US3798400A

US3798400A - Fully grounded pressure switch

Info

Publication number: US3798400A
Application number: US00341911A
Authority: US
Inventors: I Gebel; A Kahale
Original assignee: Controls Company of America
Current assignee: Eaton Corp
Priority date: 1973-03-16
Filing date: 1973-03-16
Publication date: 1974-03-19
Anticipated expiration: 1991-03-19

Abstract

The pressure switch has a switch mounted in the plastic, electrically insulative case above the diaphragm. The perimeter of the diaphragm is captured between the plastic case and the cup which has a tubular connector for connection to a source of pressure to be sensed. The chamber below the diaphragm between the diaphragm and cup is the pressure chamber and pressure variations cause flexure of the diaphragm and operation of the switch. The rim of the cup is rolled over the case flange to hold the parts assembled. The mounting bracket is secured to the case and to the appliance (or other equipment) frame - which is electrical ground - and, therefore, satisfies more stringent electrical requirements. In order to ground the cup - even though it is electrically dead - one end of a conductive ground strap is captured between the case and the cup when the cup rim is rolled over the case flange. The other end overlies the bracket and is captured by a screw mounting the bracket to the case. The arrangement meets demanding electrical requirements at very low cost and without requiring added costy manufacturing operation.

Description

United States Patent n91 Gebel et al.

[ Mar. 19, 1974 FULLY GROUNDED PRESSURE SWITCH [75] Inventors: Irving Gebel, Oak Park; Abed G.

' Kahale, Roselle, both of Ill.

[73] Assignee: Controls Company of America,

Schiller Park, Ill.

[22] Filed: Mar. 16, 1973 [21] Appl. No.: 341,911

[52 US. Cl. 200/83 R, 200/83 WM [51] Int. Cl H0111 35/34, HOlh 9/12 [58] Field of Search 200/83 R, 83 WM, 83 B,v

[56] References Cited UNITED STATES PATENTS 3,315,053 4/1967 Bauer ZOO/83 WM [57] ABSTRACT The pressure switch has a switch mounted in the plastic, electrically insulative case above the diaphragm. The perimeter of the diaphragm is captured between the plastic case and the cup which has a tubular connector for connection to a source of pressure to be sensed. The chamber below the diaphragm between the diaphragm and cup is the pressure chamber and pressure variations cause flexure of the diaphragm and operation of the switch. The rim of the cup is rolled over the case flange to hold the parts assembled. The mounting bracket is secured to the case and to the appliance (or other equipment) frame which is electrical ground and, therefore, satisfies more stringent electrical requirements. In order to ground the cup even though it is electrically dead one end of a conductive ground strap is captured between the case and the cup when the cup rim is rolled over the case flange. The other end overlies the bracket and is captured by a screw mounting the bracket to the case. The arrangement meets demanding electrical requirements at very low cost and without requiring added costy manufacturing operation.

1 Claim, 2 Drawing Figures 1 FULLY GROUNDED PRESSURE SWITCH BACKGROUND OF THE INVENTION Pressure switches of the general type shown herein have been considered electrically safe since all terminals and switch elements are mounted on insulative plastic. The pressure switch is mounted on the equipment frame by means of a metal bracket. Underwriters Laboratories now proposes that all metal parts be grounded even though electrically dead. The end cup in a pressure switch is such a dead metal part and thus requires grounding, notwithstanding the fact that it boggles the imagination to conceive of a failure which couldtresult invthe cup becoming electrically live. Obviously any part can be grounded but the problem is to do so at low cost and without jeopardizing the basic reliability of the pressure switch.

SUMMARY OF THE INVENTION The provision of the grounding strap having one end captured between the metal cup and the plastic case with the other end connected to the mounting bracket provides an extremely simple and low cost solution to the problem of meeting the new standards. The construction does not impair the diaphragm seal and thus cannot affect the pressure switch performance. No added costly manufacturing operations are required. The piece part cost is minimal. Other proposed solutions were not satisfactory for cost or performance reasons. The present solution easily meets the standards (two-volt maximum drop under overload conditions of 40 amps for two minutes and a surge of 1,000 amps at 250 volts without appreciable galvanic corrosion or structural impairment).

- DESCRIPTIONS OF THE DRAWINGS FIG. 1 is a perspective view of the pressure switch according to this invention.

