GB2197075A

GB2197075A - Explosion proof housing with magnetically actuated input device

Info

Publication number: GB2197075A
Application number: GB08723553A
Authority: GB
Inventors: Thomas Andrew Karnowski; Charles A Vitorrio
Original assignee: Eaton Corp
Current assignee: Eaton Corp
Priority date: 1986-11-06
Filing date: 1987-10-07
Publication date: 1988-05-11
Also published as: GB8723553D0; DE3734494A1

Description

1 GB2197075A 1

SPECIFICATION

Explosion proof housing with magnetically.actuated input device Technical Field

The present invention relates generally to ex plosion proof controls and in particular to an explosion proof switch by which data can be entered to a control unit.

Background Art

Explosion proof housings are typically found in harsh environments. The housings enclose process control circuitry and other hardware.

In some types of controls, digital codes, pre sets, scale factors, etc. must be changed or reprogrammed in the control unit. When the circuitry and hardware is enclosed in a sealed explosion proof housing, the changing of 85 codes or the inputting of information can be difficult. In the past it has been necessary to provide switches as part of the housing. The mounting of these types of switches require that the explosion proof housing be modified to accept the explosion- proof switches. In short, the explosion proof case had to be penetrated in order to mount and use the ex plosion proof switches. Not only were the components expensive, but the added labor required to modify the enclosure added signifi cant cost to the control.

Disclosure of the Invention

The present invention provides a new and improved method and apparatus for providing data input into a control unit sealed within an explosion proof housing. Penetration of the housing is not required in order to mount or manipulate the data input device.

In the preferred and illustrated embodiment, an array of magneticresistive switches are mounted within the explosion proof housing. Receptive regions of the sensors are located in close adjacency with an inside surface of a 110 housing panel, the exterior surface of which is accessible by an operator. The panel is constructed of a non-magnetic material such as aluminum having sufficient strength to protect the components within the controls from the 115 external environment. Data such as function codes, presets and scaling factors are entered from outside of the housing by activating se lective sensors using a magnetic field such as one generated by a small permanent magnetic. 120 In the preferred construction, as a magnetic field is brought in close proximity with the outside surface of the enclosure and in line with an axial sensing direction of a given mag netic resistive sensor, the sensor will turn on 125 to indicate that function or a corresponding number is being entered. The output of the sensor can be used to input data and provide logic level input signals to electronic controls contained within the housing. In effect, a mag- 130 netically actuated keyboard is provided and eliminates the need for expensive explosion proof switches mounted to the exterior of the case. With the disclosed invention, not only is the manufacturing cost reduced but the overall size of the enclosure can be reduced as compared to enclosures utilizing external explosion proof switches.

In the exemplary embodiment, indicia such as a label is fixed to the exterior surface of the housing panel and defines the locations of the magnetic resistive sensors that are located within the enclosure. When an operator desires to input information into the unit, the magnetic actuator is moved into close proximity with the desired sensor the location of which is indicated on the label as a "key". The information is then sequentially inputted by bringing the actuator into alignment, sequentially, with the appropriate keys. With the disclosed invention, penetration of the case is totally obviated in order to input data to the control unit.

In the preferred embodiment, the magnetic- resistive sensors are a permalloy sensor available from the Microswitch Division of Honeywell Corporation under catalog No. SS22PE.

Additional features of the invention will become apparent and a fuller understanding ob- tained by reading the following detailed de- scription made in connection with the accompanying drawings.

Brief Description of the Drawings 100 Figure 1 is a front elevational view of an explosion proof housing and control unit embodying the present invention; Figure 2 is a sectional view of the housing and control unit shown in Fig. 1; 105 Figure 3 is a front elevational view of the unit shown in Fig. 1 with a front cover plate removed to shown interior detail; and Figure 4 is a perspective view of a magnetic actuator that can be used to actuate a magnetic keyboard forming part of the present invention.

Best Mode for Carrying Out the Invention

Fig. 1 illustrates the overall construdtion of an explosion proof control unit. Referring also to Fig. 2, the unit includes an explosion proof housing indicated generally by the reference character 10 which encloses electronic control hardware and circuitry indicated generally by the reference character 12 in Fig. 2.

