Digital Input Assembly With Low-Capacitance Burst Protection
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Solution Overview
Problem
Existing digital input modules in automation devices fail to reliably detect logic levels due to burst interference, leading to incorrect signal detection.
Innovation Solution
A circuit arrangement with series-connected diodes and resistors forms separate protection paths for positive and negative interference, accompanied by a digital filter with adjustable delay, ensuring reliable logic level detection even under interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bidirectional suppressor diode is used for interference protection, then the protection coverage is improved, but the capacitance increases causing signal delay
Solution Approach 1:
The single bidirectional suppressor diode is segmented into two separate unidirectional suppressor diodes, each handling one polarity of interference independently. This segmentation allows each diode to have lower capacitance while maintaining overall protection coverage for both positive and negative interference
Solution Approach 2:
Counter diodes are introduced as intermediary elements in series with each suppressor diode. These counter diodes have small capacitance and act as mediators that connect the input signal while the suppressor diodes provide protection, resulting in a total capacitance that is smaller than a single bidirectional suppressor diode
2Speed
If no series resistor is used, then the signal transmission speed is improved, but fire safety is compromised due to uncontrolled current
Solution Approach 1:
A series resistor is added that provides partial current limitation - it is small enough (220 ohms) to not significantly impact signal transmission speed for valid digital signals, but sufficient to limit current during interference conditions to prevent fire hazards. This represents a carefully calibrated partial action that addresses safety without excessively compromising speed
3Object-affected harmful factors
If the resistance value is high, then fire safety is improved, but logic level detection becomes faulty during bursts
Solution Approach 1:
The resistance value is optimized to a specific parameter range (220 ohms) that represents a compromise point - high enough to limit current during interference bursts and prevent fire hazards, but low enough to maintain proper logic level detection accuracy. This parameter optimization resolves the contradiction by finding the optimal value that satisfies both safety and detection 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
The solution effectively suppresses interference, allowing reliable logic level detection and reduces capacitance, enabling fast digital inputs to function without shielded cables.
Implementation Method 1
The diode and additional counter diode connect a small capacitance in series with the large capacitance of the suppressor diode in each path. The resulting capacitance is thus smaller than the already small capacitance of the diode or counter diode.
Implementation Method 2
A series resistor (R11, R12) for current limitation is arranged between the input terminal and the diodes.
Data Source
Figure 1
AI summary
The invention relates to a digital input module for an automation device, comprising: - an input terminal (E1, E2, E3) acting as a digital input, - a ground connection (M), - a detection means (PE) with an input (1, 2, 3) for an input signal (11, 12, 13) applied to the input (1, 2, 3), designed to detect a logic level of the signal applied to the input (1, 2, 3) via the input terminal (E1, E2, E3), further comprising a level output (P1, P2, P3) at which the detected logic level is output, wherein, to avoid incorrectly detected logic levels, a first diode (D1, D2, D3) in series with a first suppressor diode (D4) and a first counter diode (D11, D22, D33) in series with the first suppressor diode (D4) are arranged between the input terminal (E1, E2, E3) and the ground connection (M) in front of the input (1, 2, 3). connected in series with a second suppressor diode (D3),whereby a first protection path (S1) for positive interference and a second protection path (S2) for negative interference are realized, and additionally a series resistor (R11, R12) for current limitation is arranged between the input terminal (E1, E2, E3) and the diodes.