Counter connection for PCI 6014 with BNC 2110

[yulnidaq]

Hello, 

   I am new to Labview and maybe this question is dumb. (I did search for its answer on this board).

   I am now testing the counter input of a PCI-6014 card with BNC-2110 terminal. Using the test panel in Measurement and Automation, I wish to verify my connection for counter0. According the othe documentation, it looks like I need use PFI 8 as input terminal. When I apply the 5 V output signal from BNC2110 to PFI 8, the counter reading increases by one as expected, but when I switch the PFI8 input to digital ground, the counter reading also increases by a seemingly random number. I tried to find a detailed instruction on how to connect counter input, but they all seem to tell me that PFI 8 is the counter input.
   I chose edge counting mode and PFI8 as source.

   It would be greatly appreciated if you could offer some suggestion.

   Thank you very much!

Message Edited by yulnidaq on 04-30-2008 04:57 PM

[Paul_C.]

Hi Yulnidaq,

To do a edge count on a PCI-6014 you will want to connect to pin number 37 or PFI 8.  This is internally routed to the counter 0 source which is used to count the edges of your signal.  I'm not sure why you're seeing random numbers when you connect the PFI 8 to a digital ground unless you have other connections made.  I have tried the same here on a similiar device and do not see that behavior.  You should see no count when using PFI 8 as your counter source and connecting it directly to a digital ground line.  I would recommend taking a look at the pinouts on your 6014.  These can be found by right-clicking on your device in Measurement and Automation Explorer (MAX) and selecting device pinouts.  This will give you the pin numbers for the counter gate, source, and out.  Please let me know if you have any additional trouble or the problem persists.

Regards,
Paul C.

[yulnidaq]

Thanks for your reply. I checked the pinout and it seems to be correct (pin37 corresponds to PFI8/Ctr0). I tried two simple tests. For the first one, a switch is used to choose either 5V (from the BNC2110 terminal) or digital ground is connected to PFI8. When I switch it from ground to 5V, counter0 increases by one as expected, but when I switch it from 5V to ground, counter0 increases by a random number. I also specified the source to be PFI8 in the test panel. For the second test, I simply connected PFI8 to digital ground directly. One it is connected, counter0 increases by a random number. I am afraid there might be something wrong in the way I connect the signals. Would you please suggest some other tests to help trouble shooting? Thanks a lot!

[Paul_C.]

Hello again Yulnidaq,

I tried the scenario with a BNC 2110 and I'm unable to see those results.  I run the test panels in MAX and set counter 0 for edge counting on PFI 8.  When I connect the PFI 8 line to +5V source it increases the count by a random number but then stops if I continue to press the wire against the pin.  This is probably due to some noise.  I do not see the count increase ever when connecting PFI 8 to a digital ground line.  I would verify your not accidently making the wrong connection when going to digital ground.  Perhaps try another DGND on the BNC 2110.  The best way to test this would be to use a digital line instead of the +5V source and ground.  Just connect the PFI8 line to one of the digital lines (such as DIO 0).  After you connect it up, go to test panels and start your counter 0 edge count.  Next, go to the digital I/O tab and make the digital lines all outputs.  Switch them once from low to high to low.  Once you go back to the counter tab, you should see a count increased by 1 since you generated 1 rising edge.

I hope this helps,
Paul C.

[yulnidaq]

You are right. There might be some noise that was detected as a rising edge when I connect the digital ground to PFI8. I followed your instruction and it works as expected. Thank you very much!

[yulnidaq]

Dear Paul,

       Thanks for your previous help. I am wondering if you happen to know the input impedance of counter 0 on PCI 6014. I check the data sheet, but it seems that impedance of PFI8/counter0 source is not reported. Do I have to look for it somewhere else? Thanks again!

[NI-Bongo]

Hi yulnidaq,

Are you having problems getting accurate measurements or still receiving noisy signals on the input?  What would you like to measure in your application?  Let me know some more details about what you are setting up and I can try to help.  I don't have the impedance specification immediately available, but usually that is not necessary to get most applications up and running.

[yulnidaq]

Thanks for the reply.
I am trying to count TTL pulse from a PMT with 50 Ohm output impedance. Using a BNC T, the signal is fed to a MCS-PCI card (from Ortec) and PCI-6014 card (counter0) simultaneously. The MCS-PCI card uses 1k Ohm impedance for input. I found the counts from PCI6014 is roughly 50% of those from MCS-PCI. So I am wondering if the impedance is not optimal for PCI-6014. We wish to achieve the same counts using PCI6014 since it is more flexible to program.
Thank you again!

[NI-Bongo]

Hi yulnidaq,

Looking at the specifications for the device, the counter input will have ~50kOhm bias resistor at the end of the line.  This is what your signal would see as the input impedance.  Also, see the note about  the tolerance of the resistor near the bottom of page 2.

NI 6013/6014 Family Specifications
http://www.ni.com/pdf/manuals/370844b.pdf

I would recommend taking a look at your signal with a scope where it connects to the 6014.  See what the voltage levels actually look like and if the signal looks noisy.  Do you have a test signal other than the PMT that you can use for debugging?  This will be helpful to ensure that both devices are reading the correct values.  Use on of your digital lines on the 6014 to generate the pulse and ensure that you get a count on both devices for each.

Also, are you doing a simple edge counting measurement or another type of measurement?