The reed switch was invented in1936 at Bell Laboratories. Nearly all reed switches work on the premise of an attractive force: An opposite polarity develops across a normally open contact. When the magnetism is sufficient this force overcomes the stiffness of the reed blades, and the contact pulls together. This same attractive force operates SPDT switches, the attractive force of the normally open contact pulls a common member away from a normally closed member also present in the SPDT switch. To fabricate a Form B switch, normally closed in the absence of a external magnetic field, users typically utilize the normally closed side of the SPDT form C switch OR they attach a magnet to the normally open switch to close it, and rely on an external magnetic field to override the attached bias magnet.

HSI Sensing has now developed a True form B switch. It is not a modified SPDT form C switch, and it is not a magnetically biased SPST form A switch. It features uniquely designed reed blades that ingeniously develop a like polarity in the presence of an externally applied magnetic field. When the magnetic field is of sufficient strength the repelling force developed in the contact area pushes the two reed members away from each other, thus breaking the contact. With removal of the magnetic field, their natural mechanical bias restores the normally closed contact. This is the first true innovative development in reed switch technology in decades!


Originally developed to meet the exacting requirements of many applications of implantable devices needing a battery-saving technology, the HSI True Form B reed switch is only the first in a line of custom form B switches currently in development. We welcome your application needs regarding size, function, voltage, power or other requirements you may have for normally closed applications. HSI Sensing already has the broadest line of reed switches, developed with innovative thinking and precise manufacturing. Now we have expanded it again.

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Published On: December 16th, 2014 / Categories: Making Sense / Tags: , , /

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