Two-Wire Bus Instrument Predictive Power Limiting
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Solution Overview
Problem
Two-wire bus instruments face challenges in maintaining power consumption within limited current constraints, leading to potential errors and unreliable operation due to increased power demand exceeding protocol limits, especially at low current levels.
Innovation Solution
A bus instrument equipped with a sensor, shunt regulator, and controller that predicts available power after changes in loop current, compares it to current power consumption, and reduces sensor power if necessary to prevent exceeding power limits, using measurements of loop resistance and supply voltage to adjust sensor current accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the bus instrument increases power demand to operate accurately and reliably, then the operational reliability is improved, but the electrical current requirements exceed the protocol limits
Solution Approach 1:
The controller performs preliminary calculations to predict future available power before actual power consumption occurs. By computing predicted available power based on anticipated loop current changes and comparing it to present time power requirements, the system proactively adjusts sensor power to prevent exceeding protocol limits, thereby maintaining operational reliability within current constraints
Solution Approach 2:
The controller continuously monitors loop current, supply voltage, and power consumption, using this feedback to dynamically adjust sensor power. The system compares predicted available power with actual power usage and modulates sensor current accordingly, creating a closed-loop control system that ensures reliable operation within the 4-20 mA protocol limits
2Adaptability or versatility
If the bus instrument operates at minimal flow conditions with 4 mA current limit, then the protocol compliance is maintained, but the electrical current is insufficient to operate the instrument
Solution Approach 1:
The system dynamically adjusts sensor power consumption based on predicted available power and actual operating conditions. Rather than operating at a fixed power level, the controller continuously modulates sensor current to match available power from the 4-20 mA loop, enabling the instrument to function reliably even at minimal 4 mA current conditions while maintaining protocol compliance
Solution Approach 2:
The controller changes the operational parameters of the sensor by adjusting its current draw based on predicted available power. When loop current is limited to 4 mA, the system calculates appropriate sensor power levels that enable instrument operation within these constrained conditions, allowing the instrument to adapt to minimal flow conditions while maintaining protocol compliance
3Power
If the bus instrument exceeds power limits, then the power consumption requirement is met, but an error condition results causing faulty or unreliable operation
Solution Approach 1:
The controller applies preliminary anti-action by predicting future power availability and preemptively adjusting sensor power before power limits are exceeded. By calculating predicted available power based on anticipated loop current changes and comparing it to required power, the system prevents error conditions from occurring in the first place, thereby maintaining operational reliability while meeting power requirements
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 solution effectively predicts and manages power consumption to prevent errors, maintaining a buffer from power limits and avoiding resets or faulty operations by proactively adjusting sensor power to ensure reliable operation within the two-wire bus protocol constraints.
Implementation Method 1
a shunt regulator configured for shunting excess electrical current
Data Source
AI summary
A bus instrument (10) configured to predictively limit power consumption and adapted for use with a two-wire instrumentation bus is provided. The bus instrument (10) includes a sensor (13), a shunt regulator (14), and a controller (20). The controller (20) is configured to generate a predicted available power Ppredicted that will be available to the bus instrument (10) after a change in the loop current IL, compare the predicted available power Ppredicted to a present time power Pt0 comprising a controller power Pcontroller plus a sensor power Psensor, and reduce the sensor power Psensor if the total available power Pavailable is less than the controller power Pcontroller plus the sensor power Psensor.