measuring strain with SCXI 1520/1314/PCI-6052E

[harisl]

I have problem with obtaining strain with SCXI 1520 (with terminal block 1314). From quarter-bridge II configuration I try to measure initial voltage, then load the system, obtain resulting voltage and then use Convert Strain Gage Reading.vi to obtain strain. When I try to test the system (I/O board PCI 6052) in MAX (with data mode "Continuous") I obtain only very noisy signal that is inclined at some 45 degrees. The examples that came with LabView 5.1 (AI, continuous, buffered acquisition) give the same result. When testing the I/O board in MAX (test panel) with data mode "Strip chart" I do obtain at least the shape that seems to correspont to the loading. I can obtain similar result when using WHILE loop in LabView, but I ca
nnot use it for my application because I am not able to collect data at the satisfactory rate. I use buffered acquisition (it gives me satisfactory rate, but the "treshold" is very large). What am I doing wrong? Any advice?

[Filipe A.]

Hello;

One thing you might want to test is to decrease the sample rate you are acquiring data at. In case you are using a too fast sample rate, the DAQ board instrumentation amplifier might have settling time problems.

Regards
Filipe A.
Applications Engineer
National Instruments

[Project Support]

Dear Filipe,

I have one issue regarding SCXI 1520 when using with PXI 1011 combined chassie. How can i configure one single channel for simple voltage measurement while using the other seven channels for strain gauge inputs?

This is because i am using an external amplifier to take a parallel output for my motion control card PXI 7352. This amplifier exites the load cell and amplifies the output from it which is routed to one of the analog input channels of the motion control card (and also this data is logged through SCXI 1520 unit).

What are the things i should take care if i go for external excitation rather than from SCXI 1520?

Kindly help me regarding this. (kindly reply me through ramkumard1981@yahoo.com as i am in the remote place).

Thanks,
Ramkumar. D
Soliton Technologies.

[sergesl]

Hello Project Support,

If you want to select one channel of the 1520 for voltage acquisition and the rest for strain measurement, all you have to do is select Voltage type when you are creating the virtual channel for that physical channel.
Select strain for the remaining 7 channels and you are good to go.

Serges L.

PS: The type of acquisition only changes the interpretation of the values acquired. So when you acquire on a "strain channel" the values will automatically be converted to strain. However, the real measured values are voltage levels.

[Project Support]

Dear Serges,

Thanks for your idea and timely help.

Ramkumar. D