how to increase the sampling rate display in waveform chart using DAQ assistant measuring strain from load cell

[richard260]

Hi All,

I am trying to measure the strain from a Vishay 1010 ( strain gauge + integrated wheatstone bridge) load cell using the DAQ assistant and LabVIEW 2012.
Here are the parameters I have set in the daq assisant configuration:

sampling mode: continuous

samples to read: 1 

frequency: 90Hz

My problem is that when I try to display the results in a waveform chart, it seems that I cannot get more than 3 samples displayed per second. I have highlighted the pointers in red and have discovered that for some reason the time it takes for a sample to register limits the number of samples displayed on the chart.

Also, when I output my data to a TDMS file and subsequenly read it with Excel, I get the correct number of samples 90 samples per second).

I am attaching a picture of the waveform chart to show you what it looks.
Any help would be appreciated thanks.

[richard260]

[Dennis_Knutson]

Can you attach the actual VI. Pretty hard to know what is going on from just an image of the front panel. For a quick sanity check, is the x-axis set for autoscale?

[richard260]

Thanks for the reply. I'm attaching the VI here ( LV 2012). I have tried to put some thought in the problem and, since my load cell outputs an analog signal, the problem must then be in the Analog to digital converter from the AI module, would that be right?
I am using:

NI cDAQ 9174 chassis and
NI 9219 Universal AI module.

Thanks in advance,
Richard

[Dennis_Knutson]

I don't see the same problem. I get numerous samples per second but I have different hardware. Frankly, requesting a single sample is not the best way to acquire data. If you want 90 per second, that is number of samples you should request with a rate of 90 Hz. You may be getting software timed input when you request a single sample at a time.

[richard260]

Hi,
Thanks for your response. We will try to apply this modification. As of my first question I have found the answer. The internal ADC in my DAQ hardware was set to highest resolution. I just had to change the ADC Timing mode to '' highest speed'' through the daq assistant under ''device'' and my graph is now very precise. ( see picture attached)
Thanks,

Richard