NATIONAL BUREAU OF STANDARDS REPORT

2806

ELECTRICAL TYPE DOOR INTERLOCK

by

Alfred B* Castle

to

Engineering Division, Military Construction

Corps of Engineers

Department of the Amy

U. S. DEPARTMENT OF COMMERCE

NATIONAL DUREAU OF STANDARDS
U. S. DEPARTMENT OF COMMERCE

Sinclair Weeks, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director THE NATIONAL BUREAU OF STANDARDS

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W Office of Basic Instrumentation • Office of Weights and Measures.
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

(>502°=10-'1+716 Scpterribei' 21^ 1953 ’ 2306

ELa;:miGAL doce iktehlock

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Englneerim M:ljd.tary Gone tmetion

Corps of lingi'iaers

Depai'trrjent of A"-xn7

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The publication,

, , ,

> or In pait, Is prohibited ..imp.TM,..,. Approved for public release by the

2S.D.C. S..P Director of the National Institute of

caiiy prepared I Standards and Technology (NIST) ir report for Its own use, on October 9, 2015.
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FOESMOKD

Door Interlocks of both r/s5chaaics,l and electrical, types haw

been developed concinrrent.lj.'’ for the Ikigraieerling Division^ Military

Gonstrc-ction^ Corps of Engiiieer-Sj Depar1:i^nt of th^ d-uring the

present calencSar year in the MeehanicaJL Ixistrnfflents Section

principally under NBS Projaet Noo I.GOCh=lO-»l{.?3,6 as authorized in the

letters references (l) and { 2)0 Only the electrical type is described

in this reporto

Tjio interlocks are designed priiaai’ils'' fox* use an multiple doors

of a bathrocsm in veterans- hospitals 1) to lock the bathroom so as

to afford privacy during occupancy* 2) to mke it equa.l3.y accessible

t2 all potential i^ers nhen idl.e* and 3) to open it easily in

emergenciaso

falter Ra.mberg^ Chief

Meehardcs Division

Ao Vo Asting Director

National. Bureau of Standard.^

ELKTRIGAL TYPE DOOR INTERLOCK

by

Alfred Bo Castl©

ABSTRACT

An electr-ically operated door IntcE'lock specifically for lass

on m^tiple doors of a bathroom in veterans^ hospitals was

developedo Ihe interlocks are siippleraentary controls on

ordinal door latches© VJitli tiie interlocks^ all doors to the

bathroom can be locked by the occupant^, and all doors are

locked vrhen the bathroom is 'unocc\3piedo Several interlocks

have been constructed for test in a ser^rice installationo

Design details are included in the report©

lo INTRODUCnON

Sinple and automatic means for obtaining privacy for all parties

concerned using one bathroom connecting bstweai two or mere rooms in

hospitals has been a need particiilarly of Uo So Governusent operated

hospitals©

The privacy desii'ed is such that the user cannot be intruded upon from

outside but when the room is not in use it remains equally available to all

users o Also^ in case of emergency the, room should be easily opened from

without©

Ip until the development of the electrical interlock system described

herein^ no otlier hardware was known which would fit the need and yet be

simple and easy to operate, such as by a weak patient© It had been reported

that there is one commercial tjrpe of mechanical interlock which can be

“ 1 "

« 2 «

applied b> fMG doors that are r-eassnablj close together and opposite each other

Also there ie an NBS de'^elopsd mechanical systaji (see reference (c)) Which can

applied tc two or possibly three doors regardless of orientation and np to

moderate d.l;stanees apar-t»

