Why am I unable to GPIB-Read a Digital Multimeter more than every 440 ms?

[andrewW]

I am running LabVIEW 6.0 on Win 2k Professional and
am baffled by the following:

Using the GPIB Read .vi, I read from a couple of
virtually identical Solartron/Schlumberger 7150
Digital Multimeters at a set time intervall and
subsequently write the data to file. The test routine
performs only elementary arithmetic besides GPIB
reading and writing to file.

Using the Get Time/Date In Seconds .vi to time the
read-store loop reveals that the GPIB Read operation
is excessively slow.

As the GPIB Read .vi's timeout defaults to 10000ms
(488.2 global timeout), I tried out a number of
different timeout values and found that timing only
begins to approach the value I set without GPIB read

errors when timeout is set at >=1000ms and the
read-store intervall is at least 440ms(!)
I cannot understand why the GPIB read operation should
require as much as 440ms when the CPU is otherwise
minimally loaded...

Isn't there a way to GPIB read at a rate faster than
once every 440ms?

Thanks in advance.


Best regards,

Andrew

[Ray K]

Hello Andrew,
The speed of gpib communication depends on three factors: speed of the instrument, speed of the bus, and speed of the computer. You can try changing the bus timing via MAX to speed up the bus, but you really can't change the speed at which the instrument recieves a command, processes it, performs the operation, generates a response, then sends it accross the bus.
If speed is your primary concern I would suggest getting an National Instruments DMM. An internal device will have much faster communication and will be 10x to 20x faster. Having an external instrument is like having a external CD ROM drive or an external modem attached to your computer.

Ray K
NI Applications Engineer