Here’s a real-world application where the reliability of the sensors is directly related to the reliability of the process in producing quality results.
Pictured below is a pneumatic actuator for a vacuum valve. Inside the actuator, a magnetic ring is installed around the moving piston by the manufacturer of the actuator (this is an option that must be requested when placing the order for the actuator). The magnet acts as a target to activate the sensors as it moves under them during operation. It’s important to note that the wall material of the actuator must be non-magnetic in order for this concept to work properly; typically aluminum or non-magnetic stainless steel is used.
The solid-state GMR (giant magneto-resistive) magnetic field sensors are fitted to an integrated slot on the exterior of the aluminum actuator housing. The slot allows easy adjustment of the activation point to indicate when the valve is open or closed.
As you can see, it’s important for the system to know whether or not the valve is in the open or closed position as the process is running. A false signal – such as a shorted-out low-cost Hall sensor or stuck reed switch, could have devastating consequences for the bottom line. When the risk of sensor failure is recognized – and financially quantified – the decision to invest a bit more up front to install the most reliable sensor technology available becomes pretty easy to justify.