measure time between two channel peak voltages

[radhakrishnan]

hai,

        i am using NI PXI5152 digitizer card for my application.

In that i connected two signal is two channels. Now i want to measure the time

between the channel crosses 5V and the channel 1 crosses the 5V limit.

Please give your suggessions to resolve the issue.

Thanks and regards

Radhakrishnan

[dansch]

Hello Radhakrishnan,

You can measure the time delay between the two digitizer channels using a Fetch Measurement. The particular measurement you want to fetch is the Time Delay scalar. To specify what values you want to use as reference levels, you may need to use some niScope property nodes and set the Reference Levels:Channel Based Mid Ref Level property to 5V (you will also need to set the Reference Levels:Units property to be volts and not a percentage for this to work, see below for Help location).

For more information on the Time Delay measurement, please check the High-Speed Digitizers Help file in the Contents tab under NI High-Speed Digitizers Help » Programming » Scalar Measurements in NI-SCOPE » Two Channel Measurements (Scalar) » Time Delay.

Information about the associated settings to make can be found in the Contents tab under NI High-Speed Digitizers Help » Programming » Reference » NI-SCOPE LabVIEW Reference » niScope Properties » Waveform Measurement » Reference Levels » Channel Based Mid Ref Level or Units.

For an example that you can use to perform this type of measurement, please open the LabVIEW Example Finder (within LabVIEW go to Help » Find Examples) or open the NI-SCOPE Examples folder from the Windows start menu by going to Start » All Programs » National Instruments » NI-SCOPE » Examples » LabVIEW <version>. The example you want to open is titled "niScope EX Measurement Library.vi". You may have to tweak some of the inputs, but you should be able to perform the measurement you need such as shown in the image below.

Hope this helps,

[dansch]

Just as an aside, since you are specifically wanting to measure the time delay between the peaks, you will need to set the mid reference level to 5V. This is due to the fact that the time delay measurement measures between when the waveform crosses its mid reference level value.

One method that may be similar but more straightforward would be to take the actual array of data from each channel and do some simple processing. Since you want to know the time between when each one hits its peak, you can do a peak search and find the first instance on each channel when it reaches 5V or some level, then determine what sample number that happened at and subtract them to determine how much time elapsed between them (each sample number is a sample clock period in time). For an even more accurate reading, you could interpolate the data on each channel to tell more exactly when in time the signal would have hit that specific 5V threshold. Just some thoughts... Best of luck!