SC2345 with SG04 strain gage module and PCI 6024 DAQ card

[gk1990]

Dear all
I am a grad student and i will make a force measurement with strain gages. My setup has a model helicopter rotor which is attached on the top of a steel bar. That rotor produces very little force (say 50-150 grams). Since steel has very big elastic modulus (~210 GPa), elongations will be very small. Therefore, i need to measure very little elongations.

I have SC2345 signal conditioner which is connected to PCI 6024 DAQ card and i use SG04 modules. I read a very little noisy signal which is impossible to calibrate in Labview. I am using a full bridge configuration with strain gages which have 120 ohm resistance and 2.02 gage factors. I can only realize the applied force when it is above 1 kg. Therefore, my resolution is very bad right now.

My questions

1) Can i measure these small forces (50-150 grams) with the equipments mentioned above?

2) Should i amplify my signal? If yes, how?

3) Do u have any suggestions and further improvements?

Best regards

[ikelli]

In order to know if your equipment is able to measure the forces, we need to know what amount of voltage is being output.  Once the expected output of the strain gage is known, it will be easier to determine how to amplify the device because you will have a better idea of the expected signal.

[gk1990]

Currently i use my daq card to supply voltage and it is internally supplied. The value is 2.5 volt. I tried to supply 5 volt externally to the PWR01 but on the module i read 2.5 volts.

[ikelli]

If you are only getting clear results when the mass is above 1 kg, do you have an option to use a different strain gage?  If the signal isn't strong enough, the subsequent data will be of little use.

[gk1990]

Actually, i already installed the strain gages. Therefore, i want to find a solution without changing my setup since it will be extra work. If i have to use different strain gage, i change the steel bar make it thin and aliminium etc. Therefore, i want to find a solution with current equipment and test rig.

[ikelli]

Are you using any filtering? A low pass filter should be able to clean up your noise and pull out the signal you're interested in if it is present. However, if the signal is smaller than the specifications of your module and the DAQ, your current set up will not work.  You should look at what the strain gage output will be using the small mass and compare that to the hardware specifications.  If it is not within the limits, you will need to change your setup to get reliable data.

[gk1990]

Do u think that a signal amplifier such as SCXI 1125 may solve the problem?

I expect 0.000004 mV/V from 10 grams of load. Therefore, it is very hard to have such a sensitivity from my setup.

I think i should change the setup.

[ikelli]

Your output is so small that the amplifier might have a hard time reading the signal, which will still leave you with a problem.  You could test it if you have the equipment, but overall you will have better results if you have a higher output from the strain gage.  I would recommend you switch either your bar to be one that will strain much more easily, or getting a strain gage that can pick up the extremely small strain and output a higher voltage.

[gk1990]

Thank you very much. I will search more.