Why Combine Temperature, Humidity and Altitude Testing?
A product may pass a temperature test and a low-pressure test independently but experience different behavior when both conditions occur together.
The reason is that environmental parameters can interact with the physical and thermal characteristics of the device under test (DUT).
Temperature affects product behavior
Temperature changes can influence:
• Material expansion and contraction
• Electrical component characteristics
• Battery performance
• Mechanical tolerances
• Thermal management
• Sealing materials
• Lubricants and moving components
Humidity introduces moisture-related stresses
Humidity can contribute to:
• Corrosion
• Moisture absorption
• Insulation degradation
• Condensation
• Surface leakage
• Connector and contact degradation
Altitude changes atmospheric pressure
Reduced atmospheric pressure can affect:
• Heat transfer
• Cooling performance
• Electrical insulation
• Sealing and enclosure behavior
• Pressure-sensitive components
• Internal gas or air volume
• Product thermal management
When these conditions occur together, the resulting environmental stress can be different from the sum of three independent tests.
This is why combined environmental testing is useful when the product's real operating environment involves simultaneous thermal, moisture, and altitude exposure.
What Changes When Humidity Testing Is Performed at Low Pressure?
One of the most important engineering considerations in temperature humidity altitude testing is that relative humidity should not be treated as an isolated parameter.
Relative humidity depends on temperature and the water-vapor condition of the environment. When pressure is reduced, the physical environment inside the chamber changes as well.
For this reason, a chamber designed for conventional temperature and humidity testing is not automatically suitable for humidity control under reduced pressure.
Relative humidity and temperature are linked
At a given temperature, the saturation vapor pressure of water changes with temperature. Therefore, changing temperature can significantly affect the moisture condition even if the humidity control setpoint remains unchanged.
For example, a test profile that moves rapidly from a warm, humid condition to a low-temperature condition must consider the possibility of condensation or changes in moisture state.
Reduced pressure changes heat transfer
At lower atmospheric pressure, gas density decreases. This can change convective heat transfer around the DUT.
For products with significant internal heat generation, this becomes particularly important.
A device that dissipates heat effectively at normal atmospheric pressure may behave differently at altitude because the surrounding environment provides different heat-transfer conditions.
Humidity control becomes more challenging
When temperature, humidity, and pressure are controlled simultaneously, the chamber must coordinate:
Temperature control
Moisture generation
Pressure reduction
Airflow
Condensation management
Measurement and feedback
The system therefore needs to be designed around the combined operating envelope, not simply the individual maximum ranges of the three parameters.
Temperature Humidity Altitude Test Profiles
The most appropriate test profile depends on the product qualification requirement and the failure mechanisms being investigated.
Profile 1: Constant Temperature + Humidity + Reduced Pressure
The DUT is exposed to a defined temperature and humidity condition while chamber pressure is reduced to the specified level.
This approach can be useful when the objective is to investigate environmental performance under a relatively stable high-altitude condition.
Typical applications include:
• Electronic assemblies
• Communication equipment
• Avionics
• Sensors
• UAV electronics
Profile 2: Temperature Cycling Under Reduced Pressure
The chamber changes temperature while maintaining a defined low-pressure condition.
A simplified sequence may be:
Ambient → Low Temperature → Reduced Pressure → High Temperature → Recovery
This type of profile is useful when thermal cycling and altitude exposure are expected to occur together during operation.
Profile 3: Humidity Exposure Followed by Altitude Simulation
The product is first exposed to a controlled humidity condition and then subjected to reduced pressure and temperature changes.
This can be useful for investigating how previous moisture exposure affects subsequent high-altitude performance.
Profile 4: Simultaneous Temperature, Humidity and Altitude
All three environmental parameters are controlled as part of the same test profile.
The objective is to reproduce a combined environmental condition rather than evaluate each stress separately.
This approach is particularly relevant when the product is expected to experience simultaneous climatic and altitude stresses during its service life.
What Failure Mechanisms Can Temperature Humidity Altitude Testing Reveal?
The value of combined environmental testing comes from identifying failure mechanisms that may not become obvious during single-parameter testing.
Electrical insulation degradation
Humidity can affect insulation properties, while reduced pressure may introduce additional concerns for electrical systems operating at altitude.
