Reading motor direction with quadrature encoder hardware

[Marva82]

I'm trying to find specs on which is the best USB DAQ board to purchase for my application. I'm trying to reading the direction of a spinning motor shaft. I have my own encoder. I was looking at the M-Series boards, but I need something that is a USB standalone module that will work with DAQmx in LabView and be able to tell me if my motor shaft is spinning forward or backward. Also, I'm trying to keep costs low. Any suggestions?

[Kevin_Price]

I don't know a ton about device pricing nor what your threshold is for "low".

In general, an X-series device offers substantially better counter functionality (that you'll use for an encoder interface) than an M-series.   Being newer, they're also more likely to be supported farther into the future.

If you *do* end up sticking with M-series, be sure to check specs for the onboard FIFO for counter tasks.  You'll definitely want a device where that's larger (like 128 or 1024) rather than smaller (like 2).  I don't honestly know if *any* of the USB devices have such small FIFO's -- but the PCI desktop versions do.

You might also want to consider a Compact DAQ based solution.  I don't have enough broad or deep familiarity with cDAQ to offer specific advice.  Hopefully others will weigh in.

-Kevin P

[Marva82]

Hi Kevin,

I was able to speak with tech support at NI. The rep. came up with a solution for my quadrature encoder product that he thought would be a viable one. He recommended an NI-9401 C Series Digital Module along with the cDAQ-9171 chassis. The whole system would provide the functionality I need for my measurements directly involving quadrature encoders.

Thank you for weighing in. I'm just glad I can move forward with the project.

cDAQ-9171

[Kevin_Price]

I'd just give the friendly advice to pause briefly and consider:

- the 1-slot cDAQ solution you're considering will save you $ for satisfying the particular requirement you mentioned.  I'm sure that sounds good right now.

- many projects, once the *first* requirement is satisfied, start sprouting more requirements.  The term commonly used for this is "feature creep", and it's quite common.

- the 1-slot cDAQ solution will let you do very little else besides satisfy today's one requirement

- a USB X-series device offers an awful lot of flexibility for future usage, albeit at a fairly steep increase in $

- I don't know the cost of a 4-slot cDAQ chassis, but that might be a suitable midway position.   Probably less total capability than X-series, but in some respects more flexibility as you can select individual modules based on specific needs. 

Just saying, give it some thought.  Sometimes it *does* make sense to get the thing that barely covers requirements at the cheapest cost.  Other times it's better to make things future-proof.  You're in the best position to figure out which situation you have.

-Kevin P