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Analog Input Scanning Order Shifting
Lew_Smith
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06-29-2005 05:14 PM
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I have a PCI-MIO board connected to an SCXI-1000 with an 1120 and 1102 module in the chassis to collect voltage and thermocouple readings. I am using a LabVIEW App that I developed and have extensively tested in other locations and it works great. I have installed the App in this new location and have noticed some VERY strange behavior. What seems like random occurences, the AI scans shift one place and the first channel data wraps around and becomes the last channel's data!! This occurs randomly in the scan of data, not at the beginning or end of a scan but somewhere in the scan.
The code basically sits and waits for a trigger to start saving the data to a file. When a trigger occurs, the data is saved to a file buffer in I16 form direct from the AI Read function. Right now the App is configured to save this data for 5 minutes and then close the AI Read and Clear the AI and restart looking for a trigger. The occurence of this "channel wrapping" seems to occur at random and anytime during the AI Read whether I am saving the data or not. Also when a "channel wrapping" occurs, once the AI is cleared and restarted all is well again.
The only difference between the installations that are working correctly and this strange behavior is that the SCXI chassis in the weird install sits in a large enclosure with PLC's and contact closures nearby.
I am kind of at a loss as to where to go from here since I can't seem to replicate the problem AND this App works great in other installs.
Please Help!!
The code basically sits and waits for a trigger to start saving the data to a file. When a trigger occurs, the data is saved to a file buffer in I16 form direct from the AI Read function. Right now the App is configured to save this data for 5 minutes and then close the AI Read and Clear the AI and restart looking for a trigger. The occurence of this "channel wrapping" seems to occur at random and anytime during the AI Read whether I am saving the data or not. Also when a "channel wrapping" occurs, once the AI is cleared and restarted all is well again.
The only difference between the installations that are working correctly and this strange behavior is that the SCXI chassis in the weird install sits in a large enclosure with PLC's and contact closures nearby.
I am kind of at a loss as to where to go from here since I can't seem to replicate the problem AND this App works great in other installs.
Please Help!!
e-Cash-Money
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06-30-2005 05:59 PM
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Hello Lew,
Is it possible to remove the SCXI chassis from the large enclosure to do some troubleshooting?
It would be nice to know if the environment is affecting anything as it is the only difference from the other installations of the same setup. I also think it would be good to test each module separately and see if you get the same odd behavior regardless of which module is in the chassis.
Does the channel wrap occur once or does it keep wrapping around if you leave the program running?
This is really strange behavior, but hopefully we can figure out what is causing it.
Is it possible to remove the SCXI chassis from the large enclosure to do some troubleshooting?
It would be nice to know if the environment is affecting anything as it is the only difference from the other installations of the same setup. I also think it would be good to test each module separately and see if you get the same odd behavior regardless of which module is in the chassis.
Does the channel wrap occur once or does it keep wrapping around if you leave the program running?
This is really strange behavior, but hopefully we can figure out what is causing it.
Eric
DE For Life!
DE For Life!
07-01-2005 10:29 AM
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Hi E. thanks for the reply. One thing I did not mention about the system is that we are using a bulkhead connector to pass the signals from the SCXI chassis through the enclosure to the computer. We removed this bulkhead and are now running a long cable straight from the SCXI chassis to the DAQ board. So far so good...no hiccups. If we continue to see this "shift" we will have to take the SCXI chassis out of the cabinet and rewire all the sensors.
Thanks again for your input, if you think of anything else please post.
