[time-nuts] Building a mains frequency monitor

[Bob Camp]

Hi

The same “Collins Limiter” stuff that goes along with DMTD’s applies to 60 Hz power 
measurement as well. There is a “magic bandwidth” that combined with a slew rate 
will give you an optimum result. The gotcha is that you need to know the noise 
parameters inorder to work it out. Even back in the 1960’s there was enough “stuff” 
feeding crud to the power line that a general solution wasn’t going to be possible. These 
days …. no way.

Bob

> On Apr 13, 2016, at 6:23 PM, David <davidwhess at gmail.com> wrote:
> 
> Tektronix used transformer isolation followed by a low pass RC filter
> with about a 1 kHz cutoff; this was fed directly into the trigger
> source selector just like any other trigger source.  There is still
> enough noise present that the trigger coupling can be used to select
> specific features to trigger on.
> 
> Modern DSOs often (always?) use an optocoupler circuit for isolation.
> I saw an example schematic somewhere and it is pretty simple.  It
> produces a roughly linear output referenced to the negative or
> positive peak so triggering can still occur over almost 360 degrees of
> phase.  I do not know what kind of low pass filtering was implemented.
> 
> On Tue, 12 Apr 2016 09:38:13 -0400, you wrote:
> 
>> ...
>> 
>> I have yet to dredge up the 60Hz line-lock schematic circuit used in more
>> than half a century of analog scope trigger circuits. The Tek scopes had
>> exceptionally robust trigger circuits.
>> 
>> Tim N3QE
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