Does VeriStand have timers?

[jaime_c]

Does VeriStand have timers?

I am monitoring a digital signal that is the control line of an LED that is duty cycled to control brightness.  On top of that brightness duty cycle, the LED can either be on "continuously" - at least to the human eye which can't see the brightness duty cycle - or it can flash.

I need to be able to measure the flash rate and the duty cycle of the flash (and the underlying brightness duty cycle but that is another task).

I'd like to set a timer on an alarm that is triggered by the the falling edge of the digital signal.  I would like to reset the timer on every falling edge, and then call a procedure when the timer expires.

The idea is that when the timer expires I can consider the LED off and make other measurements and calculations from there.

I have an NI PXI-1044 Chassi, NI-PXI-6229 DAQ, and VeriStand 2010.  I could get VeriStand 2011 but I'm concerned about the amount of work it would take to convert my project so I'd prefer a solution that uses 2010. 

If there are ways to do this without an actual timer I'd like to hear them.  Am I making this task too difficult?

[Pie56694]

The PXI-6229 has 2 general purpose counter/timers (page 9).  VeriStand 2010 has four built-in counter-based tasks: frequency, period, count and position.  The frequency task measures the frequency in Hz of a signal connected to a channel.  If you're not using these counters for something else, you can use one of them for the frequency measurement.  All VeriStand counter tasks are based on a simple one-counter Count Edges acquisition, so you should wire the counter's Source pin for the frequency task.  Be sure to change "Minimum [Hz]" to something other than 0 (1 should be OK).  The duty cycle is a little trickier.  Making this calculation in software (rather than hardware) may require the VeriStand system to run at a higher rate than otherwise necessary, and it will introduce jitter into the measurement.  Depending on the rate, measurement requirements, and the other requirements in the system, you might want to implement a DAQmx custom device.  See LabVIEW's example finder for Meas Duty Cycle-Buffered-Finite.vi.  Another option is to use an FPGA card with one of the Duty Cycle shipping examples.  For this task, there is no feature I'm aware of in VeriStand 2011 compelling an upgrade.

Steve K

[jaime_c]

Hmmm I will look into your LabVIEW suggestions.  I have not done anything in LabVIEW but I have to learn some time.

As far as the frequency measurement goes, I think what you described would get me the the frequency of the brightness-control duty cycle, but unfortunately that is not something I'm tasked with verifying.  I have to verify the duty cycle of the brightness control, the frequency of the visible flash rate, and the duty cycle of the visible flash rate.

[Pie56694]

Can you post a picture of what you need to measure and label the different ranges within the signal(s)?

[jaime_c]

I would love to.  Can you suggest a good tool for drawing waveforms?  It's actually something I've been looking for but haven't found yet.

[jaime_c]

I cannot find the example with NI Example Finder.  Can you tell me where it is?  I'm using LabVIEW 201.

[jaime_c]

I found the example ... somehow DAQmx was removed from my host computer.  Now I'm going to try to use the example.

[Pie56694]

I was thinking a drawing in Paint so I might understand the characteristics you're trying to measure.  You can evaluate the Digital Waveform Editor if you'd like to try something more formal.

-Steve K

[jaime_c]

Okay I've attached a drawing of the general waveform I need to measure.  Thanks for your time so far.

I've also cracked my LabVIEW book a few times so I may be able to create my own solution, but a little help would be great!

[Pie56694]

That makes sense.  Would you please add a sense of time to your drawing?  What are the expected and max/min time ranges in your waveform?

Steve K