTW to send the correctly scaled data to the module ... confirm that this is working correctly by using a meter ... once this is done, “smart money” says that the BTR will take care of itself ... personally, I’ve never seen it otherwise ...

I'll see what I can do about posting the file or at least some of it.

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the more we know, the more we can help ...

I got a little more time to work on this tonight and it turns out you were right,it was set up for BCD instead of binary. I changed bit 15 in word 5 to a 1 instead of a zero and everything started working. I just wanted to say thanks for the help. I really appreciate it.


Thanks,
Scott

it turns out you were right

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I just LOVE it when that happens ...

I changed bit 15 in word 5 to a 1 instead of a zero and everything started working.

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that statement leads to another discussion ... yes, you CAN manually manipulate the bits to set up the configuration data for the module ... but ... that’s doing it the “hard way” ... what I’m getting at is that you probably spent quite some time with the module’s user manual to figure out WHICH bit - and HOW to set it ... right? ...



are you aware that the I/O Configuration feature will generate the proper bit patterns for you? ... if you’ve never tried that procedure, you probably should experiment with it on a spare system ...



here’s another thread from just yesterday that fits PRECISELY with what I’m talking about ... post again if you have questions about the procedure ...



http://www.plctalk.net/qanda/showthread.php?p=285509&postcount=1

I just wanted to say thanks for the help. I really appreciate it

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you’re quite welcome ... glad we were able to help ...