Current Measurement Transfer Function Compensation
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Solution Overview
Problem
Existing current measurement technologies face challenges in achieving high accuracy and stability over time, particularly in high-current applications, due to factors like temperature drift and manufacturing tolerances.
Innovation Solution
The proposed current measurement apparatus applies a reference input signal to a measurement arrangement disposed in relation to a load, allowing for the determination of the load drawn current signal and electrical power consumed, while compensating for changes in the transfer function of the measurement arrangement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a shunt resistor is used for current measurement, then the measurement can be performed indirectly by measuring voltage across the shunt, but the shunt resistance changes due to temperature drift causing loss of measurement accuracy
Solution Approach 1:
The patent applies feedback by continuously monitoring the shunt resistance using a reference voltage source and measuring the actual resistance value. The measured resistance value is fed back to adjust the measurement calculations in real-time, compensating for temperature drift and maintaining measurement accuracy throughout the device's operational life.
Solution Approach 2:
The patent changes the measurement approach from assuming a fixed shunt resistance value to dynamically determining the actual resistance value. By measuring the voltage across the shunt with a known reference current and calculating the actual resistance, the system adapts to parameter changes (temperature drift) rather than relying on a static nominal value.
2Measurement precision
If factory calibration is performed to achieve desired precision, then measurement accuracy can be maintained initially, but the calibration factor may drift over time due to component aging and temperature effects
Solution Approach 1:
The system implements continuous feedback by periodically remeasuring the shunt resistance using the reference voltage source. This feedback mechanism detects drift in the calibration factor over time and automatically compensates for it, extending the effective measurement stability period without requiring manual recalibration.
Solution Approach 2:
The measurement system performs self-calibration by using its own reference voltage source and measurement circuitry to continuously monitor and adjust for shunt resistance changes. This self-service approach eliminates the need for external calibration equipment and maintains accuracy autonomously throughout the device's operational life.
3Adaptability or versatility
If a current transformer is used to measure high current, then isolation from the current carrying conductor is provided, but the transformer can only measure AC current and requires accurate knowledge of the transfer function
Solution Approach 1:
The patent uses feedback to continuously determine the actual transfer function of the current transformer by measuring the relationship between primary and secondary currents. This measured transfer function is fed back to correct measurement calculations, compensating for drift in magnetic properties and winding characteristics over time and temperature.
Solution Approach 2:
The system introduces a reference voltage source and measurement circuitry as intermediaries to indirectly determine the current transformer's performance characteristics. By measuring voltages and currents through these intermediary components, the system accurately characterizes the transfer function without requiring direct access to the high-current primary conductor.
4Adaptability or versatility
If a Hall current probe is used to measure both AC and DC current, then versatility is improved, but the probe is liable to non-linearity and temperature drift in open loop configuration
Solution Approach 1:
The patent implements feedback by measuring the Hall probe's output with a known reference input and continuously determining the actual transfer characteristics. The measured non-linearity and temperature drift are compensated in real-time through feedback calculations, maintaining measurement precision across the full AC and DC measurement range.
Solution Approach 2:
The system applies a reference voltage that exceeds the normal operating signal level to characterize the Hall probe's full transfer function including non-linear regions. By measuring with this excessive reference action, the system captures complete non-linearity characteristics and uses this information to correct normal operating measurements, improving overall linearity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables accurate and stable current measurement by relying on the reference input signal to determine the load drawn current, thereby addressing issues of temperature drift and manufacturing tolerances, and maintaining measurement accuracy over time.
Implementation Method 1
A current shunt provides for indirect measurement of current values by the measurement of the voltage developed across the shunt by the current passing through the shunt
Implementation Method 2
a signal source operative to apply a reference input signal to the measurement arrangement whereby an output signal from the measurement arrangement comprises a load output signal corresponding to the load drawn current signal and a reference output signal corresponding to the reference input signal
Data Source
Figure 1A~1B
Figure 1C~2
Figure 3A~3B
AI summary
The present disclosure relates to apparatus and methods for determining a transfer function of a current measurement arrangement (118), or a change in a transfer function of the current measurement arrangement. In one aspect, an apparatus is disclosed comprising: a signal source (112) configured to apply a reference signal to a first current transducer (110) such that a first transducer output signal from the first current transducer comprises: a current measurement signal indicative of the first current passing through a first conductor (104); and a reference signal component resulting from the reference signal; and signal processing circuitry (116)configured to determine the transfer function of the current measurement arrangement by: extracting the reference signal component from the first transducer output signal; and determining the transfer function of the current measurement arrangement based on the transducer output signal.