Posted by
Ron D'Eau Claire-2 on
Jun 24, 2004; 5:17am
URL: http://elecraft.85.s1.nabble.com/K2-resistance-checks-and-K1-KX1-tp368058p368062.html
One of the problems is that when you measure the resistance to ground in a
circuit that contains solid state devices, the value can vary widely because
of the meter you are using. Different makes of DMM's use slightly different
voltages for the ohms sense and that can cause widely varying readings in
the resistance in a "normal" circuit. That's because often the value of
resistance you are seeing is not the value of several resistors, but is
instead a slight forward conduction through junctions of transistors, and
diodes.
Also, that is why it's so important to only use a meter designed for
solid-state gear. Many older "VOMs" use sufficient voltage and allow
sufficient current to destroy solid state devices. But even among the DMMs
designed for solid state circuits, the values reported when "looking"
through junctions in IC's or transistors can vary widely.
Add to that the desire to be sure that when the book says "greater than" (>)
there follows a value that NO DMM is expected to show less than if the
circuit is correct, and sometimes the actual value your DMM reports will be
orders of magnitude larger. For example, your DMM may indicate several
megohms when the book says ">100k ohms"
Ron AC7AC
-----Original Message-----
> Perhaps these questions come from those not familiar with the 'greater
> than' symbol (>) - I can only guess.
Or from people thinking it's "too much" greater than - I did have that
thought the first time I saw > 100 k and measured a few M. I decided it was
ok and carried on...
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