RMS Measurement of Burst-Fired Currents Using Segmented Sampling
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Solution Overview
Problem
Existing methods for controlling industrial heating elements, such as SCR power controllers, face challenges in accurately measuring power consumption due to time-lag delays and degradation of temperature sensors, particularly when dealing with burst-fired currents, which are not effectively accounted for by traditional RMS calculations.
Innovation Solution
An apparatus and method utilizing a current sensor, analog-to-digital converter, and digital processor to sample and calculate the true RMS values of burst-fired currents, allowing for precise power control by determining the burst-fired current pattern and calculating RMS values from multiple samples within the pattern.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional temperature sensors are used for feedback control, then the system can provide temperature monitoring, but time-lag delays and sensor degradation prevent precise temperature control
Solution Approach 1:
The patent introduces an intermediary measurement approach by using current sensing as a proxy for temperature measurement. Instead of directly measuring temperature with unreliable sensors, the system measures the current through the heating element, which correlates to power delivery and thus temperature. This intermediary measurement bypasses the reliability issues of direct temperature sensing while maintaining control precision.
Solution Approach 2:
The patent replaces the mechanical/thermal measurement system (temperature sensors) with an electrical measurement system (current sensors and RMS calculation). By substituting the physical temperature measurement mechanism with an electrical equivalent measurement, the system eliminates the time-lag and degradation issues inherent in thermal sensors while achieving equivalent or superior control precision.
2Measurement precision
If traditional RMS calculations are used for burst-fired currents, then the calculation method is simple, but the measurements are inaccurate due to not accounting for burst-fired patterns
Solution Approach 1:
The patent segments the measurement process into distinct phases: detection of burst-fired patterns, identification of ON and OFF periods, and separate RMS calculations for each phase. By dividing the continuous measurement task into discrete segments that correspond to the burst-fired operational modes, the system achieves accurate RMS measurements that properly account for the intermittent nature of the current.
Solution Approach 2:
The patent implements a dynamic measurement system that adapts its calculation method based on the detected burst-fired pattern. The system continuously monitors the current waveform, dynamically identifies transition points between ON and OFF states, and adjusts the RMS calculation parameters in real-time. This dynamic adaptation enables accurate measurement across varying duty cycles and burst patterns.
Data Source
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AI summary
An apparatus (24) for measuring RMS values of burst-fired currents includes a current sensor (26) having a signal output, an analog-to-digital (A/D) converter (30) coupled to the signal output of the current sensor, a digital processor (32/32') coupled to an output of the A/D converter, and a digital memory (48/50/52) coupled to the digital processor. Code segments stored in the digital memory are executable on the digital processor and implement a process of: a) initially sampling the output of the A/D converter; b) determining from the initial sampling a burst-fired current pattern; c) sampling the output of the A/D converter N times within a burst-fired current pattern to provide N samples; and d) calculating an RMS value from the N samples.