A Thermo-electric Firedamp Detector and Alarm for use in Mines.
Year: 1890

page_text: Date of Application, 5th Dec., 1890
Complete Specification Left, 4th Sept., 1891-Accepted, 10th Oct., 1891
PROVISIONAL SPECIFICATION.
A Thermo-electric Firedamp Detector and Alarm for use in Mines.
THOMAS JOHN MURDAY Electrical Engineer 41, Regent Road, Gosforth,
Newcastle-on-Tyne. I do hereby declare the nature of this invention to be as
follows:-
amount.
An apparatus which is affected by the presence of firedamp in the air surround-
ing it; and capable of measuring and indicating on a graduated dial the exact
percentage or amount of the said firedamp. An alarm connection whereby a bell
is rung at a distance from the detector when the percentage reaches a certain
The said alarm arrangement is adjustable and can be set to ring the bell
on the apparatus indicating any percentage from one to ten per cent.: that is to say
if the alarm contact (hereinafter explained) be set at eight per cent. on the dial the
alarm bell will ring when the firedamp accumulates in the vicinity of the detector
to that amount. The instrument is sufficiently delicate to indicate the presence of
less than a tenth of a per cent. of firedamp in the air.
Fig. 1 is a full size drawing of the apparatus, and the following description
refers to its construction :―
A is a rigid pillar or standard fixed on a base X, and carrying the dial C;
pinion of pointer D, E; sector I, pivotted at J; and the crosspiece B. Near the
bottom it supports, in addition to the above, the two multiplying levers T T',
pivotted at QQ. The crosspiece B has a screw at each side L K, and these
screws are insulated from the metal of B by an insulating material. To these
screws L K are firmly attached the rods of brass, or copper S, S'. On rod S¹
is firmly fixed a glass tube M, and at the bottom of this tube a rod R¹ enters: the
bottom end of tube M is covered over by a membrane of india-rubber, or other
flexible airtight material, so as to exclude the outer air; and rod R pierces this
membrane in the middle. The ends of rods S¹ and R¹ inside the tubes are
connected by a fine platinum wire N, which is kept tightly stretched between the
two rods by means to be hereafter_explained. The lower end of rod R' is in
connection with lever T¹ and V. Lever T¹ is connected to sector arm I by a
spring U. This spring is under slight compression between sector and lever, and
its tendency is therefore to throw sector to the left, and at the same time press
lever T¹ to the right, thus bringing about a tension on platinum wire N, and so
keeping it always stretched. It will now be seen that, as described, the arrange-
ment will be a kind of metallic thermometer; and if we heat platinum wire Nit
will expand (agreeable to the property of metals). This expansion will give a
motion to lever T¹ and its upper end will move through an arc many times greater
in extent than the linear expansion of the platinum wire.
This motion of lever T¹
is transferred to sector 1 by means of spring U₁, and thence to pointer D by
pinion E which gears with sector. On the left side of apparatus we have a
very similar arrangement to that just described. On rod S is fixed a small tube of
steel or copper gauze, (similar to that in use for safety lamps) and a rod R enters
this gauze O at the bottom through one of the meshes of the gauze end fitted into
tube; this rod is free to move upwards or downwards, and its lower extremity
engages with the lever T at V. A platinum wire p is stretched between the ends
It will be
of rods R and S which project within the gauze tube or cylinder O.
