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about measurement method

Hellow!
Normally speaking,when taking a waveform measurement by labview,is it necessary to take a new measurement continuously(put the read waveform.VI in a While loop)? or just take one measurement each time? thanks!
 
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Hi.

LabVIEW does not limit you in the method that you chose for acquisitions.  The method you chose should be determined by your application and what you are trying to do.

If you have an application in which you want to be continously acquiring until you reach some stop conditions, then you should have a VI resembling the continuous acquisition VIs found in the help (like Cont Acq&Graph Voltage-Int Clk.vi, which is a very good example).  Notice that in the examples you do NOT read 1 sample at a time, but with each iteration of the while loop you read several samples, making the acquisition more computer-resource efficient.

If you have an applicaiton in which you previously know how many samples you will need in total, then you do a single 1-run acquisition of all the samples you need.  A good example of this is Acq&Graph Voltage-Int Clk.vi, also found in the VI examples that ship with LabVIEW.  If the number of samples you need is fixed but very large, then you might have to do a merge of the 2 VIs to avoid overflowing the buffer.

There are a few applications which do require to read 1 sample at a time, like control applications, in which you need to react and generate a response to each individual input sample.  Those applications usually have the configuration VIs for both the analog input  and output operations outside a while loop and the read and write VIs inside the while loop.

Hope this helps.

Alejandro
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Hi!
Thanks for you nice explain,what i will do is to measure the frequecy,phase ,amplitude data from a simple sine wave in an osilloscope.first i try single measurement,but i notice the data is not stable,so i put the "read waveform.VI" in a while loop to do continuously measurement.but the result is always changing.i think mabey it is because i take a NEW measurement each time for i use while loop.but i dont know what the reason. BTW,what do you mean by "number of sample" is it the sample point i take in the osilloscope or the result of measurement?
 
 
 
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Hellow! attached is a simulation of my program for measurement,i notice that the ampltitude and frequency is stable ,but why the phase is not stable? thanks!
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