VISA read & write takes ~4.5s each for GPIB instrument

Hi,

I have a large application that handles communication with 5 devices.  Three of these devices communicate using telnet via a terminal server.  The other two devices are on a GPIB bus.  The two GPIB devices are an Agilent 34970 data recorder, and a Chroma 61605 AC source.  I am having problems reading data quickly from the Chroma 61605 AC source in the large application.  The read time for 5 measurements (AC Voltage, Frequency, etc.) is ~45 seconds when in the large application.  Each measurement consists of a VISA write and a corresponding VISA read.  Both the VISA write & VISA read take ~4.5s to execute when in the large application.  So, 4.5 seconds for each read & write for five measurements gives the 45s read time (4.5s*2*5=45s).

However, when I pull the measurement functionality out and put it into simplified code, taking all 5 AC source measurements takes ~ 90 ms.  This is more along the time I was expecting for the read.  I have tried setting all VISA reads & writes to asynchronous which didn’t resolve the delays.

A few more details that may or may not be important:

1. I am dynamically calling the Vis that communicate with all the instruments
2. I am reading from & writing to some of the instruments.  When I do this I use a semaphore to ensure that I am not doing both at the same time
3. The Vis that I call dynamically for communicating with Agilent recorders are reentrant because I spawn 1-4 instances depending on how many recorders I am communicating with

Thanks in advance for your help!

B