labview >> Triggering and reading on two HP/Agilent 34401A DMMs at same time

by Brian F. » Tue, 07 Aug 2007 04:40:11 GMT

Thank you for posting to the NI Discussion Forums. 
In order to find out more about your application, I have a couple questions for you.  First, what driver are you using with the 34401A multimeter.  I ask this because there are numerous different drivers that can be used with this hardware.  For example, at the following link, there are 4 different drivers: some utilizing IVI, some plug and play.  Hewlett-Packard / Agilent Technologies 34401A <a href="" target="_blank"></a> Letting me know the specific driver being used will allow us to look at the same VI's while troubleshooting this issue.  Secondly, how exactly do you have all of your hardware hooked up to your GPIB?  What GPIB device do you have?  In terms of increasing speed, I think the best thing to do is to examine your existing code to see if it can be optimized in any way.  Also, if you are using high level VI's, using low level VI's could improve the performance as well.  Finally, using an IVI driver instead of a plug and play driver seems to be a bit faster.  Let us know a little more about your setup as well as your existing code and we will be happy to help further!
Brian FApplications EngineerNational Instruments

labview >> Triggering and reading on two HP/Agilent 34401A DMMs at same time

by tbd » Tue, 07 Aug 2007 07:40:05 GMT

Hi Plasma,
      In addition to following all Brian's advice, you might want to investigate storing results internally and not try to read any results until triggering has stopped.  According to the 34401 user-manual, there's a 512 sample "Reading Memory" (see page 46 of "User's Guide").  Had the user-manual handy having written a Driver " target="_top" rel="nofollow">[Driver Robot fixes your driver problems] recently; saw your post, interesting question - please share your solution! :smileywink:
Cheers.Message Edited by tbd on 08-06-2007 06:14 PM

labview >> Triggering and reading on two HP/Agilent 34401A DMMs at same time

by tbd » Wed, 08 Aug 2007 17:10:12 GMT

Hi plasma420,
I should have read your post more carefully - was thinking it was a 1 sec acquisition, not 1 minute! :smileytongue:
Getting your LabVIEW app to reliably respond to a measurement (detect/read) every 2 to 4 ms is going to be tough - especially if in a multi-tasking OS environment.  On a 2GHz box running a normal Windows XP or 2K install,  I suspect you could see an occasional "hiccup" even at 100Hz.  A bit of searching the forum turned up <a href=" ;" target="_blank">this</a> old-but-still-valuable (even entertaining) post related to improving determinism of DAQ applications on a PC.
Observation: The listed max measurement-rate of the 34401 (1000Hz) may assume the GPIB-bus is dedicated to one instrument - the requirement to read from two instruments sequentially, may necessarily increase time spent servicing each trigger - decreasing maximum theoretical throughput.
The first rule for "high-speed" multi-sample DAQ - especially under Windows - is to make it a hardware task instead of a software loop;  the 34401 doesn't seem well suited here.  I hate to suggest this, but... have you considered purchasing one of NIs multi-channel DAQ devices?  With a $360 PCI 6010 + cable and break-out box, you could have one of the LabVIEW DAQ examples running in ~ 30 min.  The 6010 was the cheapest 16-bit board I could find, ask your sales-rep for other alternatives if you go this route...:smileywink:

labview >> Triggering and reading on two HP/Agilent 34401A DMMs at same time

by tbd » Thu, 09 Aug 2007 11:10:15 GMT

Hi plasma420,
Attached is your example modified to configure/read two instruments.  It assumes no triggers are occuring during configuration because there will be a small amount of time between the two calls to "Initiate Measurement" and if a trigger occurs there, the two devices will be out of step. :smileysurprised:  If triggers are occurring during config, it will be more work, but can be accommodated.
Also, please confirm you're using "External" Trigger-source in this example. :smileywink:
Cheers.Message Edited by tbd on 08-08-2007 06:47 PM

labview >> Triggering and reading on two HP/Agilent 34401A DMMs at same time

by tbd » Thu, 09 Aug 2007 16:40:08 GMT

Ho!  I wouldn't have believed 300Hz was possible (me thinks this is not a typical Windows OS) - are you sure you're only reading once per [external] trigger?  (Turning sig-gen off, should stop the chart.)
That was clever to throw-in a second GPIB card!  ...but, I don't know whether the low-level VISA uses any "blocking" functions that might force all GPIB IO to be sequential at some point.
More than the current code I'd be interested in what OS you're using and how-many-Hz =  "a bit faster" :smileyhappy:
Congrats and Cheers! Message Edited by tbd on 08-09-2007 03:20 AM

