Voltage Measuring error in Labview with scxi-1100/1300

[wedge87t]

I used the Daq wizard to setup my simple loop to measure 6 channels on my SCXI-1100 card with 1300 terminal.  I actually measured the voltage on the terminal block and get 4.6 volts but labview reads from 1.1 to 0.8?  I believe it is something I setup wrong in NI-MAX or my simple labview loop because we switched out the 1100 & 1300 cards - any suggestions on what to check next?  Could my PCI card or SCXI Chassis be causing this problem?

thanks 

[Kallis]

What is the voltage source that you are using??

[wedge87t]

We are measuring voltage accross a resistor.  When I use my fluke meter I get the correct voltage measurement at the 1300 teminals but read numbers into labview all over the map...

m

[e-Cash-Money]

Hello wedge,

Are you using DAQmx or Traditional DAQ?

Also, there are some shipping examples that come with LabVIEW that are specific to certain SCXI modules.  Have you tried any of these?

[wedge87t]

Yes.  I am sure it's something simple that I am not doing but I am stumped!

I have the following setup:  

PCI-MIO16E-4

SCXI-1001

      SCXI-1100/1300

When I open the test panel it reads the real voltage (that I confirmed on the terminal block with a voltmeter) but when I run the sample program or a simple Daq Assistant scan the numbers are completely different.  I attached screen dumps - please take a look and see if you can catch what I have set wrong etc.

thanks again!

[wedge87t]

After 3 days with tech support we made some progress.  Basically my program works if I only measure one channel at a time - when I try to read more than one we get a residual voltage on the line which throws the readings off.  I have all of my inputs wired as shown in the 1100 manual.  Any suggestions as to why we get noise when scanning more than one channel?

[johnsold]

Have you terminated all unused inputs? Multiplexed boards do strange things if unused inputs are allowed to float. Since you are using Differential Mode, what is the common mode voltage and have you provided for the input bias currents? If I recall correctly in Differential Mode, a DC path to ground is required for the bias currents.

Lynn

[wedge87t]

Thanks for the help - we resolved this problem - we had a dip switch in the SCXI-1100 (SW1) set wrong (should have been floating ground) and there was a bent pin on the module.