Trying to set up a dynamic load cell in MAX

[JohnnyF]

I'm not sure if this is the correct sub-forum for this, but I am trying to connect a dynamic load cell to a CompactDAQ NI 9233 module. My local sales rep hasn't been able to help me figure out the proper way to configure this setup in MAX so I was hoping someone on here might have some experience with this sort of thing. The full specs on the dynamic load cell are found here:
http://www.omega.com/Pressure/pdf/DLC101.pdf
Thanks in advance to anyone that might be able to help me out on this one.

[Sandra_T]

Hello JohnnyF,

Thank you for posting to the discussion forum. It looks like you are trying to use the NI-9233 module. Are you using the USB-9162 carrier or are you using the cDAQ Chassis?

If you are using the cDAQ Chassis, reference the following user guide to find out how to setup the hardware and the software installation.

NI cDAQ-9172 User Guide and Specifications

If you are using the  USB-9162 carrier with the NI-9233 module, you should reference the following documentation:

USB-9233 User Guide and Specifications

NI-DAQmx for USB Devices Getting Started Guide

After getting the hardware installed and Measurement and Automation Explorer up and running, run the self test. After passing the self-test you can then open a test panel to measure an analog input signal. You can also configure a task to read information from your load cell.

For some load cells you can reference the following KnowledgeBase:

How do I Configure a Load Cell in MAX?

In this case though, you are using the 9233 which won't allow you do a custom voltage with excitation with DAQmx. I would recommend creating a Voltage Task to read the voltage and then use a custom scaling to scale the values. You need to reference your certificate of calibration for your load cell to determine the corresponding scaling values. You may need to contact the vendor of the dynamic load cell to get this information.


Regards,
  Sandra T.

Applications Engineer | National Instruments

[JohnnyF]

Sandra,

Thanks for the reply. I am using the 9233 in conjunction with the 9162 carrier.  I had set up the dynamic load cell as a voltage task but was concerned that my results might we erroneous. Upon further digging, I found more detailed info on the sensor at Omega's supplier:
http://www.dytran.com/img/products/1051.pdf
Since that document provided sensitivity information, I then set it up as an acceleration task since I was concerned that I needed to dictate the current excitation (I don't know if this is correct or not).
The issue I am concerned about is that when I use either an accelerometer and this dynamic load cell, I always end up with constant noise at approximately 1.5 g or lbs. Seeing as each is scaled differently, this is a bit of a mystery to me, particularly when I consider that the responses I see are lower in magnitude than expected.
It seems that it may be something as straightforward as an error in configuring in MAX, but I've gone through each of those several times and can't seem to figure it out.
Thanks in advance for any additional help you might be able to provide.

[Sandra_T]

Hello JohnnyF,

Your particular load cell device appears to require current excitation, which the 9233 is capable of providing through the use to the IEPE. I recommend that you use the voltage task. Is there a reason why you think the values will be erroneous? Is this something that you have observed when you tried creating a voltage task?

In terms of debugging, I would first use the test panel to test your hardware to see if it making an accurate voltage measurement. Manual do the conversion at first to see if it is giving you the correct voltage reading for the lb of load applied. This will verify that your hardware is working and there is limited noise in your system. After you have confirmed that the hardware is reading correctly, you can then create a custom scale. To create a custom scale, right click Scale on the configuration tree in MAX and select Create New. Then go through the prompts.

You will have to check with the vendor to see what type of scaling is required. I suspect that it will be linear. You can then specify the slope and y-intercept for the scale.

I hope this makes more sense.

Regards,
  Sandra T.

Applications Engineer | National Instruments

[JohnnyF]

Hi Sandra,
Thanks again for your help. My only concern with using a voltage task was born out of my lack of familiarity with this sort of thing, in that I was unsure about not specifying the excitation current. That said, I was able to set it up and verify correct functionality. All is well now!
Thanks again.

[Sandra_T]

Hello JohnnyF,

I am glad to hear that you got your application up and running. I like to hear about our customer's successes.

Sandra T.