Initial Strain Values read even though no strain is connected to the SXCI Module

[Rkanna]

Hi all,Iam working on the reading the Strain Values from the Strain gauge Sensor using SCXI 1520 and SCXI Chassis 1001. My problem is Even though no Strain is Connected to the SCXI module some Strain value in micro is read. The value is Fluctuating from -40 to 60 micros instead of showing 0.  Number of Strain Channels: 3Sample Rate : 2500HzSamples Per channel: 100 Samplessample mode : Continuous SamplesSCXI Module : SCXI 1520Scxi Chasssis: SCXI 1001 We are Creating 3 Strain Channels (with Default Settings), Setting the Sample Clock and Reading the Channels in the While Loop and logging data into the File. So When We don’t have any Strain connected then the Vi should log zero instead it is logging some value in micro. Even though the Value logging is not constant. It is fluctuating from 0.000076347059 to 0.000076358681. So when we perform some Calculations like multiplying 10000 it will give some Non Zero values. We also tried performing Null Calibration before reading the Strain Channels. But Still the Values read is non Zero. The Main objective here is reading Zero value when no strain is connected to the SXCI Module. 

 So Please provide me some help.

 

 Ramesh.K.

[Ben]

If you are performing the Null properly then you may want to average the a bunch of values and subtract that from the readings as an "offset".

Ben

[Rkanna]

Thanks Ben for Your Reply.

We also Tried both Null Calibration along with Using offset option. But Still the Vi is Not reading Zero. Still Some Value in Micro is Read.

Please have a look at the Vi and we are using for reading the Strain Channels. We are Collecting 100 Samples for each channel and Aavaerage them . We are Considering thoseValues as Offset and We are subtracting from each value read in the While Loop . But Still it is not working. Can you please have alook at the attached VI and Let me know where Iam Wrong.

Ramesh.K.

[Alain_S]

I have no experience with SCXI 1520 and SCXI Chassis 1001 hardware but it's strange to me that you expect zero with no strain gauge connected.
With no strain gauge you have an "open" input that can pick up noise and things like that.

Just a thought 🙂

What readings to you have with a connected strain gauge?

[Ben]

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Alain S wrote:

I have no experience with SCXI 1520 and SCXI Chassis 1001 hardware but it's strange to me that you expect zero with no strain gauge connected.
With no strain gauge you have an "open" input that can pick up noise and things like that.

Just a thought 🙂

What readings to you have with a connected strain gauge?

---

Thank you Alain S!

I missed that point completely!

The Strain guages is required to complete the circuit. I would GUESS all bets are off with trying to null it.

How does if behave with the SG connected?

Ben

[Rkanna]

Thanks Alan and Ben for your replies.

Sorry for miscommuniction. What I mean was? The Strain Gauge was connected and Its is Closed Loop. No Strain Applied on the Strain Guage? Is theere any Issues with my VI Logic IMplementation?

When We apply some strain , I was able to record the Appilied Strain in the Vi. But When I remove the Applied Strain then the VI Should Read Zero. But This is not Happening with my VI. When the strain on the Strain Gauge is removed , the VI value is Fluctuating i.e. sometimes it shows Zero and Some times it shows some NOn Zero Values. But What My Objective here is that when the VI is reading some Applied Strain Correctly Without any Fluctuation in the Data, why the Zero Strain Value is Flunctuating.

I think I made you Clear regarding what Iam trying to acquire with my VI.

Thanks in Adavance,

Ramesh.K.

[Alain_S]

What's the nominal range of the strain gauge and what voltage do you read then?

I mean, those 76µV what % does it represent from the nominal range of the strain gauge?

[Alain_S]

If this code is to find the average of the 3 initial readings

Then, this code will be ok

You do the same "trick" in the loop while measuring, try to modify your code according to what I showed you.