GB2119538A

GB2119538A - Fibre-optic switch

Info

Publication number: GB2119538A
Application number: GB08212507A
Authority: GB
Inventors: David Wilson
Original assignee: Standard Telephone and Cables PLC
Current assignee: STC PLC
Priority date: 1982-04-29
Filing date: 1982-04-29
Publication date: 1983-11-16
Also published as: FR2526218A1; GB2119538B

Abstract

A fibre-optic switch comprises a diaphragm (1) of magnetically soft material sealed in a capsule. The face of the diaphragm (1) can be highly polished so as to have good reflectivity. An optical fibre (9) terminated in a ferrule (8) is sealed into a tube (2) which may be magnetic, and which is on one side of the diaphragm (1) with the fibre end near to the diaphragm (1). Light from the fibre (9) is reflected back thereinto and is modulated in accordance with the movement of the diaphragm (1). Alternatively the ferrule (8) contains two adjacent fibres, one used as a transmitting fibre and the other a receiving. The fibres may be non- parallel, enhancing the optical coupling between the fibre ends. The magnetic field can come from a coil or movable permanent magnet. In one version the magnet is a rotatable disc with alternate N and S poles on its rim. This can be used as the movable element of a flowmeter. <IMAGE>

Description

SPECIFICATION Fibre optic switch This invention relates to a fibre optic switch which is magnetically operated.

According to the invention there is provided a fibre optic switch, which includes a sealed enclosure containing a diaphragm of a ferromagnetic material whose position is alterable in response to a magnetic field whose characteristics depend on a parameter to be monitored, and one or more optical fibres, the or each said fibre having an end aligned with and adjacent to one face of the diaphragm, the arrangement being such that light from the end of the fibre or one of said fibres is reflected back into that fibre or into one of said fibres, and that the amount of light thus reflected back is dependent on the position of the diaphragm.

Embodiments of the invention will now be described with reference to the accompanying drawings, in which: Fig. 1 is a schematic representation of a first switch embodying the invention.

Fig. 2 is a schematic representation of a second switch embodying the invention.

Fig. 3a to 3e show varous magnetic operating arrangements usable in switches embodying the invention.

Fig. 4 shows schematically how a switch embodying the invention may be used as the sensor for flowmeter.

The arrangements to be described herein are based on the use as the magnetic portion of a switch of a so-called diaphragm relay capsule, and relays using such capsules have been described in, inter alia, our British Patent Specification Nos.

1094334 and 1219556 (H. S. Woodhead 4 and 17). Such relays are made both with make contact capsules and with changeover capsules, and in the arrangements shown in Figs. 1 and 2 the capsules are of the changeover type.

In Fig. 1, the capsule is of the changeover type, its diaphragm 1 normally being in engagement with the break contact 2. This contact is of electrically conductive magnetically soft material and is sealed into a glass disc 3 which is itself sealed to one of two ferro-magnetic rings 4 and 5.

The make contact 6 is sealed into another glass ring 7 which is itself sealed into the ring 5. The diaphragm 1 is a flat plate of an electrically conductive magnetically soft material with arcuate slots each of which commences near the rim of the plate so as to define a substantially circular central region. The slots and the adjacent fingers defined thereby form springly supports for the circular central region, which is thus movable in a direction normal to the plane of the diaphragm under the influence of a magnetic field.

Mounted centrally of, and sealed into, the break contact there is a fibre optic ferrule 8, in which the end of the optical fibre 9, which is a single fibre, is sealed into a jewel 10 at a position adjacent to the upper face of the diaphragm 1. This upper face is treated so as to be highly reflective.

In use, light is supplied to the switch from remote opto-electronic transmitter receiver components 11. When the diaphragm 1 is contacting the break contact 2, as shown in Fig. 1, a maximum amount of light is reflected back along the fibre. If the diaphragm, as a result of a magnetic field, is moved so as to contact the make contact 6, which in this case acts as a back stop, the amount of light reflected back into the fibre 9 is significantly reduced, and this reduction enables the state of the switch to be determined.

The opto-electronics needed to monitor the state of the switch may be remote, as shown in Fig. 1, and means include a light source, which may be modulated, a Y-coupler, a receiver and drive circuitry. Various other arrangements including a single optical fibre are also possible, e.g. an optical fibre may be housed in the make contact as well as or instead of in the break contact. In addition, lenses and/or filters may be used at the fibre end.

The switch shown in Fig. 2 is generally similar to that of Fig. 1, except that in'ferrule 20 contains two fibres 21 and 22 held side by side in the ferrule, the fibre ends being close to the face of the diaphragm. One fibre, in this case 21, conveys light from the remote component 11, while the other fibre, in this case 22, collects light reflected from the diaphragm and returns it to the component 11. In this switch, unlike the switch of Fig. 1, when the diaphragm 1 is in contact with the break contact 2 it is close to the fibre ends, so that oniy a small amount of light is reflected from the transmit fibre 21 to the receive fibre 22. If the diaphragm moves to engage the make contact 6, more light is reflected from the diaphragm face into the receive fibre 22.Hence the condition of the switch can be readily monitored by the components 11.

As in the case of Fig. 1 ,fibres may be mounted in the make contact, or back plate in the case of a break contact capsule. Further lenses and or filters may be used, and the fibres may be so configured as to be non-parallel.

