of its elements, resulting in a device which accurately and reliably senses a selected external condition within a desired range.
According to the present invention, the switching device includes a deflectable member whose deflection is caused by changes in an external condition to be detected, such as temperature, pressure or acceleration. Movement of the deflectable member from a less strained to a more strained condition causes the establishment of electrical contact between a common contact and first one then progressively more switch terminals in the device. The circuit is completed by the series connection of each switch to a fusible link whose other terminal is tied in common with all other fusible links in the switching device which is in a common terminal. The common terminal connected to thefusible links is, in the preferred embodiment, within the chamber formed by the hermetic sealing of a first substrate, including the deflectable member, and a second substrate. From the common terminal, a single conductor is passed through the seal to enable electrical connection of the device to an external calibrating or monitoring circuit. This reduction in the number of seal penetrations reduces the seal failure rate.
The trimming of the device to preselect the threshold value of the external condition to be detected is accomplished easily, accurately and reliably. A chosen calibrating level of the external condition is applied to the device. The resultant force causes the deflection of the deflectable member and consequent closing of one or more switches. A voltage is then applied to the common terminals