Isolated Power Scavenging Circuit for Intrinsic Safety Pulse Output
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Solution Overview
Problem
Industrial process variable transmitters, particularly those operating in hazardous areas, face design challenges due to Intrinsic Safety standards that limit energy availability and impose constraints on circuitry, making it difficult to efficiently transmit pulse outputs while ensuring safe operation.
Innovation Solution
The use of optocouplers in a push/pull configuration for unidirectional communication, powering the output circuitry directly from the process control loop, and employing a power scavenging mechanism using capacitors and current sources to maintain low voltage and high noise immunity, simplifies circuit design and meets Intrinsic Safety requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Intrinsic Safety standards are applied to limit energy availability, then safe operation in hazardous areas is ensured, but pulse output transmission efficiency deteriorates
Solution Approach 1:
The patent implements periodic action by using pulse-width modulation (PWM) to transmit process variable information through successive pulses rather than continuous signals. Each pulse carries discrete information about the process variable, allowing efficient data transmission while maintaining low average power consumption that satisfies Intrinsic Safety requirements. The pulse train approach enables reliable communication without requiring high continuous energy levels.
Solution Approach 2:
The patent applies parameter changes by dynamically adjusting pulse width, frequency, and amplitude based on the process variable being measured. The output circuitry modifies these pulse parameters to encode process information, enabling versatile transmission of different process variables (flow, temperature, pressure, level) while operating within the energy constraints of Intrinsic Safety standards.
2Reliability
If Intrinsic Safety constraints are imposed on circuitry, then energy availability is limited, but device complexity increases
Solution Approach 1:
The patent implements universality by designing a single output circuit architecture that can transmit multiple types of process variable information (flow rate, total flow, temperature, pressure, level) using the same pulse transmission mechanism. The optocoupler-based isolated power scavenging circuit serves multiple functions: electrical isolation, power generation, and signal transmission, eliminating the need for separate circuits for each function and reducing overall device complexity.
Solution Approach 2:
The patent applies self-service through the isolated power scavenging circuit that generates its own operating power from the process control loop wiring without requiring an external power source. The circuit scavenges energy from the loop current to power the optocoupler and output stage, making the system self-sufficient and simplifying installation by eliminating additional power connections while maintaining Intrinsic Safety compliance.
3Use of energy by moving object
If isolated power scavenging is used to power output circuitry, then power consumption is reduced, but noise immunity may deteriorate
Solution Approach 1:
The patent implements an intermediary approach by introducing an optocoupler as an optical mediator between the process control loop and the output circuitry. The optocoupler transfers power and signal information through optical coupling rather than direct electrical connection, providing galvanic isolation that blocks electrical noise and interference while maintaining efficient power transfer. This optical intermediary enables low power consumption while preserving high noise immunity by eliminating direct electrical noise pathways.
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 reliable and efficient pulse output transmission with high noise immunity and reduced power consumption, enabling operation within Intrinsic Safety standards while simplifying design and installation.
Implementation Method 1
an optocoupler having a first input coupled to the measurement circuitry and a first output coupled to the output circuitry
Implementation Method 2
a power supply circuitry having a first terminal coupled to the process control loop and a second terminal coupled to the output circuitry
Data Source
Figure 1
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AI summary
An industrial process variable transmitter (20) includes a process variable sensor (30, 32) configured to sense a process variable. Measurement circuitry (154) is coupled to the process variable sensor (30, 32) and provides a measured output as a function of the process variable. Output circuitry (158) includes a loop connection configured to couple to a process control loop (160). An optical sensor (200) receives the measured output from the measurement circuitry (154). A switching device (190) applies pulses to the process control loop (160) in response to an output from the optical sensor (20). Power supply circuitry (192) powers the optical sensor (200), a comparator (214), and/or the switching device (190) with power received from the process control loop (160) and loop connection.