NI-9237 increased noise when using external power supply

[kmonk]

Hi All,

I am using an NI-9237 bridge module to measure load cell data. The load cell I am using (ATI 6 axis load cell) is sensitive to temperature which results in signal drift. As per the manufactures recommendation I would like to power the the load cell constantly in order to reach a thermal equilibrium to minimize measurement drift due to changing temperatures of the load cell from being powered on (during measurements) and off (between measurements).

When I choose the Vex source as "internal" it seems the load cell is only powered when a measurement is being made and as such the load cell is receiving current intermittently between my tests / measurements and with this there is a fluctuating temperature (heating up when measurement is made, and cooling down after measurement has ended) and this is causing thermal drift issues.

I have tried to bypass this issues by using an external power supply and by setting the Vex source to "external" and in this configuration I am able to achieve thermal equilibrium and the drift issues are less problematic (now only slowly drifting due to atmosphere/environmental conditions) but unfortunately a lot of noise is introduced when using an external power supply and the SNR is significantly poorer than when Vex "internal" is used.

My questions

- Is there a specific power supply that should be used (I am using a laboratory grade variable bench top power supply and I have tried a number of differnt power supplies with the same effect)

- Is there any method to reduce the introduced noise though a differnt wiring method or addition of components or by using certain grounding schemes?

- Is there a setting in NI max to power a load cell constantly rather than only when a measurement is taken?

I realize I can probably make a VI where the load cell is powered constantly but with data only sampled when needed but I am not a Lab view programmer so this would take me quite some time to achieve.

Thanks in advance for any help

K 

[AnalogKid2DigitalMan · Accepted solution]

Are your power supplies switchers or linears? Linears are less 'noisy'

-AK2DM

[santo_13 · Accepted solution]

When you say "laboratory grade", for most manufacturer's it is just a marketing gimmick while specs say otherwise.

Yes, a clean and stable power supply will help improve your measurements.

[kmonk]

The power supply is linear.

I have since tried differnt power supplies and have found a great deal of variability in the imparted noise. Fortunately I have also found a power supply (tenma 72-10505) that delivers only a little more noise than when using Vex "internal" so in my case the issue is sufficiently solved. 

Thanks for steering me in the right direction