[volt-nuts] Checking an LCR meter

[Will]

We have a Wayne Kerr B905 (0.05% basic accuracy), ESI 2150 (0.02%) and
HP 4284A (0.1%) at work. They have the same working principle of
course but are very different from the calibration point of view.

The WK and ESI units have no calibration trimmers inside or user
accessible software constants. The service manuals have no calibration
instructions either, just a few checking procedures to make sure that
there is no fault.

The accurary relies on crystal frequency and stable range resistors.
WK uses Vishay bulk metal foil and ESI their own mica card resistors
(similar to SR1 resistance standards). The lifetime drift of these
resistors is a magnitude lower than the best accuracy of the meter.
Both units were manufactured in the early 80's and are still within
the specs. No repairs or adjustments ever made. They are regularly
checked against a set of 3 terminal bulk metal foil resistors
(calibrated with a 3458A) and a GR 1404A nitrogen filled standard
capacitor (which visits the national lab).

There is a huge different with our HP 4284A (and other HP Yokogawa
impedance line products as far as I know) which needs to be adjusted
in yearly basis. Could be the 1 MHz frequency range which requires a
number of trimmers and more complex circuitry but also seems to ruin
the stablity.

We also use the ESI 2150 to get a traceable inductance calibration
based on traceable resistance and capacitance (and frequency). The ESI
2150 inductance specifications (after the checking procedures for
capacitance and resistance) are similar to the best uncertainty
available from the high level labs.


2015-02-07 0:10 UTC+02.00, Dr. David Kirkby (Kirkby Microwave Ltd)
<drkirkby at kirkbymicrowave.co.uk>:
> I have bought an HP 4284A precision LCR meter. This is an old model with a
> basic accuracy of 0.05% and covers 20 Hz to 1 MHz.
>
> Converting the specifications into determining the uncertainty of a
> measurement is nontrivial, but I think it reasonable to assume the
> uncertainty will always be >0.05%.
>
> Surprisingly the current precision LCR meter from Kesight, the E4980A (20
> Hz to 2 MHz) offers the same basic accuracy. So while fairly old, the 4284A
> doesn't seem to be miles behind the current crop  LCR meters from the top
> manufacturers.
>
> The recommended calibration period on the 4284A is 6 months, which would
> get rather expensive - on the current E4980A the calibration period is a
> more respectable 12 months.
>
> I am looking for suggestions on how I can get "reasonable" confidence in
> the instrument at "reasonable" cost, without returning it to Keysight every
> 6 months.
>
> I have a 3457A DVM, but mot much else in the way of precision low frequency
> equipment.
>
> It has 4 BNC connectors for Kelvin probes.
>
> I suspect that getting precision resistors and keeping them for a house
> standard might be worthwhile,  but are looking for suggestions on the best
> approach.
>
> I will send it to Keysight once when it arrives to ensure that there are no
> faults on it, but I don't currently feel I can justify getting it
> calibrated every 6 months.
>
> Maybe I can make some stable "standards", then measure them soon after the
> LCR meter calibrated been calibrated and periodically measure their values.
> Any suggestions about how to approach that?
>
> Dave
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