seen that if platinum wire P is heated similar motions will be transferred to
lever T and sector I that are given to lever T' and sector I by the expansion
of platinum N or the other side. Spring U is also under compression and
thus throws tension on platinum wire P through lever T. Sector I is free
to move between the two levers, but as the springs U U₁ press upon it in
opposite directions it finds a place of equilibrium where the tension of both

page_text: springs is equal. Now suppose both platinum wires P and N are heated equally at
the same moment, they will expand, or lengthen, and the upper ends of levers T T¹
will move in opposite directions-away from each other-actuated by the com-
pressed springs U U¹. As both levers move through the same arc and both springs
expand equally, no movement of the sector will take place :-consequently the
instrument will act simply as a differential thermometer. It will now be seen that
if wire P be heated only, lever T will fall away from sector I, and sector I will
follow it so far until it finds its place of equilibrium midway between the
springs U U¹. This movement of the sector will cause a corresponding deflection
of the pointer D:-up the scale if platinum P expands, and down the scale if
platinum N expands. It will be seen that sector I is pivotted at J, and is balanced
by a counterpoise. It should have been before stated that the flexible membrane
at the bottom of glass tube M allows rod R¹ a slight up and down motion to meet
the expansion and contraction of the platinum wire N. To use the instrument as a
firedamp detector an electric current from a battery is sent by way of wire 1
through rod S, platinum wire P, rod R, metal work of A, rod R', platinum wire N,
rod S, and to battery again by wire 2. This current must be sufficiently strong
to heat the platinum wires P and N to a temperature slightly under a dull red
glow as a result of the heating of those wires by the passage of this current
levers T T are deflected by the consequent expansion, and as the levers are
equally deflected no movement of the sector or pointer takes place. Should the
instrument now be placed in a gaseous mixture and the current passed through as
above described, combustion will take place in the gas around wire P, and the heat
generated by this combustion will cause wire P to become hotter than wire N,
(which is heated in pure air within its sealed tube M) consequently wire P will
expand more and lever T moving through a larger arc than lever T¹ will give
motion to sector I which in its turn deflects pointer D up the scale. This
deflection of the pointer is proportionate to the expansion of platinum P over that
of N. The more firedamp (hydrogen) present around wire p the greater will be
the combustion and consequent heating and expansion of that wire. When the
percentage of gas reaches ten per cent. the gas within gauze O is exploded by the
passage of the electric current through wire p, and P is glowing at a white heat :-
the pointer D then points to ten per cent, on the scale. Two seconds is sufficiently
long for the vitalizing current to continue passing through the instrument, and in
that time a deflection of the pointer will have taken place according to the amount
of firedamp present in the air surrounding the instrument.
In this
Gauze is used to prevent the lighting up of the firedamp around the instru-
ment by the combustion or explosion of the firedamp within the gauze.
respect its use is exactly similar to that which it is put in the Davy safety
lamp etc. To render this apparatus self-acting the following arrangement
obtains: A small eight days' clock (any good clock movement will do) is fitted
with a contact arrangement on one of its wheels-so that the clock will allow
an electric current to pass along wires to the firedamp detector at certain fixed
intervals of time, say every fifteen thirty or sixty minutes, or any time to be
determined upon-for the space of two seconds each time. This clock with the
necessary battery may be placed either in direct communication with the instrument
(firedamp detector) in the mine, or be situated in the manager's office above
ground the connection being then made by wires down the shaft and along the
galleries of the mine. In order that the detector may give an alarm on the
percentage of gas reaching a certain point a contact spring H is fitted on an
insulated piece G which slides along the upper edge of dial thus allowing of H
being set to any division on the scale. A pin F on pointer D strikes against this
spring H when the pointer is deflected to the division at which H has been set, and
an electric circuit is at once closed through wire 3, spring H, pointer D, metal
of A, wire 4, and alarm bell and battery situated in the manager's office above
ground, or any other place determined on: thus the alarm bell is sounded whenever
pointer D is deflected to the position at which the contact H is fixed. One or

page_text: several of these "detectors" may be used in a mine-situated in different parts and.
receiving their vitalizing current at regular intervals of time from one battery and
clock situated as before mentioned. One bell may be also used for any number of
detectors, and an indicator attached in the common circuit to show from which
detector the alarm current had come. This indicator is of the ordinary type
used in electric bell installations, and the various electric currents are conducted
between the two instruments (that is the detector or detectors down the mine and
the clock bell and battery in the manager's office, or elsewhere) as in ordinary
telegraph, telephone, or electric bell circuits.
From the foregoing it will now be seen that this apparatus is practically an
automatic searcher for firedamp; that when it discovers firedamp an alarm bell is
immediately sounded, and the section of the mine in which the firedamp has accu-
mulated is indicated at the same moment by the attached indicator. The search is
made at regular intervals, and may be made as often as deemed necessary, according
to the requirements of different mines.
Dated this 2nd d
of December 1800
T. J. MURDAY,
41, Regent Road, Gosforth, Newcastle-on-Tyne.
COMPLETE SPECIFICATION.
A Thermo-electric Fire-damp Detector and Alarm for use in Mines.
