PCI-6602 - What to do with unused counter inputs?

[drichey]

Kevin,

I agree that the GND shouldn't make a difference, however (for whatever reason) it did in my case.  I'm anxious to see if Brooks_C can reproduce this anomaly.

The encoder manufacturer specs indicate the output is TTL.

The breakout board I'm using has TBX-68 printed at the top next to the connector.  Why would you not recommend this board?  What would you recommend?

Thanks.

[Kevin_Price]

Nevermind, sorry, I was thinking of the TBX-68T, which I've used with a 4351 board for slow, high-precision temperature measurements.  I see now that the TBX-68 is just a simple, generic looking screw terminal block.

I've got no other ideas, so good luck getting this worked out...

-Kevin P.

[Brooks_C]

Hello drichey,

I tried all of the ground pins that you used and they all worked.  At this point it sounds like there is something wrong with pin 36 connecting to the actual digital ground of the card.  This problem could be with the connector block, the cable, or the PCI-6602 itself.

I used a hand held multimeter to confirm that you should get a conductivity reading between all of the D GND pins on the connector block so you could start by seeing if you see this for pin 36.  If you find that you don't have conductivity between pin 36 and the other D GND pins then test to see if the card, cable or connection block is the problem.  If you have another connector block and cable that would be the best method.

Once you localize the problem to one of these three parts you can call in to technical support to get a return merchandise authorization (RMA) and send that part in for repair.  To contact National Instruments for an RMA call (800)-531-5066 and reference this forum post.

Cheers,

[drichey]

Brooks,

I appreciate the time you put in on this for me.  I checked the continuity from pin 36 to the other GND points and everything checks out.  I've got two more computers with 6602 cards in them, that I will try to hook up and see what I get.  Unfortunately, I don't have another TBX-68 at my disposal.  I will check out the other boards and let you know what I find.

Thanks again

[Brooks_C]

Hello drichey,

If you can get continuity between pin 36 and another D GND pin in which the encoders work then I'm a little perplexed as to what it happening.  Can you measure the voltage between pin 36 and other D GND pins?  If this voltage isn't zero then this could make since, but if it is zero I'm not sure what is going on.

I just want to recap what has happened:

1.  When the encoders are grounded to pin 36 they demonstrate behavior similar to that of ungrounded encoders (loose or gain counts), but when you use another D GND pin they work correctly.

2.  You get continuity between pin 36 and the other D GND pin you use when the encoders work.

I apologize for the silly question seeing as you've been so consistent in your testing, but when you check continuity do you have any other wires on the connector block between pin 36 and other pins?--I doubt this is the case, but if it’s not I'm at a loss.

Lets see what you find out about the voltages between the D GND pins and from the other 6602’s.

Have a good night.

[drichey]

Brooks_C,

I finally had an opportunity to do some more testing and this is what I've found.

To answer your questions:

your recap is correct

no, I do not have any other wires connected to Pin 36

When I measure voltage between each DGND pin I get 0V, however when I connect the encoder GND to PinX (X=any DGND pin), I get 39mV between that pin and the other DGND pins.  Does that mean anything to you?  I think it odd, that IF they are internally connected, that I would see a potential.  If you have any insight, please share it.

I was able to get my other two computers with 6602 boards up and running and the results are the same.  That being the case, IF there is a problem with my hardware then it must be in the cable or TBX-68 board.  Those two items are the only things constant between the three systems I tested.

Thanks for your time.

[Brooks_C]

Hello drichey,

When you say "I was able to get my other two computers with 6602 boards up and running and the results are the same." Do you mean that on these boards you also lose/gain counts when you use pin 36, or do you mean that they all show a difference of 0V?

If you haven't already, I'd suggest trying the original encoder setup on the other two boards using pin 36 to see if they also lose counts.  Assuming the results are the same I agree with you that the problem is likely with the cable or connector block--and I might also be suspicious of the encoder.

I will look into possible causes of the 37mV offset on the pin where you ground the encoder.  I think this is probably okay since you see it on the pins that work as well as pin 36, but I'll let you know if I find anything different.

I know this isn't expected behavior since I can't reproduce it with my setup so if at all possible it would be great if you could borrow another cable and connector block to find out which part is the problem.  If you test another connector block and cable and still don't work then I'd think it is something with the encoder you’re using.  If the other setup does work then try swapping the cables and connector blocks until you find out which part causes the issue.

Cheers,

[drichey]

Sorry for being unclear.  That IS what I meant.  I had two other computers with 6602 boards installed in each.  I tested each one and got the same results: I lost counts on at least one channel.

I will install this equipment in the next month and at that time, I will be able to test using another TBX-68 and cable.  Hopefully, that will shed some light on the subject.  I will let you know what I find when I'm able to do further testing.

Thanks again for your help,

DREW