DT9829 Thermistor Periodic Noise

[helman44]

Hello,

 

We have a setup of two thermistor arrays (one array with 3 thermistors and one with 7 thermistors).  Each array has it's own DT9829 DAQ and is wired in as a four-wire thermistor setup.  We are sampling at 20Hz and we're currently getting periodic noise (1Hz) on the 7 thermistor array, but not the 3 thermistor array.   Each array uses it's own twisted shielded pair cable with enough conductors for a four wire setup.  We have turned off all external electronics and possible sources of noise, but still get the 1Hz sinusoidal noise.  Any thoughts on this or potential fixes?

 

Thanks!

[Fausto]

Hello @helman44.

Are all 10 thermistors identical types and with the same lead lengths?  What are the model(s) and specs of your thermistors?

Here are some troubleshooting steps.  Remove all seven thermistors from the DT9829-8 module.  Let's call it module 'A'.  Jump a wire from the 'CHn+' to the 'CHn-' terminals for all eight channels on module 'A'.  Using QuickDAQ, configure all channels to be voltage input types and run an acquisition test at a sampling rate of 20 Hz.  Record the data on the plot and save a screen capture of the plot.  Next, repeat these steps with the second DT9829-8 module ('B') and its 3-thermistor array.  Save a screen capture of that acquisition test.  Please respond to this post with those images.  Next, connect the 7-thermistor array to module 'B' and run your original tests.  Does the noise follow the array?  Connect the 3-thermistor array to module 'A' and run your original tests.  Any noise?  If the noise follows the array, then check the array's wiring.  You can also run an additional test by adding four more thermistors to the 3-thermistor array setup.  Does increasing the thermistor count cause the noise to appear in your tests?

Regards,

Fausto