Johnson Controls Gmbh

Johnson Service Company

Johnson Service Corp.

Carl F Klein

Paul E Thoma

John E Aukofer

Jeannine O Colla

Scott L Spence

Paul H Froehling

Gary F Oman

Arthur Barootian

Alexander M Blok

Gerald E Weber

Ivshin Yefim

David L Klimek

Stuart R Buchanan

Andrew R Ralston

A capacitance humidity sensor according to the invention has a film core which is in contact with a pair of conductive layers bonded to opposite faces of the core. The core is made of a polyimide having a dielectric constant which varies substantially linearly with humidity and which includes at least one ether linkage in the dianhydride portion thereof. The polyimide may also include at least one ether linkage in the diamine portion thereof and/or at least one fluorine atom in the diamine, dianhydride or both the diamine and dianhydride portions thereof.

Capacitance humidity sensor

A capacitance elastomeric pressure sensor includes top and bottom mounting plates arranged to support a pair of electrode layers. The first electrode layer is supported on the upper surface of a dielectric disc held by an upper mounting plate. The second electrode layer is located beneath the disc and includes a conductive elastomeric layer overlying an elastomeric support layer. In the preferred embodiment, the elastomer is a silicone elastomer and the conductive layer is formed by admixing a conductive carbon powder with the silicone. The sensor is particularly effective in sensing pressure changes in this low range, e.g. 0-1 inch of water. In the most preferred embodiment the elastomeric layer is prestrained for temperature compensation.

Elastomer type low pressure sensor

A sensing probe unit includes an electrically nonconductive polymeric layer charged with a permanent electric charge to form an electret and intimately bonded to a compensating metal electrode. In the fabrication, the polymeric layer is cleaned and the metal electrode affixed to one surface by vapor deposition, lamination or baking. The polymeric layer may also be applied by coating the electrode with dielectric particles and then heating the subassembly to fuse the particles into an integral layer and to bond the fused layer to the electrode. The subassembly is thermally destressed and the polymeric layer is thereafter charged by triboelectric charging, corona discharge or electron beam charging, or by liquid contact charging processes. In the latter, a Freon-type or other similar liquid having good wetting properties and high evaporation rate is used as a contact charging liquid which creates a particularly stable electret. The sensing probe is stored to prevent loss of charge and sensitivity. The sensing probe unit in a pollutant and combustion detection apparatus is mounted within a suitable apertured ground shield unit with an exposed dielectric sensing surface to form an electrostatic sensor or a capacitor sensor. The compensating electrode is connected to a high impedance detection amplifier.

Fabrication of non-conductive charged sensing probe unit

An air pollutant and/or fire combustion sensing apparatus includes a capacitive sensor having spaced sensing electrodes producing a free space mounted within an environment subject to possible fire or the like. One of the sensing electrodes has an outer dielectric layer for absorbing contaminating gaseous products. The electrodes are connected to a high voltage power source for producing a charged capacitor with a high intensity static electric field of substantially 5.times.10.sup.5 V/M up to the dielectric breakdown of air in the free space or gap. The electric field reacts upon the contaminating gaseous products of combustion and environmental pollution and produces an opposing electric field with a net change in the electric field and the summated voltage appearing across the electrodes. A high input impedance detecting circuit with good electrometer characteristics responds to the change in the field.

Broad spectrum charged electric field polar gas sensing and detection

An air pollutant and/or fire combustion sensing apparatus includes a charged insulating sensing electrode layer establishing an electric field as the result of electric dipoles and/or electric monopoles in or on the sensing layer. The layer has a high surface and bulk resistivity. The layer has a minimal water absorption at environmental humidities. The electric field of the sensing layer creates electrostatic sensing reactions with the gaseous products of combustion and environmental pollution and produces an amplification of the charge detection characteristic to alter the charge of the electrode. In a capacitive sensor, the sensing layer is mounted within and in spaced relation to a ground shield member. The sensing layer is thereby exposed and produces a sensitive capacitive detector for sensing of a wide spectrum of combustion products and the like. Optimum results are obtained by the charging of dielectric materials such as polytetrafluoroethylene (Teflon TFE), perfluoroalkoxy (Teflon PFA), fluorinated ethylene-propylene (Teflon FEP), polystyrene or polyethylene, which also provide detection as the result of their gaseous adsorption characteristics. A high input impedance detecting circuit with good electrometer characteristics responds to the change in the charge, particularly on the surface.

Charged non-conductive polar gas sensing element and detection system

An air pollutant and/or fire combustion sensing apparatus includes a sensing electrode having an electrically non-conductive or dielectric sensing layer which has a surface resistivity in excess of 1.times.10.sup.10 ohms/square (and preferably 1.times.10.sup.15), and a bulk resistivity in excess of 1.times.10.sup.12 ohm-cm, and preferably 1.times.10.sup.15 at 50% R.H., and which is essentially free of dipole-hydrogen bonding forces such that the surface energy component is primarily due to dispersion bonding forces and, if at all, only incidentally as a result of dipole-hydrogen bonding forces. The latter appears to be a principal factor and desirably has a value of less than 5.0 ergs/cm.sup.2 and preferably less than 1.0 erg/cm.sup.2. The gases detected have a large Van der Waal gas 'a' constant and dipole moment. This sensing layer adsorbs air borne polar constituents to alter the charge on the electrode. Optimum results are obtained with polytetrafluoroethylene (Teflon TFE), perfluoroalkoxy (Teflon PFA), fluorinated ethylene-propylene (Teflon FEP), polystyrene or polyethylene. A high input impedance detecting circuit with good electrometer characteristics responds to the change in the charge, particularly on the surface. A thermally stabilized field effect transistor operating as a voltage amplifier with an input impedance on the order of 10.sup.10 ohms and preferably greater than 10.sup.12 ohms is satisfactory.

Non-conductive polar gas sensing element and detection system

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.

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New Berlin, WI, United States of America

Carl F Klein