Date: Sat, 27 Mar 2010 22:26:03 -0700
From: "Bill, W6WRT" <dezrat1242@yahoo.com>
Subject: Re: [Amps] ripple in B+ supply.
On Sat, 27 Mar 2010 22:26:25 -0400, "Gary Schafer"
<garyschafer@comcast.net> wrote:
>Quote from the 2008 ARRL handbook power supply section:
>"percent ripple is the ratio of RMS value of the ripple to the dc value in
>terms of percentage".
## That's also in the 1991 book.
>
>As RMS does the same amount of work as dc does it would make sense to use
>RMS as a comparison.
REPLY:
Ok,that works if you're equipped to measure the true RMS value of a
sawtooth wave. I suspect most hams are not. Using a non-true RMS
meter, who knows what you'll get. Did the handbook mention that?
## How many Fluke DVM's don't read true RMS these days ? I bought
a Fluke 87 back in 1991.. for myself. Then we ordered a ton of 87's for
work.. + a 1/2 doz fluke scope meters. That was almost 20 yrs ago. I
prefer the 2 and also the 4 x ch Tektronix scope to the fluke scope meter.
I will try and find a Non-True Rms meter.. and compare it to my 87. My guess
is, they will very close. If that's the case, the scope can be dispensed
with,or
put another way, if you don't have a scope, no big deal.
By comparison, a P-P measurement with a scope is unequivocal.
## Providing that Joe ham even [A] has a scope.. and [B] has x 1000
probes, cause you know he will stick the probe [C] right across the
B+.. and chassis.. and [D], either kill himself.. or [E] blow up the scope.
If using a scope, and oil cap used.. I put the scope probe across the last
resistor of the string of 10 x 1 meg 1% 2 watt meter multiplier resistor's...
.. at the cold end. If hv lytics used, put the probe across the cap at the
cold
end of the string.
You won't measure any difference between the scope results... and
Duncans PSUD. The 2 x are dead on. [ for calculating /measuring ripple %],
but that's only if PSUD spits out the same loaded Voltage. No load = no ripple
so u have to load the B+ supply down.. with a cxr.
later...... Jim VE7RF
You pays yer money and takes yer choice.
73, Bill W6WRT
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