As seen in Fig. 2, the housing 10 includes a rectangular casing 14 having a peripheral.

flange 14a and a front cover plate 16 having a mating flange 16a. The cover plate 16 is securely mounted to the casing 14 by a plu rality of bolts 18 which extend through aper tures 19 formed in the cover 16 and thread edly engage threaded bores 20 formed in the casing flange 14a.

The cover plate 16 is constructive of a non- 2 GB2197075A 2 magnetic material such as aluminum and includes an annular port 22 that mounts a window 24 through which an electronic display 26 (shown in Fig. 1) can be viewed. In the illustrated embodiment, the electronic hardware comprises a module 120 that is rigidly secured to the inside of the cover 16 as by bolts 28 (shown in elevation in Fig. 2 and in phantom in Fig. 1). The display 26 and much of the control hardware is conventional.

In accordance with the invention, the front cover 16 defines a magnetically actuated keyboard, indicated generally by the reference character 30. In the illustrated embodiment, a label or other indicia 32 is secured to the front cover 16 below the display 26. As seen in Fig. 1, the label may define a plurality of "keys" 32a which may comprises numerics as well as control function keys.

Referring also to Fig. 3, each of the keys 32a shown on the label 32 define a location of magnetically responsive switch 40 forming part of the control hardware 12. A, s seen in Fig. 3, in the disclosed control an array of 15 switches 40 are located in associated apertures 42 formed in a front plate 44 of the control 12. When the control unit 12 is mounted to the inside of the cover plate 16, the sensors 40 are positioned immediately ad- jacent the inside of the cover plate 16 and each of the sensors 40 is aligned with an associated key 32a on the label 32. With the disclosed magnetically actuated keyboard, changes to function codes, presets and scale factors can be accomplished from the exterior of the enclosure.

In order to enter information, a magnetic actuator 50 such as that shown in Fig. 4, which may include a small permanent magnet 50a, can be used. The magnetic switches 40 105 are arranged such that when a magnetic field is brought to the surface of the front cover 16 and in line with an axial sensing direction of the sensor 40, the sensor will be activated.

The output of the sensor can be used to pro- 110 duce logic level input signals to the electronic controls.

In the preferred embodiment, the magnetic switches are magnetic-resistive sensors which are available from the Microswitch Division of Honeywell Corporation and are sold under catalog No. S22PE. With this type of sensor, the cover plate 16 can have a thickness of approximately 3/4 of an inch or less. The magnetic-resistive sensors have sufficient sensitivity such that they can be activated through a 3/4 inch aluminum plate using a conventional permanent magnet. Moreover, the sensors have sufficient directional sensitiv- ity so that false triggering of adjacent sensors is minimized.

With the present invention, a fully sealed explosion proof enclosure can be used to enclose and protect a control unit 12. Unlike the prior art, the case does not have to be pene- trated in order to use explosion proof switches to enable the entry of data into the unit from outside the enclosure. The construction offers a substantially lower cost unit and reduces case size over present technology in applications where in the past, explosion proof switches mounted on two inch centers were required. The disclosed magnetic resistive sensor can be used with an aluminum wall thickness of 3/4 of an inch and a sensor spacing of.8 inches center to center.

Claims

1. An explosion proof process control as- sembly, comprising:

a) an explosion proof enclosure for enclos ing a process control unit; b) said enclosure having a cover plate defin ing an exterior surface and an interior surface; c) said exterior surface defining data input key locations; and d) an array of magnetically actuated sensors located in alignment with said key locations, said sensors located inside said enclosure and immediately adjacent said interior surface of said cover plate whereby a magnetic field brought to the exterior surface of said cover plate and in line with an axial sensing direction of a given magnetic sensor, will cause said sensor to produce an output signal representing data being entered.

2. The apparatus of Claim 1 wherein said magnetic sensors are magneticresistive sensors.

3. The apparatus of Claim 1 wherein said front cover plate is constructed of a non-fer rous material substantially 3/4 of an inch thick.

4. The apparatus of Claim 3 wherein said material is aluminum.

5. The apparatus of claim 3 wherein said sensors are spaced at least.8 inches apart.

6. An explosion proof process control apparatus substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.

Published 1988 at The Patent Office, State House, 66/7 1 High Holborn, London WC 1 R 4TP Further copies may be obtained from The Patent Office, Sales Branch, St Mary Cray, Orpington, Kent BF15 3RD. Printed by Burgess & Son (Abingdon) Ltd. Con. 1/87