2 ^ HEQUIRH^IEHTS

The Siiterlocks^ ^r?hen ±R.sta.iled on bathroom doors connected ’srith tfe'o or

lonroe roor.hi^ should nieet tha following reqirlreraentsi

a) , It shGiild be possible to lock the bathroom doors from within against

Lutrvision from' without^ glibly by -closing the doors and actuating a single

l--.a;:idis or knob oa any ens door«-

b}* Ijpcn opening ao,y one door^ all (fcors nms-t the2*€by become unlocks

d

reiL-aiii bo S-s lc»2g as any doer remains opens

c) o in the bathroom^ locking any one door will sajiasltanaonsly losk

all other doors

o

d) o theii nacoseary it shall be possible to open any door from Mithont

l-f applios.tlon of a simple tool (M‘ key or by interrap tit^ the electrical

c -indent

e) «. Failure of the roltage shall sitter antematically unlock or penult

c.T-irge:acy tmloci-dng of all doors o ilo undue hazard of electrical shock must

introduced \>y operating tlie locks sleetrdcallyo

f) a Ihe raatsrialSj, 'warkimnship and design cf the locks shall afford

£ reasonabiy Icjig troiible-ff*ee life®

^ 3 -

The follc«jliig addi'bional features are deslivable

s

g) a indicator tlmt batliroom Is occi^ied shoiold be easily visibljs

from both cormacting rooms o

h) o The locks sho^ald be applicable to eiiiier old or new construction

ai.d. use existing types of barchiare with little or no modification o

i) o Xjocl<dng laidbs or handles should be similar to those normally ised

1x5 obriate learning any new locking technique

o

3o DIlSCRIPTIOM

Vinifs of ' the hardware of one interlock are diown assembled in figure 1

and disassembled 5ji figure 2o A conirentional latch with dual knbbs^ modified

to operate x-d.th the electrical. in.tsrl.ock^, is shown at the bottom Isft in

tBoh f5,g'oreo The .janib unit associated with tte latch is shoi-jn at the bottom

light and is essentially a solenoid controlled locking device for bolt 23©

The solenoid controls are sho^m at the top of the figures^ the door unit

with signal light and switch control at the left and ii?.e jamb unit with th.e

switch itself and signal lairp at tl^ righto

The electrical circuit diagram for a two-door installation is given in

figiu'e 3 and constructional defciiis in figure 6© VJhen a door is open two

msreury txqse switches and a pair of contacts^ all located in the door jamb

ivnltj are in *'open circuit”©

The general design may be illustrated by a cj'cle of operation© If both

ccors are open.:, a person enters the bathroom and closes both doors© This

closes one c^f the two mercuiy switches in each cf the door jamb units. No©

iigures 1 and 2© Traming the swi.tch knob to ”loek” closes the remaining

cp!xn svjitc'h, energizes the solenoid, actuating the locking device©
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th$ ac.t^'ted condition the solenoid ir^ch-snically holds closed the auxiliary

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"seal in*’ contacts.. 'The solenoid rsFajjas acti-vated^ and the doors locked,

t>irongh a circuit containing the ’’seal in” contacts and tbs norraally closed

’’interlock-' switch, al-idic^igh tbs switch knob returns to neutral and the

normH-j ope^n stfiteh now opens, when the operator removes his hand<,

To luilock the doors, tls switch knd> is turned to "unlock”, which opens

tho nor'inally closed sx%itch, breaking the circuit through tloB solenoido As the

sol^ioid is de-energised, door is unlocked and at the saas t5jae tbs

%

’’s^^alsd iii^ con'tacts are opened* ‘The mechanism is now ready for the next cycle

of operation.-,

3ol Door Urdts of Inter3.ock

The jfsschanieal latch assembly 23, figures 1, 2 and 6, may be of any

conventional tj^-e icith a groove mdlled in the latch bolt suitable far engageiraent

with the lock hax 1?* As long as -fee tongi® of 1? is engaged with 23, by

ac'don of the relay l6, the bolt noraially cannot be retracted for opening the

' door*

Switch actuating unit 2 contains two springs 11, figures 2 and 6, two pin

plmgers 12, which are I’etracted by tbs sprli^s after being deflected singly

bj the turning of cam 13, figures -2 and 6» I^ndb 2? is used to tiarn ti© cam •

through parts llj. aad figures 2 and 6*

Door is2l.t 2 has a Lucite rod indicator 22 which receives light from jamb

u;.i5h X, deflecting it toward both sides of the door by means of the polished

c'Xv near the udddle of the rod* The light is on when the doors are locked by
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the jamb miitso This signal is obtaiiied by wiring the lanp In parallel with

the holding relayo If preferred a pilot light jewel may be monnted in the

jamb units for transmitting directly tine indicator li^to ^ 3o2 Jamb Units of Interlock.

