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AssigneeJohnson Controls GmbH
InventorsCarl F. Klein, Stuart R. Buchanan, Paul E. Thoma, David L. Klimek
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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.
The method of fabricating a non-conductive, gas sensing probe unit having an electrically non-conductive outer charged polymeric dielectric layer defining an exposed sensing surface and said charged dielectric layer having a permanent electric charge and being intimately bonded to a compensating conductive electrode, comprising at least the three separate steps of prefabricating a solid dielectric body having a bulk resistivity of at least 1.times.10.sup.12 ohm cm at 50% RH and a surface resistivity of at least 1.times.10.sup.10 ohms/square at 50% RH, thereafter thermal destressing of said prefabricated solid dielectric body, said thermal destressing including heating of said prefabricated solid dielectric body and then slowly cooling of said prefabricated solid dielectric body at a rate which avoids stress and strain deformation in the solid dielectric body to produce an essentially charge free dielectric body free of stress and strain, thereafter charging the destressed and charge free dielectric body subsequent to said destressing step to create a permanent electric charge in said body which creates a high intensity electric field at the exposed sensing surface, and including the step of bonding a compensating conductive electrode to the dielectric body without change in the permanent charge of said destressing dielectric body to form a dielectric-electrode electret subassembly.
In the fabrication of a probe unit responsive to pollutants and to the products of combustion including those created during the incipient and initial stages of combustion, said probe unit including a base compensating metal electrode secured to an electret detection member having an exposed surface opposite the face secured to said metal electrode, comprising at least the three separate steps of fabricating an essentially non-charged dielectric solid body of a polymeric material to the configuration of the electret detection member, intimately affixing a metal electrode to the noncharged dielectric body to form a dielectric-electrode subassembly, thereafter thermal destressing the non-charged dielectric solid body by heating of said solid body and slowly cooling said heated solid body at a rate which avoids stress and strain deformation in said solid body to thereby create an essentially charge free dielectric body free of stress and strain, and applying a high intensity electron source to the sensing dielectric surface of the destressed and charge free dielectric body subsequent to said thermal destressing of said solid body and thereby creating a permanent electric charge carried by the solid body as a result of said high intensity electron source to form an electret and an electret-electrode subassembly.
Dependencies are inferred from the claim text.