PSN-L Email List Message

Subject: Re: WinSDR screen calibration
From: Brett Nordgren brett3nt@.............
Date: Mon, 21 Dec 2009 22:06:22 -0500

Hi Larry,

You are absolutely right, I meant A/D digitizer.

However I was indeed referring to the Y-scale sensitivity, as measured 
between successive horizontal lines.  Rarely are helicorder displays 
labeled to indicate their sensitivity, and even when they are it usually is 
hard for me to figure out what is meant by the label.

Working from the calibrated instrument sensitivity, I wanted to be able to 
say something like, "Each horizontal line represents a velocity of 
1um/second".  So, for example, a waveform peak six lines high would 
represent  a peak ground velocity of 6um/sec.


At 06:29 PM 12/21/2009 -0800, you wrote:
>Hi Brett,
>I think you mean A/D not D/A, WinSDR does not deal with D/A converters. 
>Also, I think
>you mean X-Scale not Y-Scale. The Y-Scale controls the signal level 
>(up/down motion)
>in the real-time window or GIF image and the X-Scale controls the time. 
>The number of
>lines per channel and the time period per line has nothing to do with the 
>Y-Scale. If
>you mean the X-Scale, the X-Scale is in minutes per line.
>Larry Cochrane
>Redwood City, PSN
>Brett Nordgren wrote:
>>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 
>>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?
>Watch our wiggles
>or watch some very very good wiggles


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