Respond quickly to a processed signal

[PhilJ]

Hi-
I need to trigger an analog output waveform to begin in response to a certain condition occurring in the analog input signal. I would like the analog output signal to begin as quickly as possible (hopefully around 1+ msec) after the condition is met. The condition is the derivative of the input signal going below a certain threshold. Therefore I need to process the signal (take the derivative) on a sample by sample basis and maintain an accurate sampling rate of 1kHz. I know Labview Real-Time is probably the best way to achieve this, but I would rather see what type of performance I can get out of my DaqCard 6062 before investing in a real-time system. I am programming in CVI 7.0 and can use either traditional daq or daqmx lib
raries. Any suggested functions, techniques, or example programs would be much appreciated. I do not know the best way to achieve single point (or close to single point) sampling with hardware sampling rate accuracy.

[JuanCarlos]

Hi,

You are right when you say that RT would be the best way to go here, given the fact that you require an accurate software-timed acquisition. However there are a couple of suggestions that I can give you:

+Use DAQmx: the new architecture of DAQmx will give you a much better performance in single point operations than traditional DAQ.

+Careful UI management: depending on the expectations of the system most likely you need to respond to user events. Make sure that the user events will not degrade the performance of your application. You can use an asynchronous timer or another thread to handle some user events, make sure that those don't take too much processing time.

+Oversample: since your system will be running in a Windows environment it's a good ide
a to do some oversampling; if you expect a consistent software sampling rate of 1 KHz you can set your system for a higher acquisition rate that will allow you to eat up some of the jitter in the processing time of your routine.

I hope this helps,

Regards,

Juan Carlos
N.I.