[Amps] LCR meter

[Carl]

Its been my experience at places Ive worked is that incoming inspection tests L and C at 1kHz using HP equipment.

I suspect that 1 kHz is an industry standard going back to the 1 kc days. What the part does at another frequency is up to the engineer using it to determine. Back in the days of the black arts and slide rules it was called the fudge factor.

Carl
KM1H




  ----- Original Message ----- 
  From: Jack/W6NF 
  To: Carl 
  Cc: Larry Benko ; amps at contesting.com 
  Sent: Tuesday, March 30, 2010 10:21 PM
  Subject: Re: [Amps] LCR meter


  D'OH...of course, I should have thought of that with the inductors.

  However, I am seeing discrepancies on capacitors, as well. For example, a good quality 5kv mica, rescued from a salvaged broadcast transmitter, has measured 2200pf (it's rated value) at 500kHz, about 1900pf at 1MHz and 1700 pf at 1.8MHz. That certainly has me puzzled.

  Let's see if there's a response that rates another D'OH :>)



  On Tue, Mar 30, 2010 at 4:51 PM, Carl <km1h at jeremy.mv.com> wrote:

    It would be interesting to see what a 1kHz instrument would read with that
    same core.

    A 2 mix is a poor performer at 50kHz and you might be reading true
    inductance.

    Also at 30 mHz it only takes a few turns in the typical input network. At 6M
    the 6 mix is the core of choice.

    Carl
    KM1H



    ----- Original Message -----
    From: "Larry Benko" <xxw0qe at comcast.net>
    To: <amps at contesting.com>
    Sent: Tuesday, March 30, 2010 1:30 PM
    Subject: Re: [Amps] LCR meter


    > Here are some real numbers I just measured on a network analyzer
    > calibrated at the plane of the core being measured.
    >
    > Core = T94-2 powdered iron u=10, 22 turns #18 occupying about 80% of core
    >
    > Msmt. freq.     L(measured)
    >
    > 50KHz           3.06uH
    > 100KHz          3.86uH
    > 200KHz          4.53uH
    > 500KHz          4.51uH
    > 1MHz            4.50uH
    > 5MHz            4.50uH
    > 10MHz           4.58uH
    > 20MHz           4.89uH
    > 30MHz           5.52uH
    > 40MHz           6.80uH
    > 68.1MHz         parallel resonant freq.
    >
    > As can be seen frequencies above 10MHz show the beginning effects of the
    > parallel resonance and low measurement frequencies underestimate the
    > inductance by a significant amount.  Also mounting the inductor in a
    > metal box will reduce the inductance. I suspect if the measurement freq.
    > was 1KHz the values would be even lower.  I always measure near the
    > frequency I intend to use the inductor at and if possible with the
    > inductor mounted in the enclosure.  Then calibrating to the inductor
    > plane gives the "real" inductance and filters and matching networks come
    > out as predicted.
    >
    > 73,
    > Larry, W0QE
    >
    >
    >
    >
    > Vic K2VCO wrote:
    >> On 3/30/2010 4:47 AM, Jack/W6NF wrote:
    >>
    >>> I have used an HP LCR meter at work but never paid any attention to the
    >>> frequency at which the measurement is made. I wonder what discrepancies
    >>> in
    >>> measurement values of L and C could be encountered if one measured at
    >>> various RF frequencies, and why they might occur. I have seen such
    >>> discrepancies, using a popular antenna analyzer, even though I was
    >>> careful
    >>> not to introduce sources of error, like lead lengths.
    >>>
    >>
    >> If the coil has a ferrite or iron core of any kind, the inductance varies
    >> a lot with
    >> frequency. Inductors with cores must be measured near the operating
    >> frequency. And in
    >> general, as you raise the frequency the various stray capacitances and
    >> inductances in the
    >> device under test become more significant.
    >>
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  -- 
  Jack, W6NF
  Silver Springs, NV
  DM09ji