Instrument Control (GPIB, Serial, VISA, IVI)

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NI GPIB-USB-HS Multiple Units Running in Parallel?

I have FOUR GPIB Devices running on a NI PCI card on a single PC.  The only problem with the GPIB Bus is it must be a sequential read.  This forces me to read data one at a time and this isn't fast.

 

I found the NI GPIB-USB-HS.  

http://sine.ni.com/nips/cds/view/p/lang/en/nid/201586

This runs from a USB cable.  Can I read four USB cables at the same time and cut my GPIB read by 75%?

 

Can anyone confirm?  If you have multiple GPIB-USB-HS on a single PC, can you read all four GPIB Devices at the same time in Parallel?  Or does the GPIB-USB-HS act just like NI PCI GPIB cards with Sequential reads?

 

I need to read four GPIB devices at the same time I'm hoping the GPIB-USB-HS will do this...any other suggestions?


Thanks,


Doug

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Message 1 of 8
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GPIB is sequential and it does not matter one bit if the controller is connected to a pci slot or USB port. Usually, it does matter of you can read at the same time. What matters is triggering them at the same time.
Message 2 of 8
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Thanks Dennis,

 

So I was hoping to trigger all of my USB GPIBs at the same time and Read at the Same Time.  My GPIB device takes about 1.5 - 2 seconds to trigger and read the data.  The best I've been able to do with my PC GPIB card is connect four GPIB devices and take each trigger/read in sequence...so one trigger/read is taking about 8 seconds for the four GPIB devices.


I was hoping the USB was it's own controller channel and I could address each GPIB USB channel at the same time.  If I could do this, then my time would be cut from 8 seconds to 2 seconds.

 

What you're saying is it doesn't matter if I have one PCI GPIB Card with four devices or if I have four GPIB USB HS on one PC, it will always read GPIB sequentially on one PC.  Bummer.  But, that helped me from purchasing additional equipment.

 

Are you saying I should first TRIGGER ALL FOUR GPIB devices, then READ all Four GPIB Devices?  Currently, I'm Trigger/Read GPIB 1, then I Trigger/Read GPIB 2, etc...  But I think you're saying I should try Trigger GPIB 1, Trigger GPIB 2, Trigger GPIB 3, Trigger GPIB 4, then Read GPIB 1, Read GPIB 2, Read GPIB 3, and Read GPIB 4.  I'll need to try that.

 

Can anyone suggest something else?  My test equipment has GPIB and I need to speed up the process.  Anykind of GPIB controller switch that can read multiple GPIB devices at the same time?

 

Thanks,


Doug

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Message 3 of 8
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No, I'm saying that one GPIB controller (pci or gpib)will always need to sequentially address the instruments. If you have multiple controllers (pci or usb), then they can operate in parallel.

What you want to do is send a single trigger to all of the instruments at the same time, not 4 separate triggers.

The basic design of gpib is your limitation and there is no magic bullet that you can use. You can try the one controller per instrument or use different physical connections (gpib, Ethernet, usb).
Message 4 of 8
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What are these devices you are trying to control?

 

Do you need them all to trigger at the same time?  If so, then you need a trigger line that goes between them all and then you send a pulse of some sort to send the trigger.


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Message 5 of 8
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The software equivalent to a common hardware trigger is the the GET - Group Execute Trigger.
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Hi Dennis,


I didn't know you could Trigger Read in GROUPS!  That might be the answer I'm looking for!  I've been doing it the wrong way.  Take a look at the example below, is this what you're saying?  I have GPIB addresses 1, 2, 3, & 4.  I'm not near my equipment now, but, I'll test this theory on Friday!  Thanks for your suggestion!

 

Group Execute Trigger Read.jpg

 

Thank you!  I'll report my results later.

 

Doug

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Message 7 of 8
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I'm not sure that syntax is correct and I have not used the low level gpib functions in a very long time. There is the VISA Assert Trigger that I've used.
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