WO2001076338A1

WO2001076338A1 - Housing for an intrinsically-safe signal conditioner

Info

Publication number: WO2001076338A1
Application number: PCT/US2001/005169
Authority: WO
Inventors: Edwin Arthur Hagerman, Iii
Original assignee: Micro Motion, Inc.
Priority date: 2000-03-31
Filing date: 2001-02-16
Publication date: 2001-10-11
Also published as: AU2001238448A1; AR029242A1

Abstract

A method and apparatus for housing intrinsically-safe meter electronics whereby a housing is formed by one or more members (200-210) affixed and sealed with a cam-lock mechanism (300). Separate housing component members are attached using an interlocking assembly whereby a first member couples to a second member using a matched set of surfaces that slide along one another to form a sealed mechanical connection. The matched surfaces are configured such that a twisting action draws the members together into a robust mechanical connection. A seal (306) is placed between members at the matched surfaces of the members (200-210), forming a sealed housing for intrinsically-safe electronics when members are mated.

Description

HOUSING FOR AN INTRINSICALLY-SAFE SIGNAL CONDITIONER

FIELD OF THE INVENTION

This invention relates to housings for electronics. More particularly, this invention relates to housings for intrinsically-safe electronics. Still more particularly this invention relates to providing a seal between attachable members of a housing.

PROBLEM Electronics for many applications may be required to operate in caustic or potentially explosive environments. However, 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 methods for 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, requiring additional wall thickness and structural support. Another solution when electronics must be 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 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 attaching the members used to form a housing for intrinsically-safe electronics are identical to the methods used for explosion-proof housings. Methods for attaching the members could include bolting, welding, or affixing via a threaded fitting. However, each of the named methods of attaching members 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 attaching 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. Patent No. 4,491 ,025 issued to J.E. Smith, et al. of January 1 , 1985 and Re. 31 ,450 to J.E. Smith of February 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. Sensors are placed at two different points on the flow tube to produce sinusoidal signals representative of the motion of the flow tube at the two points. A phase difference of the two signals received from the sensors is calculated in units of time. The phase difference between the two sensor 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 a signal conditioner. The signal conditioner generates parameter signals that indicate properties of the material flowing through the flowmeter. The signal conditioner 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 flowmeter electronics be contained in an explosion-proof container, which typically encompasses the entire flowmeter. Another method of the prior art removes metering electronics from the flowmeter 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 Coriolis-flowmeter 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.

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 an enclosure 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.

A housing in accordance with the present invention is comprised of two or more members. A cam-lock assembly is used for attachment of members and generally consists of a pin, which slides in a groove to a stop position, forming a tight member-to-member mechanical connection. The use of a cam-lock attachment system removes the need for a threaded mechanical connection, or other methods requiring machining or precision fabrication, while preserving a robust mechanical coupling and a seal. Additionally, the cam-lock attachment method provides for rapid affixing or removing of members. The cam-lock feature is an advantage over other prior attachment methods due to the ease and speed of operation of the mechanical coupling, the ability to couple members with a predetermined orientation without precise alignment, and the ability to cast the cam-lock features.

One exemplary embodiment of the invention is to enclose electronics for a Coriolis flowmeter. A housing containing intrinsically-safe meter electronics may be attached to the flowmeter. In accordance with the present invention an enclosure for intrinsically-safe meter electronics may be formed by coupling members of a housing with a cam-lock. A cam-lock may also be used for attaching a housing to the body of a flowmeter, or for mounting or support purposes. Utilization of the cam-lock system for the forgoing purposes allows ease of manufacture, rapid serviceability of all parts, and predetermined alignment of members or housings. None of the forgoing advantages has been available with prior attachment methods without undue expense. The present invention provides a solution to the prior cost, manufacturing and reliability limitations of other attachment methods, rendering the intrinsically-safe housing for Coriolis flowmeter electronics superior to an explosion- proof Coriolis flowmeter design.

These and other advantages of the present invention will be apparent from the drawings and a reading of the detailed description thereof.

