How fast can I query instruments using GPIB?

[acrmartin]

Hi,

First off, I have the following setup:

Intel 2.4GHz Dual Core
2Gb RAM
PCI-GPIB card
Measurement Studio, using VC#

I am currently working on an application that uses 4 Keithley 6487 picoammeters (along with 8 other GPIB devices).  I am trying to take a 10-point averaged measurement from each instrument every second but am experiencing some issues.  The other devices are voltage and current sources that are only periodically set based on the current measurements.

The first thing that I have done is to profile each piece of equipment for individual response times.  What I am finding is that if I have each instrument on a loop (using BeginRead to asynchronously callback), they appear to interfere with each other.  I am using the buffered option to request 10 readings from the device. 

It almost appears that the device is taking these measurements (~300ms), the GPIB bus is tied up??  My theory was that the device would start the measurement and release control of the bus, setting an SRQ once it was ready?

At this point I would really appreciate any light that anyone could shed on this and what is the most efficient way to perform this?

Many thanks,

Chris

Message Edited by acrmartin on 10-31-2007 02:05 PM

[Albert.Geven]

Hi

In Labview I would send a measurement command to each device and wait for a visa interrupt that data was available.

You probably are busy waiting for the respons and not using the service Request interrupt on gpib (SRQ)
You can also do this in visual C but I don't know how to handle it in c.

good luck

[acrmartin]

That would be a good solution - thanks!  I actually did some more experimenting and found that if I send the instruction and then wait before sending the read command, it would aleviate the problem, obviously freeing up the bus.

Thanks for the response.

Chris