Impedance meter

• US 4,409,543 A
• Filed: 03/05/1981
• Issued: 10/11/1983
• Est. Priority Date: 03/11/1980
• Status: Expired due to Term

• Current Assignee: Hewlett-Packard Company (HP Inc.)
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Sugihara, Noriyuki
• Primary Examiner(s): Krawczewicz, Stanley T.
• Assistant Examiner(s): Solis, Jose M.
• Application Number:
  US06/240,719
• Time in Patent Office: 950 Days
• Field of Search: 324/57 R, 324/83 A, 324/83 R, 324/83 Q, 324/130
• US Class Current: 324/650
• CPC Class Codes: G01R 27/02 Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant by measuring phase angle only G01R25/00

Abstract

An apparatus is disclosed for determining the impedance and dissipation factor of a capacitive and/or inductive device and to reduce measurement error by digital calculation and manipulation. A synchronous rectifying means, a phase shifter and a detecting means are employed to detect the in-phase and orthogonal components of the current through a device and to compare it to a reference voltage impressed across the device. An arithmetical calculation using the values of these components determines the impedance and the dissipation factor of the device.

Claims

1. An apparatus for measuring an impedance or a dissipation factor of a device, the apparatus comprising:

a reference oscillator, having an output coupled to the device, for applying a first voltage signal across the device to yield a current;

a converter, coupled at an input to the device, for converting the current to a second voltage signal and for presenting said second voltage signal at an output;

a phase shifter, coupled at an input to the reference oscillator, for selectively shifting the phase of the first voltage signal by either 0 or 90 degrees in response to a control signal and for presenting the 0 degree shifted first voltage signal or the 90 degree shifted first voltage signal at an output;

switch means, having a first input coupled to the output of the reference oscillator and a second input coupled to the output of the converter, for selecting one of a first and a second position in response to a control signal, whereby the first voltage signal is presented at an output when the first position is selected and the second voltage signal is presented at the output when the second position is selected;

synchronous rectifying means, having a first input coupled to the phase shifter output and a second input coupled to the switch means output, for presenting at an output a rectified signal such that said rectified signal represents a phase difference between the shifted first voltage signal and the first voltage signal when the first position is selected and the rectified signal represents a phase difference between the shifted first voltage signal and the second voltage signal when the second position is selected;

control means, coupled to the phase shifter and to the switch means, for presenting control signals to the phase shifter and to the switch means;

detecting means, coupled to the output of the synchronous rectifying means, for detecting the rectified signal and for measuring a phase difference A when the first switch position and the 0 degree shifted first voltage signal are selected, a phase difference B when the first switch position and the 90 degree shifted first voltage signal are selected, a phase difference C when the second switch and the 0 degree shifted first voltage signal are selected, and a phase difference D when the second switch position and the 90 degree shifted first voltage signal are selected; and

,

calculating means, coupled to the detecting means, for calculating B/A, D/C, and D/A and for determining the device impedance or the dissipation factor therefrom.

2. An apparatus as in claim 1, wherein the detecting means comprises a dual-slope voltage ratio meter.

3. A method for measuring an impedance or a dissipation factor of a device, the method comprising the steps of:

generating a first voltage signal;

creating a current by impressing the first voltage signal across the device;

converting the current into a second voltage signal;

creating a 0 degree shifted first voltage signal by phase shifting the first voltage signal 0 degrees;

measuring a phase difference A between the first voltage signal and the 0 degree shifted first voltage signal;

measuring a phase difference C between the second voltage signal and the 0 degree shifted first voltage signal;

creating a 90 degree shifted first voltage signal by phase shifting the first voltage signal 90 degrees;

measuring a phase difference B between the first voltage signal and the 90 degree shifted first voltage signal;

measuring a phase difference D between the second voltage signal and the 90 degree shifted first voltage signal; and

,

calculating B/A, D/C, and D/A, and determining the device impedance or dissipation factor therefrom.

4. A method as in claim 3, wherein the steps of measuring a phase difference are performed with a dual-slope voltage ratio meter.