AC Signal Monitoring Circuit With Shifted Zero-Crossing Sampling
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Solution Overview
Problem
Existing methods for monitoring sinusoidal alternating voltage signals, such as those in programmable logic controllers, face challenges due to the use of peak value detection, which limits the flexibility of comparing elements like CMOS HC gates, as they require threshold values that deviate from the effective value defined by IEC/EN 61131 standards.
Innovation Solution
A circuit assembly that includes a comparing element, a zero crossing detector, and an edge-controlled flip-flop, where the timing element specifies a state change at an instant other than T/4 after a zero crossing, allowing for the use of a threshold value lower than the peak value for monitoring sinusoidal alternating voltage signals, enabling flexible and reliable evaluation of both AC and DC input signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If peak value detection is used for monitoring sinusoidal alternating voltage signals, then the comparing element can operate with a fixed threshold value, but the threshold value must be set above the peak value which limits flexibility and prevents accurate monitoring according to IEC/EN 61131 effective value standards
Solution Approach 1:
The patent applies dynamics by making the sampling moment variable rather than fixed. The circuit samples the sinusoidal signal at different phases relative to the zero crossing, specifically at T/8 and 3T/8 instead of the conventional T/4. This dynamic adjustment of the sampling phase allows the system to capture the signal at moments when the instantaneous value corresponds to the effective value (Urms), enabling accurate AC signal monitoring while maintaining flexibility in threshold value selection for the comparing element.
2Device complexity
If a single comparing element is used for both AC and DC input signals, then device complexity is reduced, but the threshold value range is limited by the more restrictive AC signal requirements
Solution Approach 1:
The patent implements universality by designing a single comparing element that can accurately process both AC and DC input signals. By sampling the AC signal at specific phases (T/8 and 3T/8) where the instantaneous value equals the effective value, the same comparing element with a fixed threshold value can correctly evaluate both AC effective values and DC voltage levels, eliminating the need for separate comparing elements for different signal types.
3Device complexity
If the sampling moment is fixed at T/4 after zero crossing, then the circuit operation is simplified, but the detected value corresponds to peak value rather than effective value, reducing measurement accuracy
Solution Approach 1:
The patent applies parameter changes by modifying the sampling moment parameter from the conventional fixed T/4 to variable moments at T/8 and 3T/8 after the zero crossing. This parameter adjustment changes the instantaneous signal value captured from the peak value (at T/4) to values that correspond to the effective value (Urms), thereby improving measurement precision while maintaining relatively simple circuit operation through the use of basic timing circuits.
Data Source
AI summary
A circuit assembly for monitoring a sinusoidal alternating voltage signal having a comparing element receiving at an input the signal with period T and generating a first output signal at an output based upon the signal exceeding a threshold; a zero crossing detector receives at its input the signal and generates a output signal at its output; a timing element connected to zero crossing detector generates a clock signal dependent on the second output signal; and a flip-flop. The comparing element output is connected to a state-controlled input of the flip-flop and the timing element output is connected to an edge-controlled input of the flip-flop. The flip-flop generates a state signal at its output. The timing element specifies a state change of the clock signal at an instant that differs from the instant at T/4 after a zero crossing of the signal.