Improvements in Thermostats.
Year: 1893

page_text: Date of Application, 30th Mar., 1893-Accepted, 12th Aug., 1893
COMPLETE SPECIFICATION.
Improvements in Thermostats.
We, HENRY STOPFORD TUNNARD, of Bilton Road, Rugby, in the County of
Warwick, Gentleman, and ARTHUR MAITLAND KEAYS, of Wandle Cottage,
Sutton, in the County of Surrey, Electrician, 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:-
It is desirable for a variety of purposes that great exactitude should be obtained
and that great facilities should be given for regulating the temperature in certain
apparatus such as fire alarms, incubators, and other appliances.
Our present invention consists of an improved form or construction of thermostat
which has a much higher degree of sensitiveness than has been hitherto obtained in
apparatus of like nature.
In our improved form of thermostat we obviate the fault hitherto found in this
class of instrument, of the mercury getting out of order or disconnected in the
transit of the instrument. We further provide an easy, accurate and efficient
means of adjustment.
The construction of our invention is as follows:-We make in the glass tube
which contains the mercury a bulb at one end but instead of making the bore of
the tube of the same diameter from end to end we make the tube as of two parts,
the first part having a bore of larger diameter than the second part, we blow an
expansion chamber at the point of union of the two tubes and another expansion
chamber at the other end of the fine bore tube, we also provide a small expansion
chamber at the point of union that the bulb makes with the tube of greater
diameter. A platinum wire is fused into each end of the thermostat; the wire
that is fused into the bulb is always in contact with the mercury, and the wire
that is fused into the expansion chamber at the end of the tube having the
smaller bore only makes contact with the mercury when the latter expands and
runs up, first into the tube of larger bore next into the expansion chamber that
separates the tube of larger bore from that of the smaller; the mercury then
enters the tube of smaller bore, traverses its entire length coming in contact with
the platinum wire.
To each end of the base of the thermostat is fixed a plate of copper or other
conducting metal, the wires at each end of the thermostat being joined to the
conducting plates forming an electrical connection between the plate and the
platinum at each end thereof.
Movable connecting pieces of copper or other conducting metal are arranged to
form a sliding contact with the fixed plates, one at each end of the thermostat, and
are provided with binding screws in such a manner that the movable pieces can be
moved up or down, providing a means of ready adjustment. Indications are
marked on the movable pieces (such as an arrow head or the like), and on the fixed
plates a divided scale is marked off. The movable pieces are capable of adjustment
for the whole length of the scale.
In order that our invention may be better understood and more readily carried
into effect we will proceed to describe the drawings hereunto annexed. Similar
letters refer to similar parts throughout the several figures of the drawing.
Figure 1 is a plan, and Figure 2 an elevation of our improved thermostat.
a is the bulb of the thermostat, b is a slight enlargement of the tube c, d is an
expansion chamber which unites the tube c with the tube e, the tube e ends in an
expansion chamber f. Into the bulb a is fused a platinum wire g', one end of the
wire being in contact with the mercury in the bulb a, the other end is united to
the conducting plate ¹. The plate h¹ is rigidly fixed to the base m, the slotted

