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Last Updated: March 31, 2007
Last Updated: March 31, 2007
Remote temperature control is provided by a bulb-and-capillary arrangement. The metal bulb, filled with sensing fluid, is connected to the bellows and switch mechanism through a thin capillary tube about 6 to 10 ft long. The capillary transmits fluid expansion from the metal bulb to the bellows.
In contrast to differential-expansion thermostats, liquid level sensors are less sensitive and considerably slower. Because of this, liquid level sensors respond to average temperature rather than instantaneous. Average temperature measurement is appropriate for applications with a large thermal time constant. For example, liquid level sensors are suited for controlling temperatures in waterbed mattresses, commercial cooking ovens, and environmental chambers.
Bulb-and-capillary thermostats control remote switches, removed from the environment or process under control. Control switches, therefore, do not have to operate under the severe temperature conditions where the liquid level sensors are located. Also, because switches are not incorporated in the sensing element, liquid-filled bulbs can have a smooth tubular shape. Such a profile is mechanically strong and easy to design in a product. Under a waterbed mattress, for instance, the bulb withstands high forces and is not a puncture threat.
In contrast to differential-expansion thermostats, liquid level sensors are less sensitive and considerably slower. Because of this, liquid level sensors respond to average temperature rather than instantaneous. Average temperature measurement is appropriate for applications with a large thermal time constant. For example, liquid level sensors are suited for controlling temperatures in waterbed mattresses, commercial cooking ovens, and environmental chambers.
Bulb-and-capillary thermostats control remote switches, removed from the environment or process under control. Control switches, therefore, do not have to operate under the severe temperature conditions where the liquid level sensors are located. Also, because switches are not incorporated in the sensing element, liquid-filled bulbs can have a smooth tubular shape. Such a profile is mechanically strong and easy to design in a product. Under a waterbed mattress, for instance, the bulb withstands high forces and is not a puncture threat.
Liquid Level Sensors, although slower than differential-expansion types, typically handle more current because their switches are not part of the liquid level sensor system. As a result, a wide variety of interchangeable switches can provide various types of service including 20 A at 120 or 240 Vac, narrow differential, high inrush, and manual reset.
Liquid level sensors employ temperature-sensing bulbs that contain an incompressible liquid. The type of liquid determines the operating range. As the temperature varies, the volume of the liquid expands or contracts. This displacement is transmitted hydraulically through a bellows or diaphragm. Bellows motion, in turn, can be transmitted through a push rod or other mechanical linkage to actuate the contacts of a dedicated electrical switch.
Both local and remote temperature control is possible with liquid level sensors. Local-bulb types enclose the sensing liquid, bellows, and push rod in a single shell. The electrical control switch is attached to the top of the shell.
Liquid level sensors employ temperature-sensing bulbs that contain an incompressible liquid. The type of liquid determines the operating range. As the temperature varies, the volume of the liquid expands or contracts. This displacement is transmitted hydraulically through a bellows or diaphragm. Bellows motion, in turn, can be transmitted through a push rod or other mechanical linkage to actuate the contacts of a dedicated electrical switch.
Both local and remote temperature control is possible with liquid level sensors. Local-bulb types enclose the sensing liquid, bellows, and push rod in a single shell. The electrical control switch is attached to the top of the shell.
