Digital Input Receiver Circuit for Broken Wire Detection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing digital input circuitry in industrial controllers, which is input-powered and simpler, cannot detect broken wires, posing a dilemma between using more expensive field-side power providing circuitry or losing the ability to detect wire breaks.
Innovation Solution
Incorporating an optocoupler in series between field ground pins and the industrial controller's ground, along with a hold capacitor and a resistor, allows for a test pulse to isolate the digital input circuitry from field ground, enabling detection of broken wires by monitoring the charging of the capacitor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If field-side power providing digital input circuitry is used, then wire break detection capability is achieved, but device complexity and cost increase
Solution Approach 1:
An optocoupler is introduced as an intermediary component between the field ground and the digital input circuitry. This optocoupler enables wire break detection by isolating the detection circuit from the main power circuit, allowing the simple input-powered configuration to achieve detection capability without the complexity of field-side power circuitry.
Solution Approach 2:
The patent replaces the mechanical/electrical field-side power system with an optical isolation system using an optocoupler. This substitution allows wire break detection to be achieved through optical coupling rather than direct electrical connection, simplifying the overall circuit architecture while maintaining detection functionality.
2Device complexity
If input-powered digital input circuitry is used, then device complexity is reduced, but wire break detection capability is lost
Solution Approach 1:
The patent implements periodic test pulses applied to the optocoupler to enable wire break detection. These periodic pulses allow the system to periodically check for wire breaks by monitoring the charging state of the hold capacitor, maintaining detection capability in the simplified input-powered circuitry without requiring continuous complex monitoring.
Solution Approach 2:
A hold capacitor is pre-charged through a resistor during normal operation, and the optocoupler is pre-configured to isolate the digital input circuitry from field ground. This preliminary setup enables the wire break detection function to be activated simply by applying test pulses, avoiding the need for complex real-time detection circuitry.
3Reliability
If field-side power circuitry is used, then wire break detection is enabled, but manufacturing cost increases
Solution Approach 1:
The patent uses inexpensive components such as an optocoupler, hold capacitor, and resistor to enable wire break detection in the simplified input-powered circuitry. These low-cost components replace the expensive field-side power circuitry while maintaining the essential detection functionality, significantly reducing manufacturing costs.
4Ease of manufacture
If input-powered digital input circuitry is used, then manufacturing cost is reduced, but wire break detection capability is lost
Solution Approach 1:
The optocoupler serves multiple functions: it provides electrical isolation between field ground and the digital input circuitry, enables wire break detection through periodic test pulses, and allows the same simple input-powered circuitry to perform both normal operation and detection functions. This multi-functionality eliminates the need for separate field-side power circuitry, reducing manufacturing costs while maintaining detection capability.
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 wire break detection using simpler input-powered digital input circuitry, ensuring reliable operation without the need for complex and costly field-side power circuitry.
Implementation Method 1
an optocoupler is placed in series between the field ground pins of the digital input circuitry and the field ground of the industrial controller
Implementation Method 2
the digital input circuitry being disconnected from ground allows the capacitor connected between the input and ground to charge. The charge rate is controlled by various resistors
Data Source
AI summary
An optocoupler is placed in series between the field ground pin of digital input circuitry and the field ground of an industrial controller. A capacitor to field ground is provided for each digital input. A resistor is provided to the input pin of the digital input circuitry. To detect a broken wire a test pulse is provided to the optocoupler connected in the ground path. This test pulse isolates the digital input circuitry from field ground. As current is always being provided from the field when the wire is not broken, the capacitor connected between the input and ground charges. After the test pulse has completed, the output signal of the digital input circuitry is examined. If the level indicates the input is high, the wire is not broken. If, however, the output remains low indicating that the input is low, the wire has broken.