----- Original Message -----
From: "Jim Shorney" <jshorney@inebraska.com>
To: <Amateur-repairs@yahoogroups.com>
Sent: Wednesday, August 28, 2013 6:33 PM
Subject: Re: [Amateur-repairs] In search of the basic test
equipment for workbench.
Solas don't produce a pure sine wave. This will tend to
throw some voltage
readings off.
73
-Jim
NU0C
Modern regulating transformers put out quite pure sine
waves. Some very early Sola types did not. I doubt if the
impurity would cause any significant measurement error
especially after being turned to DC. The error in a meter
depends on type of AC to DC converter it uses. A single
diode, as found in RF meters, is RMS reading for very low
levels, i.e. below about 1.5 volts, and becomes a peak
reader at higher voltages. In the range where it is peak
reading the error can be as large as the percentage of
harmonics in the signal. Most audio meters and others like
the Hewlett-Packard 400 series, use a full-wave bridge.
These respond to the average of the waveform. The error from
the RMS calibration can be several percent but is much
smaller than for a peak reading meter. Of course, a
true-RMS meter is immune to these errors. Note that both
single diode and bridge type meters are calibrated in the
RMS value of a sine wave which accounts for the error since
they do not really read RMS.
Non-electronic meters such as analogue VOM's are bridge
type which respond to the average but are calibrated as RMS.
--
Richard Knoppow
Los Angeles
WB6KBL
dickburk@ix.netcom.com
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