Unusual Spikes in voltage acquisition in DAQmx

[MSKhod]

Hi All, 

I am getting unusual spikes in voltage measurement from a strain gauge based loadcell. The frequency of these spikes is nearly 15hz. I am not able to understand what is happening.

For debugging, I assumed that there are five possibilities why the expected results are not being captured or why there is sharp peaks of noises,

1. DAQ is not working, 2. The Labview Program has a problem, 3. Loadcell is not working, 4. Power supply to Loadcell has issue, 5. Power supply to DAQ is not good.

For #1, I used three different DAQ and all have similar behaviour,

For #2, I used DAQMx Test Panel and Issues are still there,

For #3, Loadcell is behaving properly with a conditioning amplifier in a separate system, it has accurate resistance, and multimeter is reading the correct voltage for a given load.

For #4, I used two different power supplies, I checked the power supplies with a multimeter and they seems to be good.

For #5, I am not sure how to check the external supplies, I connected with an UPS and Raw supplies, grounding is good, but still, the problem is there.

I am attaching the picture of spikes with a 1.63V battery voltage measurement and a 2.47mV against 31.85N load on 250N loadcell.

Best regards

[AeroSoul]

Do you have anything that could be vibrating on your test bench? Such as a computer (with a fan on)? Are there other things in the lab that could be causing vibrations?

Are you reading multiple channels and what is the frequency of those reads?

[aniket72]

Ground unconnected terminals/wires can solve the problem. Please check if there are unconnected wires.

[MSKhod]

Hi,

Thank you for the response.

There are several computers, including server with larger fans. One or more are always turned ON. 

It also has several DC power supplies 100W -3kW but they are turned off and spikes remains.

Apparently, the oscilloscope reads the frequency of these spikes nearly 60-62Hz which is AC line frequency as well. These spikes are present everywhere in the room(and decreases slightly if I hold the oscilloscope in my hands and move towards door). 

In the other adjacent room, which has 2PC units (no server), these spikes are not present.

Best Regards

Mahavir Singh

[MSKhod]

Thank you for your response. 
The grounding is good and internally connected to devices. I have an additional ground wire from other lab but that worsen the fluctuations. Still I have asked for installation of dedicated grounding line. I will post the response if I get some improvements.

I also get static charge in my body while being in this room. I am not sure what is causing that to happen.

[AeroSoul]

The oscilloscope image you appended shows spike frequency as 15Hz (1s/div and 15 spikes per div) so it's the same as with LabVIEW.

Considering that these spikes disappear in the adjacent room, it's probably nothing to do with your measurement equipment, but rather external influence.

Why spikes would decrease if you held oscilloscope (and not load cell) in your hands i don't know. Try creating several loops with oscilloscope probe cable and see if that increases the spikes.