07-19-2012 01:58 AM
at the moment I am trying to get started with strain gauges. Due to this, I bonded a strain gauge on a specimen which was included in the strain gauge starter kit of my strain gauge vendor. I thoroughly followed the video instructions of the strain gauge vendor to bond the strain gauge. To read the strain I am using the combination: PCI 6220 -> SCXI 1000 Chassis -> SCXI 1122 -> SCXI 1322 -> LabView Signal Express 2011 Version 5.0.0 (included in the hardware as Evaluation Version). In Signal Express I added a New Step: Strain Measurement. For this test I use one active strain gauge(bonded on the specimen) with a 120 Ohm dummy completion resistor (the dummy resistor is no strain gauge, it is just a normal completion resistor for testing purpose). Due to this, the bridge configuration in Signal Express is Quarter Bridge II. I connected the strain gauge quarter bridge to the terminal block (SCXI 1322) like shown in Figure 3-7. Also I entered the other informations like gage factor, gage resistance etc.... The sample rate is set to 10 Hz, and the I am using the default low pass filter of 4kHz (it is default in Signal Express). When I run the project, I get values for the strain about 11.xyz micro (E-6). When I bend the specimen (see attachment for picture) down(tension) with my hands the strain is increasing but realy less (0.x micros up to max. 1.0 micro), when I bend into the other direction (compression) the strain is decreasing (again: 0.x micros up to max. 1.0 micro). But sometimes Signal Express is just measuring a non changing value of -1.54xxyy milli, it does not change, even when I bend the specimen with my hand. To get rid off this I have to reset the SCXI 1000 chassis electrically to get the micro strain values. This 'phenomen' happens a lot of times then, when I try to calibrate the system via Signal Express in the 'Device' tab of Configuration tab. Do I have to make some other confiugrations ? What could be my mistake depended on the software side of this test measurement ? I appreciate every hint ! I apologize my bad english and the bad quality of the pictures in the attachment.
07-20-2012 07:05 AM
maybe someone could help you, if you provide other forum users the configuration of the Measurment & Automation Explorer. For this purpose, see this webpage:
Documenting Measurement & Automation Explorer (MAX) Configuration Information - National Instruments
If you choose Technical Support, you will get the report with the most information. Maybe it is a problem connected to the configuration of the SCXI-1000 chassis.
07-23-2012 01:59 AM
now I made a quarter bridge of type II (active gauge and a dummy gauge). I bond the strain gauges on a steel beam wich has a length of 940mm and the the strain gauges are placed with a distance about 45mm of the fixed point. In Signal Express I get a strain of 13micros (the beam is bend due to his own mass). To get a reference value I calculated the strain with a FEM programm and I get at the same position a strain about 170micros... there is factor 10....something is not normal. Can anyone help me ?
I just put the technical report in the attachment as a ZIP archive.
07-23-2012 02:49 AM
thanks for the report. For me, it looks ok. Unfortunately, i don't use the SCXI-Hardware and i can't help you very much.
Maybe you sould try to contact the technical support of National Instruments, because they have more knowledge about SCXI than me.
07-23-2012 03:13 AM
Hello Stephan D,
thank you for your reply. How I can contact the technical support ? Telephone ? Do they maybe have a german speaking support ? :-).
Uff... I am getting crazy right now with this problem.
thank you !
07-23-2012 03:17 AM
The NI Support is available in almost every language, even in german for customer from germany, switzerland and austria.
The information for germany can found here:
Kontakt - Germany - National Instruments - National Instruments