SC-2043 and strain gauges

[Flexrob]

I'm using a SC-2043 with an E-series DAQ to acquire strain gauges measurements but the signal appears to be corrupted by random noise.
Could it be possible? How can I solve it?
Thanks,
regards
Luca Bascetta

[Dennis_Knutson]

Noise is possible in any measurement system. Ni has a couple of articles that you should review. One is Field Wiring and Noise Considerations for Analog Signals and the other is Choosing the Right Strain-Gauge for Your Application.

[Flexrob]

I think we have chosen the right strain gauge type and also a good configuration, suitable for bending vibration measurement.
I will read again the note on field wiring but, unfortunately, I'm afraid it won't be enought. In fact, I measure the same random noise from channels connected with strain gauges and from unused channels (in which the measurement inputs are directly connected with excitation voltage, as explained in SC-2043 manual). Moreover, it is just a random noise, without any particular frequency connotation, i.e. it seems like a white noise.
For these reasons I think the noise is generated by the SC-2043 or by the DAQ card.
Thanks,
regards

Luca Bascetta

[Filipe A.]

Hello;

Noise is always a very hard issue to give advise about.
I'm attaching a very good application note though that gives some tips about possible ways to improve the signal noise ratio of the measurement system.
Hope this helps.
Filipe A.
Applications Engineer
National Instruments

[Flexrob]

I read carefully the application note on wiring and noise and I also analyze more in deep the problem. These area the results: the high frequency noise is due to brushless power supply.
However strain gauges are connected to the SC 2043 with a shielded cable. Unexpectedly is just the shield ground connection that carries into the acquisition board this noise. In fact, with all the cables disconnected from SC 2043, with the exception of the shield terminals (connected to pin 1 and 2, i.e. AIGND pins), I measure exactly the same noise.

How is it possible? Where should I connect the cable shield to avoid this problem?

Thanks,
regards

Luca Bascetta