Dual Thermistor Temperature Circuit for Wide Range Accuracy
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Solution Overview
Problem
Existing temperature detecting circuits for high-pressure hydrogen tanks in fuel cell vehicles face challenges in accurately controlling temperature fluctuations from low to high, as they either deteriorate accuracy on one side of the temperature range while improving it on the other, limiting the effective temperature detection range and requiring larger installations.
Innovation Solution
A temperature detecting circuit utilizing two thermistors with specific resistance relationships and pull-up resistors, where the controller switches between them based on a threshold temperature, ensuring improved accuracy across a wide temperature range from -50°C to 90°C, and incorporating a failure sensor for enhanced reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single thermistor is used for temperature detection, then the device complexity is reduced, but the measurement precision deteriorates over a wide temperature range
Solution Approach 1:
The temperature detection function is segmented into two independent thermistor-based detection circuits, each optimized for a specific temperature range. The first thermistor (T1) with pull-up resistor (R1) handles lower temperatures, while the second thermistor (T2) with pull-up resistor (R2) handles higher temperatures. This segmentation allows each component to operate within its optimal performance range, improving overall measurement precision without requiring a single complex device.
Solution Approach 2:
The system dynamically switches between the first and second thermistor detection circuits based on the detected temperature range. The controller compares the temperature detected by T1 against a reference temperature and switches to T2 when the temperature exceeds the reference. This dynamic switching enables the system to maintain high measurement precision across a wide temperature range while using relatively simple individual components.
2Measurement precision
If two thermistors with different B constants are connected in parallel, then the measurement precision is improved over a wide temperature range, but the device complexity increases
Solution Approach 1:
Instead of connecting thermistors in parallel, the invention segments the temperature detection function into two separate series circuits. Each circuit consists of a thermistor and its own pull-up resistor, with the controller selectively reading from one circuit based on temperature range. This segmentation achieves wide-temperature-range precision while keeping each individual circuit simple and independent.
Solution Approach 2:
The system employs dynamic switching to select which thermistor circuit to read from based on the current temperature range. The controller monitors the temperature detected by the first thermistor and switches to the second thermistor when the temperature exceeds a reference threshold. This dynamic selection allows the system to achieve high measurement precision across wide temperature ranges without requiring both thermistors to be simultaneously active, thereby reducing overall device complexity.
3Adaptability or versatility
If the temperature detection range is extended from -50°C to 90°C, then the adaptability is improved, but the measurement precision deteriorates at the extremes of the range
Solution Approach 1:
The temperature detection range is segmented into two overlapping ranges, with the first thermistor optimized for lower temperatures and the second thermistor optimized for higher temperatures. Both thermistors are calibrated with specific B constants suitable for their respective temperature ranges. This segmentation enables the system to maintain high measurement precision across the extended range of -50°C to 90°C by ensuring that each thermistor operates within its optimal performance characteristics.
Solution Approach 2:
The system changes the detection parameters by switching between different thermistors with different B constants based on the temperature range. The first thermistor uses a B constant optimized for lower temperature detection, while the second thermistor uses a B constant optimized for higher temperature detection. This parameter change allows the system to maintain measurement precision across extended temperature ranges by selecting the appropriate detection parameters for the current operating conditions.
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 provides high-accuracy temperature detection across a wide range with a compact structure, eliminating installation difficulties and spatial restrictions, while effectively managing temperature fluctuations and detecting potential failures in the thermistors.
Implementation Method 1
A thermistor disclosed in Japanese Unexamined Patent Application Publication No. 5-34208 exists as this type of technique. This thermistor is of a negative temperature coefficient (NTC) type whose resistance decreases with an increase in detected temperature.
Implementation Method 2
This thermistor is of a negative temperature coefficient (NTC) type whose resistance decreases with an increase in detected temperature.
Implementation Method 3
there is a thermistor with an embedded pull-up resistor disclosed in Japanese Patent No. 3365013. In this type of thermistor, a thermistor and a pull-up resistor are arranged side by side on the same substrate. In this configuration, by making the resistance of the pull-up resistor variable in accordance with detected temperature, it is possible to detect temperature with high accuracy over a wide temperature range.
Data Source
AI summary
A temperature detecting circuit includes a first thermistor, a second thermistor, a first pull-up resistor, a second pull-up resistor, and a controller. The controller is configured to sense a temperature based on a voltage signal from the first thermistor if a temperature corresponding to a voltage signal from one of the first thermistor and the second thermistor is below a threshold temperature. The controller is configured to sense a temperature based on a voltage signal from the second thermistor if a temperature corresponding to a voltage signal from one of the first thermistor and the second thermistor is higher than or equal to the threshold temperature. A resistance Ra of the first thermistor, a resistance Rb of the second thermistor, a resistance Rc of the first pull-up resistor, and a resistance Rd of the second pull-up resistor have a relationship expressed by Ra<Rb and Rc>Rd.