For electrical and electronic products, engineers may therefore need to monitor:
Insulation resistance
Leakage current
Functional stability
Electrical breakdown behavior
Signal integrity
Condensation and moisture migration
Temperature transitions can change the moisture condition around the DUT.
Potential concerns include:
Condensation
Moisture migration
Surface contamination
Corrosion
Connector degradation
The test profile should therefore specify not only temperature and RH but also transition rates and dwell periods where relevant.
Thermal management problems
Reduced atmospheric pressure can alter the heat-transfer environment.
This is particularly important for:
Power electronics
Batteries
Avionics
Electronic control units
High-power communication equipment
Semiconductor-related equipment
For these products, engineers should evaluate the DUT's actual thermal load during altitude testing rather than assuming that performance at sea level will remain unchanged.
Enclosure and sealing behavior
Pressure changes can affect products with sealed or partially sealed housings.
Engineers may need to investigate:
Housing deformation
Seal performance
Pressure equalization
Leakage
Internal pressure behavior
Functional instability
The most important failure may not be physical damage.
Some products may continue operating but show:
Communication errors
Sensor drift
Unexpected shutdown
Increased temperature
Reduced output
Intermittent faults
This is why DUT monitoring should be considered when defining a combined test system.
Temperature Altitude Testing vs Temperature Humidity Altitude Testing
These test configurations serve different engineering purposes.
| Test Configuration | Primary Engineering Purpose |
|---|---|
| Temperature Only | Evaluate thermal performance, temperature resistance, and behavior under controlled temperature exposure. |
| Temperature + Humidity | Evaluate climatic reliability, moisture resistance, corrosion risk, insulation performance, and condensation-related effects. |
| Temperature + Altitude | Evaluate thermal and functional behavior under reduced atmospheric pressure, including changes in heat transfer and pressure-related performance. |
| Temperature + Humidity + Altitude | Evaluate the interaction between thermal, moisture, and low-pressure stresses under combined environmental conditions. |
| Temperature + Humidity + Vibration + Altitude | Evaluate product performance under synchronized thermal, moisture, low-pressure, and mechanical vibration stresses. |
The key point is that adding humidity to a temperature-altitude test is not simply adding another specification.
It changes the required control architecture because the chamber must manage moisture while pressure and temperature are changing.
TestEQ's existing temperature-altitude systems support optional humidity control for temperature-altitude-humidity applications, while its four-combined systems address the broader combination of temperature, humidity, vibration, and altitude.
How to Specify a Temperature Humidity Altitude Test Chamber
A common procurement mistake is to specify a chamber only by:
Temperature range + humidity range + maximum altitude
This may not provide enough information for the manufacturer to determine whether all three parameters can operate simultaneously.
A better RFQ should define the combined operating envelope.
1. Define the temperature range
Specify:
Minimum temperature
Maximum temperature
Heating rate
Cooling rate
Temperature stability
Temperature uniformity
Required dwell time
2. Define the humidity requirement
Specify:
Minimum RH
Maximum RH
Humidity stability
Humidity uniformity
Condensation requirements
Required humidity at specific temperatures
3. Define pressure rather than altitude alone
Altitude is useful for describing the intended environmental condition, but the test system ultimately controls pressure.
Therefore, the RFQ should specify:
Minimum operating pressure
Maximum operating pressure
Target pressure
Pressure stability
Pressure transition rate
Required depressurization profile
For low-pressure qualification, this distinction is particularly important because IEC 60068-2-13 treats low air pressure as the controlled environmental condition. For combined temperature or temperature-humidity exposure with low pressure, IEC 60068-2-39 is specifically relevant to the combined test concept.
4. Define the simultaneous operating points
This is one of the most important procurement requirements.
For example, do not only specify:
Temperature: −40°C to +100°C
Humidity: 10–98% RH
Altitude: up to 15,000 m
Also specify whether the chamber must operate simultaneously at conditions such as:
−20°C + 85% RH + specified low pressure
or:
+50°C + 70% RH + specified altitude-equivalent pressure
The manufacturer needs these operating points to determine whether the refrigeration, humidity generation, pressure control, and chamber design are compatible.
What Should Engineers Ask a Chamber Manufacturer?
Before purchasing a temperature humidity altitude chamber, engineers should ask several specific questions.
Can humidity be controlled at reduced pressure?
Do not assume that a chamber with a humidity system can maintain the required RH throughout the low-pressure range.
Request the manufacturer's guaranteed operating envelope.
