Appliance Controller Noise Sampling Zero-Crossing
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Solution Overview
Problem
Voltage readings on input pins of controllers are skewed due to noise from alternating current (AC) signals, leading to inaccurate signal sampling and potential execution of wrong instructions, especially when the AC voltage magnitude is larger than the positive supply voltage, and existing solutions like adding filters increase the cost of control circuits.
Innovation Solution
A control system and method where a processor samples a second signal at a second input pin only when a first AC signal has a value of about zero volts at a first input pin, effectively minimizing noise by synchronizing sampling with zero crossings of the AC signal, and optionally using a clamp circuit to convert the AC signal to a square wave for identifying zero crossings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If filters and additional hardware are added to the control circuit to limit noise, then noise on input pins is reduced, but the cost of the control circuit increases
Solution Approach 1:
The system performs preliminary action by detecting the state of the first input pin (AC signal level) before sampling the second input pin. The processor checks whether the AC signal is above or below a threshold (e.g., zero volts) and only samples other pins when the AC signal is at a low level, preventing noise-induced erroneous readings without requiring additional hardware filters.
Solution Approach 2:
The sampling operation is made dynamic and conditional rather than continuous. The processor dynamically adjusts when to sample based on the real-time state of the AC signal, enabling sampling only during favorable conditions (when AC signal is low) and avoiding sampling during noisy conditions, thereby eliminating the need for static noise-filtering hardware.
2Productivity
If continuous sampling is performed on input pins, then real-time monitoring is achieved, but noise from AC signals causes inaccurate readings
Solution Approach 1:
Before performing the sampling action, the processor performs a preliminary check of the AC signal level on the first input pin. Only when the AC signal is determined to be at a low level (below a threshold) does the processor proceed to sample other pins, ensuring that sampling occurs only when noise conditions are favorable.
Solution Approach 2:
The sampling operation is converted from continuous to periodic/intermittent based on AC signal conditions. The processor periodically checks the AC signal state and samples other pins only during favorable periods when the AC signal is low, creating a rhythm of sampling that avoids noisy periods while maintaining effective monitoring.
Data Source
AI summary
A control system for controlling operation of an appliance includes a first signal source configured to produce an alternating current (AC) signal, a second signal source configured to produce a second signal, and a controller. The controller includes a processor, a memory device, a first input pin coupled to the first signal source to receive the AC signal, a second input pin coupled to the second signal source to receive the second signal, and an analog to digital (A/D) converter. The A/D converter is coupled to the first input pin and the memory device storing instructions that when executed by the processor cause the processor to sample the second signal at the second input pin only when the first signal has a value of about zero volts at the first input pin.