In both varies of switch it is possible to use one or more fibre optic bundles, in which case one or more fibres may be used to transmit light and one or more fibres may be used to receive light.

The magnetic field used to operate the diaphragm may be provided in many ways, one of which is to use the operating coil used when the capsule is part of a diaphragm relay. In this case a ferro-magnetic sleeve fits over the outer end of the break contact 2, with means to complete the magnetic circuit outside of the coil to the switch body 20, Fig. 1 or 2. The magnetic field strength and form can also be provided by other coil arrangement around or near the switch. The switch body can also be altered in various ways to optimize the magnetic circuit.

The magnetic field may also be provided by one or more suitably-arranged permanent magnets, and various magnetic shapes and switch body forms may be envisaged to optimize the magnetic circuit. Some possible arrangements are shown in Fig. 3.

In Fig. 3a the magnet is a disc or plate with a central pole (N) and peripheral poles (S), the position of which with reference to the centre of the switch controls the operating condition of the diaphragm.

Fig. 3b has a bar-type magnet rather annular to the magnet structure of Fig. 3a, with pole-piece extensions as shown on the switch, one on its central make contact and the other at its periphery.

Fig. 3c has a magnet pole as shown beside the extension of the contact member which carries the optical fibre termination, while Fig. 3d is similar but with a bent pole-piece end on the break contact portion. Fig. 3e is functionally similar to Fig. 3d, but with a bent magnet.

Thus it will be seen that the arrangements described above provide a magnetically-actuated proximity sensor with optical detection. The optical detection is provided by elements whose optical windows may be hermetically sealed within the switch body, thus eliminating difficulties of alignment and degradation of these windows. Such a device has a wide operating range, and can be used in hazardous environments.

The magnet structure can include a rotatable wheel, see 30, Fig. 4, where the device is used in a flowmeter 32 rotates the magnet 30 so that its alternate poles co-operate successively with the switch unit 33. The output of the switch is thus light modulated in a manner appropriate to the fluid flow rate, and thus is monitored by the remote circuitry 34.

Switches such as described above can also be used in proximity switches, which have application in safety, security and other situation. For instance, a permanent magnet may be attached to a movable part such as a window, door (e.g.

undercarriage door), gate, etc. and the switch then monitors the state, open or shut, of the movable part.

The magnetic field may also be provided, for example by the current to or in a machine, and the switch used to monitor that machine.

At this point we revert to the arrangement of Fig. 2, which shows a switch using two parallel optical fibres. Where two fibres are used they could be set at an angle as this has been found to .enhance the optical coupling between the fibres when the switch is on.

Claims

1. A fibre optic switch, which includes a sealed enclosure containing a diaphragm of a ferromagnetic material whose position is alterable in response to a magnetic field whose characteristics depend on a parameter to be monitored, and one or more optical fibres, the or each said fibre having an end aligned with and adjacent to one face of the diaphragm, the arrangement being such that light from the end of the fibre one of said fibres is reflected back into that fibre or into one of said fibres, and that the amount of light thus reflected back is dependent on the position of the diaphragm.

2. A fibre-optic switch as claimed in claim 1, wherein the diaphragm is of disc form, having its rim trapped between two rings each of which is integral with or sealed to a closure portion substantially parallel to the plane of the diaphragm, wherein the diaphragm is slotted so as to define a central disc like portion which is movable in a direction substantially normal to the plane of the diaphragm, and wherein the optical fibre or fibres is or are sealed into a closure portion so that the or each said fibre has its end adjacent to the face of the diaphragm.

3. A fibre-optic switch as claimed in claim 1 or 2, wherein the optical fibre is a single fibre terminated within a ferrule which is sealed into a ferro-magnetic member forming part of one of said closure portions.

4. A fibre-optic switch as claimed in claim 1 or 2, wherein there are two adjacent optical fibres terminated in a ferrule with their ends adjacent, the ferrule being sealed into a ferro'magnetic member forming part of one of said closure portion.

5. A fibre-optic switch as claimed in claim 1, 2, 3 or 4, and wherein one or more optical fibres is terminated in operative relations with each face of the diaphragm.

6. A fibre-optic switch as claimed in claim 1, 2, 3, 4 or 5, and wherein the magnetic field needed to move the diaphragm comes from a coil wound on a magnetic circuit associated with the switch.

7. A fibre-optic switch as claimed in claim 1, 2, 3, 4 or 5, and wherein the magnetic field needed to move the diaphragm comes from one or more permanent magnets whose movement causes said diaphragm's movement.

8. A fibre-optic switch as claimed in claim 7, and when the one or more permanent magnets in one are provided by a rotatable disc so poled that its periphery has a number of alternate North and South magnetic poles.

9. A fibre-optic switch arrangement for monitoring fluid flow in a pipe, which includes a switch as claimed in claim 8 the rotatable disc of which is rotated by fluid flowing along a pipe, the rate of rotation of said disc being dependent on the fluid flow rate.

10. A fibre-optic switch substantially as described with reference to Fig. 1, Fig. 2, Fig. 3a, Fig. 3b, Fig. 3c, Fig. 3d, Fig. 3e or Fig. 4 of the accompanying drawings.