Detailed explanation of current sensor technology

In any process, the measurement of electrical quantity is essential for monitoring, analysis, and control systems. To perform these types of measurements, a current sensor must be used. Physical quantities cannot be managed unless they can be measured. Let's delve deeper into the behavior of current sensors.

A current sensor is a device that converts a current signal into another analyzable signal. The signal to be measured is called "primary current", while the output signal is called "secondary current or voltage". The last signal is used for electronic boards, ADC, and other analog instruments. Due to the existence of different measurement techniques and the possibility that the primary current may vary depending on waveform, pulse type, isolation, and current intensity, the market offers a variety of current sensors. As shown in Figure 1, the most common current sensors are divided into two categories:

According to the working principle of "diverter", the first type applies Ohm's law (V=R × I )。

The second type uses Ampere's law (I=Å H × Ds) and use a magnetic field to measure the current.

Ohm's law applies to shunt measurement, with the formula V=R × I。 In practice, a shunt is a robust resistor with a known ohmic value. When the current passes through the shunt, the voltage generated is proportional to the current. By utilizing this principle, we can accurately obtain AC and DC currents for relatively low currents. On the other hand, when the current rises above 100 A, excessive heat is generated, and the measurement system may become ineffective and critical.

Hall effect current sensors can be used to overcome these limitations. Powering the Hall probe will apply a magnetic field perpendicular to the surface and generate a voltage proportional to the strength of the magnetic field. Then, the Ampere's law can be used to calculate the amount of current flowing through a conductor. The Hall current sensor uses a magnetic core to concentrate the magnetic field in the air gap where the probe is located. The output voltage is proportional to the magnetic field, which in turn is proportional to the primary current. The performance of current sensors depends on the performance of open-loop Hall probes. In order to improve linearity and reduce temperature drift, the closed circuit principle is implemented, and another type of current sensor is represented by a magnetoresistor, where the value of the resistor changes proportionally to the magnetic field. These current sensors are usually more accurate than Hall effect, but there are sensitivity limitations due to air gaps. However, the equipment must ensure efficient and accurate measurement, with very high detection quality, extremely flat frequency response, and excellent DC stability. All of these features can be found in Danisene's current sensors, which provide customized solutions to meet the exact needs of customers.

Current measurement method

Current measurement can be performed using the LT6106 integrated circuit, which is a multifunctional amplifier for current detection (see the application diagram in Figure 2). Its characteristics are highly praised:

Maximum voltage offset: 250 µ V

Maximum input bias current: 40 nA

Only two resistors are needed to set the gain of the device

Accuracy: 1%

Maximum output current: 1 milliampere

PSRR: 106 decibels

Its main applications are automotive and industrial, battery monitoring, energy management, engine control, lamp monitoring, and overcurrent and fault detection. This device measures current by detecting the voltage at both ends of an external resistor (shunt resistor). The internal circuit converts this voltage into output current. The extremely low power current of LT6106 also makes it suitable for battery applications.