A fibre-optic light switch

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A fibre-optic light switch

;er

'KL

B92

ISSN 0701-5232

A

FIBRE-OPTIC

LTGIIT SldITCH by

A-IV. Levy* and A.J. Szanto**

1. INTRODUCT

ION

It i s

q u i t e expensive

to install a d d i t i o n a l conventional light switches

in

existing

buildings. Public Works

Canada estimates the t o t a l cast

of

installing one switch in

a

federal building

at between $125 and SB50 61).

Labour

costs

f o r

i n s t a l l i n g

o r

r e - r o u t i n g

wiring

and conduit

in

walls and

c e i l i n g s

are high. Consequently, new lighting

control

systems

are

being developed w i t h t h e primary o b j e c t i v e

af reducing

the h i g h i n s t a l lation

costs.

Examples Include c a r r i e r c u r r e n t control systems

that u s e existing

wiring as a ready-made communication medium, electronic wall-timer switches,

and

ceiling

pull-cord

switches.

A fibre-optic l i g h t snitch has been developed t h a t can compete favourably

on

an

economic and performance b a s i s w i t h

conventional and

other new control

systems. I t s

prime

advantage is low installation c o s t . The fibre-optic

'kcontrcil w i r i n g " can be surface mounted i n s t e a d

of

recessed l i k e conventional

w i r i n g behind or in the wall f a b r i c , If t h e switches can a l s o be manufac-

tured at low c o s t , f u r t h e r advantages a r e apparent simply because one can

a f f o r d t o

install

a g r e a t e r number

of

switches than would be economic with

conventional controls. More switches

in

buildings, i f p r o p e r l y located and

managed,

will

makc it

possible

to reduce the

use

o f e l e c t r i c a l energy f o r

lighting, which can account f o r up to 50 per cent of t h e total energy

consumption

in

o f f i c e s , schools

and

o t h e r large

buildings.

The l i g h t switch

can thus be an important tool

in

over-all c o n s e r v a t i o n programs

i n

buildings.

2.

DESIGN

AND

INSTALLATION

T h e r e a r e v a r i o u s ways to use a f i b r e - o p t i c light switch, b u t most

will be based on the schematic illustrated in Figure 1.

Thr

total switch

system consists of t h r e e separate subsystems: the control module, t h e f i b r c -

optic materials, and t h e wall switch. The contsal module is n two-terminal

device connecting directly into t h e electrical line. A n electronic s w i t c h

*

Since May 1980, Director, Research and

Development,Engineering

Interface,

Limited,

Willowdale,

Ontario.

**

President, Foundatian

E l e c t r o n i c Instruments, 1794 Courtwood Crescent,

n1:1kcs o r h r c : ~ k s t l ~ c c i r c u i t t o t11c I;imp ~ r ' h c n i t is t ~ i g s ~ r t r l . A 1ig41t-rntitTir~g clioclr rclai~ins on whether t h e cl cctron i s w i t c l ~ i s or1 or o f f . 'l'ht* 1 i !:ht I'rom T T I P

1 i g h t - c m i t t i n g rliotlc i s t r ; i n s ~ n i t t c c l T O t l ~ c w : ~ l 1 sni t c h thrortzt~ r > l l r o S ' ~ I I C o p t i t - f i l3rcs. The same 1 ight is -passed h ; ~ c k from thc wn 1 l s w i t c h rlildess thc switch is ; i c t j v n t e d . Tlre f i h r c r e t u r n i n g from t h e

wall

s w i t c h t o t h e conTro2 module

interfaces with a p h o t o transistor and interruption o f t h e l i g h t t o t h c photo-

transistor

t r i g g e r s

t h e electronic s w i t c h

inside

t h e controller module.

The o p t i c a l f i b r e i s a

twin

t y p e , typically about 1

mm

in

diameter, t h a t

c o t ~ l d h e produced with an adhesive backing to permit e a s y installation on wall

surfaces. The l e n g t h o f t h e f i b r e s could be as much as a mile, allowing t r u e

remote control of the lights; transmission l e n g t h

depends

o n the attenuation

p r o p e r t i e s of t h e f i b r e , the i n t e n s i t y of the fight s o u r c e , and l i g h t l o s s e s

at f i b r e c o n n e c t i o n s and in t h e mechanical wall switch. The wall switch i s a

simple mechanical d e v i c e ; t h e two f i b r e s e n t e r i n g it are made

in

such a way t h a t t h e i r e n d s aye a l i g n e d and closc t o g e t h e r s o t h a t l i g h t is transmitted

from one to the o t h e r . Pressing the b u t t o n

i n t e r r u p t s

the optical p a t h ,

t h c r c b y t r i g g e r i n g t h c c o n t r o l m o d u l e .

Installation

of

the fibre-optic c o n t r o l system requires connecting thc

control modulc in the lamp(s) circuit i n t h e ceiling plenum t o t h e

wall

s w i t c h

b y a dun1 f i b r e . Both the o p t i c f i b r e s a n d the wall s w i t c h can be installed on t h e surface of the wall since b o t h a r e completely isolated electrically.

