1303 current measurement configuration.

[BME_genuis]

What signal source can you use with the 1300 (ie. no bias resistors)?  I am having an issue with ground referenced signal on the 1300.

[C-Dav]

BME_Genius,

What SCXI module are you using along with the 1300 terminal block?  Also, what type of signal are you trying to measure?  

Regards,

[BME_genuis]

I am using the 1100 module.  The signal is a 0-7.5 Vdc from a CO2 analyzer.  The output impedance is 20kohm. 

[C-Dav]

Have you verified the jumper settings in the 1100 module correspond the the grounding type of the signal source?  A description of the jumpers is available in the 1100 user manual:

http://www.ni.com/pdf/manuals/320637c.pdf

Regards,

[BME_genuis]

Yes.  Jumper W1 is in position 1-2.  However, it cannot be a module problem because it only occurs when that signal is attached to the 1300.  This was never a problem before with this signal on 1300 and started to occur intermittently and then would not go away.  The problem signal still is and always was ground referenced.

[C-Dav]

Interesting...

It seems that a ground-referenced signal shouldn't need any special wiring considerations...

From the manual:

"If you are using a ground-referenced thermocouple, connect the 

thermocouple positive and negative leads to CH+ and CH– respectively.
Leave jumper W1 on the SCXI-1100 in the factory-default (parking)
position"

This is how you have if wired, but you're still having his issue, correct?

Also, does this behavior hold regardless of input channel?

Regards,

[BME_genuis]

Yes, this is how I have it wired and always has been wired on the 1300.  No matter what channel I use on the 1300 I see the same problem.  For some reason, it works fine on the 1303.  That gave me the idea to tie the negative terminal to ground via a 10kohm resistor.  This fixes the problem on the 1300...but WHY being it is ground referenced????