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How to make a synchronous acquisition of two analog signals with a one channel DAQ ?
Carline
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09-29-2004 07:49 AM
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Hi !
It is the first time I use Labview. I have just made some easy VIs, and now, I do not know how to deal with my problem...
My problem : I have only one acquisition card (DAQ Ni 6034E) and I would like
to acquire simultaneously two analog signals. It seems to be possible, in a quasi-synchronous acquisition if the card acquires one point of the first signal, then the first point of the second signal, then the second of the first signal, and so on ... I thougth that I could made two sequencies with a VI of data acquisition in each sequency, with the AI MULT PT. But with this, I think that I will lose the precision of the sampling frequency. And I have to know the sampling fre
quency ...
Thanks for your help !
Carline
It is the first time I use Labview. I have just made some easy VIs, and now, I do not know how to deal with my problem...
My problem : I have only one acquisition card (DAQ Ni 6034E) and I would like
to acquire simultaneously two analog signals. It seems to be possible, in a quasi-synchronous acquisition if the card acquires one point of the first signal, then the first point of the second signal, then the second of the first signal, and so on ... I thougth that I could made two sequencies with a VI of data acquisition in each sequency, with the AI MULT PT. But with this, I think that I will lose the precision of the sampling frequency. And I have to know the sampling fre
quency ...
Thanks for your help !
Carline
Stuart_G
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09-30-2004 08:36 AM
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There are a couple of options. With the current board you have it is multiplexed so there is no way around the fact that you are going to read channel 1 then channel 2, etc. You can minimize the delay by using the convert rate property. If you make this faster than the default then the amount of time between samples can be minimized.
Other options would be to buy a simultaneous sampling board which acquires all the channels at the same time. Or you could buy a second board and then syncrhonize those boards to acquire data at the same time.
Stuart G
Other options would be to buy a simultaneous sampling board which acquires all the channels at the same time. Or you could buy a second board and then syncrhonize those boards to acquire data at the same time.
Stuart G
Benjamin_C
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10-04-2004 10:47 AM
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Hi Carline,
A PCI-6034E is a low-cost board, which only has one Analog to Digital Converter (ADC).
With only one ADC you can't acquire different channels at the same time. That's why you find a multiplexer before the ADC in this type of board. This enables you to acquire multi-channels at the same rate quasi simultaneously. The samples of the different channels will be interleaved as it is explained in the following knowledge base :
- http://digital.ni.com/public.nsf/3efedde4322fef19862567740067f3cc/9379ea091c264b7c86256bc90082ca5d?OpenDocument.
With this method, the sampling frequency is the same for all channels. The sampling frequency of one channel is determined with the "scan rate" parameter. There is only a small delay between the samples
of each channels. When you perform an interval scanning acquisition, this delay depends on the "sample rate" that you specify. To have more informations about this terminology, please refer to the following KBs :
- http://digital.ni.com/public.nsf/websearch/4D1435DF82EF494186256D8A006DD6D4?OpenDocument.
- http://digital.ni.com/public.nsf/websearch/4D1435DF82EF494186256D8A006DD6D4?OpenDocument.
To easily perform such a multi-channels analog acquisition, you can use the VI named "AI Acquire Waveforms.vi". You also can use an example provided with LabVIEW. You just have to browse the NI Example Finder in "Harware Input & output >> Traditional NI-DAQ >> General".
Best regards,
Benjamin
National Instruments France
A PCI-6034E is a low-cost board, which only has one Analog to Digital Converter (ADC).
With only one ADC you can't acquire different channels at the same time. That's why you find a multiplexer before the ADC in this type of board. This enables you to acquire multi-channels at the same rate quasi simultaneously. The samples of the different channels will be interleaved as it is explained in the following knowledge base :
- http://digital.ni.com/public.nsf/3efedde4322fef19862567740067f3cc/9379ea091c264b7c86256bc90082ca5d?OpenDocument.
With this method, the sampling frequency is the same for all channels. The sampling frequency of one channel is determined with the "scan rate" parameter. There is only a small delay between the samples
of each channels. When you perform an interval scanning acquisition, this delay depends on the "sample rate" that you specify. To have more informations about this terminology, please refer to the following KBs :
- http://digital.ni.com/public.nsf/websearch/4D1435DF82EF494186256D8A006DD6D4?OpenDocument.
- http://digital.ni.com/public.nsf/websearch/4D1435DF82EF494186256D8A006DD6D4?OpenDocument.
To easily perform such a multi-channels analog acquisition, you can use the VI named "AI Acquire Waveforms.vi". You also can use an example provided with LabVIEW. You just have to browse the NI Example Finder in "Harware Input & output >> Traditional NI-DAQ >> General".
Best regards,
Benjamin
National Instruments France
