Safety PLC Signal Transfer Path Resistance Reduction
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Solution Overview
Problem
Safety PLCs with duplex hardware configurations face challenges in raising the frequency of digital signals due to high resistance values in signal transfer paths, which are hindered by parasitic stray capacitance, leading to signal distortion.
Innovation Solution
Incorporating overvoltage protection units, such as zener diodes and NPN transistors, between DC power supply output terminals to reduce the resistance value in the signal transfer path, thereby minimizing stray capacitance and allowing higher digital signal frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high-resistance resistor (10 kΩ or more) is used in the signal transfer path to protect circuits from overvoltage, then circuit protection is improved, but the frequency of digital signals is reduced due to parasitic stray capacitance
Solution Approach 1:
The invention changes the resistance parameter in the signal transfer path from high (10 kΩ or more) to low (less than 10 kΩ) by adding a parallel resistance component. This is achieved by introducing a resistance component formed by a conductive layer that connects between signal lines, creating a low-resistance path that reduces the overall resistance value and thereby increases the signal frequency capability while maintaining circuit protection through the duplex configuration
Solution Approach 2:
The invention introduces an intermediary resistance component (conductive layer) that acts as a mediator between the conflicting requirements of high resistance for protection and low resistance for high-frequency signals. This conductive layer provides an additional conduction path that effectively reduces the resistance without compromising the protective function, as the duplex system continues to provide overvoltage protection while enabling higher signal frequencies
2Reliability
If a high-resistance resistor is used in the signal transfer path, then overvoltage protection is improved, but stray capacitance increases causing signal waveform distortion
Solution Approach 1:
The invention changes the resistance parameter to reduce stray capacitance effects. By lowering the resistance value in the signal transfer path through the added conductive layer, the time constant (RC) is reduced, which minimizes the impact of parasitic capacitance on signal integrity. This allows digital signals to be transmitted at higher frequencies without significant waveform distortion while the duplex configuration maintains overvoltage protection
3Speed
If the resistance value in the signal transfer path is reduced, then signal frequency is improved, but circuit protection capability is reduced
Solution Approach 1:
The invention segments the protection function from the signal transmission function. The duplex system configuration separates these functions: one system provides signal transmission with low resistance for high-frequency capability, while the other system provides overvoltage protection. This segmentation allows both low resistance (for high frequency) and protection capability to coexist by distributing these functions across the two independent systems
Solution Approach 2:
The invention changes the resistance parameter in the signal transfer path to a low value (less than 10 kΩ) by adding a parallel conductive path. This resistance reduction enables higher signal frequencies while the duplex system configuration maintains protection capability through the redundant system architecture, where the protection function is preserved despite the lower resistance value
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 enables higher digital signal frequencies, reduces manufacturing costs, and simplifies the PLC construction while protecting against overvoltage and overcurrent, enhancing communication speed and reliability.
Implementation Method 1
The overvoltage protection unit may be formed of a known electronic component, such as a zener diode or an arrester. In the safety PLC according to the above-mentioned aspect, the overvoltage protection unit may be composed of a zener diode connected between the two output terminals.
Implementation Method 2
the overvoltage protection unit may include: an NPN transistor that has a collector terminal connected to a high-potential-side terminal of the two output terminals and an emitter terminal connected to a low-potential-side terminal of the two output terminals; a zener diode that has a cathode terminal connected to the high-potential-side terminal and an anode terminal connected to a base terminal of the NPN transistor
Data Source
AI summary
A safety PLC having duplex power supply circuits, includes: a first output-stage transistor; a first DC power supply that drives the first output-stage transistor; a second output-stage transistor; a second DC power supply that drives the second output-stage transistor; a signal transfer path that includes a resistor and connect the first output-stage transistor to the second output-stage transistor; and a pair of overvoltage protection units, each of which is disposed between a pair of output terminals of the corresponding one of the first and second DC power supplies and restricts the maximum value of an output potential difference between the pair of output terminals.