A first aspect of the present invention is a first member having a cavity and an opening into a cavity defined by a first continuous side wall. A second member, having a base with a first surface and a second continuous side wall is proximate a perimeter of a first surface and extending outward from the perimeter of a first surface to be received by the first side-wall of the first member. A cam-lock affixes the first member to the second member using a pin protruding from a first side-wall which slides in a groove traversing a second side-walls. A seal is fitted between the first and said second side-walls.

A second aspect of the present invention is a substantially round side-wall on a first member and a substantially round side-wall on a second member at the surface of coupling the first member to the second member.

A third aspect of the present invention is that the first member is a casting.

A fourth aspect of the present invention is that the second member is a casting. A fifth aspect of the present invention is a housing wherein a pin is cast into a first side-wall of a first member.

A sixth aspect of the present invention is a housing wherein a groove is cast into a second side-wall of a first member.

A seventh aspect of the present invention is a housing of wherein a pin is cast into a second side-wall of a second member.

An eighth aspect of the present invention is a housing wherein a groove is cast into a first side-wall of said first member. A ninth aspect of the present invention is a housing with a detent at an end of a groove in a first or second side-wall.

A tenth aspect of the present invention is a housing with a stop position defined by a detent. An eleventh aspect of the present invention is a housing of with a spring for biasing a pin in a stop position.

A twelfth aspect of the present invention is a housing with a wave washer spring.

A thirteenth aspect of the present invention is a housing wherein a groove is cast in a first member for containing a spring.

A fourteenth aspect of the present invention is a housing wherein an o-ring is used as a seal.

A fifteenth aspect of the present invention is a method for sealing intrinsically safe electronics in a housing. Electronics are inserted in a cavity of a first member. A seal is positioned between interlocking mated surfaces of a first and a second member. The interlocking mated surfaces of the first and the second members are joined. Rotating the first member and the second member in opposing directions relative to one another thereby sliding a pin on a first or said second member into a groove on a first or second member to a stop position. The pin is biased at the stop position.

A sixteenth aspect of the present invention is a method for sealing intrinsically safe electronics in a housing. A first member and a second member are aligned for a predetermined orientation by rotating the first member and the second member in opposing directions relative to one another and biasing a pin in a notch

A seventeenth aspect of the present invention is a method for sealing intrinsically safe electronics in a housing. The first member is cast.

A eighteenth aspect of the present invention is a method for sealing intrinsically safe electronics in a housing. The second member is cast. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a depiction of a Coriolis flowmeter common in the art;

FIG. 2 is a depiction a cover for a housing in accordance with this invention; FIG. 3 is a detail of the cam-lock sealing mechanism

FIG. 4 is a first embodiment of a cam lock mechanism is accordance with this invention;

FIG. 5 is a second embodiment of a cam lock mechanism in accordance with this invention;

FIG. 6 is a third embodiment of a cam lock mechanism in accordance with this invention

FIG. 7 is an intrinsically safe housing incorporating this invention;

DETAILED DESCRIPTION Figure 1 illustrates a Coriolis flowmeter 5 comprising a flowmeter assembly

10 and meter electronics 20. Meter electronics 20 are connected to a meter assembly 10 via leads 100 to provide for example, but not limited to, density, mass- flow-rate, volume-flow-rate, and totalized mass-flow rate information over a path 26. A Coriolis flowmeter structure is described although it should be apparent to those skilled in the art that the present invention could be practiced in conjunction with any apparatus to contain electronics requiring a sealed enclosure.

