Yogesh,
there is no workaround available. The maximum samplerate for the 6259 is 1.0 MS/s in multichannelmode. So choosing to acquire two or more analoge inputs at a time, you have a sampelrate per channel of (1MS/s / # channels). Reading only from one channel at a time can be done with 1.25 MS/s since the multiplexer doesn't need to switch between the inputs and therefore does not create additional settling times.
So you have two possibilities:
a) To determine the
frequency from a periodic signal, it is sufficient to succeed the Nyquistfrequency during acquisition. Nyquistfrequency is
twice the frequency of the signal to measure. To get knowledge about the
shape of a signal, NI suggests to acquire at least
10 samples per period of the signal. So acquisitionrate has to be 10 * Signalfrequency (in your case 100kHz then). Sure, higher samplingfrequencies would reveal
even more info about the signal, but 10 is a reasonable tradeoff between amount of data vs. timing-accuracy. So taking this into amount, you should be able to acquire up to 10 channels with the 6259 without too many problems.
b) You have to use other DAQ hardware which does not multiplex the inputs to a single ADC. Those devices
- are
more expensive since the amplifier and ADC are the most expensive parts on a DAQ device
- have significantly
less number of channels since the amplifier and ADC takes a large space on the device
- sample all channels used simultaniously so the signals have (nearly) no phaseshift. Multiplexing devices like M-Series have a little phaseshift between the channels due to the switching time of the multiplexer
- have the specified samplerate available for each channel since ther is no multiplexer who devides this down.
Those devices are called S-Series and do have the numbers 61xx.
Please note that, regardless of which device you are using, you have to define which channels you are using before starting the acquisition. If you wanted to add a channel, you have to stop the acquisition, add the channel and restart the acquisition. This can be done programmatically.
hope this helps,
Norbert
[EDIT]: reworded some expressions for better understanding.
Message Edited by Norbert B on
02-29-2008 02:10 AM
Norbert
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