Electric Heating Load Control Circuit for UL-197 Power Averaging
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Solution Overview
Problem
Existing electric heating appliances face challenges in precisely controlling the input averaging current to comply with UL-197 section 48, which requires maintaining the average operating power below 80% of the plug-rated current over a three-hour period, as existing temperature-limiting circuits provide only approximate values.
Innovation Solution
An input averaging control circuit using timers is implemented to cooperate with heating timer circuits, ensuring the input averaging current remains below 80% of the plug-rated current by directly measuring electrical values and managing power distribution through programmable RC oscillator timers and solenoid control circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If temperature-limiting circuits are adapted to limit Iavg, then the appliance can prevent excessive heating, but the measurement precision of input averaging current is insufficient
Solution Approach 1:
The patent replaces temperature-based limiting circuits with direct electrical measurement circuits. Instead of measuring temperature and inferring current (which provides only approximate values), the invention directly measures electrical parameters (voltage and current) to calculate Iavg precisely, substituting thermal measurement with electrical measurement.
Solution Approach 2:
The patent introduces an intermediary computational approach by measuring voltage and current separately through dedicated circuits, then calculating Iavg through integration over time. This intermediary measurement and calculation process provides more precise values than direct temperature-based limiting.
2Measurement precision
If direct electrical measurement is implemented for Iavg, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent segments the measurement function into separate dedicated circuits: one for voltage measurement, one for current measurement, and one for time integration. This segmentation allows each circuit to perform a specific function with high precision while making the overall system manageable and compliant with UL standards.
Solution Approach 2:
The control circuit is designed to serve multiple functions: it measures voltage, measures current, integrates over time periods, and controls heating elements. By making the circuit multi-functional, the patent reduces the need for separate dedicated components for each function, thereby managing complexity while achieving precise measurement.
3Reliability
If input averaging current is strictly controlled to comply with UL-197 section 48, then safety is improved, but productivity of the heating appliance decreases
Solution Approach 1:
The patent implements dynamic control of the heating appliance by continuously monitoring voltage and current and adjusting the heating output in real-time. The system can operate at full power when safe, and dynamically reduce power when approaching Iavg limits, thereby maintaining both safety compliance and maximum possible productivity.
Solution Approach 2:
The patent employs periodic measurement and control cycles, integrating power consumption over defined time periods (such as 3-hour cycles required by UL-197). This periodic action allows the appliance to deliver high power output in intervals while ensuring compliance with average power limits over the full cycle period.
Data Source
AI summary
An appliance includes a plurality of electrical loads and a load control circuit including at least a clock enable circuit and a full power timer. The clock enable circuit is configured and operatively connected to activate the full power timer when all of the loads are energized, and the full power timer is configured and operatively connected to de-energize at least one load selected from the plurality of loads on reaching a predetermined full power time limit.