Measuring and testing – Liquid level or depth gauge
Reexamination Certificate
1999-08-27
2001-06-19
Moller, Richard A. (Department: 2856)
Measuring and testing
Liquid level or depth gauge
C073S866500
Reexamination Certificate
active
06247362
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to process instruments and, more particularly, to a high temperature, high pressure seal for a probe assembly.
BACKGROUND OF THE INVENTION
Various instruments have found use for applications requiring level sensing of, for example, a liquid or bulk material in a vessel. One such instrument comprises a time domain reflectometry measurement instrument. With any such instrument it is desirable to ensure safety of both equipment and personnel.
A time domain reflectometry measurement instrument uses guided wave radar for sensing level. The instrument includes a control housing and a probe. The probe is typically mounted to a process vessel using a threaded fitting or a flange fitting. The probe comprises a high frequency transmission line which, when placed in the vessel, is used to measure level of fluid in the vessel. The probe is controlled by electronics in the control housing for determining level in the vessel.
Process instruments are sometimes used for sensing level of a pressurized vessel. Often, the contents of the vessel is at a high temperature. In order to seal the vessel at the probe connection, an appropriate seal must be included. The seal must be appropriate for the relatively high temperatures and pressures when used in such applications.
A time domain reflectometry instrument, as well as certain other process instruments, imparts a pulse signal on the probe and receives a return signal. The relationship between the pulse signal and the return signal is used to determine level. Typically, the control housing includes a 50 ohm control connection for the probe. If the probe has a different impedance, then a mismatch results. The mismatch can cause errors in level measurement. In applications where the probe has a 50 ohm impedance process connection, matching that of the control electrical connection, the design of the process seal can cause an impedance mismatch.
The present invention is intended to satisfy one or more of the problems discussed above.
SUMMARY OF THE INVENTION
In accordance with the invention, a process instrument includes a high temperature, high pressure probe seal.
Broadly, there is disclosed herein a high temperature, high pressure process seal for use with a process instrument having a control housing assembly with a control connection having a 50 ohm impedance, and a sensing element extending into a high temperature, high pressure process vessel. The sensing element has a process connection having a 50 ohm impedance. The seal operatively connects the sensing element to the control housing assembly. The seal includes an elongate cylindrical hollow seal adaptor receivable in an opening of the process vessel. An elongate shaft is coaxial with and extends through the adaptor and is adapted to connect the control connection to the process connection. A hard seal material between a select portion of the shaft and the adaptor is bonded to the shaft and the adaptor. Radial spacing between the shaft and the adaptor is greater at the select portion to provide a 50 ohm feed-through from the control connection to the process connection.
It is a feature of the invention that the shaft has a reduced diameter at the select portion. The adaptor has an inner cylindrical wall with an increased inner diameter at the select portion.
It is another feature of the invention that the seal material has a dielectric higher than air and the radial spacing is determined by the dielectric of the seal material.
The seal material may comprise a low loss and low dielectric glass or ceramic material.
It is another feature of the invention that the adaptor and shaft are made of Inconel.
There is disclosed in accordance with another aspect of the invention a high temperature, high pressure process seal probe for use with a process instrument, having a control assembly with a control connection having a 50 ohm impedance, and for extending into a high temperature, high pressure process vessel. The probe includes a sensing element for extending into the process vessel and having a process connection having a 50 ohm impedance. An elongate cylindrical hollow seal adaptor is receivable in an opening of the process vessel and is connected to the control housing assembly. An elongate shaft is coaxial with and extends through the adaptor and is connected at an inner end to the transmission line and at an outer end to the control connection. A hard seal material between a select portion of the shaft and the adaptor is bonded to the shaft and the adaptor. Radial spacing between the shaft and the adaptor is greater at the select portion to provide a 50 ohm feed-through from the control connection to the process connection.
Further features and advantages of the invention will be readily apparent from the specification and from the drawings.
REFERENCES:
patent: 5217596 (1993-06-01), Indig et al.
patent: 5661251 (1997-08-01), Cummings et al.
patent: 5907112 (1999-05-01), Queyquep
patent: 6073492 (2000-06-01), Rosselson et al.
Magnetrol International
Moller Richard A.
Wood Phillips VanSanten Clark & Mortimer
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