I need help on triggering.

[KDGREAT.]

Hi everybody,

 I need to do curve fitting on dynamic response of a type k thermocouple but I have to capture the transient before I can go ahead. My challenge is how to capture a still or a stationary curve (exponential growth) of the thermocouple. I have tried different setting for the trigger and gate vi ( am using USB-6008 to acquire the signal) but i have  not been able to capture the signal . pls find the attached vi. any modification and suggestion will be appreciated.

Regards.

kdgreat

[Beutlich]

It sounds like you are trying to trigger the acquisition so that the data you acquire corresponds to a very particular window of time (when you stick the sensor into the new environment). If this trigger is a physical signal, like a digital pulse, then I recommend trying to edit the DAQ Express VI instead of configuring the Triggering VI. If you double click the DAQmx Assistant, you will get the settings for that VI. One tab is called triggering, and you can configure it so that the acquisition starts when that particular line has a digital edge. Also, for curve fitting there is an express VI that allows you to map a signl to a nonlinear curve like an exponential. If this is not the setup you are looking for, could you describe the setup of your hardware/sensor and also the goal of you application?

[KDGREAT.]

Thanks Eric.

The set up is this: I want to capture a transient response of a k type thermocouple to a sudden temperature change and thereafter do a curve fitting on the signal. I am using USB 6008 which does not have analog triggering from the daq assistant vi, that is why am using trigger and gate vi so that I can capture the trace (exponential growth). The problem is I have not been able to get any output from the trigger and gate vi talkless of doing curve fitting on it. I have tried different settings on the vi by configuring the start and stop triggering section.

I hope u can understand what I am trying to achieve , I will work on the option you gave but if you still have any other idea pls let me know.

Thank you very much.

kdgreat.

[Beutlich]

You may also try using the the Mask and Limit Express VI. This will allow you to filter a waveform so that you only view it within a particular range. You could put a limit so that anything at the stable point is filtered out, but as soon as it rises a little (or lowers, depending on temperature change) it passes the data for processing. The Trigger and GATE Express VI is more appropriate for sharp transitions (like a digital signal).