Max. frequency limit of DAQ's ?

[reteb]

I use a NI GPIB PCI card with LabView.
Works great.

I am considering to buy a NI DAQ which works under LabView e.g. 6030 or 6035.
I have been searching for the upper frequency limits of those DAQ's but I fail to find.

May I presume that the maximum frequency is half the sampling rate or do I miss something and am I confused with DAC's ?

Thanks for any help for this DAC(Q) beginner.

Peter van Daalen.

[reteb]

I am afraid I was not clear enough in my question.
Maybe I confused two different questions.

1.
I meant to ask what the upper ( analogue INput ) AD frequency limit is.

2. What is the maximum OUTput analogue frequency for the DA converters ?
( Do I understand correctly that digital computer data can be outputted as analalogue data ? ).

Sorry for this correction.

Thanks,
Peter.

[RikPrins]

Mr. van Daalen,

About your first question:

According to the Nyquist theorem you should sample an Analog signal twice as fast as the highest frequency component in the signal to be able to reconstruct the frequency information after the signal is digitized. To be able to reconstruct the shape of the signal we advise you to sample about 5-10 times faster as the frequency of the measured signal. The last thing you should keep in mind is that the boards you mentioned have multiplexers. This means that the input channels of the board share one ADC. So when you sample 2 channels of the board it will cut the maximum sample rate in half. When you sample 3 channels you have to divide the maximum sample rate by 3 etc..

No about outputting of signals. You are c
orrect in your assumption that you can generate a digital signal inside the PC and then output it as an analog signal. The frequency is determined as follows:

You have to generate some kind of signal (for example a sine wave). In LabVIEW this waveform is build up in samples. For example 1 period is 100 samples. When you output this period with a sample rate of the DAC of a 1000 samples per second the resulting frequency of the analog output will be (1000S/s)/100S = 10Hz. So it depends on how much samples your signal is build of and the output sample rate what your maximum output frequency would be.