FIG. 2 is a depiction of a cover for housing that encloses intrinsically safe circuitry. A first member 210 having a cavity 220 and an opening 230 into the cavity defined by the member sidewall 240. A second member, which by design, mates surfaces with the first member to create an enclosure 204. In order to affix the members to one another a cam-lock system is utilized. Figure 3 is a depiction of a cam-lock mechanism. A cam-lock system generally is a method of attaching members that utilizes a pin 301 , which slides in a groove 302 positioned so that sliding the pin in the groove draws the members together. A seal 306 is utilized between the members. A seal may include an o-ring or a gasket, a viscous compound, a washer or any other material that forms an airtight seal. Once the members are fitted to a tight position by the pin in the groove a stop position in the groove 302 locks the pin and therefore the members together. The stop position is a displacement from the groove so that the pin will not slide in the groove. This displacement may be a detent 303. In the preferred embodiment a spring 304 is utilized to hold the pin in the stop position. A spring may include a coiled spring, a wave washer, or another means for applying a spring-force to the pin so that it is biased in the stop position.

The cam-lock system may have several orientations. In the preferred embodiment, the pin or groove may be on either or multiple members. Figure 3-6 illustrate four possible but not all of the alternate embodiments of the invention. The purpose of the cam-lock attachment method is to replace other less desirable methods of attachment and to provide mass-produceable interchangeable parts. Additionally, the preferred embodiment envisions that the camlock system could be utilized to both affix members to form an enclosure, and to affix the enclosure to other members as well.

A salient feature of the cam-lock system is the ability to provide clocking or multiple selectable predetermined orientations of members when locked together with the cam-lock. It is desirable to provide predetermined orientations for member in the event that other features are cast into members that require alternate alignment. This feature allows mass production of members for a variety of installations with different physical layouts.

Figure 7 illustrates an embodiment of the invention suitable for containing intrinsically safe meter electronics utilizing two cam lock assemblies to form an enclosure.

Claims

What is claimed is:

1. A housing for enclosing intrinsically safe circuitry comprising: a first member (210) having a cavity (220) and an opening (230) into said cavity (230) defined by a first continuous side wall (240); a second member (200), having a base with a first surface and a second continuous side wall proximate a perimeter of said first surface and extending outward from said perimeter of said first surface to be received by said first side-wall of said first member; a cam-lock (300) for affixing said first member (210) to said second member (200) having a pin (301 ) protruding from a one of said first and said second side-walls and a groove (302) traversing a one of said first and second side-walls; and a seal (306) fitted between said first and said second side-walls.

2. The housing of claim 1 further comprising: a substantially round side-wall on said first member and a substantially round side-wall on said second member at the surface of coupling said first member to said second member.

3. The housing of claim 1 wherein said first member is a casting.

4. The housing of claim 1 wherein said second member is a casting.

5. The housing of claim 1 wherein said pin (301 ) is cast into said first side-wall of said first member.

6. The housing of claim 1 wherein said groove (302) is cast into said second side-wall of said second member.

7. The housing of claim 1 wherein said pin (301 ) is cast into said second side-wall of said second member.

8. The housing of claim 1 wherein said groove (302) is cast into said first side-wall of said first member.

9. The housing of claim 1 further comprising: a detent (303) at an end of said groove (302).

10. The housing of claim 9 further comprising: a stop position defined by said detent.

11. The housing of claim 1 further comprising: a spring (304) for biasing said pin in a stop position.

12. The housing of claim 11 wherein said spring comprises: a wave washer.

13. The housing of claim 1 wherein a groove is cast in said first member for containing a spring.

14. The housing of claim 1 wherein said seal comprises: an o-ring.

15. A method for sealing intrinsically safe electronics in a housing comprising: inserting electronics in a cavity (220) of a first member (210); positioning a seal (306) between interlocking mated surfaces of said first member (210) and a second member (200); joining said interlocking mated surfaces of said first (210) and said second (220) member; rotating said first member and said second member in opposing directions relative to one another thereby sliding a pin (301 ) on a one of said first and said second members into a groove (302) on a second one of said first and second member to a stop position; and biasing said pin (301 ) at said stop position.

16. The method of claim 15 wherein said step of affixing further comprises: aligning said first member (210) and said second member (200) for a predetermined orientation by rotating said first member (210) and said second member (200) in opposing directions relative to one another and biasing said pin (301 ) in a detent (303).

17. The method of claim 15 further comprising: casting said first member.

18. The method of claim 15 further comprising: casting said second member.