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2-wire 3-wire, 4-wire: Refers to connections to a sensor, typically an RTD where 2-wire has no lead wire compensation, 3-wire compensates for the lead wire resistance, making the assumption the two wires are the same and 4-wire actually senses and subtracts the resistance of both wires.


Active load: A device in a chamber or on a thermal platform that is actively producing significant heat.

Adapter Plate: A fixturing plate, mounted on top of a thermal platform, allowing custom drilling and mounting of devices.

Aperture: A porthole, typically in the side of a temperature chamber or a probing cover.

Autocascade Refrigeration: A system with multiple refrigerants in one compressor circuit with phase separators used to evaporate each of the refrigerants at the required pressures and temperatures to achieve ultra-low temperatures, below -40° C.


Bulk system: Refers to a large tank of Liquid CO2 or Nitrogen, typically outdoors, with associated distribution pluming.

Burn-in: A form of thermal testing usually represented by long periods of operation while at elevated temperatures.


Cascade Refrigeration: A refrigeration system that uses multiple refrigerants and more than one compressor to achieve ultracold temperatures.

Cascade Temperature control: reads the device temperature as well as the chamber or platform to achieve setpoint more quickly with verification.

Conduction (thermal): The method of heat transfer that requires direct contact between a driving source of heat and the device to be thermal conditioned. Generally, more effective and faster than convection which relies on air to transfer heat.

Convection (forced): An alternative to heat transfer by conduction, not requiring intimate contact between the heat source and load. A fan is used to circulate air to transfer heat. Also, as opposed to natural convection where natural air currents trend upward when heated and downward when cooled.

Coolant filter: Particulate filter on the coolant inlet of a thermal platform or chamber that prevents contamination of the control valve. It does not stop oil or water contamination.

Cryogenics: Any cooling process or liquid/gas below -50°C. Liquid Nitrogen and Liquid CO2 are considered cryogenic liquids and are often used to cool items to temperatures below -50°C.


Dewar: An insulated tank for storing cryogenic liquids. Typically vacuum insulated.

Dip Tube: An internal part of a cryogenic liquid container (dewar or cylinder) that takes liquid from the bottom of the tank as opposed to gas from the top of the tank. See Syphon tank.

Direct evaporation, Direct injection: Refers to applying refrigerant directly to the media to be cooled as in refrigerant being evaporated into a thermal platform or also liquid Nitrogen injected into the workspace air of a chamber.

Dwell time: The amount of time spent at a temperature before transitioning to the next temperature in a test. Same as Soak Time.


Environmental test, Environmental Simulation: Using thermal test equipment to simulate the environment a product or sample is expected to experience in its useful life. Also, Burn in to operate equipment over a period of time at an elevated temperature to weed out early failures.

ESS: Environmental Stress Testing: Another name for Environmental Test.

Ethernet: Computer network interface is often used to communicate with test instruments.


Flare fitting: SAE flare fitting has a 45° flange for sealing, a JIC fitting has a 38° flange. SAE fittings are used on chambers and platforms coolant inlets. The two look very much alike but are incompatible and prone to leaking if mixed. Some fittings successfully compromise with a 41-degree fitting which sometimes works for either.


GPIB: General Purpose Instrumentation Bus: An electronic interface designed by HP in the early 1960s to communicate with and control test equipment remotely and by computer. Still in wide usage however considered by some to be obsolete and much more expensive to implement than Ethernet.

GUI: Graphical User Interface.


HALT/HAST: Highly Accelerated Life Testing and Highly Accelerated Stress Testing. The process to improve and determine the expected life of equipment under environmental stress, usually ending the HALT when a product fails and HAST typically might be cycling rapidly hot and cold to verify the reliability of a product before shipping.

Hybrid Benchtop Chamber: A temperature chamber that uses both convection and conduction to heat and cool more uniformly and quickly.

Humidity chamber: An environmental test chamber designed to control humidity and typically also includes temperature control.


IEEE-488: Another name for GPIB. See GPIB.


Liquid Chiller, Recirculating Chiller: Typically, a refrigeration system cooling a liquid that typically recirculates to and back from a device to perform thermal testing. Often immersing the device in liquid or exchanging heat by another method.