labview >> Triggering and reading on two HP/Agilent 34401A DMMs at same time

by Dravi99 » Fri, 10 Aug 2007 03:10:08 GMT

i have read this post for couple of days now and have been trying to do something similar like taking readings from the 33401A DMM. I have the instrumentation Drivers " target="_top" rel="nofollow">[Driver Robot fixes your driver problems] and I use the GPIB. all the specs about gpib are followed. All the instruments show up in the MAX xplorer.
My aim is to read the 10 output voltage values from the board i am testing. I would like to know the steps that I should go about in doing the same. However for me speed is not the issue. I would be grateful if someone of you can enumerate the steps for me to do this task. I am going through the tutorials and trying to do this the best i can.
thanks a lot.

labview >> Triggering and reading on two HP/Agilent 34401A DMMs at same time

by Dravi99 » Sat, 11 Aug 2007 05:10:05 GMT

HI tbd n plasma,
Thanks for your interest. Let me explain you in a nutshell what i am trying to do. I want to read the output volage on a pin on my board. I have connected the DMM to it. i write to the part with a GUI and read the voltage. currently i have used the read measurement vi example to take read the voltage directly. Also played around with multiple measurements of the same signal.
I did get 10 readings of the same output signal. Is it possibel to implement it for the 10 different signal readings can i use a structure for the single measurement and repeat it. there is no sampling period or such required at the moment. I think i will like to trigger in using LV only.
Let me know if this can be done in any way. i have just used the single measurement Vi for 34401 and specified my visa name for the instrument..
thanks again. i will keep you posted on this thread. i m right now very new to LV and have been trying to do the tutorials and implement them accordin to the need.
RaviMessage Edited by Dravi99 on 08-10-2007 03:41 PM

labview >> Triggering and reading on two HP/Agilent 34401A DMMs at same time

by unr » Wed, 28 May 2008 17:40:06 GMT

Hi Everyone
I have no prior experience with labview but im trying my hands on it, which is esentially required for my project. I have to do the DAQ of a RF MEMS varactor, and record the different current, voltage values and at the end do the impedance matching. I have Agilent 34401A digital multimeter and a function generator.i have downloaded all the required drivers. I m using GPIB interface but the real problem is here, i m testing different instruments one by one to see which combination will work best for the experiment,for GPIB do u always have to give command in NI VISA write and then get the ans in read block.which would be better GPIB or RS232....Also i get error in running the example VI's, the error code says "1073807346 occurred at VISA Open in Agilent>Agilent 34401 Acquire and Chart -"..... I have just started using Labview and i m just reading some beginners stuff. I have a background in optical fiber communications but this NANO MEMS stuff is killing me...........cant make things work with labview. urgent help needed guys. lettme know where to start from.
thanks in advance
samMessage Edited by unr on 05-28-2008 04:34 AMMessage Edited by unr on 05-28-2008 04:36 AM

labview >> Triggering and reading on two HP/Agilent 34401A DMMs at same time

by Dennis Knutson » Wed, 28 May 2008 22:10:04 GMT

1. No you don't always need to do a read after a write. You only do a read when you issue a query. IIn SCPI, a query is a command with a '?' at the end. This tells the instrument to return some data. Non-SCPI instruments will use a different syntax. You need to refer to the manual
2. GPIB is faster, more reliable imho, more expensive, has more features, and more expandable. You can have up to 15 instruments connected to a single GPIB controller. RS-232 is cheaper, slower, non-standardized, and have to dedicate a com port for each instrument. Personally, I much prefer GPIB and if you need to do any sort of bus triggering, you have to use GPIB.
3. The error means that the VISA Resource Name you are using is nor correct. Assuming that the Driver " target="_top" rel="nofollow">[Driver Robot fixes your driver problems] has a VISA Resource Name control on the front panel, you should click on the little arrow on the right side to see a list of available resources. Pick the appropriate one. If you are using GPIB, you should first go into MAX and do a scan for instruments.

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