Ihe hardware of iiie jamb part of the interlock consists of a relay lock

unit 3 and a switch and pilot light unit lo

Tlie relay unit 3 consists principally of the relay l6 ”(a modi.fied Potter

and Bnaafield type I-1S2A.) widi a lc>ek bar ext^sion 17 attached to the regular

aimature and a contact assembly 18, figure 6s The latter is closed or

’’sealed in” mechanically by the relay i;^en it is ensrgizedo This ’’seal in”

contact maintains the relays energised and hence the doors closed after the

operating switch and switch knob return to tJjo neutral or open switch

positioHo The switch knob cf either door is naf in position to be tis'ned

to 'unlock” o

'tTlien the ’’unlock” switch, held in clip 19^ figure 6, is operated by

the 'hmiock” plunger 12 by a proper twist of the knob 27, a switch mount 8

is deflected so as to break the contact in a mercury switch 20o This switch

is open ’Jien the door associated ifith it is open because the interlock tab

or pawl 5, is spring held out and the lower roercury switch 20 is at such an

angle i±at no contact is madeo This sid.tch is ncrirjally closed whai the door

is closed because the door edge deflects the tab and rotates the switch

mount so that the merciory contacts close. This switch can be rotated

slightly as stated above, by the "-unlock” plunger, in its secondary mount 8,

because it is spring coupled -to 'bab VJhen thus rotated the switch conbacts

break tlie circuit

6

Ihe "lock” svTitch (A)^ fig7ire ds also a rasrciorj type moimted first

in clip 9 s fig-are 6$ aj^ then in bracket 10 Tyhich is both spring smd gravity

held in an inclined "-unlocked" pcsi-M.oii -until deflectsd by a plunger 12

actu3,ted from the ’dead bolt" s^tch knob 27 o

With the "interlock" contacts in their' normally closed position^ mssLZiing

that both dr/ors are closed;, eitlBr "lock" switch my be used to "seal in"

