Auto-ranging Ammeter Shunt Selection Glitch Reduction

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Solution Overview

Problem

Existing current measurement devices, such as ammeters, face challenges in accurately measuring rapidly changing high-dynamic range currents due to voltage drops and errors associated with auto-ranging mechanisms, particularly in modern digital components that require minimal impedance to maintain measurement accuracy.

Innovation Solution

An auto-ranging ammeter with multiple current sense resistors dynamically selects the appropriate resistor based on current levels, using a less sensitive always-on resistor in combination with dynamically selected sense resistors to maintain accuracy during current range changes, and includes a voltmeter and processing capabilities to compute power, energy, and charge, with software for data display.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If auto-ranging mechanism is used to adapt to different current levels, then adaptability is improved, but measurement precision deteriorates due to glitches during range switching

Engineering Contradiction:

Improvecurrent range adaptabilityVSAvoidmeasurement accuracy

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The patent implements preliminary action by pre-calculating and storing calibration coefficients for each current range before measurement. When a range switch is anticipated or occurs, the appropriate calibration coefficients are already available, eliminating the need for real-time calibration calculations that cause glitches. This pre-prepared approach ensures seamless transitions between current ranges while maintaining measurement precision.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent introduces an intermediary mechanism in the form of a calibration coefficient selection unit that acts as a mediator between the current range switching and the measurement process. This intermediary selectively applies the correct calibration coefficients based on the active current range, ensuring that the measurement system adapts to different ranges without introducing errors or glitches during the transition.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Adaptability or versatility

If multiple current sense resistors are used to expand measurement range, then adaptability is improved, but device complexity increases

Engineering Contradiction:

Improvemeasurement rangeVSAvoidresistor selection mechanism

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent applies segmentation by dividing the current measurement function into multiple discrete current sense resistors, each optimized for specific current ranges. This segmentation allows the system to handle different current levels with appropriate resistors, expanding the overall measurement range while keeping each individual resistor simple and well-defined.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent implements dynamics through a switching mechanism that dynamically selects among multiple current sense resistors based on the detected current level. This dynamic selection allows the system to adapt to varying current conditions in real-time, providing both wide measurement range and simplified operation through automated resistor selection.

Inventive Principle:

Principle #15Dynamics

3Measurement precision

If ammeter impedance is reduced to minimize voltage drop, then measurement precision is improved, but ability to handle high current decreases

Engineering Contradiction:

Improvevoltage drop impactVSAvoidhigh current handling capability

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent applies parameter changes by using multiple current sense resistors with different resistance values, each optimized for specific current ranges. For high current measurements, lower resistance resistors are selected to minimize voltage drop and prevent saturation, while for low current measurements, higher resistance resistors provide adequate signal level. This parameter variation across different operating conditions allows the system to maintain both precision and reliability across the full current range.

Inventive Principle:

Principle #35Parameter changes

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

The solution enables accurate measurement of currents up to ±3 A with 1 nA resolution and supports ±10 A bursts, measuring voltages from −15 V to 15 V with 1 mV resolution, achieving reduced cost and improved performance compared to contemporary devices while minimizing measurement errors during current range switching.

Implementation Method 1

According to Ohm's law, voltage=current×resistance

Methodology Applied

Scientific EffectOhm's law: Ohm's Law

Data Source

PatentUS11774469B2Auto ranging ammeter with accurate measurement during range changes

Publication Date: 2023.10.03 JETPERCH LLC

AI summary

An auto ranging ammeter that allows improved measurement of rapidly changing, high-dynamic range electrical currents. The ammeter computes current during range switches by using digital signal processing to combine voltage measured over both a variable shunt resistor and a fixed shunt resistor. The ammeter uses fast comparators and digital processing to select the appropriate shunt resistor. The auto ranging ammeter includes a voltmeter which enables the device to output current, voltage, power, charge, and energy consumed by a target device under test.