Combined Altitude and Temperature Chamber RFQ Guide

Start with the governing method and qualification category

IEC 60068-2-39:2015 describes tests and guidance for combined temperature, or combined temperature and humidity, with low air pressure. IEC 60068-2-13:2021 Test M addresses specimens exposed to low air pressure during transport, storage, or service. Those scopes are related but not interchangeable. A laboratory should not claim the combined test merely because a pressure vessel can also heat or cool, and it should not add humidity unless the chamber and approved procedure explicitly support that combination.
MIL-STD-810H Method 500.6 covers low-pressure altitude effects and emphasizes tailoring to the life-cycle environment. Its procedures distinguish storage or air transport, operation or air carriage, rapid decompression, and explosive decompression. Where a military program invokes combined environments, the contract may instead or additionally point to Method 520.5. State the exact revision, change notice, method, procedure, sequence, and tailored levels. A generic “MIL-STD-810H compliant” line cannot define a test.
For civil airborne equipment, FAA AC 21-16G identifies RTCA/DO-160 versions D through G as acceptable environmental qualification material for certain airworthiness requirements and strongly encourages DO-160G for new articles. The RFQ should name the required DO-160G section and category from the equipment qualification plan. Bellue’s aerospace and defense testing overview provides application context, but certification ownership remains with the applicant and approving authority.

Convert the mission profile into absolute pressure and temperature steps

“Test to 15,000 meters” is not a complete pressure specification. Altitude is normally a convenient representation of static pressure, while chamber control and calibration are performed against absolute pressure. The RFQ should state the required pressure values, their source, tolerances, ramp or decompression rates, dwell times, and recovery profile. If altitude display is required, define the conversion convention so two controllers do not show different values for the same pressure.
List each thermal condition at the same level of detail: starting temperature, transition rate, stabilization rule, dwell, permissible overshoot, specimen operating mode, and the point at which timing begins. For simultaneous exposure, require a profile table that shows pressure and temperature on the same timeline. Clarify whether pressure changes occur before cooling, during a thermal ramp, or only after the DUT reaches equilibrium. This sequence can affect seals, lubricants, heat transfer, arcing risk, and functional response.

Require loaded combined performance, not two separate range claims

Published temperature uniformity at atmospheric pressure and no load may not represent performance at low pressure. Reduced air density changes convective heat transfer, while an energized avionics unit or power converter may add a concentrated thermal load. Ask bidders for a combined operating envelope showing which temperature, pressure, ramp-rate, and heat-load combinations are guaranteed. Exclusions should be visible rather than discovered during factory acceptance.
Provide DUT dimensions, mass, materials, thermal dissipation, duty cycle, airflow, fixture geometry, cable count, and required measurement points. Ask how the supplier evaluates temperature uniformity and recovery at low pressure with a representative load. If the chamber must serve multiple programs, request option limits for future heat loads and larger fixtures. The drone and UAV testing path is a useful prompt for avionics, flight battery, harness, and mission-profile inputs that often change the equipment choice.

Define pressure ramp, leak behavior, and recovery control

Vacuum-pump capacity alone does not define a usable chamber. State the required evacuation time with the agreed empty or loaded volume, maximum pressure overshoot, steady-state control band, acceptable leak rate, and recovery method. If rapid or explosive decompression is required, treat it as a separately engineered capability with its own time-pressure curve, valves, vessel design, instrumentation bandwidth, safety assessment, and acceptance test. A standard altitude chamber should not be assumed to perform it.
Recovery conditions also matter. Define whether the chamber returns using filtered air, dry air, or another approved gas; the allowable pressurization rate; and whether temperature control continues during recovery. Fast repressurization can create condensation or impose a new differential-pressure load on sealed assemblies. Ask how the controller handles a power interruption, vacuum-pump fault, door-seal leak, or loss of cooling, including alarm records and the safest attainable state.

Plan energized testing, feedthroughs, and DUT hazards

Low pressure can reduce dielectric strength and cooling effectiveness. Energized hardware may therefore experience arcing, corona, overheating, or unexpected protective shutdowns. Sealed housings, capacitors, batteries, fluid systems, and materials that outgas can add differential-pressure or contamination hazards. The test owner should complete a DUT-specific risk assessment and tell the supplier the maximum voltage, current, stored energy, heat release, fluids, gases, and expected failure modes.
Specify vacuum-rated electrical feedthroughs, connector quantities, signal types, fiber links, thermocouple channels, fluid interfaces, and cable motion allowance. Define isolation, grounding, emergency power removal, external monitoring, and whether operation can continue after an alarm. Personnel must never enter or open a chamber under pressure differential. Where the hazard exceeds a standard platform, route it through Bellue’s custom environmental system RFQ so protection logic and chamber construction are priced as part of the project.

