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CURRENT MEASUREMENT

In various applications, measuring current is as crucial as measuring voltage. Before delving into current measurement techniques, it’s essential to understand what current entails.

Current: It signifies the flow of electrically charged particles (electrons) through a section within a specific timeframe.

Accurate measurement is paramount for circuit designers, and dealing with current values often proves challenging. To illustrate, consider our early education: voltmeters, used for measuring voltage, possess infinite internal resistance, preventing any current flow in the circuit and thus having zero impact.

Contrarily, ammeters, employed for measuring current, are designed with zero internal resistance to avoid acting as a load in the circuit. In reality, achieving infinite resistance or zero internal resistance is impossible, presenting a significant challenge in measurements. Fortunately, modern technology has made considerable progress in overcoming these challenges.

In numerous industrial applications, two widely preferred methods for current measurement prevail: the shunt resistance method and the utilization of Hall effect sensors.

1) SHUNT RESISTANCE METHOD

This method is very preferred and the method is the least cost. In short, according to the load in the circuit is a relatively small and negligible resistance, the current is read by the voltage proportional to the current, is the process of measuring the current. There are three problems that arise here;

  • The value of shunt resistance should be affected by environmental factors such as thermal changes.
  • The temperature effect of I ^ 2R losses should be considered.
  • The small volt range, which consists of a small resistance value selection, must be able to be measured.

When looking at various electronic reception sites, it can be seen that shunt resistances usually have very low value changes, such as temperature and humidity. This is of great importance when the shunt resistance value of our reference point is not changed.

input offset voltage

The temperature, which impacts resistance, poses a significant constraint on design considerations. This factor can notably affect the efficiency of circuits like inverters and converters, leading to potential challenges in system efficiency.

Another issue arises when dealing with extremely low voltage levels due to minuscule resistances and currents. Specialized operational amplifiers (opamps) are employed to amplify these low voltage signals. These opamps differ from general-purpose ones, standing out for their minimal input offset values. When selecting opamps on electronic component procurement platforms such as Digikey and Farnell, the term “op current measurement” becomes crucial, specifically due to these effects.

Shunt resistance measurement is divided into two as High-Side and Low-Side.

In Low-Side current measurement, one terminal of the shunt resistance is grounded. The other terminal, connected to the load, provides the voltage corresponding to the current flowing through the load. This simple setup finds extensive use in various applications due to its straightforward design. However, its limitation arises when one end of the shunt resistance must be grounded, rendering it ineffective, especially when precise measurement of partial currents within the circuit is essential.

Consider an application utilizing this method where the shunt resistance value is 1mΩ for load 1. The amplifier amplifies the voltage across the resistor by 100 times, and the current in the circuit is calculated using a doubling factor (represented in this software). In this scenario, when 0.1A flows through the circuit, 100uV is applied to the opamp’s input. Accurate measurement of this current necessitates the use of an opamp with low offset; otherwise, the reading will significantly deviate from the actual value.

1.B. HIGH-SIDE MEASUREMENT

In the High-Side measurement technique, unlike the Low-Side method, the shunt resistance isn’t required to be grounded. Only a differential amplifier in the amplifier section is used. Consequently, any current at any point in the circuit can be easily measured. The only challenge here lies in the fact that the amplifier setup is a bit more intricate compared to the Low-Side approach.

The current value obtained through this method is illustrated below. The distinction from the Low-Side method is immediately apparent; in this setup, the shunt isn’t connected to the ground. This arrangement necessitates more components in the amplifier. However, this design enables the separate measurement of various current points. Once again, having a low opamp input offset value remains a crucial consideration.

2) MEASURING WITH HALL EFFECT EFFECT

In essence, the Hall effect refers to the voltage disparity occurring within a conductor through which current flows, typically induced by a magnetic field. This phenomenon emerges because the magnetic field compels electrons in a specific direction, generating a force. The impact of this effect can be clearly observed in the image.

In this technique, the desired current is passed through any material, creating a magnetic flux, often in the form of a toroid. A Hall sensor then gauges the intensity of this flux, providing a corresponding voltage reading. As the quantity of flux varies linearly with the current, the output yields a linear voltage.

Consider the ACS755 as an example. As depicted, the Hall effect sensor can be connected to the desired location. Despite their high cost, these sensors find widespread use in the medical field owing to their precision.

AS A RESULT..

The process of measurement is consistently troublesome in this regard. Particularly when dealing with AC current readings and filters come into play, attempting to measure high current values adds complexity. To address these challenges, integrated manufacturers provide effective solutions. Naturally, all of this hinges on the quality of the solution, and engineers face the ongoing dilemma of balancing quality with cost-effectiveness. Achieving the best price-performance ratio remains the primary concern.

In conclusion, I want to wish everyone success in their endeavors. It’s worth noting that although I didn’t elaborate on it, current measurement can also be accomplished using a current transformer.

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