Hi,
I am using Labview 6i and NI-VISA4.2 and NI-488.2-2.4 to control a Tektronix TDS3052B oscilloscope. I use an AGILENT 823578A USB/GPIB adapter to comunicate my computer (running Windows XP SP2) with the scope. I have used "standard" library tktds3k.llb for simple control of the oscilloscope and it works fine.
However, I want to measure short pulses (currently I am testing with 400 ns wide pulses but my aim is 4 ns wide pulses) with the scope and retrieve those pulses with my computer using Labview and VISA. Pulses come at a 1 MHz rate selected by an external trigger.
And the problem arises when I want to retrieve those pulses as fast as possible in a continuos mode. I can only manage to retrieve them at a fastest rate of 2 Hz, when I was expecting a 100 Hz - 1 kHz rate (considering the speed of GPIB bus - 1 MHz and width of the pulses)
I believe I have removed from the loop anything not essential, like configuring the scope, and I am requesting only 500 point waveforms, but still I measure 0.5 secs for every waveforms to arrive to my computer. I have made several tests and I believe the bottleneck comes from the VISA command requesting the waveform recording in the scope :
":DATA:ENCDG RIB;:DATA:WIDTH 2;:ACQ:STATE RUN;:DATA:SOURCE CH1;:DATA:START 1;:DATA:STOP 500"
because when I send this command to the scope using the usual labview VISA-WRITE vi, and I send inmediately afterwards a *WAI command using the same kind of labview VISA-WRITE vi, it is this vi that takes ca. 400 ms to complete.
I don see why this is happenning: GPIB protocol is supposed to work at 1 MHz, pulses are very fast ( ca. 1 usec.). How can it ve that the scope takes 400 ms in digitizing such a pulse ?
I thought the problem might be displaying the waveform in the scope screen. If thisis the case, Is there a way to instruct the scope to digitize the waveform but not to show it on the screen ?
Moreover, some colleagues of mine are using VISA command to do the same task using a VIsual BASIC program, i.e. without labview VISA VIs, and they don't find this slow response. Could it be a problem of Labview VISA VIs ?
Thanks in advance for your help.
Juan Abel
