The Hall sensor is a magnetic field sensor. In contrast to the reed switch, it has a continuous signal response depending on the magnitude of the magnetic field. You can use continuity, for example, to determine the direction of motion of a passing magnet sensor. Thus, for the flowmeter, it is possible to create an algorithm for compensating for irregularities in the flow of fuel, which cause the measuring ring to move in the opposite direction. (In flow sensors built on reed switches, they are falsely counted as a normal flow). In practice, it is difficult to build such an algorithm, but our studies on the amplitude and frequency of flow pulsations in the fuel system of cars have made it possible to create a booth for imitating water hammers. Further studies showed that for reliable operation of the flowmeter on the Hall sensor, one sensor is not enough and it was decided to apply 3 Hall sensors. This complicated the algorithms, but allowed to get rid of a number of problems and make the system universal.
The Hall sensor, like a reed switch, registers the effect of an external magnetic field and flowmeters with such sensors can not make measurements when a strong magnet is brought to it. It’s in theory. In practice, the situation is the following: the reed switch can only show 2 states – there is an effect of a magnetic field or it is not and blocking its operation even by a relatively weak external magnet is not difficult. The signal from the Hall sensor carries information about the intensity of the magnetic field and the effect on it even of a strong rare-earth magnet only shifts the signal, which is easily compensated algorithmically and does not violate the performance of the flowmeter.
The complexity of the algorithms and the provision of the required speed caused the use of high-speed 32-bit microcontrollers with the ARM core operating at the frequency of 72 MHz in the Mechatronics flowmeter. The STM32 family of ST companies are not only high-performance, but also very reliable, noise-proof solutions, which further increased the reliability of the flowmeters.
The high stability of Hall sensors to the interference of the vehicle’s on-board network, and their high overload capacity, made it possible to create a line of cheap flowmeters on their basis without digital signal processing. Manufacture of flowmeters on reed switches without digital signal processing, due to the phenomenon of bounce of its contacts and weak protection from external magnetic influence, was discontinued.
In comparison with the reed switch, the Hall sensor has such a disadvantage as high power consumption, which makes it impossible for the flowmeter to operate from the built-in battery. Therefore, the rulers of the independent flowmeters Direct A and Delta A still use the detector on the reed switch.