Data Averaging

[Neo6]

Hello all,

I am using signal express 3.0. DAQ card PXIe-6361

 I am streaming sine wave data from 6 channels of daq card(6361), then extracting required tone, then filtering and saving data to a text file. But my file size is turning in hundereds of mega bytes. 

So I decide to average the data. Which average should I consider here??? From the previous posts I understood that it is waveform averaging (correct me if I am wrong).  My DAQ has total throughput of 1MS/s. Since I have six channels I set my rate to 160K  and number of samples to read is 16K.

1)Which avereging should I use ? statistical or waveform average???

2) If I set Number of averages to 10, what do this mean??? Will it take first 10 sets of data chunk (containing 16K samples?? or 160K sampples ??) and do the average , write it to file ???? or how it works????

other Issues

1) I am want to write data to spreadsheet, inwhich first coloumn should be time stamp and next six coloumns should be data from the channels. But in the time stamp coloumn I am not getting continuous time stamp. If i am recording for 10 seconds, time line is continuous till third second and resettting to zero, if I change sample rate or number of samples to change to different value, time stamp is setting to zero somewhere after first second. Even I tried with absolute and relative time , but facing the same problem.

2) If  I am increasing my data rate above 160Ks/s. daq is giving me error that it has not sufficient settling time, but data is recording. Is ther any way to measure the accuracy of the data recorded in such conditions ???

3) Without adding 'save data' step, program is running fine with 160Ks/s. But when I add 'save data' step, there comes DAQ error ' there is no sufficient data to read or data is over written' . How do I solve this ? 

Thank you.

[RupiDo]

Hi,

averaging of waveform signal:

1. in SignalExpress\Processing\analog Signals you can choose between running mean or "block" mean. It depends on your application and

processing after the averaging which type you choose.

I recommend to use the running mean, so you get for ech sample also the mean

2. Set number of samples to 10

This setting you decide of how many samples the median will be computed

Sampling rate - storage behaviour

If the sample rate error occurs, the multiplexer of the card hasn't enough settling time so samples will be lost and data aren't acquired according to the

Nyquist theorem.

Which fileformat are you using for logging data? UFF58 e.g is a binary format and suitable for streaming data. The text file format is more suitable for low speed data logging,

Kind regards,

Rupert Donauer,

NIG, AE

[Neo6]

Hello Rupert Donauer,

Thank you for the solutions.One of my mistake I found out from your solutions is I am not using the saving format which you mentioned.

 I will try and report you back.

Regards

Vaidhin.

[Neo6]

Hello Rupert Donauer,

I forgot to mention, I want to read data in spreadsheet. so I am opting fot text format. Time stamp in the first coloumn and remaining channels in the next coloumns.How to import data to spread sheet with high speed(without getting DAQ error )??

Also in the recorded text file, timestamp is resetting to zero for every 2 or three seconds. How to solve this time stamp problem ? How to I get time stamp continuosly without resetting to zero

[RupiDo]

Hi Vaidhin,

just to make sure, first of all you want to measure 6 channes AI with PXIe-6361, fitler the signals, logging (writing) into spreadsheet.

For logging data use save signals/ as ASCII-file/lvm file. This is a textfile where the columns are separated by tabulator sign.

I would recommend to setup the application step by step. First measure one chanel and log it into a textfile. Verify that the time stamp is correct.

There isn't a timestamp for each sample value. The signal saves the time info as following: Starting time of the measurement and delta t, which is the

reciprocal value of the sample rate; so you can figure out the time stamp for each sample value.

Make sure that the data of the logfile matches your samplerate settings.

Kind regards,

Rupert