Probems with the record time on the TDS3014C

[ErgonTW]

Hi,

I am using a tektronic TDS3014C scope to acquire data from an AC supply.  I have been playing with the single channel waveform acquire VI from the examples and added a "wirte to measurement file" palet.  I would like to record a stream of waveform data for 5 second and write this to file but if I try to input a 'time per record" greater than 100ms the data starts to break down.  I know I can only aquire 10000 data point using this hardware but is there a limit to the length of time for a continuous aquisition?

Trent

[Dennis_Knutson]

Obviously, in order to acquire that long of a record, the dt is going to increase. That is the way a scope works. What you are seeing is expected.

[ErgonTW]

No, I was expecting to see the same waveform as the first screenshot over a longer period of time....say maybe 0.2s. As is displayed on the scope

[ErgonTW]

I have modified my VI to run in a loop but I am still struggling to understand the results coming from the scope acquire.  I understand that the dt will change if I increase the record time to dt = record time/10000.  The screen shot attached adds to my confusion, I am not sure what is happen in the initial stages.

[Perry_S]

Hi Ergon,

Could you upload a picture of the waveform from the scope and the expected frequency of the sine wave generated. Also could you put a waveform indicator on the build waveform function and see if the wavrform that is being built looks like what is on the scope? That would help us figure out what is happening.

Regards,

Perry S.

[ErgonTW]

Hi Perry,

The expected frequency is 50Hz.  I have attached some screenshots to give you an idea what is happening.  I have tried a record time of 40ms which works fine but if I try 60ms or 80ms the output file shows a 100ms capture so I am not sure my build wave form VI is correct.

Thanks

Trent

[Perry_S · Accepted solution]

Hi ErgonTW,

Having looked at your Graph I think that the setup is correct. Your graph however is only showing four milliseconds of the data. You need to change the X axis of your graph to show the entire wave form. To do that just double click the .004 ont he x axis and type .2 then click any where on on the front panel. This will change the values.

Perry S.

[ErgonTW]

Thanks for verifying my setup and your advice on the graph properties.  I am very new to labview.

I have also tried running the waveform acquire in a loop and have found the results stablise after 1 or 2 loops depending on the record length.  I therefore wait 2 iterations before I enable the read to measurement file.

Trent