Measuring and testing – Fluid pressure gauge – Diaphragm
Reexamination Certificate
2000-02-22
2001-08-28
Fuller, Benjamin R. (Department: 2855)
Measuring and testing
Fluid pressure gauge
Diaphragm
C073S706000
Reexamination Certificate
active
06279401
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to process control devices, and, more particularly, to improvements in differential pressure transmitters. Differential pressure transmitters measure the difference between two pressures and produce an output signal, typically with a display, responsive to the measurement.
Differential pressure transmitters are commonly used in process control systems that require pressure measurements, or measurements of other variables associated with gases and liquids, e.g., flow rates. A typical differential pressure transmitter has two process diaphragms, each exposed to one of two fluid pressures that are to be compared, and has a transducer. An inert fill fluid is provided in a closed chamber between each process diaphragm and the transducer, to transmit pressures from the process fluids to the transducer. Each process diaphragm deflects in response to the pressure of one fluid, as applied from an input process line. The transducer responds to the difference between the two pressures of the process fluid, and produces electrical output signals for indication or control. Pressure transmitters that produce electrical output signals often include electronic circuitry to process the transducer signal and to display it by way of a read-out meter, and/or to apply the processed signal to a computer or other electronic device.
Two conventional structural types of pressure transmitters are known: planar designs in which the process diaphragms share the same plane, and bi-planar designs in which the process diaphragms are in different planes and are disposed back-to-back. Conventional planar transmitters generally have an electronics housing that extends horizontally when the transmitter is oriented so that the plane of the process diaphragms is vertical. This configuration can require special hardware to mount the transmitter. Additionally, the electronics housing is displaced from the diaphragm plane in such a way that a read-out meter on the housing is often difficult to see.
Another drawback of conventional planar transmitters is that the electronic circuitry is located close to hot process lines. Specifically, in one prior configuration, the differential pressure transmitter is close to the high pressure and low pressure input process lines. These process lines can radiate heat to the transmitter electronics, thereby creating a hot operating environment. Thus, the transmitter is more susceptible to electrical malfunctions. Additionally, exposing the electronics to unnecessary elevated temperatures reduces the life of the electrical components.
A further drawback of prior transmitters is that the conventional transmitter housing assembly limits the size of the process diaphragms. A large diaphragm diameter is advantageous because it has a correspondingly low spring rate and hence aids high measuring sensitivity. The diaphragm volumetric spring rate is inversely proportional to the sixth power of the diameter of the diaphragm. However, prior pressure transmitter structures restrict the diameter of the process diaphragms to avoid undue size, which leads to a relatively large diaphragm spring rate.
Prior pressure transmitters accordingly resort to thin diaphragms, to achieve a usable spring rate. This, in turn, presents a risk of diaphragm leakage, which is a serious problem.
Conventional planar pressure transmitters endeavor to circumvent the foregoing mounting problems by using a flange adapter, in conjunction with the existing assembly that mounts the pressure transmitter. However, this solution adds weight and cost to the system.
Conventional bi-planar transmitters are relatively heavy and relatively costly. The additional weight stems at least in part from large dual process covers that mount over the process diaphragms, and from the weight of the associated cover mounting hardware.
Another drawback of both the convention al designs is that the electronic circuitry is susceptible to fluid noise, such as mechanical shocks, pipe vibrations and like mechanical disturbances. Consequently, the pressure transmitters are susceptible to producing measurement errors when mechanical disturbances occur.
Due to the foregoing and other shortcomings of conventional pressure transmitters, an object of this invention is to provide a robust differential pressure transmitter that is relatively light in weight and relatively low in cost.
Another object of the invention is to provide a pressure transmitter that has a read-out indicator that is relatively easy to view.
Still another object of the invention is to provide a transmitter housing of relatively small size that mounts process diaphragms of relatively large diameter.
Yet another object of the invention is to provide a transmitter housing that is
A further object of the invention is to provide a pressure transmitter that shields electronic components therein from the elevated temperatures of hot process lines, and hence maintains the components in a relatively cool environment.
It is also an object of the invention to provide pressure transmitters that operate with minimal loss of performance when measuring fluids subjected to vibration and other mechanical noise.
Other general and specific objects of this invention will in part be obvious and in part be evident from the drawings and description which follow.
SUMMARY OF THE INVENTION
This invention attains the foregoing and other objects with a pressure transmitter having a body portion, a diaphragm element, a flange element, and first and second pressure passages. The body portion is generally mounted upright and includes, in that orientation, a vertical surface apertured with first and second pressure openings located at substantially the same vertical location. A transducer mounting element is coupled to the body portion and is located above the pressure openings. The diaphragm element is configured to form first and second process diaphragms respectively closing the first and second pressure openings.
This structure, in one embodiment, includes integral ribbed elements that provide support and add structural stiffening to the body portion. The body portion preferably has a neck portion that mounts the transducer mounting element to the body portion and that provides thermal isolation therebetween.
According to one aspect of the invention, the flange element overlies the diaphragm element and is removably and replaceably secured to the body portion. The flange element is configured to form first and second pressure ports that couple fluids in first and second pressure input lines to the first and second process diaphragms, respectively.
The first and second pressure passages extend at least partly within the body portion, and communicate respectively between the first and second pressure openings and the transducer mounting element. The pressure transmitter according to the invention has a flame retardation element disposed in at least one of the first and second pressure passages to be in the fluid path between a sensor element in the transducer mounting portion and a process input line. The flame retardation element thus introduces a flame barrier between the mounted sensor element and a process fluid being measured.
According to further aspects of the invention, the transducer mounting element mounts a sensor element that is in fluid communication with the first and second pressure passageways and that is located, in the upright orientation of the body portion, above the process diaphragms. The sensor element includes a transducer, located at least partly between opposed first and second faces of the sensor element, for generating a differential pressure signal. The transducer responds to the difference in pressure between the pressures applied to the first and second pressure ports.
The sensor element preferably has an overrange protection element that protects the transducer from overrange pressure fluctuations. In a preferred embodiment, the overrange protection element overlies at least the first pressure passageway, and is integral with the
Aw-Musse Abdullahi
Foley Hoag & Eliot LLP
Foxboro Company
Fuller Benjamin R.
Liepmann W. Hugo
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