Measuring Force with 6434 USB DAQ

[Amit_M]

Hi. I am using the NI 6343 X series USB DAQ. I want to measure force from a load cell (Strain Measurement Devices S415). The problem that I have is related to the DAQ assistant in LabView. When I try to use the "force bridge" option from the DAQ assist menu, it tells me that there are no supported devices. Can the 6343 daq support this option or do I have to use the "custom voltage with excitation" option? I have limited experience with LabView so any advice will be appreciated. Thanks!

[PackersFan]

The 6343 is not setup for strain measurements.  To have a force bridge task, you must have a module with part of the strain bridge built-in (that's what makes a strain DAQ special).

Yes, you can perform a voltage with excitation measurement.  I assume you have an external strain bridge and are just measuring the voltage across that bridge?

[Amit_M]

Thank you for the help. Yes. That's what I have. I plan to measure the bridge output using one of the input channels on the DAQ while providing the excitation (10 Volts) using the output channel of the DAQ. Will this work or should I change anything? Thanks.

[PackersFan]

That should work as far as I know.

[Process_Systems]

Good afternoon:

I would NOT recommend that you take the approach you have described for two main reasons.

First, you would have to use the DAQ module at its highest gain setting, and you would still not be making use of the full range of the DAC.

Secondly, and the biggest reason, the output voltage from the AO on the DAQ module would not be stable enoough, both long and short term, to use as excitation for a load cell. Also, the DAQ module does not have enough current output (driving capability) for a typical load cell.

To get around all of the above, I would suggest that you use a 5B37 series signal conditioning/load cell drive module. This unit brings the signal up to the level to use the full range of your DAC, and it also has an ultra-stable DC load cell excitation built in.

It is also 3-way isolated, so you have no ground loop worries.

I have used the described configuration successfully for many years. I wish you luck on your project.

Dave