Ther′mo-stat.
A self-acting apparatus for regulating temperatures.
The balance-thermometer is poised horizontally on an axis, and so arranged that as the mercury contracts or expands in the tube on either side of the mean temperature for which it is adjusted, one end or the other of the thermometer will tip up and actuate a device whereby the heat of an apartment or greenhouse is increased or diminished, as the case may be.
One form was invented by
Dr. Cummings of
Chester, England, and used to open and shut the windows of hot-houses A balance-thermometer.
patented in
England in 1816 by Kewley, was employed to open and shut doors.
An electrical thermostat consists of an ordinary mercurial thermometer, provided with a platinum wire connecting with the mercury in the bulb.
Through the other end of the tube is inserted another platinum wire capable of being elevated or depressed.
These two wires are in connection with the poles of a battery, and in the circuit is an electro-magnet whose armature controls the opening or closing of a valve for the admission of hot air. If it be desirable that the temperature of the air should not rise above a certain temperature, say 60° Fah, the free end of the movable wire is brought to the required number on the tube.
When the heat is such as to cause the mercury to rise to that degree, the electric circuit is completed, the armature closes the hot-air valve until the temperature is diminished, when the circuit is broken, and the valve again opened.
Other forms of thermostat are adapted to open and close the draft openings of furnaces to regulate the admission of fresh air to the fire, and insure a uniformity of combustion.
Dr. Ure. about 1830, contrived a thermostat, the action of which depended on the unequal expansion of two metals by heat, for regulating the safety-valves of
steam-engines.
A self-acting statical damper or heat-regulator was invented by
Dr. Cummings many years since, and was designed as a mode of opening windows and ventilators in apartments by the variations in the temperature of the included air.
The sash is bung upon centers, so as to oscillate readily, and a cord passes from it to an areometer tube, which is partly charged with quicksilver, and has a body of included air in a bulb at top. The open lower end is plunged in a cup of quicksilver; and as air in the bulb is expanded or contracted by heat, the weight of the suspended tube and bulb becomes relatively less or greater by the variation in the quantity of quicksilver contained, causing the tube to rise or fall, and so operate the sash or valve.
The name
thermostat was first applied by
Dr. Ure to an instrument patented by him in 1831, in which the bending of a spring composed of two unequally expansible metals, as steel and brass, was made to control a valve or damper.
A thermostat was applied by Bonncmain of
Paris, in 1777, to his calorifore.
by which he heated buildings.
The heater consisted of a boiler with an ascending hot-water pipe, which coursed through the stories or apartments of the house, and then descended again to the boiler with its contents comparatively cooled.
He heated an incubator in this manner.
The variation of temperature seldom exceeded ° R. See B, Fig. 2666.
page 1178.
The thermostat was inserted in the boiler, and acted upon the door of the ash-pit so as to regulate the admission of air to the fire.
It depended upon the unequal dilation of different metals by heat.
It was formed of a bar of iron screwed to one of brass, inclosed in a leaden tube terminating in a ring of brass and plunged into the boiler.
The dilation of the leaden tube had the effect of drawing upon the rod and bringing the ring in contact with a claw at the short end of a bent lever communicating by a wire with the ash-pit door, which acted as a damper.
Fig. 6370 shows a form applied by
Dr. Arnott to his stove.
a b is a curved tube containing mercury in the bend
b: the end
a is inserted in the combustion-chamber, and as the contained air is expanded by heat, the mercury rises in the outer leg of the tube, carrying with it the fleat
c, connected by a rod to the frame
d, from which is suspended a wire carrying the valve
f, which closes the opening of the pipe
e by which air is supplied to the combustion-chamber.
A fall of temperature produces the reverse effect.
In a simpler form, the lower end of the tube
e is brought into proximity to a funnelshaped reservoir of mercury, which on expanding by heat closes its mouth.
In Tamkin's automatic damper (
Fig. 6371), a disk turning on an axis is placed in the flue: the disk is weighted on one side so as to hang vertically when the heat is low; but when this becomes excessive, a spring composed of two metals, as copper and iron, having unequal rates of expansion, becomes bent, so as to impinge against the damper and partially close the opening
In
Dr Sternberg's electro-magnetic regulator (Figs.
6372, 6373), a thermometer
B is suspended in any apartment the temperature of which is to be regulated.
A platinum wire
a is hermetically sealed in a portion of the tube prolonged below the bulb.
An adjustable wire
b slips through the open upper extremity of the thermometer stem, and its end is thrust down the tube.
The wire passes between adjusting rollers, by which
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it is raised or lowered until its end stands at any desired degree of the scale.
By means of binding-screws, the wires
a b have electric communication with the wires
c d, which pass to the furnace or heating-apparatus, and are there connected with the apparatus by which the valve or damper is operated.
A battery-cup is interposed in the circuit at any convenient locality.
When the heat of the room in which the thermometer hangs causes the mercury to rise and meet the point of the adjustable wire, an electric circuit is completed, Oassing through the helix of a temporary magnet, causing its armature to be attracted, moving a lever by which the valve or damper is closed.
This diminishes the heat of the room, and causes the mercury to fall below the point of the wire.
The circuit being thus broken, a spring with draws the armature from the electro magnet and opens the damper.
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Tamkin's automatic damper. |
Pressure of steam may be regulated by making the steam-gage act as a regulator, the electric circuit being made and broken by the needle of the steam-gage dipping in a cup of mercury.
This may be arranged either to govern the supply of air admitted to the furnace or a valve by which steam escapes from the boiler.
A modification of the apparatus, in which the rising and falling of a float opens and closes the circuit, may be employed as a means of controlling the supply-pipe valve of a reservoir.
A thermometer (
C) in which the upper wire is fixed to a certain graduation in the tube is used for immersion into liquids or gases which are to be maintained at a given temperature.
Wilson's thermostat for steamheaters (
Fig. 6374) has a compound plate made of two metals, say of brass and steel, which bends by the unequal expansion of the two metals by increment of heat, and thus stops the steam induction-aperture
E. H is adjusting stop-valve screw.
Watkins combines a compound metallic strip
a with a closed tubular case
m by means of an insulating base
b and a metallic conducting-cap
i and indicator set-screws
n n, whereby, by the expansion or contraction of the compound metallic strip, a galvanic circuit may be closed or opened at any required degree of heat to operate a fire-alarm telegraph-instrument.
In Guest's electrical thermostat (
Fig. 6376), the circuit is closed by the rising of a column of mercury in a tube, so as to touch the upper wire
d. The instrument has a bulb
a with an expansion-tube
b, surrounded by an outer vessel
c, which is closed hermetically by a cork and sealing-wax
f. The end of the wire
e passes through this outer vessel and the bulb into the mercury, being in continuous contact with it, the action of the instrument being thus not disturbed by the changes of temperature and access of air.
Whenever the temperature shall rise to the degree to which the thermometer is adjusted, the mercury will rise in the expansion-tube, and, coming in contact with the wire therein, establish the circuit and produce the alarm.
