Two-Wire Current Signal Transmission Noise Immunity
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Solution Overview
Problem
Existing methods for transmitting discrete electrical signals over two-wire communication lines suffer from low noise immunity and high costs due to the need for independent power supplies and galvanic decoupling, which can lead to signal distortion and equipment failure.
Innovation Solution
The method employs two current sensors, one for each wire, to measure the absolute values of currents and compensate for noise by deducing the difference in readings, ensuring identical resistance conditions for both wires and reducing noise interference, thereby enhancing signal clarity and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If voltage-based signal transmission is used (RS 232 interface), then the communication method is simple to implement, but noise immunity is low and communication distance is limited to 10m
Solution Approach 1:
The patent changes the fundamental parameter of signal transmission from voltage-based to current-based. By measuring current instead of voltage, the system achieves better noise immunity because current measurements are less susceptible to electromagnetic interference and ground potential differences, while maintaining implementation simplicity through the use of straightforward current sensing circuits.
Solution Approach 2:
The patent substitutes the electrical voltage measurement system with a current measurement system. This replacement fundamentally changes how signals are detected, moving from voltage potential differences to current flow measurements, which inherently provides better noise rejection characteristics without complicating the overall system architecture.
2Reliability
If independent bipolar power supplies are provided for each device (RS 485 interface), then communication distance extends to 1000m and noise immunity improves, but device cost substantially increases
Solution Approach 1:
The patent merges the power supply function into the communication line itself, allowing a single centralized power source to supply multiple devices through the same two-wire communication medium. This eliminates the need for each device to have its own independent power supply, reducing cost and complexity while maintaining reliable communication through current-based signaling.
Solution Approach 2:
The communication line serves multiple functions simultaneously: it transmits data signals and provides power delivery to connected devices. This multi-functionality eliminates the need for separate power supply circuits at each device, reducing overall system cost and complexity while maintaining robust noise immunity through current-based measurement.
3Reliability
If galvanic decoupling is employed to prevent ground potential mismatch, then device reliability is maintained, but information transmission cost increases substantially
Solution Approach 1:
The patent substitutes voltage-based signaling with current-based signaling, which inherently eliminates ground potential mismatch problems. Since current measurements are reference-independent and do not rely on a common ground, galvanic decoupling components become unnecessary, reducing system cost and complexity while maintaining reliability.
Solution Approach 2:
The patent extracts and eliminates the ground reference requirement from the communication system. By using current measurements instead of voltage measurements, the system no longer needs a common ground connection, thereby removing the need for galvanic decoupling components and associated costs.
4Device complexity
If two-wire current-based transmission is used, then device interconnection is simplified and power supply cost is reduced, but noise immunity deteriorates due to different noise propagation conditions in grounded and non-grounded wires
Solution Approach 1:
The patent introduces asymmetric resistance values in the two wires to compensate for their different noise propagation characteristics. By deliberately creating unequal resistance values that match the noise propagation differences, the system balances the total voltage drops and eliminates noise-induced voltage differences, maintaining noise immunity while using a simple two-wire current-based system.
Solution Approach 2:
The patent changes the resistance parameters of the two wires to compensate for their different electromagnetic coupling characteristics. By adjusting the resistance values to be unequal, the system creates equal total voltage drops in both wires under noise conditions, thereby eliminating differential noise voltages and maintaining high noise immunity.
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 approach significantly reduces noise interference, allowing for longer communication distances and increased reliability while reducing the overall cost of information transmission by minimizing the impact of noise voltage and current.
Implementation Method 1
transmission of a logic signal in binary code by the transmitter closing the line with the aid of an electrical switch and the receiver reading the voltage value in the wire relative to ground
Data Source
AI summary
The present invention relates to methods for transmitting information, and in particular to communication interfaces of electronic devices. The method makes it possible to increase the distance and reliability of communication by raising noise immunity owing to compensation of the noise signal, in the course of both propagation and reading of the signal in both wires of communication line. A receiver is connected to a two-wire communication line between a transmitter and a voltage supply source, and is equipped with two current sensors. The reading signal is determined as a sum of absolute values of measured currents (difference of values of measured currents, with the sign taken into account).