Control condensation, humidity, contamination, and cleanliness

Temperature and pressure sequencing can cross condensation or frost conditions during recovery even when humidity is not a controlled test variable. The RFQ should identify the permitted ambient moisture, DUT preconditioning, dry-gas purge or backfill, recovery temperature, and inspection delay. If combined humidity and low pressure under IEC 60068-2-39 is required, state it explicitly; many temperature-altitude systems are not humidity chambers under vacuum.
Ask about chamber-wall conditioning, cold-surface management, condensate handling, pump backstreaming, oil mist, particulate control, and materials compatible with the required cleanliness. Optical equipment, sensors, flight electronics, and contamination-sensitive assemblies may require oil-free pumping or additional traps. Define whether the buyer or supplier provides cleanliness verification and how the chamber is restored between programs with different outgassing risks.

Make instrumentation and data records audit-ready

Pressure measurement should use appropriate absolute-pressure sensors across the requested range. Ask the supplier to identify sensor types, ranges, accuracy, calibration points, location, redundancy where needed, and traceability. Temperature sensors should cover chamber air and required DUT locations. The measurement plan should state scan rate, resolution, uncertainty or tolerance allocation, alarm thresholds, and how stabilization is determined when both conditions are changing.
Require a single time-aligned record containing recipe revision, pressure, temperature, DUT channels, power state, controller events, door status, alarms, interruptions, operator actions, and pass/fail observations. Exported data should remain usable without proprietary software. Recipe permissions, audit history, and backup procedures matter for shared labs; the third-party test laboratory overview helps frame changeover, traceability, and uptime needs across varied customer programs.

Size the working zone, fixture, and service access

Send a dimensioned DUT and fixture drawing rather than relying on nominal chamber liters. The working zone must allow pressure-tight feedthroughs, sensor routing, thermal circulation, door clearance, and service access without placing the specimen against a wall or temperature source. State the heaviest loaded configuration, center of gravity, loading method, shelf or floor load, observation requirement, and any external support equipment.
Large hardware may make a walk-in altitude system more practical, but room scale also increases evacuation time, stored energy, utility demand, and installation complexity. Compare cabinet and walk-in directions against the real test cadence. If multiple small articles can be tested together, define spacing and failure isolation. If one large assembly requires frequent access, include carts, rails, removable fixtures, and door-seal protection in the commercial scope.

Use FAT and SAT to prove the actual combined envelope

Factory acceptance should demonstrate a representative combined profile, not only separate hot, cold, and vacuum checks. Agree on the load simulator or representative DUT, sensor layout, stabilization criteria, data sample rate, acceptance bands, and allowable interruptions. Witness pressure and temperature transitions, steady-state holds, control recovery after load changes, safety interlocks, alarms, power-failure behavior, recipe protection, and raw-data export.
Site acceptance should repeat an agreed profile after the system is connected to the buyer’s power, cooling, exhaust, ventilation, and monitoring infrastructure. Confirm installation leveling, door and vessel sealing, pump performance, background noise, exhaust routing, emergency stops, user training, and report generation. Bellue’s installation and commissioning service is relevant when defining which preparation, verification, and handover activities belong to each party.

RFQ comparison table

Compare lifecycle scope before purchase price

A lower initial price can hide a restricted combined envelope, slow pull-down, insufficient heat-load capacity, limited feedthroughs, or site work that the buyer must add later. Request a base configuration, required options, future expansion limits, annual calibration plan, vacuum-pump service schedule, seal and sensor spares, remote-support boundaries, and response times. Compare test throughput and downtime risk as well as chamber cost.
Keep engineering, facilities, EHS, quality, certification, and procurement in the final review. Engineering owns the profile; certification owns the approved method; EHS owns DUT and pressure-system hazards; facilities owns utilities and exhaust; quality owns evidence; procurement owns commercial boundaries. A multidisciplinary sign-off makes the quotation easier to defend and the delivered system easier to use.

Send a method-complete combined altitude chamber RFQ

Prepare the controlled standard references, profile table, DUT and fixture drawings, thermal load, powered-test interfaces, hazard assessment, site utilities, data requirements, and FAT/SAT acceptance limits. Then contact Bellue with that single technical package. Bellue can review whether a catalog combined altitude and temperature platform is an appropriate starting point or whether the pressure vessel, thermal system, feedthroughs, controls, safety logic, or installation must be customized.