Dual-Channel Current Measuring Device for Wide Dynamic Range

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Solution Overview

Problem

Current measuring devices face challenges in achieving a wide dynamic measuring range with low input impedance and reliable operation, especially when measuring strong AC currents, due to the need for high-gain amplifiers which amplify noise and introduce measurement errors.

Innovation Solution

A current measuring device is designed with a first and second measuring resistor in series, along with parallel voltage limiting means, and separate signal amplifiers to manage current flow and impedance, allowing for a ratio of gain channels that matches the dynamic measuring range, thereby reducing noise and measurement errors.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a low-value measuring resistor is used to reduce circuit disturbance and prevent transformer saturation, then the measuring range is improved, but the signal amplitude becomes very weak requiring high-gain amplification

Engineering Contradiction:

Improvemeasuring rangeVSAvoidsignal amplitude

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The patent divides the measuring system into two separate channels: one for weak currents (using a higher-value resistor R1 with higher-gain amplifier) and one for strong currents (using a lower-value resistor R2 with lower-gain amplifier). This segmentation allows each channel to be optimized for its specific current range, avoiding the need for a single high-gain amplifier that would amplify noise for weak currents while preventing transformer saturation for strong currents.

Inventive Principle:

Principle #1Segmentation

2Measurement precision

If high-gain signal amplifiers are used to amplify weak signals from low-value measuring resistors, then the signal amplitude is improved, but noise and stray signals are also amplified

Engineering Contradiction:

Improvesignal amplitudeVSAvoidnoise amplification

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent creates separate measurement channels for different current levels. The first channel (R1 and amplifier 2A) handles weak currents with appropriate gain, while the second channel (R2 and amplifier 2B) handles strong currents. This prevents the amplification of noise that would occur if a single high-gain amplifier were used for all current levels.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Each measuring channel is configured with locally optimized components: resistor R1 and amplifier 2A are optimized for weak current measurement, while resistor R2 and amplifier 2B are optimized for strong current measurement. This local optimization ensures that each channel has the appropriate signal-to-noise ratio for its specific operating range.

Inventive Principle:

Principle #3Local quality

3Adaptability or versatility

If automatic amplifier gain control circuits are implemented to handle different current levels, then the adaptability is improved, but the device complexity and measurement errors increase

Engineering Contradiction:

Improvecurrent level adaptationVSAvoidcircuit complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

Instead of using a single amplifier with automatic gain control, the patent segments the measurement into two fixed-gain channels. Each channel has a dedicated amplifier (2A and 2B) with fixed gain optimized for specific current ranges. This eliminates the complexity of automatic gain control circuits while maintaining adaptability through the dual-channel architecture.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Rather than using one amplifier with variable gain controlled by complex circuits, the patent inverts the approach by using two amplifiers with fixed gains and selecting between them based on current level. This simplifies the control logic while achieving the same adaptability.

Inventive Principle:

Principle #13The other way round (Inversion)

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 provides a simple and dependable structure for current measurement with improved noise reduction and accurate signal processing across a wide dynamic range, suitable for monitoring and protection of electrical switchgear.

Implementation Method 1

first voltage limiting means connected in parallel on the first measuring resistor to branch a first shunt current off when a first limiting voltage is reached on said first measuring resistor

Methodology Applied

Scientific EffectVoltage limiting: Diode

Implementation Method 2

a first measuring resistor to receive a measurement current, a first signal amplifier having an input connected to said first measuring resistor

Methodology Applied

Scientific EffectOhm's Law: Ohm's Law

Data Source

PatentUS8160829B2Current measuring device and processing unit comprising one such device

Publication Date: 2012.04.17 SCHNEIDER ELECTRIC IND SAS

AI summary

The current measuring device comprises a first measuring resistor to receive a measurement current, and a first signal amplifier having an input connected to said first measuring resistor and an output to provide a first measurement signal. A second measuring resistor is connected in series with said first measuring resistor, and first voltage limiting means are connected in parallel on the first measuring resistor to branch a first shunt current off when a first limiting voltage is reached on said first measuring resistor. The value of the first measuring resistor is greater than the value of the second measuring resistor A processing unit comprises one such current measuring device.