Facsimile Line State Detection with Dynamic Voltage Thresholds
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Solution Overview
Problem
Facsimile devices inaccurately judge the state of an external telephone connected to a public line due to interference from digital service units, leading to erroneous messages indicating the external telephone is busy even when it has released the line.
Innovation Solution
A facsimile device with a voltage detector and open-circuit voltage detector that assesses the voltage difference between a reference voltage and the detected line voltage to accurately determine whether the external telephone has released or closed the public line, preventing erroneous judgments by considering both immediate and delayed voltage changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a digital service unit (PBX or terminal adapter) intervenes between the public line and communication devices, then the voltage of the public line does not recover quickly to the standby voltage after release, but the facsimile device cannot appropriately judge whether the external telephone releases the public line
Solution Approach 1:
The facsimile device performs preliminary voltage detection during the communication process to establish a baseline of voltage characteristics. By detecting voltage at multiple timing points (during communication and after release), the device builds knowledge about the specific line's voltage behavior pattern, enabling accurate judgment even when recovery is delayed by digital service units.
Solution Approach 2:
The judgment threshold is made dynamic rather than fixed. The facsimile device adjusts the voltage threshold based on the detected open-circuit voltage and the specific line characteristics. This dynamic adaptation allows the device to accommodate varying voltage recovery speeds caused by different digital service units while maintaining accurate telephone state judgment.
2Device complexity
If the facsimile device uses a fixed voltage threshold to judge telephone state, then the judgment is simple, but the device erroneously judges that the external telephone closes the public line when voltage recovers slowly
Solution Approach 1:
The facsimile device changes the judgment parameter from a fixed voltage threshold to a dynamic threshold based on detected open-circuit voltage. By calculating the threshold as a proportion of the detected open-circuit voltage, the system adapts to different line conditions and digital service units, preventing erroneous judgments while maintaining reasonable complexity.
Solution Approach 2:
The system implements feedback by continuously monitoring the public line voltage and comparing it against dynamically adjusted thresholds. The detection results feed back into the judgment logic, allowing the device to distinguish between genuine telephone on-hook states and temporary voltage fluctuations caused by digital service units during the voltage recovery period.
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
The solution ensures accurate judgment of the external telephone's line state, preventing false busy indications and allowing secure operation of the facsimile device even when digital service units intervene, thereby improving user experience and device reliability.
Implementation Method 1
a voltage detector that detects a voltage of the public line
Data Source
AI summary
A device includes a facsimile circuit, a voltage detector, an open-circuit voltage detector, and a telephone status monitoring unit. If a first voltage difference is less than a predetermined voltage difference, the monitoring unit judges that the public line is released if a second voltage difference is less than the predetermined difference, and that the public line is closed if the second difference is not less than the predetermined difference. If, when the facsimile circuit has released the public line, the first difference is not less than the predetermined difference, the monitoring unit judges that the public line is released if the second difference is less than the predetermined difference or if the detected line voltage equals the open-circuit voltage, and that the public line is closed if the second difference is not less than the predetermined difference and if the detected line voltage is different from the open-circuit voltage.