IRLabs recently completed a research paper on the “Comparative Analysis of Reed Switches and Hall Sensors at Cryogenic Temperatures,” which examines the feasibility of using reed switches as a cost-effective alternative to Hall effect sensors for cryogenic motion control. While Hall sensors offer precise positional feedback, they require additional electronics and are expensive. Through a Position Comparison Test at 77K and a Bulk Test down to 4.2K, the study found that reed switches provide comparable accuracy (±150µm) with no significant degradation over multiple thermal cycles. However, a 20% failure rate was observed during the initial cooldown, though surviving switches remained reliable at cryogenic temperatures. Given their lower cost, ease of implementation, and sufficient accuracy, reed switches present a viable alternative to Hall sensors for many cryogenic applications, with further research needed on their long-term durability and performance in high-vibration environments.
Switches are often used in motion control applications to indicate home positions, limits of travel, or positions-of-interest within the range of motion. Cryogenic systems also feature motion control, but many switches stop functioning properly at cryogenic temperatures. Magnetic switches are of interest since they are non-contact, minimizing component wear and contamination inside the vacuum chamber.
Often with systems developed at IRLabs, cryogenic Hall sensors are used as magnetic switches in cryogenic motion control applications, however, these sensors do have some disadvantages. Because they are precision sensors for measuring magnetic fields, they add additional costs and functionality not necessary for the application. Furthermore, Hall sensors output a small analog voltage that needs amplification and conversion into a switch output for the motion controller.
Because of the high unit costs and extra implementation costs, this paper investigates using non-contact magnetic reed switches as an alternative. Reed switches are commonly used in room-temperature motion control applications and are actuated by magnets like a Hall switch. Unlike Hall sensors however, there is no need for separate electronics to convert the analog output—the outputs of reed switches are two wires that are ready to connect to IO pins on most commercial motion controllers.
Cryogenic Reed Switch vs. Hall Sensor
Reed Switch and Hall Sensor testing set up and the placement of the wires
