Can I use an unmodified feedthrough module as a counter input

[J Bowen]

I have a SCC-FT01 with an SCC-2345 carrier and a DAQ Pad 6015 (mass thermination) and was hoping I could use it as a counter input.  I've used it before with a photo tach I have (outputs pulse per revolution based on white tape) just as a voltage input (tach is battery powered) and calculating frequency of pulses.  I'd like to free up this voltage input and use the feedthrough in the counter slot.

Do I need to modify the feedthrough module to do this?  I would think the feedthrough module/counter input combo can be used to aquire the a simple pulse input.  Thanks for any feedback.

I've checked the FT01 manual and the only mention of using counter input is in reference to customizing the module using the breadboard.  Is this required to gain access to the counter channels?

[stilly32]

Hi J Bowen,

You won't have to modify the module to use the counters. If you use the J17 or J18 sockets, you will have access to the PFI line 5. You can set this up in software as the counter source and perform counter operations. To set the PFI line as the source for a frequency measurement, you will need to use a DAQmx channel property node and select the counter input >>frequency >>source terminal. I added the property node to the "Meas Dig Frequency  - Low Freq 1 Counter" shipping example so you should use something similar to this:

Hope this helps,

Andrew S.

National Instruments

Message Edited by stilly32 on 09-07-2006 10:01 AM

[J Bowen]

I tried that and still can't seem to get it to work.  I put the FT01 module in slot J18.  Connected the + (Where the pulses are coming from) from my tach to the PFI 5 line (AI Grnd on the FT01 module)  and the - from my tach to the AO Gnd.  When I run the VI (basically same as yours) I get frequencies very very high (10 MHz).  Does this not mean the PFI 5 line has a signal already on it?  I also get an error periodically saying that 2 input pulses occured at the same time and to use a faster timebase.  I'm using the 20MHz timebase and am assuming that this is from the very high frequency already present on PFI5.  Also for my selection of counter in the create channel vi is just Dev1/ctr0.  I assume this is fine because I'm changing the counter frequency input terminal to PFI5. 

Any suggestions?

Thanks.

[AnalogKid2DigitalMan]

What is the upper and lower range of the signal that the photo-tach outputs? Is it a clean square wave?

[J Bowen]

It is a relative clean square wave from 0 to 6V.  It is not a even cycle between high and low but more of a pulse to 6V when the photo tach is triggered.  I will capture some voltage measurements and post them today.

[J Bowen]

Hello all,

Turns out it was a 2.5V square wave, which I believe is not enough to trigger the counter intput on the DAQ 6015 pad.  I'm going to try externally exciting the sensor to 10 V and see if that works.  Just out of curiousity what is on the PFI 5 line?  Why was I getting any input from it without having a 5V pulse on it? 

Thanks.

[stilly32]

Hi J Bowen,

Are you doing any other operations with the 6015? It is possible that other timing sources (AO) could be routed to that pin. I would try the measurement without other tasks running to see if that resolves the issue. Also, if it turns out you need access to the other pfi lines, you should be able to access them from the screw terminals on the 2345:

http://digital.ni.com/manuals.nsf/websearch/09FC2D464C3C38A1862571850066A88D

Check pg 27.

Hope this helps, let us know what you find out.

Andrew S.

National Instruments

[J Bowen]

I got it figured out!!! I think.  Turns out the signal was 6V, it just happened to be one of my AI channels is messed up (USB-9221).  And I did have an analog out task running at the same time which accounted for the extra signal.  When I removed that task I was able to get it t work.  I still am intermitently getting -200140 errors (2 consecutive active edges of the input signal occured without a counter timebase edge...Use a faster counter timebase) which I believe is from the tach signal not being a completly clean square wave, and I just ignore those iterations that have those errors. 

Can I just wire my signal right to the

Are there PFI lines which are never used?

[stilly32]

Hi J Bowen,

The descriptions of the PFI lines and normal use is actually in that table referenced above. For the counter application, I would use PFI lines 8 or 3 for counters 0 and 1 respectively.  

I didn't get the rest of your question, but hopefully you can work from there.

Cheers,

Andrew S.

National Instruments