Bridge Heater Temperature Control for High-Accuracy Sensor Heating
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Solution Overview
Problem
Conventional temperature control devices for heaters suffer from temperature accuracy issues due to resistor tolerance and temperature coefficient errors, leading to deviations in maintaining a constant heater temperature, which affects sensor sensitivity and variability.
Innovation Solution
A heater temperature control circuit with a bridge circuit configuration that includes a first circuit with a heater and a resistor in series, connected in parallel with a second circuit containing a D/A converter or multiplexer, where the output from the second circuit is input to an operational amplifier, allowing for precise control of the heater temperature by adjusting the division ratio of the target resistance value with a reference voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a conventional Wheatstone bridge with multiple resistors is used for heater temperature control, then the circuit can operate with automatic negative feedback, but temperature accuracy deteriorates due to resistor tolerance and temperature coefficient errors
Solution Approach 1:
The patent extracts and eliminates the problematic resistors R2 and R3 from the conventional Wheatstone bridge circuit. By removing these resistors that introduce tolerance and TCR errors, the circuit achieves higher temperature accuracy while maintaining automatic negative feedback operation through the remaining resistor R1 and heater resistance Rh
Solution Approach 2:
The patent changes the circuit configuration from a conventional four-resistor Wheatstone bridge to a modified bridge with only one resistor R1. This parameter change in circuit topology eliminates the accumulation of resistor errors and achieves the dual goal of maintaining automatic feedback operation while improving temperature measurement precision
2Measurement precision
If high accuracy resistors are used to improve temperature control precision, then temperature accuracy improves, but device complexity and cost increase
Solution Approach 1:
The patent removes two resistors from the circuit, reducing the total resistor count from four to one. This extraction simplifies the device while simultaneously improving temperature accuracy by eliminating the error sources associated with the removed resistors
Solution Approach 2:
Instead of improving temperature accuracy by using higher precision resistors (adding complexity), the patent inverts the approach by reducing the number of resistors. This inversion achieves the same accuracy improvement goal while reducing device complexity
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 configuration significantly improves temperature accuracy, enabling flexible and precise adjustment of the heater temperature, reducing errors to ±1°C or lower, and enhancing sensor sensitivity compared to conventional methods.
Implementation Method 1
an operational amplifier, and an output portion of the D/A converter or the multiplexer is connected to a non-inverting input terminal (Vin+ terminal) 12b of the operational amplifier 12
Implementation Method 2
a heater that applies heat to the sensor element
Data Source
AI summary
The present invention provides a heater temperature control circuit including a heater and a control circuit that controls a temperature of the heater, wherein the control circuit includes a bridge circuit in which a first circuit and a second circuit are connected in parallel, and an operational amplifier connected to the bridge circuit, wherein in the first circuit, the heater and a resistor are connected in series, and a midpoint of the first circuit is connected to one input portion of the operational amplifier, and an output value Vout from the second circuit is input to the other input portion of the operational amplifier, the output value Vout being obtained by multiplying a division ratio of a target resistance value Rh of the heater and a resistance value R1 of the resistor with a reference voltage Vref of the bridge circuit.