I THOMAS JOHN MURDAY, of 41, Regent Road, Gosforth, Newcastle-on-Tyne,
Electrical Engineer, do hereby declare the nature of this invention and in what
manner the same is to be performed, to be particularly described and ascertained
in and by the following statement :—
This invention relates to an apparatus which has for its object the detection of
small percentages of fire-damp in the atmosphere of mines, etc. It consists essen-
tially of an arrangement of parts which may be described as a form of differential
metallic thermometer. The expanding and contracting element is in the form of a
fine platinum wire heated by the passage of an electric current which becomes more
heated when surrounded by a mixture of hydrogen gas (fire-damp). By a system
of levers this expansion give motion to a pointer or contact arm which indicates on
a dial or rings an electric bell.
The following description with the accompanying drawings will fully explain the
construction and working of this invention:-
:
Fig. 1. shows the mechanical arrangement. a is a rigid plate of metal serving as
a base. bare two pillars screwed in base but electrically insulated from the
same. ccare brass rods sliding in slots cut in pillars b', and can be clamped in
any position by side screws as shown these rods terminate at the upper end in
binding screws and at the lower end in slots cut to receive the ends of platinum
wires dd. Cross screws are used to clamp the slotted ends. e el are levers used
to multiply the motion due to expansion of the platinum wires; they are pivotted
at ff and carry at their upper ends two weak springs 9 9. The projections at the
lower ends of levers are connected with rods h h at ii; the upper ends of rods are
slotted and clamp on ends of platinum wires similar to the rods c c¹. Springs gy¹
are connected to cross piece of lever j. Lever j is pivotted at and at its lower
end carries a contact point l. Platinum wire d is surrounded by a cage or
cylinder m of fine wire gauze (similar to the gauze used in miners' safety
lamps), the ends of this cage or cylinder are made of insulating material-the
upper end fitting firmly on rod c, but the hole in the lower end allows rod h to slide
freely. Around platinum wire d' a cylinder (of glass or brass or other non porous
material) m is placed its upper end is closed by a disc of insulating material which,
like the end of gauze cage m, is fixed firmly on rod c¹. The bottom end of this
cylinder is made of a flexible material such as india rubber and rod / pierces this
material in the centre. This arrangement is for the purpose of excluding the outer

page_text: air from contact with wire d¹ and at the same time to allow the expansion or
contraction of wire d¹ to act properly on the levers e¹ j. Springs g g¹ are under
tension and their tendency is to throw levers e e¹ outwards at the top, thus bringing
about a tension or pull on rods h h¹ and platinum wires d d¹. n is a contact spring
carrying a contact point at o for point to strike against: it is fixed to an
insulated bracket p. q is a micrometer screw arrangement by means of which
spring n is adjusted to any distance desired from contact point 1 on lever j. A
pointer y on screw indicates on a dials the value of this distance. tt is the case
surrounding the apparatus, and may be of wood or any suitable material. v is an
electric bell which rings when contact between the points lo of lever ; and spring n
takes place.
-
The action of the instrument may be described as follows-An electric
current from a battery is passed through platinum wires d d' by depressing
the press button . This current passes from the + pole of battery by wire to
push spring then to spring r and wire attached to the terminal on rod c, down
rod c, platinum wire d, rod h, levers f¹ and metal base a, then rod h¹ platinum
wire d', rod c¹ and return wire attached to terminal on rod c' to pole of battery.
The current flows only so long as the press button is kept down and the current
used must be sufficiently strong to heat the platinum wires to a temperature of
about two hundred degrees Fahrenheit. On the passage of the electric current
the platinum wires lengthen and the levers c c' open outwards from the top under
the tension of the springs 9 9. As both wires are heated, and consequently
expand, equally both levers move over the same arc-away from each other: thus,
no movement is transmitted to lever j. Should wire d be more heated than wire d'
then lever c will move through a larger arc than lever c¹ and a corresponding
deflection of lever i will follow, bringing its contact point nearer to contact
spring n. An opposite movement of lever i would follow if wire d¹ became more
heated than wire d. Thus in pure air when the press is pressed no deflection
of lever takes place because both platinum wires are equally heated, but on
placing the instrument in a mixture of firedamp (hydrogen gas) and air, and
pressing the push, lever j at once moves with its point 7 towards spring n owing
to the fact that the exposed platinum wire d ignites the hydrogen surrounding it,
thus adding the additional heat due to combustion to the already electrically heated
wire, and bringing about a greater expansion of wire d. The heat thus generated
is in proportion to the percentage of hydrogen present in the air: at a percentage of
eight to ten the platinum wire d glows at a white heat. The micrometer screw
arrangement is used to bring the contact spring a measured distance from the contact
point of lever and this distance is indicated by a pointer y on a dial s which is
graduated in divisions corresponding to per cents. and smaller amounts.
