The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Nov. 02, 1976
Filed:
Aug. 26, 1975
Carl F Klein, Milwaukee, WI (US);
Paul E Thoma, Burlington, WI (US);
Gerald E Weber, Ben Brook, TX (US);
Johnson Controls, Inc., Milwaukee, WI (US);
Abstract
An air pollutant and/or fire combustion sensing apparatus includes a pair of sensing electrodes separated by a free space to define a capacitance unit. At least one of the electrodes includes a corrosion-resistant, conductive material which interacts with air borne products to alter the permittivity and/or charge transfer characteristic of the unit. The material is in the form of a highly corrosion-resistant metal selected from a metal or metal alloy including at least one of the metals selected from the Group VIII, periods 4, 5, and 6 of the periodic table, particularly rhodium and stainless steel. Carbon and copper respond to produce a detectible output. An amplifying and alarm circuit is connected to the capacitance unit, and responds to either an increase or a decrease in the capacitance as a result of the interaction with the sensing electrode material. The circuit includes a thermally stabilized field effect transistor as a buffer input amplifier connected in differential configuration to produce a high input impedance and a high gain. The transistor is connected to a high gain DC operational amplifier having a feedback compensation network to compensate for thermal and low frequency drift change. A constant current source provides the bias supply to the input amplifier to improve common mode rejection and the thermal stability. A pair of programmable unijunction transistors are connected to the output of the operational amplifier and to the input of an alarm device to detect either an increase or a decrease at the amplifier output which may arise as a result of the decreased or increased capacitance characteristics of the air borne material.