DaqPad 6507 DIO speed limit

[steve h]

I am using LabView (7.1) to read a single DIO port of a DIO DaqPad 6507 (USB 2) with a pentium 4 PC. If I put the LabView read icon in a loop I notice that the fastest read rate of a single port is about 5mS. Can this be made faster and  what is the limitation: LabView, USB, or NI Daq driver?

[Sarah_Coleman_NIUK]

Hi Steve,

How is the measurement configured? Have you the code set up to acquire data for every iteration of the loop (single point) or is the timing configured to be continuous?

During single point operstions the USB DAQPad devices require a complete set of configuration commands. This is done through serial communication making the process slower then in PCI-based boards. So for every iteration of the while loop the USB device is going through this configuration command set.

The speed obtained for single point operations in a DAQPad is system dependent. This means that your computer processor, memory, bus speed and other factors affect the speed at which you can do these operations.

You may be able to improve this performance by configuring the read to be continuous but as far as I can recall, the 6507 is software timed so the timing is going to be system dependent anyway.

Do you have access to a PCI card you could use instead? What acquisition rates are you looking to achieve?

Regards,

[steve h]

The LabView read icon is within a while loop with no delay within the loop & the task id is connected to the read icon.  The read command takes about 5mS, therefore I can only get 5mS resolution and would like something closer to the 1mS theoretical target; is there a different way to configure the DaqPad 6507 or driver? It is a bit late in the day to change to a DIO PCI card, but can you be sure it would be faster anyway?

[Sarah_Coleman_NIUK]

Hi Steve,

If you look at the code for that Read VI your using you'll find that it configures the port for each iteration of the while loop. Wire the iteration count of your while loop to the iteration input of the read VI, that may speed things up a little bit.

What are you using the device for exactly? There is another acquisition mode supported by this device called handshaking which may be faster but you would need to be communicating with another device. If it's just a finite state device you're monitoring this mode won't work.

With regards to PCI being faster, even if you got another static (software timed) PCI card it would be faster as the DAQPad-6507 is USB 1. You can also get PCI devices that offer hardware timed DIO so you wouldn't be relying on timing from Windows.

[steve h]

Looking at the read icon, it does not appear to have a iteration input, only Task ID (in/out),Line mask, pattern, error in/out, maybe you have a different read icon?

The DaqPad 6507 does not appear to state whether it is USB 1 or 2, if it is USB 1 then does NI have a USB 2 version? What difference in time will USB1/USB2 make?

[Sarah_Coleman_NIUK]

Hi Steve,

I was looking at the Read from Digital Port VI. If you had been using that VI then wiring the iteration count may have improved performance slightly, though probably not to the resolution you're looking for.

The 6507 device is quite old, it's not supported on our latest DAQmx driver so I don't believe it is or will be available on USB 2. I don't know the quantifiable difference that a USB 2 device would have over USB 1 but there's bound to be a marked improvement as the transfer rates are 480 Mb/s for USB 2 as opposed to 12 Mb/s for USB 1.

My recommendation for your application would be to use a hardware timed PCI DIO device so you can achieve the resolution you need. Even one of our Multifunction M Series devices would probably do the job. There is a USB version of our M Series that you could consider.

If you don't want to change your application too much (ie from USB to PCI) and it's too late in the project to consider investing in another device, there is a USB DIO device that is USB 2 compatible.

It's only £65 but I can't say if it will give you the resolution you're after. I'm only suggesting it as a "try it and see" option. It's probably faster then the 6507 due to the fact that it's USB 2 and is supported under our new drivers which are more efficient then traditional NI DAQ. I can't say how fast it will be as, again, it's software timed so performance is system dependent.
https://www.ni.com/en-us/shop/model/usb-6501.html

Message Edited by SarahB on 08-21-2006 04:07 AM