NAMUR Sensor Redundancy via Dynamic Impedance Switching
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Solution Overview
Problem
In high-availability automation systems, operating a NAMUR sensor redundantly across multiple digital input modules is challenging due to inconsistent signal states caused by the impressed current, as the measuring resistors are connected in parallel, leading to incorrect voltage drops and signal interpretations.
Innovation Solution
Implementing a configuration where one digital input unit is designated as the master with a low-impedance resistor and the other as a slave with a high-impedance resistor, allowing the sensor current to flow primarily through the low-impedance resistor, ensuring both units detect the same voltage drop and signal state, with each unit capable of generating a switchover signal to maintain redundancy and correct signal evaluation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a NAMUR sensor is connected to multiple digital input modules for redundant operation, then system availability is improved, but signal state consistency deteriorates due to parallel measuring resistors causing incorrect voltage drops
Solution Approach 1:
The patent implements dynamic impedance switching where the measuring resistors can change their resistance values between high and low states based on operational mode. During redundant operation, resistors are switched to high impedance to prevent parallel connection effects, while during single-mode operation, they switch to low impedance for accurate measurement. This dynamic adaptation resolves the contradiction between reliability improvement and measurement precision maintenance.
Solution Approach 2:
The patent changes the electrical parameter (impedance) of the measuring resistors from fixed to variable. By controlling the resistance values of the measuring resistors to be either both low or both high through switching devices, the system can operate in different modes: single-module mode with low impedance for accurate measurement, or redundant mode with high impedance to prevent signal interference. This parameter change enables the system to maintain measurement precision while achieving redundant operation.
2Adaptability or versatility
If measuring resistors are connected in parallel across multiple digital input modules, then redundant operation is enabled, but voltage drop accuracy deteriorates leading to incorrect signal evaluation
Solution Approach 1:
The patent employs dynamic switching of the measuring resistor configuration. Switching devices connected in series with each measuring resistor enable the system to transition between parallel connection mode (for redundancy) and high-impedance mode (for accurate voltage measurement). This dynamic reconfiguration allows the system to achieve both redundant operation capability and voltage drop measurement accuracy at different operational stages.
Solution Approach 2:
The patent introduces switching devices as intermediary elements between the sensor and the measuring resistors. These switching devices act as mediators that control the connection state of the measuring resistors, enabling the system to switch between operational modes. The intermediaries allow the system to achieve redundant operation when needed while maintaining accurate voltage measurement when operating in single mode.
3Quantity of substance
If a single NAMUR sensor is shared between multiple digital input modules, then component quantity is reduced, but signal state inconsistency increases due to current division
Solution Approach 1:
The patent implements dynamic impedance control where all measuring resistors connected to the shared NAMUR sensor are switched to high impedance states during redundant operation. This prevents current division effects and ensures that the sensor current produces a consistent voltage drop that can be accurately evaluated by all connected modules. The dynamic switching maintains signal state consistency while enabling single-sensor multi-module operation.
Solution Approach 2:
The patent changes the resistance parameter of the measuring resistors from low (measurement mode) to high (redundant operation mode) through electronic switching. This parameter change ensures that when a single sensor serves multiple modules, the measuring resistors do not create parallel current paths that would divide the sensor current. Instead, the high impedance state allows the sensor current to flow through a single effective path, maintaining consistent voltage drops and signal states across all modules.
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 configuration allows for accurate redundant detection and evaluation of NAMUR signals without the need for multiple sensors, ensuring continuous availability of the signal status even if one unit fails, by maintaining consistent voltage drops and enabling error detection such as wire breaks or short circuits across both units.
Implementation Method 1
a low-impedance measuring resistor (shunt) of the digital input module, whereby the current impressed by the NAMUR sensor flows through the measuring resistor and causes a voltage drop at this measuring resistor that is proportional to this impressed current
Data Source
Figure 1
AI summary
An arrangement comprising at least two peripheral units (1, 2) and a sensor (7) is proposed, wherein each of the peripheral units (1, 2) is provided with a terminal (5, 6) for connecting the sensor (7) to a supply voltage, with a sensor input (10, 11) for connecting the sensor (7), and further with a measuring resistor (12, 13) for detecting a sensor current representing a signal state. By means of suitable measures, redundant detection and evaluation of the sensor current or redundant operation of the sensor on the at least two peripheral units (1, 2) is enabled.