AI-100 Channel always reading 24ma

[smoenra]

I have a strange situation where I have a cfp-2110 with a number of cards, all of which have been running fine for 9mo. Recently, I had a situation where the DO-410 card turned channels 5&6 on for roughly 21hrs (until noticed) - I doubt my labview 8.2 code had anything to do with it. Around 14hrs into this strange situation, my AI-100 card had a channel input go to 24ma and stayed at this value with no wires connected to channel. After much troubleshooting, everything came back to life and is working fine except for the one analog channel. Any ideas?

[smoenra]

Any help is appreciated...

[Eric A.]

Hi,
I would inspect the pins and connections on your FP.  Check for stray wires, bent pins and other things of this nature.  You also might consider connecting the analog input that is misbehaving to the com or ground of the connector block.  You should try to measure a known voltage such as a battery or power supply to see if it can read correctly.  Also, switch out the connector block that the module is using.  If this does not correct the problem you may want to consider returning the device for repair.

[smoenra]

Eric - per our phone discussion, have you determined any reason why the DO-410 card may have turned two digital outputs on and held them on for nearly 24hrs until power was cycled to the cFP-2110? Thanks in advance.

[Wayne.C]

Any chance your cFP is being subjected to electrical  noise from nearby contactors, relays, VFDs or large motors?  Here is a link to a thread with a similar problem.

http://forums.ni.com/ni/board/message?board.id=110&thread.id=6652  Hope this helps.

[smoenra]

Centerbolt, thanks for the reply. I saw the link you posted and researched the TVSS listings. My concern however, these inexpensive suppressors only last so many times and when they fail there is no way of knowing that they've failed until its too late. Since I have 220VAC power to my 24vdc power supplies, a real surge suppressor (industrial rated) appears to be very expensive.

It's difficult to determine what other devices are on the same line that I'm using, the equipment location is 6hrs away at a customer site. There was no other equipment in the facility that experienced any electrical issues on the days in question (transient noise, spike, etc.).

[Wayne.C]

You mentioned that a couple of DO channels acted up.  What are these channels connected to?

[smoenra]

The two DO channels are both connected to 24vdc small 2way solenoid valves (10w coil).

The part I don't quite understand yet, is the fact that I record data every 60s on an HMI connected to the cfp-2110. During this time period of over 24hrs, I recorded that the digital outputs (ch 5&6) were held on. This log is stored on the HMI, in which I use shared variables and data sockets. If the outputs were held on by some external means, would labview still record the outputs as being on?

[Wayne.C]

Do you have flyback diodes installed across the coils of the valves?  Diode needs to be installed as close as physically possible to the coils.

My guess would be that a large pulse is being produced when the coils are being de-energized.  Such a pulse could then cause your problem.

Message Edited by centerbolt on 12-19-2007 08:15 AM

[smoenra]

Centerbolt, I was told that the DO-410 card has flyback diodes installed in the card to prevent such an occurance. This card is also protected from short-circuits. Thanks