DAQ basics

[AshaG]

Hi,
  I have some confusion regarding signal conditioning parameters. I have a SCXI 1102 module with a Bandwidth of 2 Hz which means that 2 Hz is the maximum frequency in the input signal that I can measure. Beyond that frequency, it gets attenuated. I have a digitizer module  SCXI - 1600 which has a sampling rate of 200 kS/s.  Does this mean I am wasting the capacity of SCXI -1600 because of the limited bandwidth of SCXI 1102?

Thanks,
Asha

[Dennis_Knutson]

That module is designed to measure thermocouples and those are dc signals. If you want to measure an AC signal, then you need to find something else. If you are using the 1102 for thermocouples, I don't understand your concern.

[SLewis]

Dennis, I have two waveform wires and I am trying to create a xy graph.  How do I do this???  Need help.

Scott

[Dennis_Knutson]

Please don't hijack unrelated threads.

How about looking at this answer from earlier today? A search should have found that pretty easily. If that doesn't answer your question, please provide some more details. Attaching an image of your block diagram or the actual VI would help.

[AshaG]

Hi,
   Does the Bandwidth parameter have any meaning for signal conditioners designed for DC measurements alone? What does it indicate?
  I wanted to measure a 2-10 kHz signal and I was told that if I have a SCXI 1102C, which has a Bandwidth of 10 kHz, I could use it for the measurement.

Thanks,
Asha

[Dennis_Knutson]

Now you are talking about a different module. The 1102 has a 4 Hz filter. The 1102C has a 10 kHz filter. The issue I see with measuring a 10 kHz signal is that you would not meet the Nyquist criteria of sampling at twice the highest input frequency.

Actually, looking at the data sheet again, the 1100 is 4 Hz, 10 kHz, or full bandwidth (jumper selectable).

[SLewis]

I appoligize for wanting info throught the wrong threads.  Pretty new at labview and using there discussion forum. 

Thanks...scott

[AshaG]

Thank you for pointing out the problem regarding the Nyquist criterion.
I have got a SCXI 1102 and the manual talks about SCXI 1102/B/C together. So i had no means of knowing which one my conditioner is until I got my Part number.
So, coming back to my previous question, SCXI 1600 can acquire at a rate of 200 kS/s while my conditioner(SCXI 1102) has a Bandwidth of 2 Hz(as given in my manual) and a scan interval of 3 micro second which gives a maximum sampling rate of 333 kHZ.
How do these correlate as regards my measurements?

[RnDMonkey]

I think you are confusing frequency response with sampling rate. The "2 Hz bandwidth" is a low-pass filter cut-off frequency. The sampling rate is merely how many times you take a reading. Think of a spectrum analyzer and realize that the spectral content is limited to a very small span, but that does not limit the sweep time/sample rate. Assuming a 20dB/decade filter with 3 poles, the frequency response would look something like this:

You really only need a sample speed that is at least twice as fast as you wish to take measurements, so unless you have VERY high-speed temperature fluctuations, something in the 100s of samples/second would be a very fine thermometer. 🙂

Message Edited by morgol on 07-03-2008 05:28 PM

[AshaG]

Thank you for the information.