Temperature Sensing Circuit Across Isolation Barrier
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Solution Overview
Problem
Existing temperature sensing technologies face challenges in accurately measuring temperature across isolation barriers in industrial applications, such as HVAC systems, due to the need for reliable and efficient methods to determine temperature without direct electrical connection.
Innovation Solution
A temperature sensing system utilizing a thermistor and an isolation circuit that charges and discharges a capacitor, with a control module determining temperature based on the ratio of charging and discharging periods, and utilizing an optocoupler for galvanic isolation, allowing for accurate temperature measurement across the isolation barrier.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thermistor is used to measure temperature across an isolation barrier, then temperature measurement capability is achieved, but direct electrical connection is lost making signal transmission difficult
Solution Approach 1:
The patent introduces a capacitor as an intermediary energy storage element between the thermistor and the control module, separated by an isolation barrier. The capacitor charges and discharges to transmit temperature information across the isolation barrier without requiring direct electrical connection, thus maintaining measurement reliability while enabling galvanic isolation.
Solution Approach 2:
The patent replaces direct electrical signal transmission with optical signal transmission using an optocoupler. The control module converts temperature data into optical signals that can pass through the isolation barrier, eliminating the need for direct electrical connections while maintaining reliable temperature measurement.
2Reliability
If an optocoupler is used for galvanic isolation, then electrical isolation is achieved, but signal transmission efficiency decreases
Solution Approach 1:
The patent employs periodic charging and discharging of the capacitor to transmit temperature information across the isolation barrier. By converting continuous temperature data into periodic charge-discharge cycles, the system maintains signal integrity through the optocoupler while achieving reliable galvanic isolation. The periodic nature of the signal helps preserve information despite the isolation barrier.
3Reliability
If capacitor charge-discharge cycles are used to transmit temperature data, then isolation barrier transmission is achieved, but measurement time increases
Solution Approach 1:
The patent utilizes changes in capacitor voltage parameters during charge-discharge cycles to encode temperature information. By monitoring voltage thresholds and transition times, the system efficiently extracts temperature data from the periodic charge-discharge behavior, minimizing measurement time while maintaining reliable transmission across the isolation barrier.
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
Enables precise temperature measurement of compressor systems, including discharge line temperature, by effectively using a thermistor and isolation circuit to determine resistance and temperature, ensuring reliable operation and fault detection in HVAC systems.
Implementation Method 1
The isolation barrier includes an optocoupler
Implementation Method 2
A thermistor measures a temperature of a compressor system
Data Source
AI summary
An isolated temperature sensing system includes a thermistor that measures a temperature of a compressor system. An isolation circuit charges a capacitor, sets an output signal to a first state during charging of the capacitor, discharges the capacitor to the thermistor, and sets the output signal to a second state during discharging of the capacitor to the thermistor. The first state is different than the second state. A control module receives the output signal via an isolation barrier and determines the temperature of the compressor system based on a ratio of: (i) a first period that the output signal is in the first state to (ii) a second period that the output signal is in the second state.