load cell data oscillation NI 9172/9237

[hygeia44]

Hi there,

I'm  trying to record the  load cell reading using NI cDAQ-9172 and NI9237. The vi file I used is the example from http://zone.ni.com/devzone/cda/epd/p/id/5902.

The problem is The data I recorded is really noisy and oscilates a lot when the reading from muitlmeter was continuely increasing. I connected a multimeter  to the  signal output of the load cell. 

What I can think about is the difference of data rate. For the NI9237 the minimum rate is 50KHZ/31=1612HZ , but the reading showing from the multimeter should be around 1-2 Hz. Attached is the  load cell reading. Is there any suggestion how to get clean data? 

The sample is sitting on the load cell and load( which is slowly increasing)  is applied on top of the sample. So there is no motion which will bring noise to the load cell. That's why I suppose the data should  continully increase.

 I also have a question about the internal excitation voltage. I put 10v there on the front  panel of the vi, but the measure  value is 7.8 volts. Is that normal?  I also tried to put 5 volts there, and the measure value is exactally 5 volts. It's kind of confused.

The load cell information is http://www.transducertechniques.com/GSO-load-cell.cfm

Any help would be appreciated>

[CharlesD]

This may sound trivial, but please ensure that you have wired the load cell properly into the 9237, and that you are selecting the approriate channel inside of the VI.  To me that data looks like complete random erronous data - as thought the terminal was open.  Check all wire connections.

For the internal excitation option, please realize that the 9237 can only source 15mA (150mW @ 10V)..  Therefore if your load cell impedance is less than 66.67 ohm you will pull too much current and therefore the voltage will be limited to a lower voltage because the current limit is reached.  To fix this use a smaller voltage excitation, use external excitation, increase load cell impedance.

[hygeia44]

Hi CharlesD,

Thank you for your reply. I found some wrong connection and the data recording works now.

Regarding the 150mW limitation, my load cell has 'Terminal Resistance: 350 ohms '. In that case, the 10 V internal excitation voltage exceed the limit.  I am not quit sure how load cell works. If the load cell asks for 10V excitation voltage. does 5 V can  keep the load cell working normally? Or I should connect the external excitation source to NI 9237?

Thanks!

[CharlesD]

Glad to hear you found one problem at least.  As for how yuour load cell works if you provide 5V then your load cell will pull half the amount of current and therefore twice as much less power.  however... I would verify with the manufacturer of the load cell that it can handle running on 5V.  It is very possible that the load cell only works with 10V of excitation.  If that is the case than you will have to use external excitation and you can follow the instructions in the user manual for more information on using external excitation and how to wire it up.

hope this helps

[Christopher.J]

Hi CharlesD,

I am new to Labview, I have the same issue. Load cell works fine but the digital data of load on the Labview 8.5 is continuously increasing and after that, oscillates a lot. Moreover, when I touch wires on the back of load cell, it goes back to normal for a while (30 sec) and increases again. When my hand gets close to the load cell indicator, the load data on Labveiw is significantly dropped. I suspect a mulfunction of DAQ but I am not sure. 

It is for micro-indentation test.  

DAQ : NI SCB-68

Load cell indicator : Sensotec, Part : 060-3147-01 

http://www.ebay.com/itm/Sensotec-060-3147-01-GM-Digital-Display-Signal-Conditioner-In-Altered-Box-/3...

PZT  : PI, E-501.00

Any advices would be appreciated. Thanks in advance for your help. 

[Captain_K]

Hi Christopher.J

My first thought is that this sounds like a grounding issue. Can you describe your setup in a little bit more detail? I’ve attached a link to our Field Wiring guide that might be useful.

http://www.ni.com/white-paper/3344/en/

Like CharlesD asked in his previous posts, can we verify that everything is wired correctly?

Can you send in a screen shot of the data you’re receiving?

Are you using the NI 9172 and NI 9237 as well?

Also, this is a really old thread. You’ll probably have better luck with responses if you create a new one and include as much information about you setup as possible (screen shots of data, code snippets, a complete list of hardware, the steps taken for data acquisition, what the error is, what your goal is, and troubleshooting steps taken thus far).