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34972a high speed logging


34972a high speed logging

We have the above logger with a high speed card. We need to log at around 50 scans/sec and would like to use a labview programme.  I have looked through the various samples and we can communicate with the device no problem.

On the examples I cannot see how the scan rate for the device can be set.   If it can be set, do we also need to increase the number of bytes read per scan?

On other high speed data logging set ups I have used, the data comes across in an array or block of data, but I can't see how to do this with the examples.

Any help or pointers would be much appreciated







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Message 1 of 7

Re: 34972a high speed logging

The channels per second scan rate is "set" by many factors:

  1. Type of measurement
  2. Accuracy settings 
  3. Integration time (NPLC or aperture)
  4. Ranging (auto range takes more time)
  5. Channel delay

To name a few right off the top of my head, I believe the manual covers this quite extensively. 

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Message 2 of 7

Re: 34972a high speed logging

I don't understand your "number of bytes read per scan" question?


A scan returns all of the measurements you program it to take.  


If it is not, then you are doing it wrong...


Post some code.

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Message 3 of 7

Re: 34972a high speed logging with 34902a card




On the benchlink software package ( supplied with the agilent loggers), there is a direct setting that allows you to set  how often any channel is scanned per second.   There doesn't seem to be an equivalent in the labview examples. Nor looking through the agilent programming guide  does there seem to be any direct reference to the syntax you would use to set this.


The software examples are dependent on the rate at which the 'while loop' executes. As the number of channels increases, this may become a problem.


On other logging systems, these have the function to store the data on the logger and transfer across to the labview programme   which is a much more efficient why of doing it.  You can scan 10 channels, each at 100 times a second and this is then downloaded to the labview programme for processing say once a second. I am pretty sure the same can be achieved with the hardware we have, but I can't see an easy route at present.


The packages I am looking at are downloadable at:


The card used in the logger is now included in the title of this post.












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Message 4 of 7

Re: 34972a high speed logging with 34902a card

You are going to want to look at the Advanced Scan example included with the LabVIEW driver you mentioned. 


Notice the trigger setting VI has a timer setting, and a time scan interval with 3 options (minimum, maximum and manual).  If you specify Trigger source "Timer", timer scan interval "manual", timer interval "x"s, specify trigger count and # of triggers then you should be able to achieve what you want.  You will need to read back the appropriate number of channels of data.


You will also want to read up on your switch card options and limits to see if the rate you want to read is possible.


Hope that helps.

Message 5 of 7

Re: 34972a high speed logging with 34902a card

Thanks - makes sense. I will give it ago tomorrow.







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Message 6 of 7

Re: 34972a high speed logging with 34902a card

Are you familiar with the SCPI command set for this instrument?  I have been controlling the 34970a Data Acquisition Switches with the 34901 cards for well over 15 years.  The BenchLink software is using these same commands.  LabVIEW can control the instrument just fine.

MEAS:VOLT:DC? 10,MAX (@101,102,205)

This command is to measure the DC Voltage at the 2 wire connections for module 1 connections 1 & 2 plus module 2 connection 5.  In this case, I did not wish it to use auto-range and set it for the 10V range.  Additionally, I am showing the resolution here as MAX, which going from memory here, means that it will use the largest resolution to acquire the value in the shortest amount of time possible.


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Message 7 of 7