Energy Metering Circuit with Changeover Switch for Dual Measurement
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Solution Overview
Problem
Existing measuring circuits for energy metering are limited in their ability to accurately measure both currents and voltages without additional power from the grid, often requiring complex configurations and multiple components, which can lead to inaccuracies and increased power dissipation.
Innovation Solution
A configurable measuring circuit with a changeover switch and low-pass filter allows direct connection of input terminals to a measuring resistor, enabling both current and voltage measurements without additional grid power, using MOSFET switches to minimize voltage drops and reduce component count, and incorporating a surge protection circuit to manage high-frequency interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a measuring circuit uses multiple switches and components to enable both current and voltage measurements, then the versatility and adaptability of the circuit is improved, but the device complexity and component count increase
Solution Approach 1:
The measuring circuit is designed with a single switch that can operate in multiple modes: connecting the measuring resistor in series for current measurement, and connecting the measuring resistor in parallel for voltage measurement. This multi-functional design allows the same circuit components to perform different measurement functions without requiring separate dedicated circuits for each measurement type, thereby reducing overall device complexity while maintaining versatility
Solution Approach 2:
The circuit employs a dynamically switchable configuration where a single switch changes the circuit topology based on measurement requirements. The switch can connect the measuring resistor in different positions (series or parallel) depending on whether current or voltage measurement is needed, allowing the circuit to adapt its structure dynamically rather than requiring fixed separate circuits for each measurement mode
2Measurement precision
If a switch is placed in series with the measuring resistor for current measurement, then the current measurement function is achieved, but voltage drops across the switch and resistor cause power loss and measurement inaccuracies
Solution Approach 1:
The circuit uses periodic switching where the switch is closed only during the specific time interval when current measurement is required, and open otherwise. This periodic action minimizes the time during which voltage drops and power losses occur across the switch and measuring resistor, thereby reducing overall energy loss while maintaining measurement precision when the measurement is actually being performed
Solution Approach 2:
The measuring resistor serves as an intermediary element that converts current into a measurable voltage signal. By using a precision measuring resistor with known low resistance value, the circuit achieves accurate current measurement through voltage measurement across the resistor, while the controlled switching minimizes power dissipation in this intermediary element
3Use of energy by moving object
If the measuring circuit operates without additional power from the grid, then energy independence is improved, but the ability to power active components like switches and filters is limited
Solution Approach 1:
The measuring circuit is designed to be self-powered by utilizing the energy from the measurement signal itself. The circuit draws minimal operating power from the voltage present at the measurement terminals, eliminating the need for external power supplies or batteries. This self-service approach ensures energy independence while maintaining operational reliability through passive component design and ultra-low power consumption switching mechanisms
4Measurement precision
If high-frequency interference signals are filtered out using a low-pass filter, then measurement accuracy is improved, but additional components and circuit complexity increase
Solution Approach 1:
The low-pass filter function is merged with the existing measuring resistor and switch components rather than being implemented as a separate dedicated filter circuit. The measuring resistor itself provides inherent filtering characteristics, and the switching action naturally attenuates high-frequency signals. This merging approach achieves signal filtering and measurement functionality using the same components, thereby improving measurement precision without increasing device complexity or adding separate filter circuits
Data Source
AI summary
A measuring circuit for determining the magnitude of a current flowing through a conductor, the measuring circuit having an input terminal pair that can be connected to the current transformer with a first switch, which connects a measuring resistor between the input terminals in a current measuring position, and which, in a voltage measuring position, separates the measuring resistor from at least one of the input terminals, and having an output terminal pair, at which, alternatively, a voltage-dependent measuring voltage present at the input terminal pair or a current-dependent measuring voltage present at a first measuring point of the measuring resistor can be tapped. The measuring circuit includes a changeover switch which can be switched synchronously with the switch. The changeover switch is used to connect an output terminal to the first measuring point in the current measuring position, and to the second measuring point in the voltage measuring position.