PXI 5105 noise

[vinod_p]

Hi

I want to use PXI 5105 on PXIe 1071 chassis for strain measurment by conneting the strain gauge via wheatstone bridge circuit to 5105 using BNC cables.I am using Labview for the same.

(i) I am getting variable noise (0.008 to 0.010 V) without any connection to input channel.

(ii) I am unable to balance/ minimize the noise to zero by substracting signal from one channel to another (differential input).

Parameters of data acquisition:

Input voltage:5V via DC power supply

All cables used are copper sheathed cables

Sampling rate:5MS/s

Number of samples to read:2000

We have been working on reducing the noise since a long time.Any help will be much appreciated.

Thanks

Vinod

[Austin_W]

What range and impedance are you using?

When you're measuring the noise, is the input terminated, or driven by the 5V DC source?

[vinod_p]

(i) First we tried PXI 5105 wihtout any connection to input channel. The screen shot of Labview Signal express is attached. The input impedance in 50 ohm with DC coupling with sampling rate 5 MS/sec

(ii) Secondly we tried with differential input to two channel from using only one strain gauge bridge circuit, and substract one signal to other using labview but could not minimize the noise. (tried with both- with and without power supply to whistone bridge)

Description of experimental setup-
We want to measure Strain from four strain gauges (foil type) mounted on bar (Kolsky bar setup), simultaneously. Each gauge is being used in wheastone bridge (quarter) configurationcon. The excitation voltage of the bridge is 5 V DC via DC power supply. The output voltage of the bridge, to be measured is connected to PXI 5105 input channel (two channel for each bridge- differential input) through shielded copper wire, with BNC connector. Initially the bridge is balance- output voltage is zero, measured by multimeter.

[TimmTheEnchanter · Accepted solution]

Hi Vinod,

Keep in mind the accuracy of the 5105 device is specified at +/-2mV.

Also, you can double-check that your device has been externally calibrated and is within it's external calibration cycle. 

When I looked at the digitized signal of a 5105 in a similar configuration to yours, I saw the same kind of (roughly) +/-2mV noise.  I don't think this is unexpected.  Especially if you leave the front end of your digitizer unterminated, it could be picking up extra ambient noise.

Why are you choosing to use this digitizer for a strain gauge measurement?  There are several other NI products that are high-channel count and designed specifically for strain measurements.  Here are some resources:

Measuring Strain with Strain Gauges

https://www.ni.com/en/shop/data-acquisition/sensor-fundamentals/measuring-strain-with-strain-gages.h...

PXIe-43xx Bridge Module Product Pages

https://www.ni.com/en-us/shop/model/pxie-4300.html

Dynamic Signal Acquisition board

https://forums.ni.com/t5/Dynamic-Signal-Acquisition/bd-p/100

-Andrew

[TimmTheEnchanter]

Sorry, to be clear, when I said the accuracy is specified to +/- 2mV, I meant to say I got that result by putting in the value for the full-scale (FS) range setting you have your digitizer configured for (6v) and putting in 0v for the signal term.

-Andrew