Roy Lewallen wrote in
:

Owen Duffy wrote:

The '259B is no doubt a handy device, but very limited for measuring
components. Have you tried to measure at an inductance that has more
than 250 ohms of reactance at some frequency of interest? Have you
tried to explore self resonance of a coil..., invariably it runs into
the same problem of inductive reactance going off scale way below the
point at which self resonance bites in.

When talking about ferrite or powdered iron cored inductors of
reactance over 200 ohms, where mu is frequency dependent and flux
dependent, I find the '259B nearly useless.


I've had just the opposite experience. I find the 259B to be extremely
useful in determining ferrite types and the impedances of inductors.
Generally a single "turn" (pass through the hole) is adequate for
measurement. For most toroidal inductors the impedance is closely
proportional to the square of the number of turns, so the value of
multi-turn inductors can be extrapolated with reasonable accuracy. Of
course, two or three turns can be used for measurement if the unit
can't resolve the impedance of a single turn.

The frequency dependence of the mu and loss is just why the 259B is so
useful -- I can find the impedance at the frequency or range of
frequencies it'll be used at.

Roy, with respect, you are describing work-arounds for the inability of
the '259B to make useful measurements on inductors over about 200 ohms
reactance.

Sure, the instrument can be used to characterise a core, and that
information extrapolated to design an inductor with higher reactance, but
you cannot measure the larger inductance directly, or discover reliably,
the properties of the larger inductor like self resonance effects, or
loss.

I won't address defensive posts by others who seem to have chosen to
ignore my qualification "When talking about ferrite or powdered iron
cored inductors of reactance over 200 ohms".

An example of the traps: a chap recently confirmed to me that indeed mu
is frequency sensitive as demonstrated by the '259B measurement of the
inductance of an inductor over HF which showed inductance was highly
frequency dependent. The problem was that the inductive reactance was
over 250 ohms at most frequencies of measurement, and the '259B
calculates inductance without warning that the value is unreliable
because of the magnitude of reactance on which the inductance is
calculated. Try measuring a 30uH coil's inductance over 2-30MHz using a
'259B and you will see what I mean.

Owen