How do sensors for magnetic sensing applications work? Pt 1

At Sensors Expo 2019, Neil Cersell, President of the Cersell Company Inc., explains his company’s magnetic sensors that are available for magnetic actuation market. The magnetic actuators can be the round line ISO-6432 disposable style, a rectangular box style, tie-rod cylinders, short stroke clamp cylinders and even rotary actuators. All of these designs have a piston and a magnet inside of them. The magnet provides the magnetic field for the sensor, a reed switch.

With a see-through, demonstration version of a cylinder type actuator, Cersell shows how a very strong magnet and a very weak magnet impact a sensor. As the piston moves forward, at as little as 20 mm from the sensor, a standard sensor starts to trip. Moving forward it trips on and off, called double and even triple tripping. This occurs because the strong magnet gives out a wide field so the sensor is prematurely impacted by the magnet. From the weak magnet’s perspective, as the piston moves past the sensor, the magnet is is so weak that it does not detect the sensor because the gauss rating is very small.

With Cersell technology, instead of measuring the magnetic field, the sensor actually sense the thickness of the magnet itself, which is about 3 to 4 mm in width. As a result, very crisp on and off states are detected for a one-time actuation with the strong magnet and the weak magnet. This technology applied to a much smaller cylinder, for example one with only 1-mm stroke, avoids magnetic field confusion from the two sensors on the actuator and no cross-over action occurs, since the thickness of the magnet is what is being detected. This allows very small control elements.