Changing the polarity of a start trigger the results doesnt affect the result

[Peter_02]

Hello everybody,
I use the 6602 board. My problem is that I have set up start triggers to start several counters simultaneously.
I changed the polarity of the start trigger. However the results in the buffer dont changed.
I thought if I change the polarity the result have to change, too.
I perform the buffered semiperiod measurement. There is one very short state (< 1ms) followed by a long state (>1ms and <5ms) of the signal.

For example the polarity of the trigger is "positive" and the first value in the buffer is the short one.
If I change now the polarity of the trigger the first value have to be the long one. Or not???

Does anyone have an explanation why it don't change?


Regards Peter

[JustinBritten]

Peter,

The start trigger is just a means of simultaneous arming multiple counters. It will not change the polarity of your result nor switch data in your buffer. For a thorough description of how to configure buffered (semi)period measurement, please refer to the User Manual for your hardware. I have included a link to this User Manual below.

Under the section on how to perform Buffered Semiperiod Measurement you will see that you specify which phase of the cycle is the active phase by specifying the GATE polarity.

6601/6602 User Manual
http://digital.ni.com/manuals.nsf/websearch/DD0DBB6404BC139886256721007CF16D?OpenDocument&node=132100_US

Regards,
Justin Britten

Applications Engineer
National Instruments

[Peter_02]

Hello, first of all thank you for the fast answer.

However I still have a question. What if I want to analyse the date stored in the buffer.

The back is I want to do the buffered semi-period measurement over a long time, maybe one day.

Now it's unclear to me when the best point of time is to do the analyses.
Will I have to read the buffers in an while loop and do the analyses in this while-loop?
Or after the while-loop and then execute the whole vi in an for/while-loop?
Because the measurement can last one day I can't store all values in one buffer.
So I want to read the buffer everytime it is full an analyse these values. After that I want to read the bufer again and so on...
Is this possible at all?



Any hints?

[JustinBritten]

Peter,

You can take two approaches to this issue. First, you could acquire data until you have a sufficient buffer and then analyze it. This will definitely slow down your acquisition rate depending on the intensity of your analysis. You may even miss data during the period when you are performing your analysis. If your operation is time critical, you may want to store your results and perform post-analysis. This would mean writing your data to a file and then performing the analysis after you have acquired your full day of data. The issue here is that you must ensure you have sufficient disk space and that processing a file that could potentially be very big is realistic (you will need enough RAM).

Regards,
Justin Britten


Applications Engineer
National Instruments

[Peter_02]

Hello Justin,
thanks a lot, too for your fast answer. I think I will take the approach to store the data and perform the analysis after I have acquired the whole data.

Regards Peter