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Make a bit setback of signal imitate circuit and experience
From;  Author:Stand originally
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Becoming the issue of monitoring of signal of a railroad some time ago, everybody knows railroad engine runs signal cent to be two kinds, one kind is 18 information, one kind is UM71, I want to use same kind circuit board will measure these two kinds of signal. But arrive after the spot, the working environment that discovers the site is very harsh, it is very strong relay is disturbed. More annoying is, and power source ripple also is not very good.

The processing that measures signal is such:

Signal input---Damply- - prevent thunder---Segregation---Enlarge----Rectification----Filter wave---Output

But be after segregation,the signal of output can be used scarcely. So special affliction.
Circuit revises to be after:

Signal input---Damply- - prevent thunder---Segregation---Enlarge---Connect high---Imitate switch---Low---RVS/DC changeover---Output.

The result still cannot be used. But my brainwave easily, the purify that prevent thunder, get very ideal result unexpectedly,
The reason is me use preventing thunder is canal of two two-way TVS (7V) butt joint, but signal is more than 7V in peak value of the peak after attenuation, bring about TVS canal to guide so, signal is absorbed by TVS, segregation transformer produces self-excitation, so the signal after segregation cannot be used.

Here, write down my experience, so that each brother is drawn lessons from. Still look at the program with can give out better.