What pressure stability is guaranteed?
The theoretical minimum pressure is not necessarily the useful test pressure.
For qualification testing, stable pressure control at the actual setpoint is often more important than the lowest pressure the vacuum system can theoretically achieve.
Which temperature-humidity combinations are supported under pressure?
Ask the supplier to identify the conditions that can be controlled simultaneously.
How are pressure, temperature and humidity measured?
Request information about:
Sensor range
Accuracy
Resolution
Calibration
Measurement location
Data acquisition frequency
Can the DUT operate during testing?
If the product must remain powered during the test, specify:
Power feedthroughs
Signal feedthroughs
Thermocouple connections
Communication interfaces
Electrical load
Internal heat generation
Can the complete test profile be recorded?
For qualification and failure analysis, useful records may include:
Time + Temperature + Humidity + Pressure + DUT Data + Alarm Status
This creates a more useful test record than simply recording the final chamber conditions.
Standards for Temperature, Humidity and Altitude Testing
The applicable standard depends on the product, industry, qualification program, and customer specification.
Common references may include:
IEC 60068-2-13
IEC 60068-2-13:2021 addresses low-air-pressure environmental testing. It is primarily a pressure-focused test method.
IEC 60068-2-39
IEC 60068-2-39 addresses combined temperature or temperature and humidity with low air pressure. This makes it particularly relevant when the engineering requirement involves the interaction of these environmental parameters.
MIL-STD-810
Military environmental qualification programs may include low-pressure and altitude-related testing. The actual method and tailored test profile should be determined by the applicable procurement or qualification requirement.
RTCA DO-160
For airborne equipment, RTCA DO-160 may be relevant depending on the aircraft equipment qualification program.
The standard should be selected according to the actual product qualification requirement rather than simply choosing a chamber based on a manufacturer's advertised compliance list.
Applications of Temperature Humidity Altitude Testing
Combined temperature humidity altitude testing can be useful for products where environmental stresses overlap during actual operation.
Aerospace and avionics
Potential concerns include:
Thermal management
Electrical performance
Pressure effects
Moisture exposure
Functional stability
UAV systems
UAV electronics can experience rapid changes in altitude and temperature during flight. Combined environmental testing can help evaluate the interaction between these conditions.
Automotive electronics
Electronic control systems, sensors, communication modules, and other components intended for high-altitude operation may require environmental qualification under reduced pressure.
Batteries and power electronics
Reduced pressure can influence heat dissipation, making thermal management an important consideration for products with significant internal heat generation.
Communication equipment
Communication equipment may need to maintain stable operation while exposed to temperature, humidity, and atmospheric-pressure changes.
How TestEQ Approaches Temperature Humidity Altitude Testing
TestEQ develops environmental test systems around the required environmental operating envelope rather than selecting equipment solely by nominal temperature or altitude range.
Depending on the application, a system can be configured for:
• Temperature and altitude testing
• Temperature-humidity-altitude testing
• Low-pressure environmental testing
• Programmable pressure profiles
• Temperature cycling under reduced pressure
• Humidity control under selected low-pressure conditions
• DUT power and signal feedthroughs
• Data acquisition and monitoring
• Customized chamber dimensions
• Walk-in combined environmental testing
TestEQ's altitude simulation systems currently list integrated temperature and humidity control, with configurations supporting reduced-pressure operation and customized chamber designs. The listed systems include pressure control down to approximately 0.5 kPa and temperature ranges depending on configuration.
The temperature-altitude product line also identifies humidity control as an optional temperature-altitude-humidity configuration.
For a new project, the engineering requirement should therefore start with the actual test profile:
DUT → Temperature → Humidity → Pressure → Duration → Operating Condition → Monitoring → Acceptance Criteria
rather than starting with a generic chamber name.
