SC-2345 pinout Counter is not gather all angle points

[TWGomez]

I have an SC-2345 Carrier, and I am using the pinouts (37 and 16)  for angular encoding. This works, however I do not get all data points, there are several points missing even if I turn it slowly by hand, the faster I turn the more points missing. It seems that the data aquisition isn't very fast here, so I was wondering if there is a way to capture more data points.

I am basically just using the NI example to do this, so it vexxes me a bit that it is not capturing all angles.

[Chris_K_]

Hi TWGomez

I am assuming that you are using the three tired terminal breakout terminal block on the SC 2345 to gain access to the needed pin on your DAQ card.  Since you are able to get your application counting, but you are just missing points, I think changing the time you read the encoder might help.  I am not sure what example program you are using, but since you say you are using only pins 16 and 37 so I will assume that you are using the digital edge counting and doing a basic quadrature encoder read. If I am wrong, please let me know what example program you are using.

If you use the Count Digital Events-Buffered-Continuous-Ext Clk.vi from the example finder, then you can specify an external sample clock and create a more deterministic application where the counter buffer is read at a particular time.  You will have to carefully choose a sample clock rate such that it allows you to acquire the accurate position, but not too fast such that it overflows the counter buffer.

If you still have questions, can you please let me know what DAQ card you are using, and what type of encoder you are using.  Also let me know what example program you are using and give me a brief description of your application, so we are on same page, and I can better help you.

Chris_K

[TWGomez]

Yes digital edge counting, you are correct.

I have also been working with an NI engineer, to no avail, unfortunately.

He gave me the same answer you did basically. I reconfigured things to use the sample clock of one of the other modules in my confguration, and it didn't help much, I get errors if I go about 2k samples per second, and I still miss points. I am using a 6034E pcmcia DAQMX card.

I'll attach the VI I am using to init the angle reading. To read I am just using the read VI in a loop (1d array of u32).

LV 8.2.1

[Chris_K_]

Hi TWGomez

I have been doing a bit more research, and I am unsure why you are missing points in your acquisition.  It sounds like you are connecting your signal correct for an E-Series card, and your program sounds fine as it is getting some pulses, but it is just missing a few.  To ensure that it is not your LabVIEW VI, can you use the exact VI from the example finder, Count Digital Events.vi, and let me know this VI works. 

Next, I found another forum post that points to another potential problem. 

http://forums.ni.com/ni/board/message?board.id=250&message.id=31118&requireLogin=False

We should ensure that your encoder is outputting a proper signal.  I have attached a VI that combines the Count Digital Events.vi and the Acq&Graph Voltage-Int Clk.vi, together so you can view the signal that is being sent to the counter on the DAQ card.  I realize that you are using the SC-2345 as a breakout box for your DAQ card and there is no way to access the analog input channels without SC modules, but if it is possible either use another terminal box to view the encoder signal in LabVIEW or a use a scope to verify that the signals are ok.  If you can connect the A and B signal from your encoder to analog input channels 0 and 1 of your DAQ card the signals can be viewed.  It is possible that the A and B signal that are being outputted from your encoder are noisy or phased incorrectly and is the reason your application is skipping pulses.

Lastly one other point that was brought up in the other forum post is the signal reference voltage.  Can you ensure that your encoder is providing a proper TTL signal, and if possible power the encoder from the DAQ Card itself.  You can use terminal 14 from your SC-2345 to provide the 5V signal.

Here is another link that gives a bit more information about this issue.

http://digital.ni.com/public.nsf/allkb/B4ED7F3603ABBF7D86256F43004AFF87?OpenDocument

Once we have a better idea of the signal that the counter on your DAQ card is seeing, it might better diagnose the problem. 

Chris_K