Field Device Wireless Power via 4-20 mA Loop Energy Harvesting
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Solution Overview
Problem
Field devices equipped with wireless modules face challenges in power supply, requiring battery replacement or external wiring, which complicates maintenance and integration with asset management systems.
Innovation Solution
A field device configuration that accumulates extra electric currents from the 4-20 mA signal loop for powering the RF unit, eliminating the need for battery replacement or external power, and allowing seamless integration with existing DCS systems while enabling wireless communication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If a wireless module is added to a field device to enable wireless transmission of diagnostic information, then the ability to transmit process operation information and diagnostic information to the asset management system is improved, but the device requires additional power supply (battery replacement or external wiring) which increases device complexity and maintenance burden
Solution Approach 1:
The 4-20 mA signal line is made multi-functional by enabling it to serve both its traditional control function and as a power supply for the wireless module. The power supply unit extracts and stores electrical energy from the current flowing through the signal line, allowing the same infrastructure to power wireless communication without adding separate power connections.
Solution Approach 2:
The field device supplies its own power needs through the existing signal line without requiring external power sources or battery replacement. The power supply unit continuously harvests energy from the operational current in the 4-20 mA loop, making the wireless module self-powered through the normal control signal infrastructure.
2Ease of operation
If batteries are used to power the wireless module, then wireless transmission capability is achieved, but battery replacement is required which increases maintenance costs and downtime
Solution Approach 1:
The wireless module is made self-sustaining by continuously harvesting power from the operational 4-20 mA signal line. The power supply unit with storage capacitor provides continuous power without requiring periodic battery replacement, eliminating maintenance downtime and costs associated with battery changes.
Solution Approach 2:
Instead of using disposable batteries that need replacement, the system recovers and stores electrical energy continuously from the existing signal line current. The storage capacitor accumulates energy during periods when wireless transmission is not active and supplies power during transmission, creating a sustainable power cycle without waste.
3Duration of action of stationary object
If external power wiring is added to power the wireless module, then continuous power supply is achieved, but integration with existing DCS systems becomes more complex and requires additional wiring
Solution Approach 1:
The existing 4-20 mA signal line is utilized for dual purposes: maintaining its control function while simultaneously serving as the power supply conduit for the wireless module. This eliminates the need for separate power wiring and simplifies integration with existing DCS systems.
Solution Approach 2:
Power is extracted directly from the current flowing through the existing signal line without requiring separate power connections. The power supply unit taps into the operational current to harvest electrical energy, removing the need for additional power infrastructure.
4Loss of information
If filters are inserted in series with the 4-20 mA loop to increase impedance for smart communication, then communication capability is improved, but voltage drops may exceed the output voltage capability of the DCS side
Solution Approach 1:
The power supply function is segmented from the signal transmission function by using a storage capacitor to decouple them. The capacitor stores energy during periods when communication is not active and supplies power during transmission, preventing voltage drops from affecting the overall system 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
Enables wireless transmission of diagnostic and process information without battery replacement or external wiring, maintaining control stability and reliability, and reducing maintenance costs by using stored power from the 4-20 mA signal loop.
Implementation Method 1
a power supply block for accumulating extra electric currents when the block is neither transmitting nor receiving radio signals
Data Source
AI summary
The present invention provides a field device whereby the device's additional information can be transmitted wirelessly without the need for battery replacement or external wiring. The present invention also provides a field device whereby the firmware of a wireless module in the field device can be developed at minimum cost and whereby it can be made easy to link the firmware to applications, such as an asset management system, on the host system side.The field device in accordance with the present invention is installed in a plant, factory, or the like, connected to a higher-order distributed control system through a signal line, configured to input or output 4-20 mA signals, and comprised of:an RF unit for transmitting or receiving radio signals; anda power supply block for accumulating extra electric currents when the block is neither transmitting nor receiving radio signals;wherein electric currents accumulated in the power supply block are supplied to the RF unit so as to be used as electric power for transmitting or receiving radio signals.