Seal for a joint or juncture – Seal between fixed parts or static contact against... – Contact seal for other than internal combustion engine – or...
Reexamination Certificate
1999-04-28
2001-12-04
Trettel, Michael F. (Department: 3628)
Seal for a joint or juncture
Seal between fixed parts or static contact against...
Contact seal for other than internal combustion engine, or...
C277S312000, C277S630000, C277S920000
Reexamination Certificate
active
06325391
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a process window seal that will transmit microwave energy and includes a surrounding ring with seals to reduce or prevent microwave energy leakage. The ring contains the window seal to avoid creep or cold flow across a wide range of temperatures to avoid failures under operating pressures.
In the past, there have been considerable developments in the use of microwave (radar) gauges for determining tank levels. These gauges depend upon transmitting microwave energy toward a surface of material inside a tank or container, and then receiving an echo or return signal to determine the level of the material sending the echo. The correct type of device depends in part on the overall distance that needs to be measured, that is the height of the material in the tank between its lowest level and its highest level. Also, the surface conditions of the materials are of importance in measuring tank level, as are the dielectric constant or conductivity of the material to be measured.
In using a radar gauge, the process tank or container that is to be monitored can sometimes be at a very high temperature, as well as at a high pressure. In such instances, it is necessary to have a pressure containing window seal between the radar instrument and the interior of the tank, to protect the instrument from harsh, corrosive process materials. The window seal has to be able to transmit microwave energy for operation of the radar gauge.
Various manufacturers have advanced radar gauges, including the MICROPILOT radar gauge made and sold by Endress+Hauser. These devices are used for determining levels of various materials.
Window seals made of polytetrafluoroethylene (PTFE) are commonly used, but under high temperatures and high pressures they will tend to flow, so that the pressure carrying capability is reduced at such high temperatures. Usually the need for high pressure performance is when the temperature is high as well. Thus, being able to control the flowing of the PTFE at process temperatures is desirable for maximum utilization of the window materials.
SUMMARY OF THE INVENTION
The present invention relates to a process isolator seal and microwave energy transmitting assembly for determining the level of material in a container. The container has a top opening surrounded by a bounding surface. A microwave energy gauge or transmitter is mounted above the opening on a microwave transmissive window seal member which is of size to close the opening, and which has a flange supported on the bounding surface. An electromagnetic shielding material containment ring surrounds the microwave window seal member and encloses the edge surface of the microwave window seal member. The edge of the containment ring carries a resilient electromagnetic shielding O-ring that also seals on the bounding surface. The containment ring preferably controls the peripheral size of the microwave window seal member under clamping forces adjacent the periphery of the seal.
The container as shown is a process fluid tank on which a microwave radar level gauge or transmitter is mounted. As shown, a support flange of the window seal is clamped between the bounding surface on the tank flange on the customer's tank, and a stand off pipe that surrounds a horn antenna on the microwave level gauge or transmitter. The clamping of the microwave window seal member between flanges will retain it securely, and create a seal, but under high tank pressures, and high temperature and humidity, and with highly corrosive materials, the preferred PTFE material for the window seal member will tend to cold flow or to creep. Creep can occur even under lower temperatures when the pressures are high. The containment ring surrounding the window seal member controls the amount of creep or cold flow radially outwardly, thereby reducing the shear stress in the PTFE and increasing the pressure rating for a given temperature in a comparable size seal.
The containment ring helps to maintain the shape of the PTFE window seal member over time. The containment ring preferably has an inwardly extending lip that overlies a portion of the seal flange. Clamping forces are applied to the containment ring, and the lip provides a cross sectional area engaging the seal flange on which the applied clamping loads act that is less than the stand off pipe flange. Also, the load from pressure in the process fluid tank is applied over this smaller cross sectional area defined by the lip of the containment ring. Shear stress is reduced and the pressure rating is increased.
The containment ring is made of a material such as stainless steel, which provides the electromagnetic interference (EMI) shielding. Other gaps where microwave radiation can escape are closed by an O-ring that contains materials which will provide EMI shielding between the edge of the containment ring and the bounding surface. The O-ring also forms a pressure seal between the edge of the containment ring and the bounding surface of the tank flange.
The reduction in stray electromagnetic radiation emissions from the radar gauge or transmitter permits installation without obtaining a separate license from agencies such as the Federal Communications Commission.
A metal, spiral gasket is used above the lip of the containment ring and is clamped in place with the stand off ring to further increase the integrity of the seal.
A process fluid environmental seal O-ring also can be provided on the PTFE window seal. As shown the O-ring is mounted in a shouldered groove open at the periphery of the PTFE window seal flange. The containment ring closes the shouldered groove so the environmental seal O-ring is trapped in place.
REFERENCES:
patent: 3019281 (1962-01-01), Hartwell
patent: 4566321 (1986-01-01), Zacchio
patent: 4932673 (1990-06-01), Domnikov et al.
patent: 5061467 (1991-10-01), Johnson et al.
patent: 5115104 (1992-05-01), Bunyan
patent: 5115218 (1992-05-01), Jean
patent: 5117066 (1992-05-01), Balsells
patent: 5200722 (1993-04-01), Wolf
patent: 5305237 (1994-04-01), Dalrymple et al.
patent: 5495218 (1996-02-01), Erb et al.
patent: 5507181 (1996-04-01), Fox et al.
patent: 5508712 (1996-04-01), Tom et al.
patent: 5594449 (1997-01-01), Otto
patent: 5703289 (1997-12-01), Mulrooney
patent: 5770990 (1998-06-01), Lubbers
patent: 6155112 (2000-12-01), Eckert et al.
patent: 0 992 942 A1 (1999-06-01), None
Published AdvertisementMeasureTech™RCM Features and Benefits, date not available (undated).
Kruse Steven D.
Olson Randall C.
Smith Dennis J.
Hewitt James M
Rosemount Inc.
Trettel Michael F.
Westman Champlin & Kelly PA
LandOfFree
PTFE window seal with EMI shielding does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with PTFE window seal with EMI shielding, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and PTFE window seal with EMI shielding will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2592311