Is the Smart Tweezers R-L-C Meter Accurate Enough for Through-Hole Devices?

[chrisych]

Recently, I found a R-L-C Meter called Smart Tweezers R-L-C Meter from the
website of http://www.advancedevices.com/products_tw.htm" .

It is quite similar to the Chinese Chopsticks that can be used to take
measurements from the devices already mounted on a board.

For the through-hole devices, we should desolder one of the legs (two-pin
components) in order to measure the specified value, said R value,
correctly.

However, it can take the measurement directly without any desoldering
process. Is it accurate enough? Any comment?

 

[xez]

If you have a R or L or C component already in a circuit
with other components, there could be any arbitrary
other 'R', 'L', or 'C' components electrically wired in parallel
with that component.

Thus the reading you would get across the two circuit
nodes of one component would measure not only that
component's reactance, but the parallel combination
of that component and whatever else is in parallel with
it.

So it cannot be possible to measure the R, L, or C in
of one such component while it is wired in parallel with
an unknown set of other components.

What is the resistance of a 1 million ohm resistor in parallel
with a 3 ohm resistor in parallel with an
1 ohm resistor? Whatever component you could seek
to measure would not be accurately measurable because
of the presence of the others unless you desoldered
one of the leads to remove the paralleled components
from the device under test.

I would not apply any active impedance probe to a
completed board either because it is possible that the
probe applies voltages to the board that might be of
a polarity and magnitude that would damage circuits on
the board. I guess it'd be safe for most things if
the applied voltage was limited to 0.05V peak, though
if there was resonance even that could lead to high enough
voltages to damage something that wasn't designed to
encounter signal magnitudes of that level.

Proper ESD control is of course always necessary.

 

[edmondng]

actually I've use one of these before. convenient to determine surface mount capacitor value. i wouldn't trust this whole accurately it does work to some extend (you do not need to unsolder etc) but often times you will need to remove 1 leg.

I use this just to give me a rough idea of the capacitor i am measuring but don't rely on it so much, sometimes comes up is weird but often times it is quite close.