Analog input values jumping

Hi everybody.
I have a CompactLogix system with some 1769-IF4XOF2 analog input modules that has an strange behavior. Its analog values changes very quickly from a good value to zero, then to a medium value, then to a big value in in 2 seconds. I have connected these sensors to a IF4 modules that are working fine, just to make sure that there is no noise.
As this is happening in all four channels and in all IF4XOF2 modules, I think it could be a mistake in any configuration. I have set the config word 0, bit 15 (enable) and word 1, bits 8 and 9 (4-20mA)
Does anyone have experienced the same problem?

Take a look at the manual and your wiring. In some A-B modules you need to jumper unused channels to common.

I've had similar problems with a SLC before. Same deal, the signals worked fine on one kind of card (IF4 I think) but went crazy on another (I believe it was an IF8). Wish I could remember for sure what my problem was. If memory serves, I think it was as simple as one of the scaling modes not being supported in that module (Theoretically it was supported .... it just didn't work in practice). There was nothing about this in the documentation, and it even came as a surprise to tech support, but if if i used any other scaling other than the one I really wanted, it worked fine. The guy in tech support told me that those cards are made and designed by completely different companies. So, even though the spec sheets look the same, they often act very differently. That might be going on with the contrologix cards as well.

I think the scaling I wanted was raw/proportional, and I wound up having to use the old scaled for PID. At any rate, try changing the scaling on the card.


-jeff

I was just looking and I could not find a way to change the scaling on on an if4xof2. So, I'm probably barking up the wrong tree. So, Tom's probably right. Check the wiring diagrams.

-jeff

Once had a problem on some remote I/O modules, the only way to cure them was to ground the 24V common.
Sometimes earthing problems give this effect.

ademirpsantos said:

Hi everybody.
I have a CompactLogix system with some 1769-IF4XOF2 analog input modules that has an strange behavior. Its analog values changes very quickly from a good value to zero, then to a medium value, then to a big value in in 2 seconds. I have connected these sensors to a IF4 modules that are working fine, just to make sure that there is no noise.
As this is happening in all four channels and in all IF4XOF2 modules, I think it could be a mistake in any configuration. I have set the config word 0, bit 15 (enable) and word 1, bits 8 and 9 (4-20mA)
Does anyone have experienced the same problem?

Click to expand...

I have not had your problem but these thoughts cross my mind

I have used these modules and I found I needed to think hard when making the connections as it was easy to misunderstand the manual

As the OF2 has greater power demands is the processor back plane power supply large enough ?

The IF4XOF2 modules are a lower resolution module against an IF4

End of thinking

I had a problem before like this with siemens s7-200
Make sure that the signal cables are shielded, and make sure to hook the shield to the -(ground)- of the 24V DC from -(one side only)-