Relay Contact Resistance Current Sensing
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Solution Overview
Problem
Conventional energy monitoring devices require bulky current shunts to measure load current, leading to additional costs and inefficiencies due to heat dissipation, which complicates the measurement of current and reduces accuracy.
Innovation Solution
An energy monitoring device that uses the relay contact resistance of a relay to determine load current without the need for a current shunt, employing a power supply circuit, a relay circuit with multiple coils, a sensing circuit with a differential voltage amplifier, and a controller with an analog-to-digital converter to calculate load current based on the delta between hot and load voltages and relay contact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a current shunt is added to measure load current, then current measurement capability is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The relay contact serves dual purposes: it functions as both a switching component and a current sensing element. By measuring the voltage drop across the relay contact resistance, the system obtains current measurement capability without adding a dedicated shunt resistor, thus achieving multi-functionality and reducing device complexity
Solution Approach 2:
The relay contact's inherent resistance, which would normally be a source of power loss, is utilized as the sensing element for current measurement. The system 'services itself' by using the relay contact's own electrical property (resistance) to provide the measurement function, eliminating the need for external sensing components
2Measurement precision
If a current shunt is added to measure load current, then current measurement capability is improved, but manufacturing cost increases
Solution Approach 1:
The relay contact serves dual purposes: it functions as both a switching component and a current sensing element. By measuring the voltage drop across the relay contact resistance, the system obtains current measurement capability without adding a dedicated shunt resistor, thus achieving multi-functionality and reducing device complexity
Solution Approach 2:
The relay contact's inherent resistance, which would normally be a source of power loss, is utilized as the sensing element for current measurement. The system 'services itself' by using the relay contact's own electrical property (resistance) to provide the measurement function, eliminating the need for external sensing components
3Measurement precision
If a current shunt is added to measure load current, then current measurement capability is improved, but heat dissipation increases reducing efficiency
Solution Approach 1:
The relay contact's inherent resistance, which would normally be a source of power loss, is utilized as the sensing element for current measurement. The system 'services itself' by using the relay contact's own electrical property (resistance) to provide the measurement function, eliminating the need for external sensing components
Solution Approach 2:
The system measures current by detecting the voltage drop across the relay contact resistance rather than forcing current through a separate shunt resistor. This parameter-based measurement approach (measuring voltage drop across existing resistance) eliminates the need for additional resistive elements that would generate heat, thereby reducing energy loss
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 reduces manufacturing costs and prevents unnecessary heating, providing an efficient and accurate energy monitoring mechanism for relay-based devices without the need for additional current shunts, enhancing the monitoring of energy consumption in home or office environments.
Implementation Method 1
determine a load current based at least in part on a relay contact resistance of the relay contact and a delta between the load voltage and the hot voltage
Implementation Method 2
a sensing circuit including a differential voltage amplifier circuit, wherein the differential voltage amplifier circuit comprises a differential operational amplifier (OPAMP)
Data Source
AI summary
An energy monitoring device includes a power supply circuit electrically coupled to a power source via a hot conductor and a load via a load conductor; a relay circuit including a relay and a relay driver circuit, where the relay includes a plurality of coils and the relay contact electrically coupled to the hot conductor and the load conductor; a sensing circuit including a hot voltage sensor and a load voltage sensor; and a controller electrically coupled to the power supply circuit, the relay driver circuit, and the sensing circuit, and structured to receive a hot voltage from the hot voltage sensor and a load voltage from the load voltage sensor, and determine a load current based at least in part on a relay contact resistance of the relay contact and a delta between the hot voltage and the load voltage.