Liquid CO2: A cryogenic liquid is also referred to as ASHRAE refrigerant 774. Can be used in a recirculating or expendable method. Often vilified as a greenhouse gas, however, CO2 for industrial use is captured from the environment for the purpose. Cheaper to use than Liquid Nitrogen but has some operational quirks.

Liquid Nitrogen: Readily available and inexpensive in bulk. Used as a refrigerant, typically expendable, not recirculated. also referred to as ASHRAE refrigerant 728. The boiling point is -196°C, so it has great capacity however the ultracold temperature can make it difficult to store and transfer to point of use.


Mechanically refrigerated: Cooled with a system employing one or more refrigeration compressor(s).


PRV Pressure relief valve: Always recommended where coolant could be trapped in a device or hose.

Purge / Purge gas: Typically Nitrogen. A small flow of inert gas that is flowed over devices, thermal platforms, or chambers decreases the condensation that happens at temperatures below the dew point and frosting that happens below freezing. Also can reduce corrosion at high temperatures. Low flow rates are used to displace air that contains water or Oxygen without influencing the temperature.

Probing Cover: A polycarbonate or other cover that goes over a thermal platform to reduce thermal loss and condensation/frosting. Often has a purge inlet too.


Ramp rate: How fast a temperature chamber or thermal platform can transition between two given temperatures. Stated in minutes between given temperatures or degrees F/C per minute.

RS-232: A very common serial communication interface, often used to communicate between computers and instruments. Available on most computers but is limited in that one bus interface can only communicate between a host and a maximum of one remote device.

RS-485: A less common but very useful communication interface, often used to communicate between computers and instruments. It has the advantage over RS-232 in that it can have several instruments on the same bus, only requires two wires, and is often considered more robust than RS-232.

RTD: Resistance Temperature Detector. An industry-standard device that can accurately and precisely be used to indicate or control the temperature of the air or a device. Typically made of platinum wire or printed circuit. Wire wound units are generally considered more reliable.

RTFM: Read the fine manual.


Serial Communications: Typically, RS-232 is frequently used to communicate between computers and devices such as a temperature controller. USB is a serial communication interface and technically, so is Ethernet although Ethernet is rarely considered a serial interface. RS-485 is also a serial communications interface that is used to communicate with temperature controllers.

Soak Time: The amount of time a temperature profile spends at one temperature before transitioning to a new temperature when temperature cycling.

Solenoid valve: An electrically actuated valve used to control the flow of a gas or liquid. Typically, in an On/Off fashion although there are some variable solenoid valves.

Solid State Relay (SSR): An electronic switching device often built with Triac’s inside, typically used to switch on and off heating/cooling and other electrical functions.

Space Simulation: Thermal testing with a thermal platform in a vacuum environment designed to simulate conditions in space.

Syphon Tank: A tank such as is used for LN2 and CO2 that is designed with a dip tube inside to take liquid off the bottom as opposed to gas from the top.

Temperature chamber: An insulated box with the ability to control the temperature inside the box. For thermal testing and other scientific purposes.


Thermal Platform: A widely used alternative to temperature chambers. Often more effective due to the advantage of superior heat transfer of conduction over forced convection.

Thermal Screening: Another name for thermal testing.

Thermal Shock: Rapid and controlled transition between given temperatures.

Thermistor: A low-cost alternative for a temperature sensor. Generally considered not of adequate reliability when compared to RTDs and also less reliable than thermocouples.

Thermocouple: A temperature sensor made from two dissimilar metals joined together. A small repeatable voltage is produced between these metals that vary as temperature changes. There are exceptions but are typically considered less reliable than RTD’s. See RTD.

Touch and go: Thermal testing where as soon as a temperature is achieved, the setpoint is changed to a new temperature.

Triac: A 3-terminal thyristor semiconductor device similar to a transistor that often is used to switch on and off electricity for heating or cooling functions. See Solid State Relay.


Vacuum Jacketed Hose: Delivery hose for Liquid Nitrogen with two walls and vacuum in between for superior insulation.

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