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.
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.
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)
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
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.