There are several different methods available to sense and measure current inside a circuit or conductor. In this article, we will discuss how to measure current using various different sensor types, each with their own benefits and drawbacks.
Hall Effect Sensors
Hall Effect sensors can measure the difference in charge between one side of a conductor and the other to determine the voltage of the current, as well as the direction and intensity of a magnetic field that is being applied to it. Though the reading will be accurate, the output voltage is very low and needs to be amplified to a useful value by using a high gain amplifier with very low noise. One key advantage of Hall Effect sensors is that they are nearly contactless and are able to measure a current without breaking the circuit to place a meter. In addition, they can be used with both AC and DC, as well as in higher frequency applications.
Fluxgate sensors use a saturable inductor as their main component, so they are typically called Saturable Inductor Current Sensors. These sensors work very similarly to Hall Effect sensors, but with a difference in the material of their cores. In a fluxgate sensor, there are two coils (primary and secondary) that are wrapped around a saturable inductor core. The changes in the current flow can alter the core permeability and cause a change of inductance across the other coil as a result. Saturable Inductor Current Sensors have the advantage of being able to measure in a wide range of frequency with great accuracy, low offset, and drifts. Some limitations to consider are that they exhibit high secondary power consumption and are only suitable for DC or low-frequency AC.
Rogowski Coil Sensors
A Rogowski coil sensor is made using a helical shaped air core coil that is wrapped around a conductor for current measurement. Typically, they require additional circuitry to make an output voltage which is proportional to the current, as Rogowski coils provide an output voltage depending on the rate of current change. Moreover, Rogowski coils are excellent at detecting fast, high-frequency current change, and they are low-cost and very safe to operate. However, it should be noted that they are only suitable for AC and have lower sensitivity than current transformers.
Current Transformer Sensors
Current transformers are used to sense the current by a secondary voltage which is proportional with the current in the secondary coil. They are transformers which convert the large value of voltage or current into a much smaller value in the secondary coil, that way a readable measurement can be taken. Current transformer sensors are particularly useful for their large current handling capacity that does not require additional circuitry to make a useful output. Nevertheless, some limitations to consider are that they require ongoing maintenance, and can exhibit hysteresis due to magnetization.
Shunt Resistor Current Sensing Method
The most commonly used method in current sensing techniques is to use a shunt resistor, that of which is a low-value resistor used in a series to sense current. When a current flows through a low-value resistor, it produces a voltage difference across the resistor which can be used to indicate the voltage. Since the output voltage will be very small, shunt resistor sensors must use a high gain amplifier to give a usable value for calculating the voltage of the circuit. The benefits of these sensors are that they are very cost-effective and can work with both AC and DC. However, they are not suitable for high current operation and can create a decrease in system efficiency due to energy loss in the resistor.
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