The l e n g t h of o p t i c f i b r c can be a d j u s t e d either by c u t t i n g on-site or

by

coiling cxtra f i b r e l e n g t h s

in

t h e ceiling plenum. The latter method is

attractive bccausc t h e switch assembly could then b e factory-packa~ed without

t h e n e c e s s i t y f o r a tradesman to make f i b r e connections at t h e installation.

As t h e wall s w i t c h

requires

no s w i t c h box and is no larger t h a n a cigarette

packet, there is great flexibility i n both

i t s

d e s i g n and l o c a t i o n .

3 . ADVANTAGES AND

DISADVANTAGES

The advantages of t h e fibre-optic Iight switch i n c l u d e :

- low instnllntion c o s t s because ' k o n t r o l wires" and the interrupter can

be s u r f n c c mounted,

- switches c a n be i n s t a l l e d on external walls without puncturing vapour

h r r i CTS

,

- s w i t c h e s c a n be installed c l o s c to or at work s t i t t i o n s ,

- increased s a f e t y since the s w i t c h is completely isolated from the power circuit,

- electrical isolation means t h a t t h e switch can be installed s a f e l y i n e x p l o s i v e , damp, or

generally

hostile

environments,

- f 1 esibility ; office spaces espcc i a l l y o f t e n undergo c l ~ a n g e s i n

statiori layout; the fibre-optic s w i t c h can be covered o v e r o r relocated

Or1r r l i s;lJvi~riti~y,c is t l i r b r.i s h 1scr.h:111 i ch:i 1 cl:~ii~:~gr~ to t lit. t'i l ~ r - c b s r ~ ~ i c c -

i !,st:! 1 lccl ( f a r c x : ~ m ] ~ f r - , f r o m iihrlcnt:it i o n s t o r.rwnp1et.c i n c i . . ; i c l n s )

,

r c s ~ r l t i ny i n t r a n s m i s s iort loss. SucFi J:~m:~gc can b c prevented, howc\rc~-, by

c n c a p m l a t i ng tkt. f i h r e s .

4 . ESTIMATED COSTS

T a b l e T g i v e s a

cost

comparison of a conventional lighting control system

and a fibre-optic installation. Using 1979 prices, i t is b a s e d on a distance

o f 3 0 m between wall switch and

lighs

f i x t u r e

and

a p r o j e c t e d c o s t f o r tIlc

fibre-optic system assuming a volume production of 20,000 u n i t s .

5. (ITIIER USES

Although the patent liscrature is replete w i t h a p p l i c a t i o n s for fibse-

o p t i c switches to c o n t r o l v a r i o u s mechanical and elcctrical l o a d s , o n l y p a s -

sin2 a t t e n t i o n seems to have b e e n ]?aid to controlling e l e c t r i c lnmps.

I f t h e fibre-optic snitcIl now described c o u l d Ire successfully nraiiufac-

t u r e d , there could be a f u r t h e r application to security systems. b l o v e r ~ ~ e n t of

doors and

windows

c o u l d b e d e t e c t e d by thc

fibres,

u s i n g a system approach

s i m i l a r t o t h a t i n F i g . 1 with a m o d i f i c a t i o n of t h e mecl~anical s w i t c h .

The concept

is

best e x p l a i n e d i n

Figs.

2 F, 3 . The mechanical switch is s i m p l y

removed and t h e t w o f i b r e s marked X and Y are brought c l o s e to the d o o r o r

window to b e monitored. A s m a l l s t r i p

of

k i g h r e f l e c t i v i t y f i l m [aluminized

mylar or simply aluminum f o i l ) is attached t o t h e door o r

window

surface.

Movement o f t h a t surface interrupts t h e l i g h t

flow

through the f i b r e l o o p ,

activating e i t h e r the l i g h t s in t h e

building

o r an a u d i b l e alarm, o r boZ11.

6 . CONCLUSIONS

'Ile fibre-optic l i g h t switch p r o m i s e s t o become a n economic and effective

ighting control device. It

i s

especially attractive f o r r e t r o f i t where h i g h

nstnllation costs a r e n o r m a l l y i n c u r r e d when conventional light switches arc

I I S E ~ . A number of o t h e r a r e a s exist a l s o where t h e srlritch h a s potential

impact, For example, for residential light controls and f o r residential

s e c u r i t y systems.

RIIFERENCES

COST

COMPARISON

OF CONVENTIONAL SYSTEEiS AND

FIBRE-OPTIC

CONTROL

SYSTEMS

I t e m Conventional F i b r e O p t i c Toggle s w i t c h or s p r i n g mechanism $ 0.80 $ 0.10 S w i t c h box 0.80 0 - 8 5 Cover p l a t e 0 , 2 0 0 . 2 0 Connectors 0.198 4 .OO Electronics - 6 . 0 0 Hydro u s a g e p e r year - 0.07 Wise or f i b r e Conduit: 3 0 . 0 0 - Labour (alteration to f i n i s h e d location)

C Q M M E C T O R \'! A L L S U I KCH F I G U R E 1 S C H E ~ ~ ~ A T I C O F T F T E F I B R E o p a r c L I G H T S W I ~ T C H F I B R E R E F L E C T I N G A- ' F I B R E O P T I C S I I L R I O P ~ I C S F l G U R E 3 P L A h V I E V J O F S E C U R I T Y S Y 5 T C p b Z