Receptacles – Sectional – Electrical housing
Reexamination Certificate
2001-06-19
2004-03-23
Yu, Mickey (Department: 3728)
Receptacles
Sectional
Electrical housing
C206S305000, C073S204220
Reexamination Certificate
active
06708834
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to housings, and more particularly, to housings that enclose intrinsically-safe electronics.
BACKGROUND
Electronics for many applications may be required to operate in caustic or potentially explosive environments. The operation of electronics in a potentially explosive environment can result in ignition of volatile material. One solution is to enclose the electronics in an explosion-proof housing isolated from the environment. Making a housing explosion-proof includes issue of encapsulation, pressurization, and flameproof containment. An explosion-proof housing design requires a flame-path of a sufficient length to cool any material escaping from a container if combustion does occur within the housing. Flame-path length is a function of the length of a machined thread. Explosion-proof housings are generally more expensive to fabricate and require additional wall thickness and structural support.
Another solution when electronics are used in volatile environments is to design the electronics to intrinsically-safe standards. Intrinsically-safe electronics operate at a low power level below a particular energy threshold. Operating a device at a low power level ensures that heat or spark generation will not occur. The power-level requirements for intrinsically-safe electronics are established by regulatory agencies such as the Underwriters Laboratory (UL) in the United States, CENELEC in Europe, CSA in Canada and TIIS in Japan.
When intrinsically-safe electronics are operated in a caustic or volatile environment, it is necessary to protect the electronics in a housing to prevent circuit damage or failure. A problem with housings for intrinsically-safe electronics is that the housing must be sealed to prevent environmental intrusion. It is also desirable that a housing for intrinsically-safe electronics be modular and interchangeable so that housing parts can be mass-produced. A housing may be formed using one or more members that are combined to form an enclosure that contains the electronics. There is a cost advantage to using intrinsically-safe electronics instead of explosion-proof designs because of the less stringent requirements for an intrinsically-safe electronics housing. However, prior methods of assembling the members used to form a housing for intrinsically-safe electronics are virtually identical to the methods used for explosion-proof housings. Methods for assembling the members could include bolting, welding, or affixing via a threaded fitting. However, each of these methods of assembling has cost, manufacturing, or logistical limitations that render such methods undesirable, and which offset the cost savings of an intrinsically-safe design. Actual cost-benefits depend upon finding a solution for assembling and sealing parts of a housing that is as robust and reliable as prior methods, and also allows rapid precision alignment of parts, but does not require precision machining.
One application for electronics that operate in a volatile environment is a Coriolis flowmeter. A Coriolis mass flowmeter measures mass flow and other information of materials flowing through a pipeline in the manner described by U.S. Pat. No. 4,491,025 issued to J. E. Smith, et al. of Jan. 1, 1985 and Re. 31,450 to J. E. Smith of Feb. 11, 1982. A Coriolis mass flowmeter has one or more flow tubes of a curved or straight configuration. Each flow tube configuration in a Coriolis mass flowmeter has a set of natural vibration modes, which may be of a simple bending, torsional, radial, or coupled type. Each flow tube is driven to oscillate at resonance in one of these natural modes. The natural vibration modes of the vibrating, material filled systems are defined in part by the combined mass of the flow tubes and the material within the flow tubes. Material flows into the flowmeter from a connected pipeline on the inlet side of the flowmeter. The material is then directed through the flow tube or flow tubes and exits the flowmeter to a pipeline connected on the outlet side.
A driver applies a vibrational force to the flow tube. The force causes the flow tube to oscillate. When there is no material flowing through the flowmeter, all points along a flow tube oscillate with an identical phase. As a material begins to flow through the flow tube, Coriolis accelerations cause each point along the flow tube to have a different phase with respect to other points along the flow tube. The phase on the inlet side of the flow tube lags the driver, while the phase on the outlet side leads the driver. Pickoffs are placed at two different points on the flow tube to produce sinusoidal pickoff signals representative of the motion of the flow tube at the two points. A phase difference of the two signals received from the pickoffs is calculated in units of time. The phase difference between the two pickoff signals is proportional to the mass flow rate of the material flowing through the flow tube or flow tubes.
The sensors transmit the sinusoidal signals to meter electronics. The meter electronics generates parameter signals that indicate properties of the material flowing through the flowmeter. The meter electronics also generates a drive signal applied to the driver to vibrate the flow tubes. The parameter signals are then transmitted to a host system which provides the desired properties to a user.
Coriolis flowmeters have inherent power requirements necessary for ordinary operation that generally have required conformance to explosion-proof designs. In the prior art, the standard practice has been to design flowmeters to explosion-proof standards. An explosion-proof design requires that the meter electronics be contained in an explosion-proof container, which typically encompasses the entire flowmeter. Another method of the prior art removes the meter electronics from the flowmeter and into another housing that is explosion-proof, but attached to the flowmeter. This method requires that the meter electronics housing comply with all appropriate mandates for an explosion-proof design, which includes precision thread machining of fitted members of the housing for proper flame path length. Precision thread machining is expensive, and is easily damaged under normal use. Additionally, machining of parts contributes a step to the manufacturing process, adding time to fabrication and also increasing costs.
Another method is to use intrinsically-safe electronics in a separate housing for the meter electronics. This method allows the use of housings designed to the more relaxed intrinsically-safe housing requirements. The primary advantage of the intrinsically-safe design approach is the application of less stringent housing requirements. However, in the prior art the cost of attaching and sealing parts to form enclosures for this purpose has not provided a commercial benefit because of the cost of manufacture. A method for enclosing electronics meeting intrinsically-safe standards is desired that provides a rapid, effective, robust, and reliable means for sealing multiple members of a housing as well as prior methods while providing ease of manufacture and cost savings.
STATEMENT OF THE SOLUTION
The above and other problems are solved and an advance in the art is achieved through the provision of a cam-lock assembly for affixing and sealing members of a housing for containing intrinsically-safe electronics. The first distinct advantage of the present invention is the ability to cast a cam-lock feature, thereby avoiding the expense of precision machining after casting as in threaded attachment methods. A second distinct advantage of the present invention is the ease of coupling and sealing members used to form a housing for intrinsically-safe electronics. Members of a housing may be attached or detached with ease using a twisting action as in threaded assemblies. Another feature of the cam-lock is that members may have one of several predetermined orientations when coupled simply by casting multiple cam-lock features into the members.
In one example of the invention, the ho
Arnold Troy
Duft Setter Ollila & Bornsen LLC
Micro Motion Inc.
Yu Mickey
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