Dynamic Power Control for Two-Wire Process Instruments
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Industrial process instruments operating on a two-wire control loop with varying current (4-20 mA) often waste power due to fixed shunt resistor designs, limiting functionality and efficiency, especially in remote locations where failure could halt operations.
Innovation Solution
Incorporating a secondary control circuit that selectively utilizes excess power from the two-wire interface to enable additional functionality, such as adjustable LED backlighting and increased processor speed, by routing current to a secondary load independent of the primary power control loop, maintaining existing shunt resistor designs and avoiding intrinsic safety issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a shunt resistor is used to control current in a two-wire process instrument, then the device can operate at minimum current (3.5 mA), but excess power (16.5 mA or more) is wasted in the shunt resistor
Solution Approach 1:
The patent segments the current control function by separating the primary current control (through shunt resistor) from the secondary power utilization (through additional control circuitry). This allows the instrument to maintain reliability at minimum current while capturing and utilizing excess power for additional functions such as LED backlighting, display drivers, and communication interfaces.
Solution Approach 2:
The patent changes the operational parameters by enabling the instrument to dynamically adjust its power consumption based on available current. The additional control circuitry monitors the current level and selectively activates secondary functions when excess power is available, transforming the fixed-parameter shunt resistor design into a variable-parameter system that optimizes power usage.
2Illumination intensity
If LED backlighting is provided by replacing the shunt resistor, then backlighting is achieved, but the intensity cannot be controlled and may be overly bright at 20 mA
Solution Approach 1:
The patent applies dynamics by making the LED backlighting intensity adjustable rather than fixed. The additional control circuitry dynamically regulates the current flowing to the LED based on the available power and user requirements, allowing the backlight intensity to adapt to different operating conditions and user preferences.
Solution Approach 2:
The patent implements feedback control for the LED backlighting system. The additional control circuitry monitors the current level and provides feedback to regulate the LED current, ensuring that the backlight intensity is appropriate for the available power and preventing excessive brightness at 20 mA while maintaining adequate illumination at lower currents.
3Adaptability or versatility
If additional functionality is enabled by utilizing excess current, then device capabilities are enhanced, but power consumption increases
Solution Approach 1:
The patent applies partial action by selectively enabling additional functionality based on the available excess current. Rather than always consuming maximum power, the instrument activates secondary functions (LED backlighting, display drivers, communication interfaces) only when sufficient power is available, allowing enhanced capabilities without permanently increasing power consumption.
Solution Approach 2:
The patent achieves multi-functionality by designing a universal control architecture that can support multiple functions using the same two-wire interface. The additional control circuitry can selectively activate different secondary functions (backlighting, displays, communication) depending on available power and operational needs, making the instrument adaptable to various applications without requiring separate power supplies.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A process instrument includes a transducer (12), a two wire interface (34a, 34b), a microprocessor (20), a digital to analog converter (22), a first control circuit (23a, 23b, 23c, 23d, 23e, 24, 26, 28, 30, 32), and a second control circuit (38). A current (IL) passing through the two wire interface indicates a condition of the transducer (12). The microprocessor (20) is interfaced with the transducer (12). The digital to analog converter (22) receives a signal from the microprocessor (20) indicating a current value. The first control circuit (23a, 23b, 23c, 23d, 23e, 24, 26, 28, 30, 32) is coupled to the digital to analog converter (22) and adapted to control the current (IL) passing through the two wire interface (34a, 34b) to the current value. The second control circuit (38) is coupled to the digital to analog converter (22) and supplies current to a secondary load (50).