Quadrature Encoder with PCI-6030E and DAQ BNC-2110

[PJ Turner]

Hi,

I have a PCI-6030E board connected to the BNC-2110 breakout box and I'm trying to access an AB quadrature encoder from within LabVIEW 8.2.

I can access the PFI pins from within the Measurement & Automation Explorer and register edge counts on PFI 8 & 9, however I don't see a way to have it automate the +/- stepping required for the encoder.

I have searched within the NI Example Finder and see that there is no associated example VI for a quadrature encoder that works with this card (eg. Measure Angular Position.vi is incompatible with my 6030E card).

Does this mean that my hardware does not have the capability to perform the necessary sequence counting for the quadrature encoder?

Is the simplest way forward to get a different card?

Any help is most welcome.

Thanks,

Patrick.

[Kevin_Price · Accepted solution]

Sorry, the E-series boards didn't support quadrature.  Here were the tricks I knew of before the 660x timer/counter

boards were introduced with quadrature support:

1. Poor man's pseudo-quadrature.  Search the site here for "E-series" and quadrature and you should be able to find a related article, if it hasn't been pulled down.  The idea was to do edge counting on ch A with count direction (+/-) controlled by the state of ch B.  This method mostly almost kinda works, but isn't truly reliable.  The way I recall, every direction change gives you a risk (or maybe a guarantee?) of accumulating an additional +/- 1 count of error. 

  While I wouldn't recommend relying on this method for an important measurement, and I think you should look for an alternative, don't discount the valuable information you might be able to get in the meantime with this simple approach.

2. Quadrature decoder circuit/chip/interface board.  I remember buying a few for about $10 each or less from U.S. Digital back in the 1900's.  Dunno what's out there these days but there's gotta be options.  These decoders turn quadrature into correctly-timed pulse and direction info that is programmed like option #1 above, but will be truly reliable.

That said, get a newer board if you (or your boss) has the budget.  The newer multifunction boards (either 7 year old M-series or better yet, 1 or 2 year old X-series) support quadrature natively, and have a lot of improvements over their E-series counterparts.

Look at the breakout boxes as well -- make sure all the signals you need access to are available.  Maybe I'm not remembering right,

but I thought I remembered that some of the BNC connector blocks were heavily geared toward analog work and that digital and counter signals weren't as readily available.

-Kevin P

[PJ Turner]

Thanks Kevin, you've confirmed what I was thinking. There is no easy solution with the E series card.

I'll definitely find another board for my application.

All the best,

Patrick.