How to reset a counter on external signal in LabView?

Question

Hallo there!
I am using LabView v 8.5 and the NI USB-6211 to acquire signals, among them are the following:
1) angular pulses from a rotary encoder
2) a reference pulse for the rotary encoder witch will give a pulse on a specific position of the movement for every rotation
3) value from a pressure sensor
What I am trying to do is to create a pressure/volume diagram based on the pressure and volume inside a cylinder of an IC engine. To do this, I will need the angle of the engines crankshaft to calculate the pistons position in the cylinder. This way I can calculate the volume and put it in a xy graph to represent the volume (x-axis) and the pressure(y-axis).
I am using clk0 to count the pulses from the angular encoder, and this works great. However I now need the reference pulse to somehow reset the count at the precise time it goes high in order to precisely know the angular position.
How can I do this? And how precise will this be? And will I need any kind of synchronization with my pressure measurements? If so, how?
The relevant part of the program I am working on resembles the Count Digital Events with reset.vi 33 KB as found in this thread. However, I don't know how to get the reference pulse to reset as the stop button is. How can I do this?
In addition: the fast pulses of the angular encoder = 0-> ~10kHz. I seem to lose information if I use the basic level trigger detection.vi when I put this signal on an analog port.
-J

Answer 1

Hi Nick,
If you have an X Series or 2nd Generation cDAQ chassis (basically any cDAQ chassis except for the 9172 or 916x sleeves) then you can implement:
1,2,3,4,5,6,7,8,9,10,(reset),1,2,3,4,5,6,7,8,9,10,(reset),1,2...
You would have to configure an Edge Count Task, set the initial value to 232 - 6 (such that the 6th count causes the counter to rollover, which generates a pulse on the counter output), and enable the count reset using your external signal:
The count reset isn't currently available for other DAQ devices, but I believe it should be available on M Series (62xx) and TIO (660x, 6624) with a future driver release (some time in 2012).
If you don't have an X Series (or gen II cDAQ), don't despair.  On other hardware, you can get close to the previous behavior with a counter output task, with the exception that the "reset" signal would only be detected after the 2nd tick after your pulse is output.  Also, the reset signal would have to occur at the beginning to arm the counter the first time.
Or, you can get the 3rd behavior that you asked for by doing a continuous counter output task with the external signal as the source of the timebase ticks.  For example:
1,2,3,4,5,6,7,8,9,1,2,3,4,5,6,7,8,9
In toggle mode (default):
6 ticks of initial delay, 2 ticks high, 7 ticks low, 2 ticks high, 7 ticks low, ... etc.
In pulse mode:
6 ticks of initial delay, 9 ticks high, 9 ticks low, 9 ticks high, 9 ticks low, ... etc.
See here for an overview of the difference of the two modes.  Basically, pulse mode will emit a short pulse when TC is reached, and toggle mode will toggle the state of the counter.  You can't have less than 2 ticks as a high time, low time, or initial delay.
Best Regards,
John Passiak