Power Measurement Take Too Long

Question

Hi All,
I am using Agilent 8163B
with 2 slots:  81619A (2 heads) and 81618A (1 head) for power
measurements.  I setup my measurement with Agilent's time sutup driver
vi at 5 seconds average time.  However it took over 20 seconds total to
complete the measurement of 3 channels using the Agilent's 816x Read
PMW Value.vi (this VI calls a DLL hp816x_32).
My
question is that can I get this measurement done close to 5s with a
parallel read of 3 channels at the same time?  i.e., Is the DLL
hp816x_32 reentrant?
I tried to have a parallel wiring of
816x Read PMW Value.vi to test this, but still get a measuement time of
21 second.  Does anyone has a suggestion to improve this?
Thanks,
Bryan
Solved!
Go to Solution.

Answer 1

Lynn and Bill, thanks a lot for following up on my questions.  In my testing VI module I put "fetch" vi in a while loop after sending "initialize" and "average time" commands outside the loop.  When I set the "averaging time" to 5 seconds, I can see the power values from 3 channels are updated at about every 5 seconds. At the same time I monitored the loop index which updates at a far faster rate. This behavior must suggesting that the "fetch" vi was getting the same value within that 5 seconds when my loop was running repeatedly.  This value must be an average value as it didnt change within the 5second time window.  I guess my observation is indeed different from what Lynn posted. I did come across the programming guide yesterday as shown in Bill's link, but didnt look in detail, you know how we LabVIEW programmers got spoiled by the graphic code
After another look at the guide, it made more sense to my observations, i.e., Fetch command returns an average value right away and you can fetch all 3 channels. While the Read command triggers an measurement and exclude access to other channels after one read command was sent.  I also googled arount a little, and found the following text (not exactly for 8163B though) maybe also helpful to others in a similar situation.
Thanks again
Bryan
The READ? command provides a sequential method to make
measurements and retrieve the results. READ? will hang the GPIB bus
until the measurement is completed, or until the timeout value has been
exceeded. Associated SETup commands (for each measurement) are used
with the READ? command to retrieve desired measurement results in a
sequential manner.
Sending a READ? command is equivalent to an INITiate/FETCh cycle for a
measurement. A READ? command executes an abort action on that
measurement followed by an INITiate and a FETCH?.
READ? commands can be mixed with FETCH? queries in order to make
combinations of sequential and overlapped operations. One measurement
can be issued a READ? command (sequential), and the next measurement
can be issued INITiate/FETCh? commands (overlapped), if necessary.
The advantage of using the READ? commands to obtain measurement results, as opposed to the INITiate/FETCh method is:
It is simpler. Fewer commands are required to obtain measurement results.
Some disadvantages of using READ? over INITiate and FETCh are:
The test set does not process any additional GPIB commands until the requested measurement results are available.
The sequential nature of the READ? command does not allow the user to
make concurrent measurements. Concurrent measurements require the
overlapped commands INITiate, DONE? and FETCh? .
The READ? command does not provide measurement results such as statistics that are available using the INITiate/FETCh method.
The READ? commands have pre-defined measurement results. If additional
results are needed from a measurement they may be obtained with a
FETCh? query.