FIG. 2 is a vertical section taken along a longitudinal line showing the internal construction of the pressure switch.

DESCRIPTION OF THE PREFERRED EMBODIMENT The pressure switch has a plastic, non-conducting case and a bottom metallic cup 12 sandwiching and gripping the rim of the diaphragm 14 between the case and the cup, the upstanding rim 16 of the cup being crimped or rolled over the flange 18 of the case. The cup has a tubular connector 20 welded therein affording means for introducing pressure variations into the chamber 22 below the diaphragm so the diaphragm may flex in accordance with the pressure in the chamber. The diaphragm is provided with a rigid diaphragm pad 24 with an upstanding actuator 26 acting on the tongue 28 of the switch 30. The switch has a contact supporting blade 32 which is interconnected with the tongue by means of the barrel spring 34 imparting overcenter action to the blade 32 between lower contact 36 and the upper contact 38. The actuator 26 is opposed by spring 40 compressed between seat 41 and plunger 42 which is positioned by lever 44 controlled by cam member 46 fixed on shaft 48 and actuated by lever 50 which is adapted to project through the front of a splash panel on a washing machine, for example. Details of such construction are not important here nor are the details of the switch actuation. It is necessary only to appreciate that the switch 30, the switch blade and the two contacts are connected to terminals 52, 54, 56 on the exterior of the case.

Bracket 58 is secured to the case by screws 60, 62 and serves to support the pivot 48 for the cam member 46 and is provided with

tabs

64, 66 which are adapted to be secured to the machine frame which, in machines of this type, is considered electrical ground. The bracket 58 is, of course, an electrically dead member and complies with the new standards for grounding dead metal parts.

The problem solved by this invention is the requirement that the electrically dead metal cup 12 must now be grounded. One can conceive of many methods of accomplishing this including redesigning the cup, electrically conductive paint on the case, etc. but the solution provided by this invention represents simplicity in itself and yet has proven highly satisfactory by way of meeting the functional and electrical requirements at extremely low cost. Thus the grounding strap 68 has one end positioned between case flange 18 and rim 16 prior to the rim being crimped or rolled onto the flange. Thus when the rim is crimped onto the flange, the lower end of the strap 68 is mechanically clamped between the case flange 18 and rim without adverse effect on the seal at the diaphragm. Preferably a copper strip is used to take advantage of the high electrical conductivity and easy forming. The strap is formed with a sharp bend 70 to reduce precision required in forming this part. The screw hole in the secured end 72 of the strap can easily be positioned over the corresponding hole in the mounting bracket 58 and, of course, in the case 10. Then when the screw 62 is tightened, the strap 68 is securely mounted on the pressure switch providing a good electrical path between the cup 12 and the metal bracket 58 and, hence, to the machine frame when the switch is in its operating environment. This meets all requirements of the new standards, which standards are applicable even though it is difficult to see how a rather substantial disintegration of the switch itself could result in the cup becoming electrically conductive since all the switch parts are insulated from the cup by the rubber diaphragm. A more probable hazard, albeit most unusual, would be some sort of short between a terminal (52, 54, 56) and the cup.

We claim:

1. A pressure switch including a non-conducting case,

a conductive cup secured to the case,

a diaphragm having its periphery captured between the case and cup to provide a pressure chamber between the diaphragm and cup,

a switch mounted in the chamber between the case and diaphragm,

a conductive mounting bracket secured to the case,

said cup including a rim and being secured to the case by crimping the rim onto the case,

an electrically conductive grounding strap having one end captured between the rim and case and secured thereto when the rim is crimped onto the case, I

the other end of the grounding strap being connected to said conductive bracket, said strap bridging the portion of the case lying between the two points of connection of the strap.

m s =0 1: t

Claims

1. A pressure switch including a non-conducting case, a conductive cup secured to the case, a diaphragm having its periphery captured between the case and cup to provide a pressure chamber between the diaphragm and cup, a switch mounted in the chamber between the case and diaphragm, a conductive mounting bracket secured to the case, said cup including a rim and being secured to the case by crimping the rim onto the case, an electrically conductive grounding strap having one end captured between the rim and case and secured thereto when the rim is crimped onto the case, the other end of the grounding strap being connected to said conductive bracket, said strap bridging the portion of the case lying between the two points of connection of the strap.