page_text: piece k¹ is fixed to the plate h' by means of the binding screws 1, 1. When the
screws, are slackened the slotted piece can be moved up or down and a
scale of divisions 'is marked off on the fixed plate '. The mark or arrow head is
fixed in such a manner that its point is capable of being brought opposite any of
the divisions of the scale admitting of adjustment for the entire length of the
scale; the bore of the tube c is of greater diameter than that of the tube e, one
end of the platinum wire g is fused into the expansion tube f at the point o and
this end of the wire extends to the commencement of the tube e (but does not
enter said tube) terminating at the exact point at which the tube e ends and
the expansion chamber of commences. The other end of the wire g is fixed to
the plate h, the latter in its turn being fixed to the base m. k is a slotted
conducting piece fixed to h by means of the binding screws 1, 1, and is capable
of adjustment for the entire length of the scale; n, n, n, are clips or retaining
pieces which hold the thermostat to the base m.
The operation of our apparatus is as follows:-In cases where we adapt our
apparatus for use in fire alarms, we provide an electric battery of any convenient
form in conjunction with an electric bell or other form of indicator or alarm. One
of the wires from the battery is joined to the terminal screw o.
The wire from the electric bell or other alarm would be attached to the other
terminal screw o', the circuit being completed from the battery to the alarm.
When
Our apparatus illustrated in Figure 1 is fixed in such a position that the slotted
conducting clips k, k' are in electric contact with the binding terminals o, o'.
the mercury in the bulb a is not in contact with the platinum wire g the electric
battery will be out of circuit, the circuit being broken. On an increase of tem-
perature and the mercury in the bulb a expanding and making contact with the
platinum wire g the electric circuit would be completed and the battery would be
brought into operation with the electric indicator or alarm.
When the temperature falls the mercury in the bulb a contracts and is drawn
away from the platinum wire g, the circuit is broken and the battery is thrown out
of action.
For use in incubators, our improved apparatus is fixed in a convenient position
in or above the egg drawer, the terminals o, o' being in connection with an electric
battery and other apparatus.
0,
o are
With regard to the application of our improved apparatus for use in incubators,
the object of the slotted clips k, k¹ is to provide a means of adjusting the thermostat
in its position in or above the egg drawer. The binding screws o, o¹ are rigidly
fixed in the case of the incubator. When the binding screws or terminals
rigidly in contact with the slotted clips k, k¹, if the screws 1, are slackened back
the thermostat can be either raised or lowered in its position in relation to the
length of the slotted clips. The arrow heads fixed to the slotted clips k, k¹ when
the thermostat is in its normal position will be opposite to the figure 0 on the fixed
plates h, h. Supposing it is necessary to raise the height of the thermostat, the
screws, would be slackened back, the thermostat would be lifted until the arrow
heads point to any convenient position between 0 and 10 on the lower portion of
the scale according to the height it is required to be raised, the screws 1, would
then be screwed down and the thermostat would be held in its raised position.
Assuming that it is required to lower the thermostat in the drawer, the screws 1,
would be slackened back, the thermostat would be allowed to drop until the arrow
heads point at any convenient position between 0 and 10 on the upper portion of
the scale.
It will thus be seen that whereas the slotted clips k, k¹ are immovably fixed, the
thermostat itself has a range by which it can be either raised or lowered.
In practice the object of making the thermostat adjustable in its position in the
egg drawer is for the purpose of controlling to a nicety the particular temperature
at which it is desired to maintain in the egg drawer, for instance, it may be
necessary to maintain a uniform temperature of 104 degrees Fahrenheit on the
egg-drawer thermometer; to obtain this in practice it is found that the thermostat

page_text: when in position in the drawer will have such a position that the arrow heads on
the slotted clips k, k¹ will be exactly opposite the figure 0 on the scale. Let us
suppose it is necessary to maintain the temperature of the egg drawer at a uniform
temperature of 102 degrees Fab. instead of 104; to effect this result it is simply
necessary to alter the position of the thermostat in its place; in this case the
thermostat would be raised and the arrow heads on the slotted clips k, k' will be at
some position between 0 and 10 on the upper portion of the scale. The reason of
this is as follows:-The temperature of an egg drawer in an incubator is hotter at
the upper portion than it is at the bottom, consequently, if we raise the thermostat
in its position in the drawer it will come into operation sooner than it otherwise
would, on the other hand, if we lower the thermostat from its normal position and
place it in such a position that the arrow heads on the slotted clips k, k² are in any
position between 0 and 10 on the lower portion of the scale the thermostat will
then come into action at a later temperature with the result that the temperature
of the egg drawer will be allowed to increase till it reaches a normal somewhere
between 104 and 106 degrees Fah., according to the actual position of the arrows.
It is obvious that our improved form of glass tube may be employed for
thermometers. In this case we should prefer to make the tubes e and c of equal
length and the diameter of the bore of c three times as great as the diameter of the
bore of e.
We do not pretend to bind ourselves to the exact size of the bore of C, other than
it should be much greater than the bore of e.
It is also obvious that the length and the diameter of the tubes c and e will vary
in thermostats having different ranges of the Fahrenheit scale.
Having now particularly described and ascertained the nature of our said inven-
tion and in what manner the same is to be performed, we declare that what we
claim is:-
C
1. In a mercurial thermostat, the combination of the tube c communicating with
the tube e, the diameter of the bore of the tube e being smaller than that of the
tube c, substantially as described and illustrated on the drawing.
2. In mercurial thermostats, the combination of the bulb a, an expansion
chamber b, a tube c communicating with the tube e through the expansion chamber d,
the tube e also ending in the expansion chamber f, all substantially as described
and illustrated in the drawing annexed.
3. In a mercurial thermostat the plates h, h¹ fixed to the base m, in combination
with the slotted slides k, k', binding screws 1, 1, 1, 1, the slotted slides k, k¹ being
adjustable, all substantially as described and illustrated in the drawing annexed.
Dated this 30th day of March 1893.
'JOHN P. O'DONNELL,
70 & 71, Palace Chambers, Bridge Street, Westminster, S.W.,
Agent for the said Applicants.