There are various current detection products on the market. How can we find a suitable current sensor for our system among the dazzling array of products? This requires multiple interpretations, including the actual usage environment, spatial limitations, signal requirements, temperature range, and so on, all of which will affectHall Current Sensor Propose various requirements, and together with the engineers from Weikewei, analyze the differences between these products and conduct a comprehensive analysis of their advantages and disadvantages.

1 Current Transformer CT/Voltage Transformer PT

In transformer theory, the ratio of primary and secondary voltage is equal to the ratio of turns, and the ratio of current is the reciprocal of the ratio of turns. CT and PT are special transformers.

In terms of basic structure, CT has fewer turns on the primary side and more turns on the secondary side. If the secondary side is open circuited, the voltage on the secondary side will be very high, which will break through the insulation of the winding and circuit, causing damage to equipment and personnel. On the contrary, PT has more turns on the primary side and fewer turns on the secondary side. If there is a secondary short circuit, the current on the secondary side will be high, causing the circuit to heat up and burn out the winding and load circuit electrical components.

CT, Current Transformer, spelled as Current Transformer in English, is a transformation device that proportionally converts a large current on the primary side into a rated current of 5A or 1A, suitable for use through instruments or relays. Its working principle is similar to that of a transformer. Also known as TA or LH (old symbol) working characteristics and requirements:

1. The series connection between a primary winding and a high-voltage circuit depends only on the current of the high-voltage circuit, and is independent of the size of the secondary load.

2. Open circuit is not allowed in the secondary circuit, otherwise it will generate dangerous high voltage, endangering personal and equipment safety.

3. The CT secondary circuit must have one point directly grounded to prevent high voltage to ground caused by insulation breakdown of the primary and secondary windings, but only one point grounded.

4. Accuracy of transformation.

PT， Voltage transformers, spelled as Phase voltage Transformers in English, are transformation devices that proportionally convert high voltage on the primary side into a rated voltage of 100V suitable for use in instruments or relays. The working principle of an electromagnetic voltage transformer is the same as that of a transformer. Also known as TV or YH (old symbol).

Job characteristics and requirements:

1. The primary winding is connected in parallel with the high-voltage circuit.

2. The secondary winding is not allowed to short-circuit (short-circuit current burns PT) and is equipped with fuses.

3. The secondary winding has a point directly grounded.

4. Accuracy of transformation

This type of CT and PT usually have a large volume, heavy weight, and significant temperature drift at high temperatures.

2 Modular Hall current sensor

Modular Hall current sensor with separate loop mode and closed-loop mode.

Open loop mode, also known as direct measurement Hall current sensor, has an input of current and an output of voltage. The advantage of this method is its simple structure, high accuracy and linearity of measurement results. Can measure current of DC, AC, and various waveforms. But its measurement range, bandwidth, etc. are subject to certain limitations. In this application, Hall devices are magnetic field detectors that detect the magnetic induction intensity in the air gap of the magnetic core. After the current increases, the magnetic core may reach saturation; As the frequency increases, eddy current losses and hysteresis losses in the magnetic core will also increase. All of these will have an impact on measurement accuracy. Of course, some improvement measures can also be taken to reduce these effects, such as selecting magnetic core materials with high saturation magnetic induction intensity; Make multi-layer magnetic cores; Using multiple Hall elements for detection and so on.

The structural principle of open-loop mode is shown in the following figure

According to the requirements of the detection range, there are generally two winding modes. The left figure shows the structure diagram of the small range, and the right figure shows the structure diagram of the large range.

Closed loop mode, also known as zero flux mode or magnetic balance mode, has both input and output terminals as current signals.

Amplify the output voltage of the Hall device, then amplify the current to pass through the compensation coil, and make the magnetic field generated by the compensation coil opposite in direction to the magnetic field generated by the measured current, ultimately achieving magnetic balance.

This balancing process is automatically established and is a dynamic equilibrium. The time required to establish balance is extremely short. At equilibrium, Hall devices are in a zero flux state. The magnetic induction intensity in the magnetic core is extremely low (ideally 0), which will not saturate the core and will not cause significant hysteresis or eddy current losses. Proper selection of magnetic core materials and circuit components can result in high-performance zero flux current sensors.

The module Hall current sensors on the market nowadays are generally larger in size, powered by dual power sources, and more expensive. The closed-loop mode Hall current sensor has better performance than the open-loop mode, but the price is also much higher than that of the open-loop mode.