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Chronos => Chronos User Discussion => Topic started by: jbehler on May 15, 2020, 02:00:09 AM

Title: Accuracy of Chronos 1.4
Post by: jbehler on May 15, 2020, 02:00:09 AM
We plan to use the Cam for measurement of particle speeds.

What is the accuracy of exposure time and frame rate?
I couldn't find details in the manual or the data sheet.

Best regards
Title: Re: Accuracy of Chronos 1.4
Post by: tesla500 on May 26, 2020, 01:43:01 AM
Hi jbehler,

The frame period is internally quantized on 10ns increments, and the accuracy of the period/frequency is +/- 50ppm based on the internal clock's tolerance.

The exposure time is internally quantized on the image sensor's horizontal line readout period. The exact value is a little bit complicated to calculate, but it's approximately the frame period divided by the frame height in pixels. For example, say your frame period is 1ms (1000fps), and you're at a resolution of 1024 pixels. The horizontal line period is somewhere close to:

0.001 / 1024 = 976.6ns

So the ultimate exposure time will be a multiple of ~976.6ns periods, whichever is closest to the set exposure time.

You can observe this behaviour on an oscilloscope if you set frame sync output on one of the triggers. This signal active when the image sensor is actually exposing.

Let me know if you need any more info.

Cheers!
David