Page 18: of Marine Technology Magazine (November 2025)

LANDER LAB #16 to solid state devices. They have low resistance. The reeds are

Hall Effect Sensor hermetically sealed within a tubular glass envelope, which A Hall Effect sensor is another magnetically activated will implode with direct exposure to increasing depth. Thus, a switch. They produce a low signal level and require ampli? ca- reed switch must be placed inside a nonferrous housing, such tion. Its output is controlled by the presence or absence of a as plastic, aluminum, or titanium. They can be potted in a hard magnetic ? eld. Like a reed switch, a Hall Effect sensor can be epoxy for medium depth applications. A circular ring of reed operated inside a nonferrous housing, such as plastic, alumi- switches can be simultaneously triggered by a single magnet num, or titanium.

located in the center. Hot switching, switching with maximum Because the Hall Effect sensor is a solid-state device, it is not power on, can damage the part. As the switch opens or closes, prone to breakage, mechanical wear, and is pressure tolerant. an electrical arc can burn or weld the contacts. As the contact A Hall Effect sensor can be potted and operated in a high- plating is damaged, the resistance will eventually rise until the pressure water environment.

reed switch no longer works. Hall Effect sensors are sensitive to higher temperatures, but generally not within the range most ocean landers will see.

Higher temperature variants are available.

Hall Effect sensors come in two ? avors: Unipolar and Bipo- lar. Each have uniquely useful characteristics.

Unipolar Hall Effect sensors act like a SPST switch. The

Unipolar Hall Effect switch is normally closed. The part can be selected to be sensitive to either a north or south pole magnetic ? eld. Exposing the part to the opposite magnet- ic polarity does not affect the output state. (ref: Melexis

US5881, Cost: $0.60))

Bipolar Hall Effect sensors act like a latching relay. They can be selected to latch open with a north or south pole mag- netic ? eld. The opposite magnetic ? eld will latch the bipolar

Hall Effect switch in the closed state. (ref: Melexis US2882,

Cost: $0.63)

Microswitch, Momentary On-Off

A microswitch is a miniaturized mechanical device. The momentary on-off push button type can be used to determine position limits of components, such a piston in a bore. The smaller the switch, the smaller load it can handle.

Figure 5

Other sensors include Light, temperature, salinity, and vi-

Reed Switches come in a variety of sizes and packages, small to bration.

large, with different power, switching voltage and current ratings.

A better design uses these to control a MOSFET to handle the

Experimenters Workshop real power.

For those interested in tinkering with the parts discussed (Photo: Littelfuse) here, consider some of the components and kits offered by

SparkFun.com, Adafruit.com, Makershed.com, and Addi- core.com, among others. Some are under a dollar or two.

Practice makes perfect, or at least gives room for thought.

Future developments

New pressure tolerant and pressure protected battery tech- nologies are being developed for marine applications. Like- wise, globally, sensor engineers are investigating, character- izing, and developing new sensors to translate the marine environment into a digital equivalent for scienti? c investiga- tion, machine control, and government oversight.

Figure 6

A bipolar Hall Effect Switch acts like a latching relay. (Photo: Melexis) 18 November/December 2025

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