This section provides overview, applications, and principles of current sensors. Also, please take a look at the list of 39 current sensor manufacturers and their company rankings.
A current sensor is a device that measures the current flowing in a circuit.
Current sensor must be built into current circuits, which can be dangerous and require the circuit to be disconnected, but there are also types of current sensor that can measure current by simply clamping a portion of a circuit from the outside.
Current sensors are used in situations where the value of the current flowing in a specific circuit needs to be determined.
Current sensors that are directly integrated into circuits are often used to measure and record the value of the current that flows in a circuit on a regular basis. In this case, the information is used for self-maintenance of equipment in operation.
On the other hand, current sensors that clamp the circuit from the outside are useful in non-routine situations, such as pre-and post-checking of energization during electrical work or checking the energized part to investigate the cause when an electrical circuit fails.
Current sensors directly connected to a circuit acts as a resistor and measures the current flowing through the circuit based on the voltage applied.
Clamp-type current sensors cannot measure the actual current flowing in a circuit because they are not directly connected to the circuit. Therefore, the magnetic field generated from the current flowing in the wires of the circuit is measured and output as a current equivalent value.
Specifically, the clamp section has a magnetic core, and the magnetic field is detected at that section and converted to a current value.
Among the various measurement methods, the Hall element method is one that can detect both DC and AC. In this method, a Hall element is incorporated in the magnetic core to measure the magnetic field generated in the circuit under test as a voltage, which is converted into a current value via a built-in amplifier.
As mentioned briefly in the Principles section, there are two types of current circuits: DC circuits and AC circuits. It is important to select an appropriate current sensors according to the current component of the circuit you wish to measure and the accuracy you wish to measure.
In general, if you do not need high accuracy, you should select a Hall element that can handle both DC and AC circuits, but it may not clamp well depending on the installation position of the circuit.
In the case of AC, Rogowski-type current sensors without a core can be selected to allow measurement while bending the clamping section.
Current sensors have different applications depending on the characteristics of the detection method. There are two main current detection methods. The two methods are the resistance detection type and magnetic field detection type.
The resistive detection type detects current by inserting a shunt resistor at the point where the current to be measured flows. According to Ohm's law, a voltage drop occurs when a current flows through the resistor. The current can be determined by measuring this voltage value and dividing it by the resistance value. Although it depends on the circuit design, it is common to select a small resistance value for the shunt resistor so that it does not affect the operation of the circuit. However, heat generation and breakdown voltage of the resistor value can be a problem when measuring large currents. If the voltage drop is small, a current sense amplifier must be used to amplify the voltage to be detected.
The magnetic field detection type measures the magnetic field created by the flowing current. According to Ampere's law, when a current flows, a magnetic field is generated in the direction in which the right-hand thread turns when the direction of the current is the direction in which the right-hand thread moves. This magnetic field is detected using a Hall element. A Hall element is an element that uses the Hall effect, a phenomenon in which an electromotive force appears in a direction orthogonal to both the current and the magnetic field and is used to detect the magnetic field.
The resistance detection type using a shunt resistor is used for overcurrent detection in power supplies such as DCDC converters, LED drivers driven by current, and current control and circuit protection in motor drive circuits. The magnetic field detection type using a Hall element does not require an element to be placed on the circuit pattern where the current is to be measured, so it is also used for clamp ammeters to measure current by clamping wiring and for motor position detection.
Current detection using resistance detection type with a shunt resistor or magnetic field detection type with a Hall element often produces a small output, so when a circuit is configured with discrete components, it is common to combine a current sense amplifier or operational amplifier in the circuit.
Manufacturers also offer dedicated ICs with built-in amplifiers instead of discrete components, which can be selected according to the application and characteristics.
*Including some distributors, etc.
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