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[DPRG] Frequency Counter Question

Subject: [DPRG] Frequency Counter Question
From: Chuck McManis cmcmanis at mcmanis.com
Date: Sat Oct 4 16:05:01 CDT 2003

Glad to hear you got it working!

At 10:21 AM 10/4/2003, Earl Bollinger wrote:
>I think the HP engineer who came up with that weird supply should have
>been shot. All they needed was a transformer, rectifier, some filter
>caps and a voltage regulator, what's with the extra 5 IC's, several
>transistors, big inductor, ferite beads, diodes, and zeners, choke
>coils, 30 or so resistors and caps? It doesn't even have the battery
>option installed either, that's a bunch more parts to add.

Typically the supply in DMM's and Frequency counters have to be very 
careful about not introducing any ripple into the power bus. The reason 
being the obvious one that various input and measurement circuits depend on 
the power being what it is supposed to be. At low input voltages a 
frequency counter can read 60 hz if there is cross coupling between the AC 
line through power supply.

All that being said, the HP guys are particularly over-the-top fanatics 
when it comes to such things! The HP supply I got for testing H-bridges 
specs something less than 10mv ripple at full load (1KW!) But it also means 
that these things often work for a long time because changes in tolerances 
of their components are often compensated in other ways.

--Chuck



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