Current Loop Signal Transmission with Analog-Digital Superposition
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Solution Overview
Problem
Current signal transmission methods in process automation, particularly in potentially explosive areas, face challenges with galvanic isolation increasing circuit complexity and obstructing diagnostic information, while existing solutions for digital communication over two-wire current loops are cumbersome and costly due to the need for multiple lines across isolated areas.
Innovation Solution
A method where a control unit generates a data stream by digitally encrypting direct and alternating current signals, which are then converted into a current signal for transmission over a single line, simplifying the signal transmission and reducing hardware requirements by eliminating the need for multiple lines across galvanically isolated areas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If galvanic isolation is implemented to ensure operational safety in potentially explosive areas, then operational safety is improved, but circuit complexity increases and diagnostic information transmission is obstructed
Solution Approach 1:
The patent combines multiple signal types (analog process variable signal and digital diagnostic signal) into a single current loop transmission channel. By encoding both signal types within the same physical medium using frequency division multiplexing, the invention eliminates the need for separate transmission lines across the galvanic barrier, thereby reducing circuit complexity while maintaining operational safety through galvanic isolation.
Solution Approach 2:
The current loop is designed to serve multiple functions simultaneously: it transmits both the analog process variable signal and the digital diagnostic signal through the same galvanically isolated barrier. This multi-functional approach allows a single transmission channel to handle both control and diagnostic tasks, reducing the overall number of components and simplifying the circuit architecture.
2Loss of information
If multiple lines are used to transmit digital communication signals across galvanically isolated areas, then diagnostic information transmission is improved, but hardware complexity and cost increase
Solution Approach 1:
The invention merges the transmission of analog process variable signals and digital diagnostic signals into a single current loop channel. By using frequency division multiplexing, both signal types share the same physical transmission medium, eliminating the need for multiple separate lines across the galvanic barrier and thereby reducing hardware complexity while maintaining complete diagnostic information transmission.
Solution Approach 2:
The patent resolves the limitation of single-channel transmission by introducing a frequency dimension. Instead of using multiple spatial channels (multiple wires), the invention separates signals in the frequency domain, allowing analog and digital signals to coexist on the same current loop without interference, thus transmitting complete diagnostic information through a single line.
Data Source
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AI summary
The invention relates to a method for signal transmission between a first and a second system (S1, S2) that are interconnected by means of a current loop (L). A direct current signal is transmitted in a first frequency range (AB) and an alternating current signal in a second frequency range (DB) via the current loop (L). The direct current signal and the alternating current signal are superimposed, the alternating current signal being used for digital signal transmission and the direct current signal being used for analog signal transmission. A control unit (CPU) produces a first data flow (U1) in which the direct current signal and the alternating current signal to be adjusted in the control loop (L) are digitally encoded, the first data flow (U1) being transmitted to a current output circuit (S), and the transmitted first data flow (U1) being converted into a current signal by the current output circuit (S), the current signal consisting of the superimposed direct current signal and alternating current signal, or the current output circuit (S) converts the transmitted first data flow (U1) into the direct current signal and the alternating current signal. The current signal or the direct current signal and alternating current signal are adjusted in the current loop (L).