wrote:

On 12 Jun 2005 16:59:08 -0700, wrote:


To properly use an LCR meter, I believe the following would be
appropriate.

1) Realize the meter measures total impedance and computes inductance
using the impedance figure in the place of reactance. (I read this on a
web page)
2) Measure the inductance and resistance, or capacitance and
resistance.
3) Find the impedance associated with the inductance, using the meter's
test frequency.
4) Recombine the impedance and resistance to find the reactance using
Pythagoras.
5) Once again using the meter's test frequency, find the new inductance
or capacitance associated with the reactance.

Right? Assuming the real component is strictly L-R or R-C.

Doug


Most LCR meters are pretty crude devices and simply indicate
the scalar impedance of the test device. However the dial calibration
is based on the assumption that the test device is a pure lossless L
or C.

IF the loss component of an inductance is pure series R
loss AND you know the value at the test frequency (which may be
considerably higher than the DC value), as you have assumed, the true
value of L can be arrived at by quadrature addition. Based on AC and
DC LCR measurements on an air cored coil this method can give
reasonably accurate results.

However, if the test piece is an iron cored component the
measurement does not take into account the shunt losses (iron eddy
currents, hysteresis etc.) and permeability variation both with
frequency and flux density. These are all second order effects but
mean that the "true" inductance of an iron cored device is a pretty
variable quantity unless the measurement conditions are closely
defined.

Fortunately, with power frequency electric
motors, the low working frequency and the significantly air gapped
iron circuit reduces the effect of these second order components.
However measurement accuracies are likely to be limited to one, or at
best, two significant figures,

Jim
If you want to call RF/AF bridges crude. Just not uP I guess. Some are.
Owner and long time user of low tech to high tech versions.

Martin

--
Martin Eastburn
@ home at Lion's Lair with our computer lionslair at consolidated dot net
NRA LOH, NRA Life
NRA Second Amendment Task Force Charter Founder

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