Shunt Current Sensor Relay Switching for Noise-Free Resistance Correction
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Solution Overview
Problem
Current sensors face challenges in accurately detecting current due to resistance value changes in shunt resistors over time, which are exacerbated by noise interference, particularly in noisy environments like motors and power converters, leading to decreased accuracy in resistance value correction.
Innovation Solution
A current sensor design incorporating a relay, relay control unit, and resistance value correction circuit, where the relay is turned on during current detection and off during resistance value measurement, allowing for noise-free resistance value correction using a higher-accuracy correction resistor in series with the shunt resistor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If resistance value correction is performed in a noisy environment, then current detection can be maintained, but measurement precision deteriorates due to noise interference
Solution Approach 1:
The patent segments the measurement process into two distinct time periods: a first period for current detection with the relay closed, and a second period for resistance value measurement with the relay open. This temporal segmentation allows the system to perform both functions without interference, as the relay switching isolates the measurement circuit from the noisy current path during correction measurements.
Solution Approach 2:
The relay is switched periodically between closed and open states to alternately enable current detection and resistance measurement modes. This periodic action creates distinct measurement windows where noise interference is minimized during resistance correction, while maintaining continuous current detection capability through the alternating relay states.
2Productivity
If relay is closed during resistance measurement, then current detection is maintained, but measurement precision deteriorates due to noise from current flow
Solution Approach 1:
The patent divides the operational cycle into distinct segments where the relay is closed during current detection and opened during resistance measurement. This segmentation physically isolates the measurement circuit from the current flow path during correction measurements, eliminating noise interference while maintaining continuous detection capability through the alternating states.
Solution Approach 2:
The patent extracts the resistance measurement function from the current detection path by opening the relay during correction measurements. This extraction removes the noisy current flow from the measurement circuit, allowing precise resistance value correction without interference from the load current while maintaining continuous current detection when the relay is closed.
3Measurement precision
If relay is opened during current detection, then resistance measurement accuracy is improved, but current detection capability is lost
Solution Approach 1:
The relay operates periodically, opening during resistance measurement periods to eliminate noise interference and closing during current detection periods to maintain detection capability. This periodic switching ensures that both functions are performed with high accuracy in their respective time windows, with no permanent loss of either capability.
Solution Approach 2:
The system performs preliminary resistance value correction measurements when the relay is open and the circuit is in a known low-noise state. These preliminary corrections are then applied to maintain accurate current detection during normal operation, ensuring that the resistance value is up-to-date without interfering with continuous detection capability.
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
Enhances the accuracy of resistance value correction and current detection by isolating noise interference, ensuring precise resistance value calculations without complicating the sensor's configuration.
Implementation Method 1
A current sensor may detect a detection target current by adopting a terminal voltage of a shunt resistor provided in series with a path through which the detection target current flows
Implementation Method 2
the relay is turned on during current detection and off during resistance value measurement, allowing for noise-free resistance value correction
Data Source
AI summary
A current sensor includes a current detection unit, a relay, a relay control unit, and a resistance value correction circuit. The current detection unit detects a detection target current based on a terminal voltage of a shunt resistor located in series with a path through which the detection target current flows and a detection resistance value for current detection corresponding to a resistance value of the shunt resistor. The relay is located in series with the path through which the detection target current flows. The relay control unit controls the relay to be turned on or off. The resistance value correction circuit calculates the resistance value of the shunt resistor as a calculated resistance value and corrects the detection resistance value based on the calculated resistance value.