[Elecraft] Elecraft DMM vs VOM

Thu Mar 27 10:37:00 2003

Thanks Don,

Yeah I guess 22.5V is not good idea for semiconductors. OK on forward
biasing semiconductors, so you have to be careful what/where you are
measuring. I haven't got to the testing parts yet in the manual but when I
do I will use the DVM. Thanks for the explanation. BTW it's great to have
such a wealth of advise on tap. Back to toroid winding!

73's
Martin (M0KWV)

"Don Brown" <[email protected]> on 27/03/2003 15:06:10

To:    <[email protected]>, <[email protected]>
cc:

Subject:    Re: [Elecraft] Elecraft DMM vs VOM

Hi

Many of the older VOM's such as the Simpson and Triplet types had a high
voltage battery in the ohms circuit. If I remember right this wad a 22 1/2
volt battery. They also had 1 D cell battery used for the lower ranges. The
possible high voltage or high current applied to the circuit under test
could damage semiconductors. If your meter only has a 3 volt battery it
will
probably not hurt the circuits. However a DVM uses a different method of
measuring Ohms than a VOM so the readings may be different from the manual.
In fact there has been some confusion in the past with variations in DVM
readings on ohms. Resistance measurements are ballpark only. The problem is
the way the meter reads resistance and how much voltage is applied to the
circuit. Some meters on some ranges will forward bias semiconductors and
some will not giving different readings. I put more faith in the voltage
tests in the manual. They should be very close to the manual.

Don Brown
KD5NDB

----- Original Message -----
From: <[email protected]>
To: <[email protected]>
Sent: Thursday, March 27, 2003 8:05 AM
Subject: [Elecraft] Elecraft DMM vs VOM

> Hi guys. I've just started putting together my K1 and I've seen a couple
of
> refs to using a DMM rather than a VOM for resistance and voltage checks
on
> K1/K2 kits. For the English around here I presume that a VOM is the US
term
> for an analogue moving coil instrument (volt-ohm meter?). Now I know that
a
> DMM has a very high input impedance so that it doesn't load the circuit
and
> therefore is superior to a VOM for accuracy, but what is wrong with a VOM
> for simple checks. The voltage on the test leads is normally very low ( a
> few volts, max of 3V for my little unit) can this damage semiconductor
> devices, I wouldn't have thought so.
>
> I do have a DMM but rather like using my little ICE multiple plug steam
> powered tester for continuity and component value checking. For
continuity
> of joints there is something comforting about seeing a moving coil meter
> swing over to the fat zero!
>
> Any thoughts.
>

Why not take a look at our Web site?
http://www.simoncarves.com

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