Optically Isolated Null Detector for Noisy Bridge Measurements
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Solution Overview
Problem
Existing null detection devices face challenges in precision electrical measurements within electrically noisy environments and at points incompatible with electrical test equipment, particularly in achieving high accuracy and stability over wide current and voltage ranges.
Innovation Solution
A null detection device employing a resistive bridge circuit with light-dependent resistors optically illuminated by synchronized optical signals, coupled with a null detector and synchronization circuit for remote operation, allowing for precise measurements with optical isolation from the electrical test equipment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If electrical test equipment is placed directly at the measurement point, then measurement accessibility is improved, but measurement precision deteriorates due to electrical noise and crosstalk
Solution Approach 1:
The patent introduces an optical intermediary (light) to transmit measurement signals between the remote measurement point and the test equipment. Light-dependent resistors convert electrical signals to optical signals, which are then converted back to electrical signals at the receiver, eliminating direct electrical connection and thus reducing crosstalk and electrical noise interference while maintaining measurement accessibility
Solution Approach 2:
The patent replaces the traditional electrical signal transmission system with an optical transmission system. By using light-dependent resistors and optical coupling, the system substitutes electrical fields with optical fields for signal transmission, thereby eliminating electromagnetic interference and improving measurement precision in electrically noisy environments
2Measurement precision
If optical isolation is implemented to reduce crosstalk, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent uses light-dependent resistors as optical intermediaries that provide inherent optical isolation between the measurement point and test equipment. This passive optical coupling mechanism achieves signal transmission with electrical isolation without requiring complex active isolation circuits or multiple conversion stages
Solution Approach 2:
The patent creates an optical copy of the electrical signal through light-dependent resistors. The electrical signal at the measurement point is converted to an optical signal that carries the same information, which is then transmitted to the test equipment. This optical copying process provides natural isolation while maintaining signal fidelity
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 accurate precision electrical measurements in noisy environments and inaccessible points, achieving high accuracy and stability with reduced crosstalk and input bias current, supporting measurements at parts per billion levels.
Implementation Method 1
a first resistor having a first end coupled to the upper signal rail of the input port; a second resistor having a first end coupled to the upper signal rail of the input port; a third resistor having a first end coupled to the other end of the first resistor and a second distal end coupled to the lower signal rail of the input port; a fourth resistor having a first end coupled to the other end of the second resistor and a second distal end coupled to the lower signal rail of the input port... in a first configuration the first resistor and fourth resistor are light dependent resistors which are each optically illuminated with first synchronized optical signals having the same time dependent variation in illumination
Data Source
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AI summary
Within electrical test equipment systems comparator bridges are employed to provide the required dynamic range, accuracy, and flexibility. However, whilst bridge based measurement configurations remove many of the issues associated with making measurements at accuracies of sub-parts, a part, or few parts per million they still require, in many instances, that a null point be determined where the bridge is balanced. However, this becomes increasingly difficult within electrically noisy environments, with modern digital multimeters, and where the desired measurement point within the electrical system is physically difficult to access particularly when improved accuracy in calibration, standards, and measurements on circuits and components means measurement systems must operate at 50 parts per billion (ppb) and below. In order to address this a null detector design is provided supporting operation within such electrically noisy environments with physical separation of the null detector measurement circuit from the electrical test equipment.