How to setup "Stop Trigger"?

Question

There’s a signal(only persist a few seconds) to be measured.I use a digital trigger to start the measurement,but the question is:how to config a digital trigger to use its falling slope to stop a test?
The DAQmx’s function to config a “stop trigger” is called “Reference trigger---DAQmxCfgDigEdgeRefTrig”,which means set up a trigger in finite samples(to set up preSamples count, and the “postSamples”can be auto caculated using “samples per channel” minus “preSamples”.----What does postSamples mean?When then pre-defined slope comes ,the measurement stops,isn’t it? ).
But I want to acquire the data continuously,not stopping until received the digital trigger signal’s falling slope. So before the trigger singal’s falling slope comes,I don’t know how many samples I might have acquired.
What’s more,the “reference trigger” doesn’t support “continuously measurement”,it supports only “finite measurement”.So,when the samples reaches the sample count defined in “DAQmxCfgSampClkTiming”,while the falling slope have not come yet, then the measurement might stop. how can I set up the “stop trigger”?
If there is a way to config this trigger,then the total sample count might exceed the “samples per channel” count,how can I detect when buffer is full?Should I write a cycle to detect the buffer status(using the function “DAQmxGetReadTotalSampPerChanAcquir”)? Would this kind of detection slow down the sample speed?
^_^^_^

Answer 1

There’s a signal(only persist a few seconds) to be measured.I use a digital trigger to start the measurement,but the question is:how to config a digital trigger to use its falling slope to stop a test?
The DAQmx’s function to config a “stop trigger” is called “Reference trigger---DAQmxCfgDigEdgeRefTrig”,which means set up a trigger in finite samples(to set up preSamples count, and the “postSamples”can be auto caculated using “samples per channel” minus “preSamples”.----What does postSamples mean?When then pre-defined slope comes ,the measurement stops,isn’t it? ).
But I want to acquire the data continuously,not stopping until received the digital trigger signal’s falling slope. So before the trigger singal’s falling slope comes,I don’t know how many samples I might have acquired.
What’s more,the “reference trigger” doesn’t support “continuously measurement”,it supports only “finite measurement”.So,when the samples reaches the sample count defined in “DAQmxCfgSampClkTiming”,while the falling slope have not come yet, then the measurement might stop. how can I set up the “stop trigger”?
If there is a way to config this trigger,then the total sample count might exceed the “samples per channel” count,how can I detect when buffer is full?Should I write a cycle to detect the buffer status(using the function “DAQmxGetReadTotalSampPerChanAcquir”)? Would this kind of detection slow down the sample speed?
^_^^_^