To use the instrument as a searcher for fire-damp the pointer is set by means of
the milled screw head q to a half or one per cent. on the scale, and the press x pushed
down with the finger at frequent intervals, as the person making the inspection
traverses the galleries of the mine. One second is a sufficient length of time to
keep the press down. So long as the air is free from fire-damp or the percentage of
same is under the value at which the pointer is set the bell will not ring, but on
entering a mixture of air and fire-damp the value of which equals or exceeds
the figure at which the pointer is set and pressing the push the bell will
immediately sound. The electric circuit of bell is from the same battery which
supplies the current to heat the platinum wires dd' and may be traced as follows,-
from pole of battery by wire to windings of electro magnet under bell dome v,
thence by wire to spring n, across points ol, by lever j and base plate a and wire to
- pole of battery.
-
ย
Fig. 2. shows the instrument complete in its case: the case may be made
sufficiently large to contain the battery or the battery may be in a separate case
attached to the instrument case. As shown here the apparatus is that arrangement
designed to use as a hand searcher in place of the ordinary searching lamps of the
Davy principle.

page_text: By altering the fulcrum of levers e e¹ and j, Fig. 1, so as to multiply still more
the motion due to expansion of the platinum wires d d¹ the end of lever j is made
to move through a much larger arc and may be thus converted into a pointer
having a dial on which it indicates directly the amount of deflection and consequent
values in per cents. of fire-damp present in the air. In this arrangement the micro-
meter screw and spring n are not required, and the side of case opposite the dial is
replaced by glass so that the indications of the pointer (lever j) may be observed.
A contact spring is made to slide along the edge of dial so as to be adjustable to
any division thereon, and when the pointer (lever ;) strikes this contact spring the
bell circuit is completed and the bell sounds.
Another modification of the apparatus is that form in which it may be made to
needs very
automatically signal to a distance. The instrument for this purpose
little
alteration from the form shown in the accompanying drawings. The bell v is
detached from the apparatus and the wires leading to spring n and base plate a are
extended to the distant station at which the alarm is required to be given and
there attached to the same bell (or preferably a more powerful one) and battery.
No battery is placed in or connected to case, Fig. 2. Press button is detached
from the circuit and the wires leading from the términals on rods c c Fig. 1,
extended to the distant station and there connected to a battery of sufficient power
and any ordinary eight days' clock movement fitted with a contact arrangement
for completing the electric circuit for one second each time at certain fixed
intervals of time-say once every hour. This clock battery and bell may be placed
in the manager's office above ground and connected by wires to any number of
instruments situated in the mine workings below. By an ordinary contact
arrangement on the clock each instrument or detector receives a current of one
second's duration in turn at hour intervals, and an electric bell indicator shows from
which detector (when the bell rings) an alarm has come-consequently indicating
to the officials in attendance the particular section of the mine in which the accu-
mulation of fire-damp is taking place. The adjustable pointer y would be set on
each instrument at a low per cent.-a quarter or one half per cent. so that the alarm
would be given on the slightest trace of accumulating firedamp.
In order to admit of free circulation of air through the instrument there must be
one or more large opening or openings in the case tt, Figs. 1 and 2, covered by fine
wire gauze o' as shown on the front of case t t in Fig. 2.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed I declare that what I
claim is-
1. The arrangement of rods levers etc. as shown in Fig. 1, whereby the expan-
sion and contraction of the platinum wires are made to balance each other so long
as their temperature is equal-be that temperature high or low, and the device
whereby any difference of temperature between the two platinum wires is indicated
and accurately measured.
2. The closing of an electric circuit through a bell (either attached directly to
the instrument or at a distance away from it) whenever the beforementioned
platinum wires become unequally heated owing to the presence of fire-damp as
described in the foregoing Specification.
3. The general construction and arrangement of the apparatus for the purpose
specified substantially as described and shown.
T. J. MURDAY,
41, Regent Road, Gosforth, Newcastle-on-Tyne.