Adjustable: A thermostat of any type whose set point or calibration may be adjusted within the designed temperature range.
Ambient Temperature: The normal or typical temperature range of the environment surrounding the device.
Automatic Reset: A type of thermostat that will automatically reset at a specific temperature.
Bimetal: The mechanism that opens or closes the electrical contacts. It consists of two dissimilar metals bonded together then formed with a specific curvature. When heated, the different thermal expansion coefficients of the bimetal cause the disc to reverse its curvature with a snap action at a fixed, preset temperature and operate the electrical contacts.
Close On Rise (NO - Normally Open): Refers to operation of the contacts. When the temperature rises to its set point, the contacts close or make contact and complete the circuit. The contacts automatically open at the low end of its design differential. It is also referred to as a Fan Type Device.
Constant Cut-In Control: Forces an off cycle defrost at the end of each run cycle. The control will remain open until the evaporator has reached a temperature which indicates that any frost accumulated during the previous run cycle, has been melted (eg frost free).
Contact Resistance: The electrical resistance of closed contacts as measured at their respective terminal ends
Creep Action: Slow make/Slow break switching action. No built in differential between the opening and closing temperature.
Differential: The difference between the temperature to operate and the temperature to reset a thermostat. Also known as hysteresis.
Dielectric Strength: The value of insulation between two electrically conducting parts.
DPDT (Double Pole, Double Throw): An electrical term where “pole” is a leg of an electrical circuit and “throw” describes the switch action. Therefore, a DPDT will switch two legs and each leg will open a set of contacts, and close another set (4 sets of contacts).
DPST (Double Pole, Single Throw): An electrical term where “pole” means a leg of an electrical circuit and “throw” describes the switch action. Therefore, DPST will switch two legs and each leg is switched open or closed by one mechanism.
Epoxy Seal: The sealing of a device against the entrance atmosphere contamination by the use of an epoxy film.
Fixed Temperature: A thermostat of any type in which the temperature setting or calibration is set at the factory.
FLA (Full Load Amps): Current taken from the line by the motor when the motor is yielding the rated Horsepower at the rated voltage and frequency.
Hermetic Seal: A device which is sealed against entrance of atmospheric contaminants (moisture, dust, etc.) by means of welding or soldering the enclosure. A gas tight seal from the environment.
Life Cycles: The endurance rating of the thermostat expressed in number of operations with stated electrical load applied.
LRA (Locked Rotor Amps): The amount of current the motor can be expected to draw under starting conditions when full voltage is applied, also known as starting inrush current.
Manual Reset: A bimetal thermostat with a reset button that must be pressed to reset the contacts. A type of thermostat that must be reset manually, such as by depressing a push button.
One Shot: One time only switch, thermal fuses must be replaced once tripped, however a one shot ½’’ disc can be reset by lowering the disc temperature to -35°C. Available only in Open On Rise/Normally Closed contact configuration.
Open On Rise (NC - Normally Closed): Refers to the operation of contacts. When the temperature rises to its set point the contacts open, terminating the circuit. Typically a high limit or safety application.
Operating Temperature: (Thermostats) Temperature at which normally closed contacts open or normally open contacts close.
Over mold: Encapsulation with an insulating material.
Overshoot: The temperature of the medium or device which the thermostat is subjected to, which exceeds the maximum set or control point. Example, a thermostat is set to close its contacts at 300°F, however the air in a duct where the thermostat is installed continues to rise in temperature to say 600°F. Therefore, 300°F is the possible overshoot.
Probe: That portion of a thermostat which extends into the substance whose temperature the thermostat is sensing.
Self-Hold: Built-in PTC Heater prevents thermal protector from resetting. Power must be shut off from circuit to turn off heater and reset thermal protector. A device that, upon opening, will not reset until power is removed from its circuit regardless of ambient temperature.
Set Point: The nominal temperature at which the thermostat operates.
Snap Action: Bimetal disc or switch mechanical thermostats that function via the thermal expansion and contraction of a bimetal.
SPST (Single Pole/Single Throw): A switch with one current path which can be either open or closed. A switch with a single set of terminals and a single set of contacts.
S.P.D.T. (Single Pole/Double Throw): A three terminal switch possessing both Normally Open and a Normally Closed contact configuration.
Tolerance: The allowable range above and below the set point temperature. The maximum allowable deviation from the nominal set point under all specified environmental and operational conditions. It represents the total of setting deviations due to calibration, manufacturing, environmental and temperature changes, etc.