Power Meter ADC Self-Calibration for Integral Nonlinearity
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Solution Overview
Problem
Existing electrical power meters face challenges in accurately measuring electrical energy due to integral nonlinearities introduced by their components, requiring costly external signal sources and time-consuming calibration processes, which can delay manufacturing and increase costs.
Innovation Solution
An intelligent electronic device with an internal calibration system that generates a clean RC decay waveform, samples it, and uses best-fit curve estimation to calculate distortions, applying correction factors to improve measurement accuracy across the entire measurement range without external equipment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If external signal sources and measurement systems are used for calibration, then measurement accuracy can be improved, but device complexity and cost increase significantly
Solution Approach 1:
The electrical power meter performs self-calibration using its own internal components (DAC, RC circuit, ADC) without requiring external calibration equipment. The device generates its own test signals and processes the measurements internally, eliminating the need for complex external calibration systems while maintaining measurement accuracy.
Solution Approach 2:
The calibration function is extracted from the main measurement path and implemented as a separate self-contained calibration mode. The device switches to calibration mode where the DAC output is connected to the ADC input through the RC circuit, isolating the calibration process from normal measurement operations and avoiding interference with regular metering functions.
2Measurement precision
If traditional external calibration equipment is used, then accuracy standards can be met, but calibration time increases significantly
Solution Approach 1:
The calibration constants are determined and stored in memory before normal measurement operations begin. The device performs preliminary calibration measurements using the RC decay waveform, calculates the correction factors in advance, and applies them during subsequent measurements, eliminating the need for time-consuming real-time calibration during operation.
Solution Approach 2:
The calibration process is implemented as a periodic operation that can be performed at scheduled intervals or during manufacturing testing. The device enters calibration mode periodically to update correction constants, rather than requiring continuous calibration, thus reducing overall calibration time while maintaining accuracy compliance.
3Measurement precision
If calibration is performed across the entire measurement range, then measurement accuracy is improved, but calibration complexity increases
Solution Approach 1:
The calibration process utilizes changes in the RC circuit's time constant parameter to generate decay waveforms with varying characteristics. By adjusting the RC time constant and measuring the resulting decay curves across different amplitude ranges, the system obtains calibration data for the entire measurement range using a single unified approach, avoiding the need for multiple separate calibration procedures.
Data Source
AI summary
An intelligent electronic device, and in particular, an electrical power meter, includes an internal calibration system capable of calibrating its measurement mechanisms for the integral nonlinearities introduced by the components which make up those mechanisms, in particular, the analog-to-digital converter. The analog-to-digital converter is coupled with at least one sensor which is operable to sense electrical energy in one or more conductors and output a corresponding electrical signal indicative thereof, the analog-to-digital converter being operative to convert the electrical signal output by the sensor to at least one corresponding digital signal. Integral non-linearity describes the deviation between the ideal output of an analog-to-digital converter and the actual output (after offset and gain errors have been removed). The intelligent electronic device, using internal INL calibration calibrates for such INL substantially across its entire measurement range and significantly improves the measurement accuracy thereby.