usb6008 and load cell

[Jammin]

Hi, I have a Honeywell 50kg S-type model 127 load cell, it outputs 3mV/V at 10V excitation. I have connected the output of the load cell directly to a USB6008. I am having a problem in that the incoming signal is noisy, up to 1 kg, where I need at least 50 g accuracy. When I unplug the load cell the incoming signal to my labview program, still has the same noise range. Does anyone have any suggestions on how I can overcome this? Additionally, do I need to amplify the cell's output or can the USB 6008 pick up this small of a voltage?

Thanks.

[Jammin]

I realized that I cannot use the load cell without an amplifier, so I will run the load cell through a campbell data logger.

[Brooks_C]

Hello Revy,

You are correct that you're measurements will be improved greatly if you amplify your signal to match one of the ranges of your ADC.  However, even if you amplify your 0-30 mV signal to 0-10 Volts, I don't think the USB-6008 can meet your accuracy specification.  If you want +/- 50 grams accuracy and the full scale of your device is 50 Kg then that is +/- 0.1 % accuracy.  If you take a look at the accuracy specification of the USB-6008 (shown below) you can see that the range accuracy of the card is 138 mV for the +/- 10 Volt range--an accuracy of 1.38%.

If this accuracy is acceptable then just make sure that you amplify your signal to scale it to the full 10 volt range.  If you require more accuracy than this then you may want to consider getting a M Series DAQ device for improved accuracy.  If you were to use an M Series card in conjunction with your amplifier then you could obtain accuracy more like +/- 0.05% or better, depending on which device you choose.  To check the accuracy of particular devices you can use the tool at www.ni.com/accuracy.  If you'd like to speak with a sales representative for help choosing a DAQ device that best suits your enitre applicaiton you can use the contact information at www.ni.com/contact.

I hope this helps, and have a good night.

Cheers,

Message Edited by Brooks_C on 04-29-2008 05:16 PM

[Jammin]

Thanks Brooks, I have solved my issues.

[fabiancam]

hi ....

i have a pressure sensor with 

RANGE: 10000 PSI

OUT: 3mv/V 

POWER: DC 10V

n i want to measure the signal of the transducer in labview with a usb daq 6009

is it possible .??? i need an aditional hardware???

thanks

[Steven_K.]

Hi fabiancam,

It is possible to to measure the signal from the pressure sensor on the USB-6009. You will need an external excitation source and potentially an amplifier to get the signal into range of the 6009.

[Jammin]

If you have done the math that Brooks provided above and that fits within your parameters then it is OK. However, I found that I needed the amplification to get my output into a range that met my needs. I would suggest getting an amplifier. If you do not have access to a datalogger, a quick search in google can point you in the direction of voltage amplifier alternatives. good luck

[eyta]

hello,

my project is similar with you, which dealing with load cell and daq6008. i'm using Vishay load cell 615 s-type.

the signal was so small value. Is that possible if i just amplifier that signal using formula block which i times the signal  X1*1000..

[eyta]

And one more thing why i got the signal so flactauted (noisy signal perhaps) eventhough i didn't put any force to the load cell. Can anyone give me any suggestion how i'm going to minimize that noisy signal.

Hope will get feedback for my prblem.

TQ.

[Steven_K.]

Hi eyta,

Using a formula block to amplify the signal isn't going to change how the hardware measures the signal. The problem is the signal coming off the load cell is in the millivolt range and the USB-6008's accuracy is 37.5mV at the lowest gain setting. (+/-1V). To get useful data, you will need to amplify the signal so that it better fills into the +/- 1V gain range. In regards to the noise, this issue could be helped after amplifying the signal. Since your signal is taking so little of the range, small noises can seem large in comparison to the signal.