OVER-TEMPERATURE SWITCH
If your application is such that large decreases in liquid level or flow can occur without warning, GLO-QUARTZ® recommends that you add an O.T. (over - temperature) Sensor to your heater to prevent catastrophic failure. Because side-mounted tank heater designs are especially vulnerable to falling liquid level, GLO-QUARTZ® includes an overtemperature sensor as standard on these models.

GLO-QUARTZ® offers two basic devices that can sense over - temperature: bimetallic switches and thermocouples. Bimetallic switches are used almost exclusively for heaters immersed in a liquid and operate at a relatively low temperature (up to 302°F (150°C.) Thermocouples can be used in both liquids and gases. Because thermocouples can operate at much higher temperatures (close to the melting point of most heater sheath materials) they are sometimes the only choice for gases (air) and steam heating equipment.

Bimetallic Switches
These devices are designed to break an electrical circuit by opening their contact at a preset temperature. The contact automatically re-closes after the temperature has dropped below the operating point by 2ºC to 10ºC. The maximum contact current is 7.8 amps at voltages up to 230vac and 4 amps from 230 up to 240 volts, which is the maximum operating voltage.

This means that in most cases, the switch can only be used to pilot a higher current/voltage device such as a contactor. Bimetallic switches are typically placed in their own thermowell, which is located very close to or touching a heating element sheath. GLO-QUARTZ® bimetallic switches are available in 5 different operating temperatures ranging from 95ºF (35ºC) to 302°F (150°C)

Thermocouples
A thermocouple is the sensing portion of a large control device and performs no useful function by itself. A thermocouple type over-temperature controller is more complex and expensive than a bimetallic switch but also more versatile, because the temperature "trip point" is adjustable. GLO-QUARTZ® installs both type “J” and “K” thermocouples, which have only slightly different operating characteristics. The junction is normally "ungrounded" (not electrically connected to the sheath).

GLO-QUARTZ® thermocouples are contained in metal sheaths over their entire length. Several choices of sheath material, including 304 stainless steel, 316 stainless steel, incoloy, and titanium, are available depending on the chemical content of their operating environment. The sheath is usually banded directly to one of the elements in the heater. GLO-QUARTZ® can install the complete over-temperature control device, including thermocouple, or provide only a thermocouple that is compatible with the input of the customer's own control device.

 
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