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What do I use for continuous waveform differentitation?
coolmoodster
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09-30-2003 06:05 PM
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I have labview 7.0, pxi-1042, pxi-6070E, scb-68, and windows xp.
I am trying to differentiate an analog signal. I create a square wave with the arbitrary signal generator with slow rising and falling edges. From 0 to 1 seconds, my voltage rises from from 0 to 4 volts. From 1 to 2 seconds, my voltage stays at constant at 4 volts. From 2 to 3 seconds, my voltage falls from 4 to 0 volts. from 3 to 4 seconds, my voltage stays at 0 volts. And then the signal repeats. This signal is an analog output. I take this signal and inject it back as an analog input. This is to test the system.
Using the NI-DAQ time domain math differential, I do not receive a continuous waveform response. I expect a continuous wav
eform pulse during the rising and falling edges otherwise zero.
It looks like I am receiving discrete points which approximate the pulse signal response I desire. In other words, the differentiator function gives me points at finite sample periods which are random (no set pattern to the sample points). Anyway to overcome this in the NI system? Do I have to go with a hardware approach using an R and C configured like a high pass filter?
I am trying to differentiate an analog signal. I create a square wave with the arbitrary signal generator with slow rising and falling edges. From 0 to 1 seconds, my voltage rises from from 0 to 4 volts. From 1 to 2 seconds, my voltage stays at constant at 4 volts. From 2 to 3 seconds, my voltage falls from 4 to 0 volts. from 3 to 4 seconds, my voltage stays at 0 volts. And then the signal repeats. This signal is an analog output. I take this signal and inject it back as an analog input. This is to test the system.
Using the NI-DAQ time domain math differential, I do not receive a continuous waveform response. I expect a continuous wav
eform pulse during the rising and falling edges otherwise zero.
It looks like I am receiving discrete points which approximate the pulse signal response I desire. In other words, the differentiator function gives me points at finite sample periods which are random (no set pattern to the sample points). Anyway to overcome this in the NI system? Do I have to go with a hardware approach using an R and C configured like a high pass filter?
rgharrison
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10-01-2003 04:46 PM
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Hi Cool,
What function in specific are you using? Also, what do you mean by random sample periods for the signal response?
Typically, discrete functions such as the input array from an analog to digital converter will yield a discrete function in response. The more sample points in your input array or function, the more closely together the discrete points of your signal response.
The main thing to note is that although the signal being input into the analog input of the card is "analog" in nature, the card converts this analog input into a digital signal representing the analog signal. The operations are then performed using "discrete" math. Thus, any function you use to process your signal in software will be discrete in nature.
There are howeve
r some boards that allow you to perform analog functions right on the card itself. These functions will morelikely be pure analog in nature unless they are using an onboard DSP (digital signal processor). Your PXI-6070E does not have onboard analog function processing. It must be converted to a discrete waveform before being processed in software.
Anyway, I've included a link to a general tutorial on the NI site describing data acquisition. Let me know if I misinterpretted your question. Hope that helps. Have a good day.
Data Acquisition Fundamentals
http://zone.ni.com/devzone/conceptd.nsf/webmain/139DFA3645B29BE586256865004E742A?opendocument
Ron
What function in specific are you using? Also, what do you mean by random sample periods for the signal response?
Typically, discrete functions such as the input array from an analog to digital converter will yield a discrete function in response. The more sample points in your input array or function, the more closely together the discrete points of your signal response.
The main thing to note is that although the signal being input into the analog input of the card is "analog" in nature, the card converts this analog input into a digital signal representing the analog signal. The operations are then performed using "discrete" math. Thus, any function you use to process your signal in software will be discrete in nature.
There are howeve
r some boards that allow you to perform analog functions right on the card itself. These functions will morelikely be pure analog in nature unless they are using an onboard DSP (digital signal processor). Your PXI-6070E does not have onboard analog function processing. It must be converted to a discrete waveform before being processed in software.
Anyway, I've included a link to a general tutorial on the NI site describing data acquisition. Let me know if I misinterpretted your question. Hope that helps. Have a good day.
Data Acquisition Fundamentals
http://zone.ni.com/devzone/conceptd.nsf/webmain/139DFA3645B29BE586256865004E742A?opendocument
Ron
