## PSN-L Email List Message

Subject: WinSDR screen calibration
From: Brett Nordgren brett3nt@.............
Date: Mon, 21 Dec 2009 09:38:48 -0500

```Hi all,

I had recently been working with calculating the per-line scale factor for
some GIF's
being produced by WinSDR, so I took the opportunity to try to characterize
how that
generally relates to the number of lines displayed and the Y scale factor
setting.

So far what I have observed seems to suggest:

Given that
n is the number of lines displayed
Y is the WinSDR Y scale factor

For my screen (and possibly for any screen),
D/A counts per line = 913 / (n+1) * Y
So for a 24 hour - 24 line screen with Y = 2:
counts per line = 913 / 25 * 2 = 73.04

If you are using a 16-bit, +-10V D/A you can go on to calculate:

Volts per line = 73.04 counts/line / 3276.8 counts/Volt = 0.0223

The constant 3276.8 is 32,768 counts / 10 V, the maximum values
for a 16-bit +-10V D/A

And finally, from that, if you know your instrument's Volts / unit of
ground motion,
you can divide by that number to get the ground motion represented by each
line.

This seems to hold true for both the screen displays as well as for GIF
file creation.

Larry, I'd be interested in whether this seems to make sense to you, and have
I missed anything?

Regards,
Brett

Watch our wiggles
http://bnordgren.org/seismo/gif_images.htm

or watch some very very good wiggles
http://aslwww.cr.usgs.gov/Seismic_Data/telemetry_data/ANMO_24hr.html

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