Can't stand this any more

[redoo]

Hi all. I've been working on the problem for several days and still
can't figure out what the error means. Can anyone help me please?

I'm using LabVIEW 6.1. I just setup a simple VI, which read the
standard 1 kHz square wave from a Tektronix 520 osilliscope via GPIB.
I followed the application function example in Tektronix 520 driver
llb. But I found two problems I can not understand.

1. Although the run button is fine, there is always a chance (50%)
that I will receive an error message saying "Error -1073807339
occurred at VISA Write in TKTDS 5XX Config Meas.vi->test 2.vi.
Possible reasons: VISA: (Hex 0xBFFF0015) Timeout expired before
operation completed." It does happen whenever I waited a little while
and run the VI. But if I clear
the message and run again within 5
seconds, it can work. what does this mean?

2. when it does run with no error, sometimes I got a strange readout
from the VI. say the frequency, it should be 1000 Hz. But sometimes,
again a chance, it gives 999839999999999 Hz instead. Again, it won't
always do this but it comes out again and again. All i can do is clear
the whole VI to default and run again. But it is annoying. Did someone
else met the same problem before?

btw, I have another question about labVIEW. How fast can labVIEW
acquaire data from GPIB? I need to read 1000*1000 numbers in one
second, which is 1M Hz. Can GPIB and LabVIEW do this. I'm asking
because I found the waveform reading is extremly slow.

thank you all for your patience in my dumb questions. :)))

[Dennis_Knutson]

1. Without seeing your code and instrument setup, it's a little difficult to diagnose the problem but I'd say you have some sort of timing problem. Maybe you're requesting a new measurement before the scope has completed a waveform transfer or it needs to reset it's trigger, or any number of things it might be busy doing. If you're repeatedly sending setup commands to the scope, you'll want to eliminate those and just concentrate on what you need to trigger and acquire. The scope's manual may have a section on optimizing a program andeven if it doesn't mention LabVIEW, the principals should still apply. A call to your local Tek representative may be the best source of hints on how to best utilitze the instrument.

2. You don't mention the type of GPIB
card that you're using but the maximum transfer rate for the PCI-GPIB card is 1.5 Mbytes/sec and in practice, the rate is much slower than that. The rate doesn't take into account any time it takes for the instrument to process commands and change settings. Some instruments also have a binary transfer mode that you might want to investigate if you're not already using it.

[Randy Solomonson]

Hello-

1 MByte/sec is the optimum transfer rate for most GPIB transfers. The reality with the overhead of features like Windows kernel/user mode transitions can be much slower. However, there are PXI-based instruments that can achieve much faster transfer rates between the CPU and the instrument. PXI is based upon the PCI bus, so the optimum transfer rate is about 133MByte/sec. Call the local sales rep for more details about a PXI-based instrumentation.

Randy Solomonson
Application Engineer
National Instruments