Field Device Signal Integrity via Controllable Current Source
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing field devices for detecting limit values in process automation face reliability issues due to systematic deviations in current intensity caused by impedance changes over time, leading to unreliable signal transmission, which can result in hazardous conditions in process plants.
Innovation Solution
A field device with a controllable current source that adjusts the sensor signal based on a control signal output, incorporating a resistance element between the current source and the sensor unit to maintain signal integrity, ensuring reliable transmission even with impedance changes, and designed to comply with explosion-proof standards.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a two-wire line with NAMUR protocol is used for signal transmission, then the field device can be supplied with electrical energy and signal transmission is simplified, but systematic deviations in current intensity occur over time due to impedance changes, leading to unreliable signal transmission
Solution Approach 1:
The patent implements a feedback mechanism where the actual current intensity is continuously monitored and compared with a reference value. Based on this comparison, the system automatically adjusts the excitation signal to compensate for impedance changes, ensuring the sensor signal remains within the reliable range (0.2-10 mA) while maintaining NAMUR protocol compliance
Solution Approach 2:
The field device performs self-calibration by using its own sensor signal to detect impedance changes and automatically adjusting its operating parameters. The system monitors its own current intensity and compensates for drift without external intervention, maintaining reliable signal transmission throughout its operational life
2Object-affected harmful factors
If low current intensities (0.4-1 mA) are used for sensor signal transmission, then explosion-proof compliance is achieved, but systematic deviations easily occur and signal reliability deteriorates
Solution Approach 1:
The patent employs dynamic current intensity adjustment where the excitation signal is continuously adapted based on detected impedance changes. The system can vary the current intensity within a wide range (from below 0.2 mA up to 10 mA or more) while maintaining the sensor signal within the safe and reliable range, allowing optimal signal quality without compromising explosion safety
Solution Approach 2:
The system changes the excitation parameter (current intensity) dynamically to compensate for impedance drift. By adjusting the excitation current, the system maintains the sensor signal within the reliable range even when component impedances change over time, ensuring both safety and reliability
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
Ensures reliable signal transmission of limit value information, maintaining accuracy and safety by isolating the signal from impedance changes and adhering to low current intensities required for explosion-proof compliance.
Implementation Method 1
systematic deviations in current intensity caused by impedance changes over time
Implementation Method 2
incorporating a resistance element between the current source and the sensor unit to maintain signal integrity
Data Source
Figure 1
Figure 2
Figure 3
AI summary
The invention relates to a field device for determining a limit value of a physical or chemical process variable, comprising a sensor unit (4) for detecting the limit value and comprising an interface (5). Here, the sensor unit (4) can be connected to a superordinate unit (6) for the purpose of transmitting a current-based sensor signal (sI) via the interface (5). According to the invention, the interface (5) comprises: a signal input (51) having a first and a second signal path (52, 53), a controllable power source (54) which is arranged in the first or second signal path (52, 53), and a resistor element (55, 55') which is arranged in parallel between the power source (54) and the sensor unit (4). The power source (54) is designed in order to control the sensor signal (sI) at the signal input (51) depending on a control signal (sv) which is output by the sensor unit (4). The arrangement according to the invention of the resistor element (55) between the power source (54) and the sensor unit (4) has the effect that, even with the presence of a parasitic impedance (Rshunt) in the sensor unit (4), the signal value (sI) to the superordinate unit (6) is not corrupted.