Which Component is the limiting factor?

[Crusher]

Greetings.  A previous employee at my company had set up a an Instron Universal testing machine station that communicated with Labview via GPIB.  This station has served us well for the past 6 years but now we need to upgrade and I am not sure which component to upgrade.  Sorry this my first experiance with labview (other than using the gui front).  In the past few days I have read the Labview manual and it seems intuitive enough.

Pretty much all I want to do is read my load and position many more times per second.  From reading other posts and the manual I was able to move the I/O instrument assistant into a flat sequence structure and surrond it by two millisecond timers.  This confirmed that the I/O intrument assistant is the limiting factor in the block diagram.  Currently we are getting readings about every 160-220 ms (it is surprisingly inconsistant).  This is about the same value I am getting from the timers.  I would like the delay between readings to be more like 20ms or even 2 ms.

Here is my system breakdown:

Labview 7 Express

Windows NT 4.0

Pentium 2 400MHz

NI PCI-GPIB card

Instron 8511 Controller

In order to get the performance that I desire which components do you think I will need to replace and what tests can I do to learn more?

Any help is greatly appreciated.

-Daniel

[Dennis_Knutson]

You really need to break things down a bit further before blaming the assistant and asking for help. You haven't provided any information on what you have set the assistant to do - i.e. how many steps there are, how much data you are writing, how much data you are reading.

You could try using VISA Writes and Reads instead of the I/O Assistant but the bottlenect could very well be the Instron. A write/read cycle time of 200ms is not out of the ordinary and a 20ms time for GPIB would be very fast and unusual. The manual from the vendor should specify the GPIB transfer time.

Message Edited by Dennis Knutson on 08-25-2009 10:55 AM

[Crusher]

Dennis:

Thanks for your rapid reponse.  Below are some screen shots of my I/O assistant.  I have already read all three 400 page manuals to the Instron and it says absolutlely nothing about parse or response delays.  All it says is that it has 1.5 Mbyte/s GPIB.  I am very dissappointed with the manual.  I am thinking that I will call Instron customer service.

-Daniel

[Crusher]

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[Dennis_Knutson]

It looks like you have 3 separate read/write actions so ~70 msec would not be unusual. The stated rate may be accurate (though you need a GPIB board that supports it - it's non-standard) for just the data transfer but as you said, the instrument's time to receive and process the command could be significantly different.

[Henrik_Volkers · Accepted solution]

The user?  SCNR

The GPIB speed of your Instron just tells you that it would be able to send you the data fast enough. I don't know that instrument, however I would dig into the manual to find out if it is possible set it up in a way it could make use of that speed. Maybe by internal scripts, hardware triggered acquisition, lower resolution....  request 1000 values once instead of one 1000 times.

[Crusher]

Henrik:

You actually guessed correctly; you can set it up to send 1000 values instead of 1 value 1000 times, however this will give me disjointed data because I need to record data over several minutes.  The buffers on the Intron are not nearly large enough.  I would have to request multiple sets of 1000.  (I think that the buffer only holds about 1000 pieces of data.)  Plus I could not display the data live this way.

It looks to me that GPIB will never give me what I want.  I think my best option will be to use a different DAQ that can read the analogue outputs.  If I swaped out the PCI card and read the analogue output with everything else the same, do you think I will obtian my goal of 20ms?  Do you know off the top of your head if Labview can support two PCI cards simultaniously?

[JeffL]

Hi Crusher,

Yes, LabVIEW can handle multiple DAQ boards in one computer. You can synchronize over RTSI if need be. I would recommend calling a sales person and they would figure out the best cards for your requirements.

http://sine.ni.com/apps/utf8/nicc.call_me

[Henrik_Volkers]

Crusher,

if you want a scale able system for industrial use look for a PXI Sytem. (Personal fav. ) However start with a complete requirement list ( with columns for "current need", "known future need", "nice to have")

And request / reflect the requirements. For example: "We NEED a 500kHz 10ppm voltage measurement with live display to monitor the temperature" 

[Crusher]

Thanks for the suggestions.  If I were to add analogue capabilities, I would need 1kHz at 10000ppm accuracy :).

I talked to a tech at Instron and he says that it is possible to send blocks of data over GPIB without having gaps between the blocks.  I am going to try to get this to work.