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Ther′mo-e-lec′tric a-larm′.

An apparatus designed to indicate the rise of temperature in bearings for shaftings, or in any kind of machinery or any branch of manufacture where a fixed temperature is desirable.

Hot-bearing alarm.

It resembles a common thermometer, except that it has a wire secured at top and bottom. The wire at the bottom passes through the bulb and touches the mercury. The other wire enters the glass at the top and extends part way down the inside. Each of these wires is connected with a small open circuit having a battery and an electric bell. When this connection is made and the battery in order, the glass may register (say) 40°. The upper wire hangs down in the glass (say) to 85°, the circuit being open by the space between the top of the column of mercury and the bottom of the wire. When the mercury rises and touches 85°, the circuit is closed and the bell sounded. When the column of mercury sinks, the circuit is broken and the bell stops. The upper wire may be adjusted to any figure on the scale. For refrigerators, the end of the wire may touch the freezing-point; for chambers or school-rooms, it can be set at 70°; to indicate the presence of fire, it may be set at 100° or upward. In the case of hotels, a glass in every room, each with its wire circuit, may ring an alarm-bell in the office the instant the temperature rises above a fixed hight. To indicate the particular room, a common electric annunciator is attached to the system of circuits, and the clerk or watchman informed of the exact position of the danger. By fixing the glasses at a comparatively low figure (say 90°), they serve a double purpose, — show if the room is too warm from overheating or in danger from fire. When used as an indicator of the want of oil or other lubricant on bearings for car-wheels, shafts, and the like, the hot journal quickly raises the mercury, and, by closing the circuit, starts the alarm-bell, which continues to ring till the shaft is stopped or cooled. For this purpose a hole is drilled in the bearings, and the thermometer sunk in it till the bulb rests on the shaft. This device is also used to indicate any required temperature in boiling drugs, dye-stuffs, or other liquids.

Fig. 6346 consists of a cylindrical box a provided with a perforated bottom b, and placed directly over the journal. The box is filled with a prepared grease which melts at a certain temperature, to which it must be raised by the shaft becoming hot. As the compound liquefies and escapes through the perforations, a disk c, which rests thereon, descends, thereby tilting the lever d, and so making contact between the plates e and f. The latter are connected by an electric circuit with a bell which sounds when the current is established. The pipe g serves for the ordinary lubrication of the journal.

See also temperature-alarm; thermoscope; thermometric alarm; etc. See also testing-machine, Fig. 6330.

1877.

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