Triggering the HP34401A DMM/Parallelism Question

[Roons1159]

Another question for you guys!

I'm used to setting up a DMM just to take basic measurements after I do some sort of action.  I am trying to do something a little different.

I want to check a reading while performing a specific action.  In this case I'm generating a pulsed load that changes an output voltage during the pulse.  So basically I cannot set up my program to do the pulse then check  the voltage with the DMM.  It has to be during the 300ms second pulse that Im generating.  I'm trying to refrain from using a scope.  Is there a way I can trigger the DMM to take a measurement during that specified time interval in which the pulse is on?

[Dennis_Knutson]

Do you have this pulse wired to the external trigger input of the meter and have your programmed the meter for external triggering?

[Roons1159]

No... I program the pulse loads via labview.  So I set up the pulse for a high time of X at an amplitude of Y and while that pulse is high I'd like to check the voltage at any given output.

[Dennis_Knutson]

But is there something physical that is actually generating a pulse? If so, then you connect that pulse to the external trigger input. Or are you talking about some sort of 'software' pulse?

[Roons1159]

I am using electronic loads that can change pretty much anything you want at any given time.  I am setting up a dynamic pulse via a labview instrument driver.  I could monitor the current pulse via a scope as well as the output and do it that way, but I don't want to do that.  My code would be much simpler if I could set up the pusle then during that high time take a measurement. 

[Dennis_Knutson]

I guess I still don't understand the problem. If you can look at the pulse with a scope, that means it has some sort of actual, physical existance (current or voltage). Can you not take a real wire from where this pulse is generated and connect to the external trigger input of the meter?

[Roons1159]

I see what your saying now.  I cannot since I am doing this on 15 different loads with one DMM.  But I thought there would be away to use code to trigger the DMM like an external trigger would.

[Dennis_Knutson]

There is a way to generate a software trigger. The example that comes with the driver and LabVIEW 8.x called Agilent 34401 Acquire and Graph - SW Triggered does exactly that. The problem arises in trying to synchronize this software trigger and the pulse that is getting generated. There will be some delay between the time you issue the command to the load and when the pulse is generated. You can't simultaneously write a command to the load and software trigger the DMM so there will be some delay there as well.

[gchristi1]

300msec is a relatively long pulse, how about single triggering the 34401 from LabVIEW and gathering timestamps before and after your actions to get a rough idea of where the data was collected during the pulse?

I'm also not for sure why you can't send the same signal you're looking at on a scope to the DMM's trigger in.

[Roons1159]

I'm starting to think a lil more about it, and i could use my switch cards I have on there, I just really don't want to get into re-wiring my test station which happens to be controled  and would take an extreme amount of time to get though.  I just thought I could do everything through code.