LCR Meter
LCR meter is very common measurement equipment in R&D
centers or manufacturing floors. Even some more the more professional DIYer
will have 1 at home, but of course, it will not be as common as the multi-meter
due to the price.
A simple low end LCR meter will be able to measure at fixed
frequencies of maybe 100Hz, 1kHz, 10kHz and 100kHz. This will be good for
sanity check but for real analysis, a precision unit that can do continuous
sweep from 20Hz to 100kHz would be required and it is usually in price range of
USD$2,000 and above.
With continuous sweep, one would be able to measure the
components value at the actual working frequency. It can even measure
transformer impedance and that’s why it’s very effective tool to have to
analyze the various input, output and inter-stage transformers we have in the
market, single ended or push-pull.
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| Different inputs for different measurement range. |
With DC bias option that some of the LCR meters have, it can
even bias the components and transformer at designated operating condition for
more accurate measurement. This is
especially useful for single ended output transformer where it would be gapped
for a certain DC on the primary winding. When DC is injected, the core will be
loaded and the electrical characteristics will change drastically. The data
gathered will be closer to what the real operating condition is.
Common LCR meter will be able to bias the components to
around 30Vdc @ ~200mA maximum, depending on the quality level of the equipment
used. With impedance measurement function on transformer, user will be able to
know how good the transformer is at various frequencies to plot the frequency
response chart.
For capacitor measurement, other than the capacitance, it
can measure the Q factor and the D factor, which are equally important. D – Dissipation
factor, the lower the better. Q – Quality factor, the higher the better. So,
with this data being available, one will know whether the capacitor under test
is really fitting the applications or not, rather than just trusting the
marketing materials.
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| Agilent E4980AL Screen |
As for inductor measurement, with the frequency sweeping
function, one can really know whether the inductor is good for only power
supplies working at the range of 50Hz to 120Hz, or it can be used for anode /
plate load function (plate choke), or even the grid choke function. The
inductance will need to hold steady at higher frequencies for plate or grid
applications. With LCR meter capable of doing so, one can only trust their
ears.
Even for power supply filtering applications, it will be
applicable too. Say one wants to filter a 1MHz noise using inductor and
capacitor. If both the inductor and capacitor have good values at 1MHz measured
with the LCR meter, users will be able to ensure that the filter will be
effective. Without such data, one will never know.
The Agilent E4980AL Precision LCR Meter is one that you can
consider for audio applications.
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| Agilent E4908A LCR Meter |
It can measure from 20 Hz to 300
kHz/500 kHz/1 MHz, with 4-digit resolution in any range. Now that’s really
SOMETHING! Of course, one can go higher end but this unit is more than
sufficient. It sells for around USD$6,000 a unit.
J&K Audio Design
21/12/2013
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