Communications: electrical – Systems – Call station
Patent
1975-06-09
1977-01-11
Swann, III, Glen R.
Communications: electrical
Systems
Call station
307310, 340244R, 340239R, G08B 2100
Patent
active
040030385
ABSTRACT:
A thermal discriminator including two temperature sensitive switching devices having substantially identical electrical characteristics and exhibiting regenerative switching at a power level which is dependent on the temperature sensed by the switching devices. Both switching devices are exposed to the same ambient temperature in a surrounding medium but only one of them is exposed to variations in the heat exchange properties of the surrounding medium. Sufficient power is applied to both switching devices from an increasing voltage source to cause the switching devices to dissipate about the same amount of heat under certain conditions of the medium so that both switching devices would normally switch substantially simultaneously. A coupling device is connected between the two switching devices and includes regenerative switching in one of the switching devices in response to unbalance in the heat dissipated by the switching devices due to variations in the heat exchange properties of the surrounding medium from such conditions of the medium, and so inhibit the other switching device from switching. Discriminating means are connected to the two temperature sensitive switching devices for sensing which one of the switching devices has switched as an indication that the heat exchange properties of the medium have changed.
REFERENCES:
patent: 3343004 (1967-09-01), Ovshinsky
patent: 3402131 (1968-09-01), Futaki et al.
patent: 3766395 (1973-10-01), Keir
patent: 3781839 (1973-12-01), Bodge
patent: 3878541 (1975-04-01), Dodson
patent: 3882728 (1975-05-01), Wittlinger
Multi-State Devices Ltd.
Swann III Glen R.
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