SCXI Module Multiplexing Issue?

[Tech12]

I have a SCXI-1000 chassis with 2 SCXI-1125/1328s installed in slots 1 and 3.  I can read a Type K TC ok on module 3, but when I add a Voltage channel from module 1, neither of the signals read correctly.  By themselves, the signals read fine, but together they read junk.

I have replaced everything but the chassis and even moved the chassis to a different computer with different cabling and MIO and the problem tends to follow the chassis.

Any help would be appreciated,

Earl

[Seth_B.]

Earl,

I have a couple of questions for you that should help us sort out what you are seeing.

• What DAQ device do you have the chassis connected to?
• When you say that you are reading junk, what specifically are you seeing?  Is there noise, ghosting, etc.?  Screenshots of the task running in MAX when both channels are used vs. when they are read separately will help.

Thanks in advance!

Message Edited by Seth B. on 01-08-2009 08:42 AM

[Tech12]

Seth,

I have a PCI-MIO-16XE-10.

Here are the particulars:

Volts alone read ok

Put in 4 volts and read 4 volts

Add TC channel

Reset Chassis

Volts now read 1.5volts

Put in 60DegC and read 52

Remove Voltage channel

 Put in 60DegC and read 53

Put in 20DegC and read -270

Change CJC Type to Constant and the reading comes back to 20.

Replace 1328 and I see the same behavior

[Seth_B.]

This is a very strange issue.  If you pull up Measurement and Automation Explorer (MAX) while your acquisition is running with both sensor connected and your task running and select your PCI-MIO-16XE-10 and switch to the Calibration tab at the bottom, what readings does it show?  Also, what is this information for the two 1125 modules?  Also, how are you applying the known temperature?

Message Edited by Seth B. on 01-09-2009 09:45 AM

[Tech12]

I  have a TC calibrator(NIST traceable) that I am using to supply the TC values and a voltage supply for the channels on the other module.

MIO Calibration

http://i34.photobucket.com/albums/d150/angrypistols/SCXI%20Issue/MIO_Calibration.jpg

Mod1 Calibration

http://i34.photobucket.com/albums/d150/angrypistols/SCXI%20Issue/Module1_Calibration.jpg

Mod2 Calibration

http://i34.photobucket.com/albums/d150/angrypistols/SCXI%20Issue/Module2_Calibration.jpg

Could it be that Module 2's calibration got zapped somehow?

Earl

[Seth_B.]

It's possible, but the values you are seeing are erratic enough that I'm not sure that would be enough.  Though your DAQ card is decidedly out of calibration based on the last external calibration date, so you'll probably see at least a few degrees of offset.  Running a self calibration should help a bit, but the card was calibrated a long time ago and at a significantly different temperature than the current operating temperature.

Lets try hooking both the voltage and the TC signal into the same module to see if we are having an issue communicating across modules. Lets do this for both modules and see if we get erratic results.  Lets also try hooking up the voltage source or the TC calibrator to each separate module(so that we are measuring just voltage or just TCs on the separate modules).

I know it seems like we are just shooting in the dark at the moment, but the more we can isolate the problem, the better off we will be.

[Tech12]

Why does the temperature read wrong when I use the 'Built-In' CJC?  For example, I put in 60 degC and the channel reads within a few degrees different, but when I put in 20decC, MAX reads -270?  If I change the CJC to 'Constant' it appears to read right?

This issue maybe seperate from the direction you might have been working.

Per your suggestion, I added the voltage channel to the module where I am reading the TC, the TC reads ok, but the voltage doesn't. 

I might mention that the issue seems to follow this particular SCXI chassis.  I have tried the chassis in another test cell, and it's still there.  I have also tried different 1125 modules with the same results.

[Logan_K]

Have you checked the fuses that are behind one of the fans of the SCXI chassis to make sure that none of them are blown? I would also check to see if any of the pins on the backplane are bent - however this could be debugged by putting the modules in different slots, or connecting the DAQ board to a different module, which I figure you've already done.

Regards,

Logan K

[Margaret F.]

Hello Earl,

Checking the fuses is an excellent point. Please take a look at this knowledgebase article for fuse information and information on how to check for bad fuses. I have had a case in the past where a cable was the culprit. Have you tried swapping the cable that connects the SCXI system to the computer? Let's check these two things and continue from here. Thanks!

[Tech12]

Fuses behind the fan are ok, no bent pins on connector or backplane. 

Cable swap shows same problematic behavior, as does moving modules to different slots.

Earl