serial baud rate vs. high speed CAN

[Jochen]

Jim,

as you have already ordered the CAN board, I guess you are referring to a data acquisition board.

If your computer has a PCIe slot, the NI PCIe-6320 X Series board would be a very good solution. The new architecture of the X Series provides very high data rates for buffered counter operations. With an X Series boards you can read position data wih 10 MHz acquisition rate on four counters simultaneously. Buffered position acquisition is not too hard to accomplish. Basically you define a task for buffered position acquisition and run the read operation in a while loop - very similar to analog data acquisition with DAQmx. There are shipping examples that you can refer to.

If your PC doesn't provide a PCIe-slot, I'd recommend a PCI-6601 counte/timer board.The maximum data rate is much lower, but depending on the chipset of your PC you still should be able to acquire position data with a rate ranging in the several hundred kHz area. The position acquisition rates of M-Series devices are a bit lower.

I hope that helps,

Jochen

[jimmyinct3]

Jochen 

I got the renishaw usb decoder today.

It outputs position at 1kthz when run in open loop.

Thats far to slow although beats the 340htz from just serial (NI VISA)

Apparently the renishaw usb decoder is really just a serial emulated device which is why its slow.

So we are still waiting on the CAN card.

Im hopeful we can read position faster than 1kthz.

Id like to hear more about  PCI-6601.

How do we decode the quadature pulses with it?

Do we have to run a VI on the main CPU, is there programming required?

How much range does it have?

The reinshaw puts out around 50k pulses over the 2" path.

that wont be a problem, right?

thanks

Jim

[Jochen]

Hi Jim,

with a counter/timer device like the 6601 you just configure a position measurement task for the 6601 on the PC and start it. You need to connect the encoder signals to the board's input. The counters on the board (NI-TIO) decode the encoder signals in hardware and a second counter can generate the clock to transfer the data to the PC's RAM via DMA. This results in both, high data rates and low CPU usage.

The pulse rate for a 6601 board can be up to 20 MHz, so 50 kHz is definitely no problem.

Jochen

[jimmyinct3]

apparently the PCI 6601 does not have the ablity to truely decode the renishaw or other common encoders..

These decoders have /a /b channels which cant be decoded by these types of cards.

atleast that is my understanding from tech support which helped point out

https://knowledge.ni.com/KnowledgeArticleDetails?id=kA03q000000YI7DCAW&l=en-US

so this  is some type of loss of signal?

how much is lost for resolution wihtout the /a and /b

[Jochen]

Without the inverted signals /a and /b you don't loose any resolution. The reason why encoders use this signal is increased immunity against noise. Depending on your environment (e. g. lab or production floor) this may or may not be relevant for you. If you need to use these signals (e. g. because of long cables and very noisy environment), you could think of some external signal conditioning to convert the differential signals back to single ended signals. The signal conditioning should be connected with a short cable to the 6601 or you could even integrate it into the connector block of the 6601.

I'm sorry, that I can't elaborate more on that, but you may check with Renishaw or some of the semiconductor vendors for such a device. I think a keyword could be "RXTX converter".

Kind regards,

Jochen

[jimmyinct3]

ok, thats not a big deal then.

SNR loss is not a problem in this instance.

I did try the CAN card, it more difficult to program

the counter is very easy.

this is a done deal

 thanks!

kudos

Message Edited by jimmyinct3 on 11-03-2009 08:30 AM