how to take quick measurements with hp34401a instrument driver

[weatherhound]

I am creating a labview program where I have to take measurements from (1) analog input channel (from PCI-6014 board), (2) 34401a multimeter via GPIB, and (3) a TDS 3034B oscope also via GPIB. These measurements basically have to happen simultaneously. My problem is this, invoking the 34401a Read measurment vi seems to slow down my program considerably. Is there a quicker method with less overhead where I can take a measurement on the .1 sec and lower time scale?

thanks
J Turner

[cktears]

34401a has a buffer of 512 readings. Have you tried to just trig it but wait to read until the buffer is full? I guess it is the data transfer slowed down your program.

[B-man]

J.

I had the same problem using a 34401 with Windows 2K and Labview 5.1. Whenever the read measurement vi was called, processor usage went to 100% until the read was finished. I tracked the cause to the Visa Wait on Event Async.vi that is called by the Wait for RQS.vi that is called by the HP34401 Read Measurement.vi
The Visa Wait on Event Async.vi has a wait set to 0. If you change the wait value to 2 it will free up the processor usage so that your other process will not slow down. I am using visa 2.6.

Bman

[tca-adam]

Has anyone seen with the 34401 drivers a problem where if you get a single point measurement on AC volts it gets the decimal place wrong?

eg  if you are measuring  5.1mV ac, the VI returns a value of 5.1, not  0.0051

if I then apply 1.5Vac, the VI returns a value of 1.5 as expected.

I have downloaded the latest drivers of the NI website.

Depending on whether I use the RESET or INITIALISE commands before the MEASURE commands the problem seems to come and go.......

Very tedious.....

Adam

[Rimasaurus]

Hi Adam,

You may try updating the firmware to see if that helps you record the correct measurements.  Are there any changes in configuration when you switch from measuring 5.1 mVac to measuring 1.5 Vac?  If you're still having trouble with the decimal place, you may record an NI Spy log of the messages the instrument passes back, and attach the log. 

Thanks,

Rima