Environmental Testing Terminology for Test Chambers

This glossary defines key environmental testing terms related to temperature, humidity, airflow, and chamber performance. These definitions support accurate testing, system selection, and data interpretation.

Load and Test Sample Terminology

Device Under Test (DUT)
The device under test (DUT) is the product being tested inside the environmental chamber.

Dead Load
Dead load refers to any mass inside the test chamber that does not produce heat. This is used to properly size the chamber’s refrigeration and heating systems.

Live Load
Live load is the portion of the test chamber load that produces heat. This may include electrical, mechanical, chemical, air purge, or continuous product processes.

Temperature and Humidity Terms

Absolute Humidity
Absolute humidity is the amount of water vapor in the air, typically expressed in grains per pound.

Relative Humidity (RH)
Relative humidity is the amount of water vapor in the air at a given temperature compared to the maximum amount the air can hold at that same temperature.

Dew Point Temperature
Dew point temperature is the temperature at which moisture condenses on a surface.

Dry Bulb Temperature
Dry bulb temperature is the temperature of a given air sample.

Wet Bulb Temperature
Wet bulb temperature is the temperature that results when water evaporates and cools a sensor.

Airflow and Chamber Environment

Air Velocity
Air velocity is the speed at which air moves through a space.

Air Volume
Air volume refers to the total amount of air within a space.

Chamber Operating Environment
The chamber operating environment refers to the external conditions surrounding the test chamber, such as ambient temperature and humidity.

Chamber Performance and Accuracy

Control Tolerance
Control tolerance is the variation in temperature at the control sensor after stabilization. It reflects relative variation, not absolute accuracy.

For example, with a setpoint of -65°C and a tolerance of ±1°C, the actual temperature may vary between -64°C and -66°C. These specifications are based on an empty chamber, and the presence of a test sample may affect the variation.

Controller Accuracy
Controller accuracy is the ability of the temperature controller to display a temperature measurement compared to a known standard.

Total system accuracy includes sensor accuracy (thermocouple or RTD) and additional factors such as lead wire resistance. This reflects measurement accuracy, not overall chamber performance.

Uniformity (Temperature Gradient)
Uniformity is the measure of temperature variation at different locations within the chamber after stabilization.

Uniformity is typically specified as ± a temperature range (e.g., ±1°C) and is measured away from chamber walls. The presence of a test sample may impact uniformity, particularly if the sample generates heat.

Change Rates and Timing

Change Rate (Ramp Rate)
Change rate, or ramp rate, is the speed at which an environmental chamber heats up or cools down.

Average Change Rate
Average change rate refers to variable heating or cooling speeds across different temperature ranges. For example, the chamber may heat or cool faster at higher temperatures and slower at lower temperatures.

Linear Change Rate
Linear change rate is a consistent rate of temperature change across all temperature ranges.

Transfer Time
Transfer time is the amount of time required to move a test sample from one chamber to another, typically in thermal shock applications.

Recovery Time
Recovery time is the time required for the chamber temperature to return to setpoint after a transfer or disturbance. This may be measured in the air stream before or after the test load.

Frequency

Frequency
Frequency is the rate of wave movement measured in cycles per second. It is typically expressed in hertz (Hz), where one hertz equals one cycle per second.

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