DT9837A - DC Voltage measurement using Matlab R2018b - How to disable excitation current?

[NicolasJ]

Hi there,

I am facing an issue while attempting to measure voltage signals with DC content (an XBPM device). These devices deliver voltage signal, and both the DC and AC component carry useful information.

In order to double check my programs (which work perfectly well with a DT9824 card), I started by measuring the analog input self-noise.   I plugged a 50 Ohm BNC terminator, and expected near-zero voltage.

Using Matlab, the voltage is quiet, but there is an offset of 200mV. This corresponds to an intensity flowing through the resistor of 4mA, which is exactly the excitation current (used for IEPE) devices.

I repeated the same test with QuickDAQ, and the same offset was there, except tihs time I could sucessfully disable the excitation current, and remove the DC content.

Using matlab, I used the following function to add my AI#0:

addAnalogInputChannel(mySession,DAQID,0,'Voltage')

And indeed, the session output reads as expected:

=====================================================================
Data acquisition session using Data Translation hardware:
   Will run for 60 seconds (60006 scans) at 1000.116 scans/second.
   Number of channels: 1
      index Type    Device    Channel   MeasurementType         Range          Name   
      ----- ---- ------------ ------- ------------------- ------------------ ---------
      1     ai   DT9837-A(00) 0       Voltage (SingleEnd) -1.0 to +1.0 Volts DAQ#1-AI1

=====================================================================

If I try do disable excitation source by setting the 'ExcitationCurrentSource' to 'None', Matlab returns an error, since 'ExcitationCurrentSource' is not a property for a analogInputChannel.

This seems like a pretty basic problem, but I am stuck there.

Any help would be greatly appreciated !

With kind regards,

Nicolas

 

 

 

[Fausto]

Hello @NicolasJ.

Which version of MATLAB are you using?

There is a known support issue with Data Translation hardware and MATLAB R2022a.  Please use a previous version of MATLAB until an update is released.

Reference the following knowledgebase article 'Configuring a Windows system to use Data Translation hardware'.

https://kb.mccdaq.com/KnowledgebaseArticle50741.aspx

Please test the attached .m script with your DT9837A and report back with your results.

Regards,

Fausto

ML_R2021b_DT9837A_IEPE_simple_test_v1.m

[NicolasJ]

Hello Fausto,

thanks for the hint. The revision I am using is matlab R2018b.

I also tested using the same procedure with another DT9837-A card (revision 1.1), and since time the problem doesn't occur.

The problem I am having is with a DT9837-A (revision 1.2).

Both cards seem to behave quite differently.

For example: Rev1.1 card accepts terminal config of 'SingleEnded' and 'Differential', whereas the rev 1.2 only accepted 'SingleEnded'.

I am away from office this week, so that I don't have the revision 1.2 with me, only the old (almost 10 years) rev 1.1

I will report back next week if using IEPE without excitation current solves the case for the 1.2 version. In the meantime, I can use the old 1.1 for development purposes (but in the end I will need to use both cards simultaneously, some channels with IEPE, others with voltage DC inputs). 

Thanks for your efforts,

Nicolas

 

 

 

 

 

[Fausto]

Thanks for the additional information.  Please reply with an image of your module showing the serial # on the label and an image of the revision #.

Regards,

Fausto