and lock the dooi^©

Admittedly the interlock s^^ltshes tabs and openings e^roosed can be

manually "fooled" and thereby mde ineffective for performing -fceir normal

functioBo To make the picking of "ihe interlock difficult ifould probably

unduly co^i^licate the de\dce» However, unless something is act-ually p-ushed

into the mits so as to damage the mechanism the units id.ll function properljr

even after bajtiperingo

3o3 Installation Details

The interlock syst-em may be installed in old as well as in new work

provided that the latch bolt in the -fcwo doors selected can be modified as

shewn for part 23, figure 6o Identically wired units are installed at each

door© One of tlie interlock switch pawls may require reversing on its pivot

screw depending on the opening cf the door, ri^t or left hand© Opposite the

regular 'Latch unit^ the strll^ier plate and interlock relay unit 3 is so

located and mortised into the jamb that the locking bar -will engage the

recess cut in 'the latch bolt© Refer to tenplatc, figure Above unit 3,

also in the jamb, is located the switch and p-ilot light unit 1» The switch

actuating unit 2 Is installed in the door directly facing unit 1, located

as for a separate dead bolt <>

» 7 -

For installation 3n new construction mits 1 and 3 are mounted directly

on plate figure 6e

liach switch housing unit has a terrainal strip to which iiie external

leads are connected to the electrical service and to the other housing unit

as shown in figure 3o

The power si5>ply required Is 110 volts^ a^c® Ihe lainp and magnet

together require a current of about «0? amperes and consume about 6 watts

while the door is locked^

3 oil. Op^ijjyg of Locked Doors

a) Konnal Opening® hither door of tlie bathroom is unlocked sinply 1:^

mon^ntarily turning the switch control icaob of tlie door unit in the

direction Indicated for opening and then releasing it® The cbor itiay

then be opened by ihe custonaiy operation of the primary door knobo

jCncidentlys turning the knob in the altsma-te direction from timt

required to open the door does no fermi the doors siiiply remain

locked®>

b) Fraergency Opening ® Either door mj be unlocked from without siiiply by

interrupting the electrical current to thg doors® If this is inconvenient

the shaft 15 which extends to the outside of either door may be turned

with a screw driver or preferably with a I’adiatcr type key and thereby

iSiEde to unlock the doors®

I«.o EXOTSION TO MORE SiftN TdO DOORS

The irrberlock although made initially for use on two doors can be extended

theoretically to apply to any nuiiiber of doors® Ihe practical limit is determined only by the size of electrical ccoiductors required to carry ‘fehe lockii^
I 1
- 6 .

Slid indicating cnrs’ant* Tlie hook-up diag;ram foui’ ac more sncIi door miits

ij3 given in fignre Eis voltage supply may te com-^cted to any of the

terrdnal pairs irarked (l) aid ( 6) . Tao Initial, aid final units each bave an

goctcTmi iuriigper ccisnected betueen a certain pair of terdjials as shovm in.

fig'ore hs As can be noted all ''seal In*’ contact pairs a2re In paralleli hence

the complete system xd.ll xfork reliably as long as the ’’seal in*’ switches in

at 3„east two door units make proper contact® VJhen only one ’’seal in” swi.teh

remaiiia isitect a vigorous !r*anipul,aticn of -l±!.0 door may momentarily breaie liie

sircirlt allowing the rel^^ to release*. .In respect to ’’seal in” contacts

the units eomeeted in parallel the raore reliable the operation^

RE.FERHICES

/

li, Letter from Engir^ariag Division^ !'Iilitaiy Constiuction^

Corps of Engineers^ Departent of the Amy^ da.ted <janm.rj 13^

195*3# reference MGES®

2 a Letter frem Irigineeriiig Divisionjj Hilitazy Cons true tion^

Corps of Engineers j Departir^nt of die Aimy^ dated May 13^

19^3;* reference MGES«

3® Repox't Moe 2807 on Mechanical. Type Door Interlock^ imder

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4

THE NATIONAL BUREAU OF STANDARDS

Functions and Activities

The functions of the National Bureau of Standards are set forth in the Act of Congress, March

3, 1901, as amended hy Congress in Public 'Law 619, 1950. These include the development and

maintenance of the national standards of measurement and the provision of means and methods

for making measurements consistent with these standards; the determination of physical constants and properties of materials; the development of methods and instruments for testing materials,

devices, and structures; advisory services to Government Agencies on scientific and technical

problems; invention and development of devices to serve special needs of the Government; and the

development of standard practices, codes, and specifications. The work includes basic and applied

research, development, engineering, instrumentation, testing, evaluation, calibration services, and

various consultation and information services. A major portion of the Bureau’s work is performed

for other Government Agencies, particularly the Department of Defense and the Atomic Energy

Conunission. The scope of activities is suggested by the listing of divisions and sections on the

inside of the front cover.

Reports and Publications

The results of the Bureau’s work take the form of either actual equipment and devices or published papers and reports. Reports are issued to the sponsoring agency of a particular project or program. Published papers appear either in the Bureau’s own series of publications or in the

journals of professional and scientific societies. The Bureau itself publishes three monthly periodicals, available from the Government Printing Office: The Journal of Research, which presents

complete papers reporting technical investigations; the Technical News Bulletin, which presents

summary and preliminary reports on work in progress; and Basic Radio Propagation Predictions,

which provides data for determining the best frequencies to use for radio communications throughout

the world. There are also five series of nonperiodical publications: The Applied Mathematics

Series, Circulars, Handbooks, Building Materials and Structures Reports, and Miscellaneous

Publications.

Information on the Bureau’s publications can be found in NBS Circular 460, Publications of

the National Bureau of Standards ($1.00). Information on calibration services and fees can be

found in NBS Circular 483, Testing by the' National Bureau of Standards (25 cents). Both are

available from the Government Printing Office. Inquiries regarding the Bureau’s reports and

publications should be addressed to the Office of Scientific Publications, National Bureau of Standards, Washington 25, D. C.
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