Optically Isolated Null Detector for Remote Bridge Balancing
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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 due to issues like lead resistance insensitivity and physical accessibility limitations.
Innovation Solution
A null detector design employing light-dependent resistors (LDRs) with synchronized optical signals and a resistive bridge circuit configuration that includes optical isolation to minimize crosstalk and input bias current, allowing for remote operation and improved timing information through dual optical chopping.
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 lead resistance
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 optical signals to electrical signals, enabling electrical measurements to be performed remotely without direct electrical contact at the measurement point, thus eliminating lead resistance and electrical noise while maintaining accessibility
Solution Approach 2:
The patent replaces the traditional electrical connection system with an optical system. Instead of using electrical leads and wires to connect the test equipment to the measurement point, the invention uses optical signals transmitted through light-dependent resistors, substituting the mechanical/electrical connection with an optical one to eliminate electrical interference
2Measurement precision
If optical isolation is implemented to reduce electrical noise, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent employs light-dependent resistors that serve multiple functions: they act as optical detectors, signal transducers, and circuit elements simultaneously. This multi-functionality reduces the need for separate isolation components while achieving the required optical isolation and measurement precision
Solution Approach 2:
The invention changes the operating parameters of the light-dependent resistors by using synchronized optical chopping at specific frequencies. This parameter change enables the system to achieve high precision null detection while managing the complexity through frequency-domain separation of signals
3Measurement precision
If light-dependent resistors are used with synchronized optical chopping, then null detection precision is improved to parts per billion levels, but energy consumption increases
Solution Approach 1:
The patent uses periodic optical chopping at synchronized frequencies to modulate the light signals. This periodic action enables precision null detection through frequency-domain analysis while allowing for efficient energy management by concentrating the optical energy at specific time intervals rather than continuous illumination
Solution Approach 2:
The system implements feedback control where the output of the null detector is used to adjust the optical chopping parameters. This feedback mechanism optimizes the energy consumption by adjusting the optical signal strength and chopping frequency to achieve the required precision with minimum energy expenditure
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 precise electrical measurements with improved accuracy and stability, achieving null detection at parts per billion levels even in challenging environments, by isolating the measurement circuit from the electrical test equipment and using optical driving of resistors within the resistive bridge.
Implementation Method 1
light-dependent resistors (LDRs) with synchronized optical signals
Data Source
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.