Transformer Correction Circuit Reduces Cross-Talk Current
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Solution Overview
Problem
Digital multi-meters powered by mains voltage experience undesired current flow due to voltage differences between transformer windings, degrading measurement quality.
Innovation Solution
A transformer with a primary winding, two secondary windings, and a shield between them, along with a correction circuit that generates a correction voltage to drive the shield and reduce cross-talk current between the windings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a transformer with multiple secondary windings is used to power floating circuitry, then the device can perform floating measurements, but voltage differences between windings induce cross-talk current that degrades measurement quality
Solution Approach 1:
A shield is introduced as an intermediary component between the first and second secondary windings. The shield is driven by a correction circuit that generates a correction voltage based on the first voltage, creating an electromagnetic field that cancels the cross-talk field from the first winding, thereby eliminating the harmful coupling while preserving the floating measurement capability
Solution Approach 2:
The correction circuit proactively generates a correction voltage that produces an opposing electromagnetic field before the cross-talk current can fully develop. By driving the shield with this preliminary counteracting field, the system prevents the harmful current induction rather than merely mitigating it after occurrence
2Measurement precision
If shielding is added between transformer windings to reduce cross-talk, then measurement quality improves, but device complexity increases
Solution Approach 1:
The shield serves multiple functions simultaneously: it acts as an electromagnetic barrier to block cross-talk, functions as a driven element that generates correction fields through the correction circuit, and maintains electrical isolation between windings. This multi-functionality reduces the need for additional separate components
Solution Approach 2:
The correction circuit dynamically adjusts the voltage applied to the shield based on the first voltage from the first secondary winding. By changing the electrical parameter (voltage) applied to the shield in real-time, the system adapts to varying operating conditions and optimizes cross-talk cancellation without requiring complex mechanical or structural adjustments
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
The solution effectively reduces cross-talk current between the transformer windings, improving the measurement quality of digital multi-meters by minimizing unwanted current injection.
Implementation Method 1
a correction circuit configured to generate a correction voltage responsive to the first voltage, wherein the correction voltage drives the shield to induce a correction current in the second secondary winding to substantially cancel cross-talk current induced between the first and second secondary windings
Data Source
AI summary
An apparatus and technique that reduces induced cross-talk current between transformer windings. The apparatus includes a transformer having a first secondary winding that provides a first voltage relative to earth ground, a second secondary winding that provides a second voltage relative to floating ground, and a shield disposed between the first and second secondary windings. A correction circuit connected to the first secondary winding is configured to generate a correction voltage. The correction voltage drives a shield to induce a correction current into the second secondary winding to reduce cross-talk current induced between the first and second secondary windings.