Common Mode Current Calibration in Test Measurement Devices

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Solution Overview

Problem

Test and measurement systems face challenges in accurately measuring electrical properties due to common mode currents caused by common impedance coupling, which can lead to inaccurate results, especially at high frequencies.

Innovation Solution

A mechanism is introduced to generate a nulling current using a transformer, resistive network, or switch network to cancel out common mode currents by applying the nulling current to a capacitive element, ensuring accurate measurement by minimizing interference from common mode noise.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If electrical isolation is used to mitigate unwanted signal noise, then measurement accuracy is improved, but common mode currents still couple through common impedance causing measurement errors

Engineering Contradiction:

Improvemeasurement accuracyVSAvoidcommon mode current interference

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent applies preliminary anti-action by generating a nulling current that is equal in magnitude but opposite in phase to the common mode current. This nulling current is injected into the measurement path before the common mode current can corrupt the measurement, effectively preemptively canceling out the interference. The system detects the common mode current and generates the opposing current in real-time, ensuring measurement accuracy despite the presence of common impedance coupling.

Inventive Principle:

Principle #9Preliminary anti-action

2Productivity

If test and measurement systems operate at high frequency, then productivity is improved, but signal noise is generated that enters the DUT causing inaccurate test results

Engineering Contradiction:

Improvetesting speedVSAvoidsignal noise

Core Design Contradiction:

ProductivityVSObject-generated harmful factors

Solution Approach 1:

The patent converts the harmful high-frequency signal noise generated by the test system into a beneficial effect by using the same noise sources to generate the nulling current. The system captures the common mode noise that would otherwise corrupt measurements and transforms it into a corrective signal. By injecting this transformed noise as a nulling current, the system cancels out the harmful effects, allowing high-frequency operation without sacrificing measurement accuracy.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This approach effectively cancels common mode currents, enhancing the accuracy of measurements in test and measurement systems by isolating unwanted noise, thereby providing reliable data even at high bandwidths.

Implementation Method 1

A mechanism is introduced to generate a nulling current using a transformer

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Implementation Method 2

applying the nulling current to a capacitive element

Methodology Applied

Scientific EffectCapacitance: Capacitance

Data Source

PatentUS10514434B2Calibration for common mode current

Publication Date: 2019.12.24 KEITHLEY INSTRUMENTS LLC

AI summary

A mechanism is disclosed for mitigating common mode current in a test and measurement device. A measurement current can be received from a device under test via a measurement lead that couples a transformer in the test and measurement device with the device under test. The test and measurement device can then be calibrated to apply a nulling current to cancel the common mode current from the measurement current. Other embodiments can be described and/or claimed herein.