Hall Effect Sensor Types: Unipolar, Bipolar, Omnipolar, and Linear

This article explores different types of Hall Effect sensors, including Unipolar, Bipolar, Omnipolar, and Linear sensors. We’ll examine the characteristics and differences between these variants.

What is a Hall Effect Sensor?

Introduction:

• When an electrical current flows through a conductor’s length and a magnetic field is applied across its width, a force is generated. This force causes electrons/holes to accumulate asymmetrically on opposite sides of the conductor. This phenomenon is known as the “Hall Effect.”
• Hall effect sensor components include amplifier circuitry in addition to the sensing element. They typically use an open collector output and a comparator/Schmitt trigger to provide hysteresis.

Figure 1 depicts Hall Effect current sensing.

• There are four main variants of Hall Effect sensors: unipolar, bipolar, omnipolar, and linear.

Unipolar Hall Sensor

The following are characteristics of Unipolar Hall Sensors:

• They activate when an external magnetic field exceeds a specific threshold value.
• These sensors switch OFF when the applied magnetic field diminishes or is removed.
• Unipolar sensors can be activated by either the north or south pole of a magnet.

Bipolar Hall Sensor

Here are the features of Bipolar Hall Sensors:

• Proximity to one magnetic pole will switch the sensor ON.
• Proximity to the opposite magnetic pole will switch the sensor OFF.
• In the absence of a magnetic field, the sensor remains in its current state (either ON or OFF).

Omnipolar Hall Sensor

The following describes the characteristics of Omnipolar Hall Sensors:

• Proximity to a strong magnetic field of either polarity will switch it ON.
• Removal of the magnetic field will switch it OFF.
• Omnipolar sensors can be constructed using a pair of unipolar sensors mounted in opposite directions with their outputs (open collector) wired together.
• This component functions similarly to a reed switch, but it requires a power supply.

Linear Hall Sensor

The following are the features of Linear Hall Sensors:

• Their output voltage varies proportionally to the external magnetic field strength.
• When no magnetic field is detected, the output voltage is typically half of the supply voltage.
• In response to one magnetic polarity, the output can drop almost to zero. The opposite polarity can increase the output almost to the supply voltage.
• It is also known as an analog Hall Sensor.
• The output from a linear sensor is usually supplied from the emitter of an internal NPN transistor and not the collector.