Sensors between the magnet pole pieces measure the flux leakage field. The purpose of sensor systems is to convert the flux leakage field into a signal that can be stored and analyzed. Shown below is a typical sensor system. The sensor system consists of the sensors themselves, the mounting system used to support the sensors, wear plates between the sensors and the pipe, and cabling between the sensors and other electronic components.

The two types of sensors commonly used in MFL tools are induction coils and Hall elements (field sensor). Coils measure the rate of change of a magnetic field, while Hall elements measure the actual magnetic field strength. Historically, induction coils were commonly used type of sensor on MFL inspection tools because they do not require a power source. However, Hall effect sensors are becoming more commonly used.

Sensor size directly impacts the resolution of the measurement system, with many inspection vehicles exceeding 200 or more sensors for a 30-inch tool. Magnetic fields have three vector components, and a single sensor measures in only one direction. So, each sensor measures only one component of the flux leakage field. While most commercial MFL inspection systems measure only one component of the flux leakage field, some newer tools measure two or three.