Large number of USB connections

[JBrew]

I have a potential project (not currently mine, so I don't know all the details) where there are >50 BK precisions with USB outputs.  These USB outputs are ganged together into hubs, so that the number of physical PC inputs are reduced, but each instrument will still need controlled independently.  I think the measurement is likely easy (apply bias, measure current), but I have not controlled this many devices before.  How could this be managed?   Could I cycle through ports with a For Loop, taking the measurement for each device?  Any examples of this?

[Intaris]

Hubs don't reduce the number of devices on a Bus, they increase it.

Although USB theoretically supports up to 128 devices on a single port (Hubs count as devices too) you've generally well off staying well below the limit of 64 per port.

Try to spread the devices over as many hardware ports as possible.

I would have a loop to start each measurement and then a following loop to record the results.  That wa you should get good throughput.

i.e. for 50 devices, 50x "Start", followed by 50x"Read" instead of 50x "Start"-"Read"

[JBrew]

Thanks for the reply. 

Will I essentially have 50+ independent VISA sessions?

[Ranjeet_Singh]

You can extract the current wanting VISA. Will you need multiple VISA all the time or one at a time?

[Intaris]

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@JBrew wrote:

Thanks for the reply. 

Will I essentially have 50+ independent VISA sessions?

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Yes, you will have as many VISA sessions as you have USB devices if you're using VISA for the measurements.

You don't have a driver for the devices?

[JBrew]

I'm guessing I could cycle through them one at a time, not knowing the requirements for sure. 

[JBrew]

I'm sure there are drivers. 

[Intaris]

Well then if there are drivers, don't use VISA.

Use the drivers instead.  How you cope with multiple devices depends ont he driver.

Shane.

[billko]

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@Intaris wrote:

Well then if there are drivers, don't use VISA.

Use the drivers instead.  How you cope with multiple devices depends ont he driver.

Shane.

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I would add a caveat here.  Some supplied drivers are absolute cr*p, especially if they are from small companies.  Check out the drivers to make sure they make sense.  You can't do anything about a buggy dll, but maybe you can avoid some obvious LabVIEW stupidity.

[LV_Pro]

Actually I was "able to do something about a buggy dll", browbeat them into opening up the hood and letting me see that their dll was just a wrapper around the USB chip hardware dll from the USB chip manufacturer. I wrote LabVIEW to call this "lower level" dll directly, fixed my crashes. As mentioned, a lot of "drivers" supplied by smaller equipment makers is less than useful. I cringe when starting a project where the hardware has be already ordered when I'm told "don't worry, there are LabVIEW drivers for it!"   Yikes!