Field Device Fault Notification Circuit
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Solution Overview
Problem
Conventional positioners fail to reliably notify a fault state to external devices when the power supply to the calculation processing portion is OFF while the power supply to the communication processing portion is ON, leading to potential extended periods of undetected faults.
Innovation Solution
A field device with a calculation processing portion and a communication processing portion, connected through an isolating circuit, an inverting circuit, and a selecting circuit that maintains a predetermined voltage level for burnout signal output when the power supply to the calculation processing portion is OFF and the communication processing portion is ON, ensuring reliable fault state notification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the power supply to the calculation processing portion is OFF while the power supply to the communication processing portion is ON, then the communication processing portion can still communicate with external devices, but the burnout signal direction becomes undetermined and fault states cannot be reliably notified
Solution Approach 1:
The patent applies preliminary action by pre-setting the voltage level of the output line from the isolating circuit to a predetermined level that indicates burnout signal in a specific direction. This is achieved through the selecting circuit that is configured in advance to select between different voltage levels, and the inverting circuit that is prepared to invert signals as needed. When the calculation processing portion is powered OFF, the selecting circuit automatically ensures the output line maintains the predetermined voltage level, so that fault notification is already prepared and reliable without requiring complex real-time decision logic.
2Reliability
If an isolating circuit is provided between the calculation processing portion and communication processing portion, then electrical isolation is achieved, but the burnout signal direction cannot be determined when calculation processing portion power is OFF
Solution Approach 1:
The patent uses the output line from the isolating circuit as an intermediary element that maintains a predetermined voltage level indicating burnout signal direction. The selecting circuit acts as a mediator that ensures this voltage level is maintained by switching between different signal sources (normal operation signal or inverted signal). This intermediary mechanism bridges the isolation gap created by the isolating circuit, allowing the communication processing portion to reliably determine burnout signal direction even when the calculation processing portion is powered OFF.
Solution Approach 2:
The patent applies inversion by using an inverting circuit that can invert the voltage level of signals. When the calculation processing portion is powered OFF, the selecting circuit switches to use the inverted signal from the inverting circuit to maintain the predetermined voltage level on the output line. This inversion capability ensures that the burnout signal direction information is preserved and can be reliably interpreted by the communication processing portion, solving the problem of undetermined signal direction across the isolating circuit.
Data Source
AI summary
To provide reliable notification of a fault state when a power supply to a calculation processing portion is in the OFF state when a power supply to a communication processing portion is in the ON state. An isolating circuit, an inverting circuit inverting a signal branch-outputted through an output line of the isolating circuit, and a selecting circuit that uses the signal outputted from the output line of the isolating circuit as a first input and the inverted signal from the inverting circuit as a second input, to select either the first input or the second input, depending on a selection setting status thereof, to output the selected signal to the communication processing portion are provided. A +5 V voltage is applied through a resistor to the output line of the isolating circuit. This +5 V voltage is produced through the power supply supplied from the second double-wire transmission path.