Thermistor Temperature Sensing Circuit With RC Noise Termination
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Solution Overview
Problem
Self-heating of thermistors due to impedance mismatch and normal mode noise generation during EMC testing leads to erroneous temperature measurements in in-vehicle ECUs.
Innovation Solution
Implementing RC termination circuits between conductor lines and a body ground to match characteristic impedances, using resistors and capacitors to attenuate noise and prevent self-heating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If chip beads are provided to reduce impedance difference and suppress noise intrusion, then noise suppression is improved, but self-heating of thermistor element occurs due to reflected noise
Solution Approach 1:
The patent introduces an RC termination circuit as an intermediary component connected between the wire harness and the thermistor. This circuit includes a resistor (R1) and a capacitor (C1) that work together to match impedance and suppress reflected noise without causing self-heating of the thermistor element, thereby resolving the contradiction between noise suppression and temperature stability.
Solution Approach 2:
The patent changes the impedance parameters by introducing the RC termination circuit with specific resistance and capacitance values. This modifies the characteristic impedance of the circuit to match the wire harness and thermistor interface, suppressing noise reflection while preventing the thermistor from self-heating, thus resolving the technical contradiction.
2Measurement precision
If impedance matching is improved to suppress normal mode noise, then temperature measurement accuracy is improved, but device complexity increases due to additional RC termination circuit
Solution Approach 1:
The RC termination circuit serves as a simple intermediary component that provides impedance matching functionality. By using a series combination of resistor and capacitor, it achieves noise suppression and measurement accuracy improvement without requiring complex active control circuits, thus limiting the increase in device complexity.
Solution Approach 2:
The patent uses passive RC termination components (resistor and capacitor) that are inexpensive and simple in structure. These components provide effective impedance matching and noise suppression without adding significant complexity to the overall system, making the solution practical for vehicle ECU applications.
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
Suppresses self-heating of thermistors, maintaining accurate temperature measurements by converting high-frequency noise into thermal energy and ensuring DC insulation.
Implementation Method 1
the resistor (R1) and the capacitor (C1) connected in series between the frame ground and at least one of the positive wire (WHp) or the negative wire (WHn)... converting high-frequency noise into thermal energy
Implementation Method 2
a capacitor (C1) connected in series between the frame ground and at least one of the positive wire (WHp) or the negative wire (WHn)... ensuring DC insulation
Implementation Method 3
a thermosensitive element (Rt) of which resistance value changes in accordance with a temperature
Data Source
Figure 1~2
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AI summary
In the temperature detection system, the resistance value of the thermosensitive element changes in accordance with temperature. The temperature detection circuit is disposed on the substrate in a state of being insulated from the frame ground. The positive wire connects the positive terminal of the thermosensitive element and the positive terminal of the temperature detection circuit. The negative wire connects a negative terminal of the thermosensitive element and a negative terminal of the temperature detection circuit. A resistor and a capacitor connected in series are connected between at least one of the positive wire and the negative wire and the frame ground.