Temperature Humidity Altitude Test Chamber Procurement Checklist
Before requesting a quotation, engineers and procurement teams should define the following parameters. The most important requirement is the combined operating envelope, because the specified temperature, humidity, and pressure may need to be maintained simultaneously rather than independently.
| Parameter | What to Define |
|---|---|
| Test Standard | Applicable IEC, MIL-STD, RTCA, customer specification, or other qualification requirements |
| Temperature | Minimum temperature, maximum temperature, temperature ramp rate, stability, uniformity, and dwell time |
| Humidity | Required RH range, humidity stability, humidity uniformity, and specific temperature/RH operating points |
| Pressure | Minimum pressure, maximum pressure, target pressure, pressure stability, and required operating range |
| Altitude | Equivalent altitude or altitude range when required by the applicable test specification |
| Combined Conditions | Temperature, RH, and pressure combinations that must be maintained simultaneously during testing |
| Chamber Volume | DUT dimensions, fixture dimensions, required working space, and internal clearance |
| DUT Condition | Operating, non-operating, powered, partially powered, or functional testing condition |
| Thermal Load | Heat generated by the DUT, total internal heat load, and required cooling capacity |
| Feedthroughs | Power, signal, thermocouple, sensor, communication, and other required electrical or mechanical feedthroughs |
| Pressure Transition | Required depressurization rate, pressurization rate, transition time, and pressure profile |
| Data Logging | Temperature, RH, pressure, DUT operating data, alarms, test status, and other required measurement channels |
| Calibration | Required calibration accuracy, calibration interval, traceability, and calibration certificates |
| Safety | Pressure protection, over-temperature protection, humidity protection, alarms, interlocks, emergency stop, and other safety functions |
| Software | Programmable test profiles, automatic parameter control, data recording, real-time monitoring, alarms, and test report generation |
| Customization | Custom chamber dimensions, fixtures, feedthroughs, DUT interfaces, special sensors, and application-specific configurations |
This information allows engineering and procurement teams to compare suppliers using the same technical requirements instead of comparing equipment only by chamber size or maximum altitude.
Frequently Asked Questions
1.What is temperature humidity altitude testing?
Temperature humidity altitude testing is a combined environmental test method that evaluates product performance while temperature, humidity, and reduced atmospheric pressure are controlled within a defined test profile.
2.Why combine temperature, humidity and altitude?
Because products may experience these environmental stresses simultaneously during real-world operation. Combined testing can reveal interactions that may not appear when each environmental stress is evaluated independently.
3.Can humidity be controlled under low pressure?
It can be engineered for selected operating conditions, but the required temperature, humidity, pressure, chamber design, and control system must be considered together. A standard temperature humidity chamber should not automatically be assumed to provide stable humidity control at reduced pressure.
4.Is altitude the same as pressure?
No. Altitude describes an environmental condition, while the test system controls atmospheric pressure. For a reproducible laboratory test, the required pressure condition should be clearly defined.
5.What is the difference between temperature-altitude testing and temperature-humidity-altitude testing?
Temperature-altitude testing primarily combines thermal and reduced-pressure conditions. Temperature-humidity-altitude testing adds controlled moisture exposure, requiring the chamber to manage temperature, humidity, and pressure simultaneously.
6.What should be included in an RFQ for a temperature humidity altitude chamber?
At minimum, provide the temperature range, humidity range, target pressure or altitude, simultaneous operating points, DUT dimensions, DUT heat load, operating condition, test duration, feedthrough requirements, data logging requirements, and applicable test standards.
7.Which standard covers combined temperature, humidity and low pressure?
The applicable standard depends on the test requirement. IEC 60068-2-39 specifically addresses combined temperature or temperature and humidity with low air pressure, while IEC 60068-2-13 focuses on low-air-pressure testing.
8.Can TestEQ customize a temperature humidity altitude test chamber?
Yes. TestEQ's altitude environmental systems can be configured according to required temperature, humidity, pressure, chamber volume, DUT condition, instrumentation, and test-profile requirements.
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CTA
Need a Temperature Humidity Altitude Test Chamber?
Designing a test that combines temperature, humidity, and reduced atmospheric pressure requires more than specifying three independent parameter ranges. The chamber must maintain the required combined operating conditions while providing stable control, reliable measurement, and repeatable test profiles.
Send TestEQ your test requirements, including:
Temperature range and ramp rate
Humidity range and required RH conditions
Target pressure or altitude
Temperature + humidity + pressure combinations
DUT dimensions and chamber volume
DUT operating condition and heat load
Test duration and cycling profile
Applicable IEC, MIL-STD, RTCA or customer specifications
Power, signal and instrumentation feedthrough requirements
TestEQ can evaluate the required combined environmental operating envelope and recommend a temperature humidity altitude test system configured for your application.
Request a Technical Solution
Tell us your temperature, humidity, pressure, DUT and test-profile requirements.
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