Reach-In Environmental Test Chambers: How to Specify One That Actually Fits Your Programme

The specification read "220-litre environmental test chamber." The test programme called for JESD22-A104 temperature cycling — twenty devices per run, each mounted on a PCB, each PCB on a carrier fixture. The engineer who specified the chamber had measured the devices. He had not measured the carrier fixture configuration. He had not added the 100 mm clearance required on all sides between the DUT and the chamber walls. He had not accounted for the shelf that would occupy approximately 20% of the internal volume.

The chamber arrived. Twelve devices fit. Twenty did not. The test programme ran in two batches instead of one — doubling the test time and halving the throughput of every qualification programme that used that chamber for the next eight years.

A reach-in chamber is the right choice for the vast majority of component, subassembly, and small product qualification programmes. Most JEDEC, IEC 60068, and MIL-STD-810H qualification tests are run in reach-in chambers. The selection question is not whether reach-in is appropriate — it usually is. The question is which reach-in, specified how, to avoid a volume calculation error that cannot be undone after delivery.

01What a reach-in chamber is — and when it is the right choice

A reach-in environmental test chamber is a free-standing enclosure with front-access doors, available in internal volumes typically ranging from 20 litres to 2,000 litres. The DUT is placed inside through the door. Personnel do not enter the chamber during operation — access is through the door opening, glove ports, or cable feed-throughs.

Reach-in chambers are the standard configuration for:

If the DUT — including its test fixture, instrumentation, and the minimum clearances required around it — fits within 2,000 litres, a reach-in chamber is almost always the better choice than a walk-in. Reach-in chambers are less expensive, simpler to install, more energy efficient, and do not introduce personnel access as a test integrity variable.

02Volume selection — the calculation most engineers skip

The volume calculation for a reach-in chamber follows the same logic as for a walk-in chamber, scaled down. The correct approach starts with the DUT, not with a volume target:

Step 1 — Define the DUT envelope in test configuration. The external dimensions of the DUT including all test fixtures, mounting hardware, and instrumentation that will be inside the chamber during the test. For a PCB on a carrier fixture, this is the carrier fixture dimensions — not the PCB dimensions.

Step 2 — Apply the 100 mm clearance requirement. IEC 60068-1 §4.2 requires a minimum of 100 mm clearance between the DUT and the chamber walls, floor, and ceiling on all sides. This is not optional — it is required to ensure adequate air circulation and to prevent the chamber walls from influencing the temperature at the DUT surface. A DUT touching the chamber wall is not being tested under IEC 60068-compliant conditions.

Step 3 — Account for shelving and fixtures. Shelves, mounting rails, and cable management hardware occupy internal volume. If the test programme uses a standard shelf configuration, its volume must be subtracted from the usable workspace before checking whether the DUT fits.

Step 4 — Add a margin for test programme growth. A chamber sized exactly for the current DUT has no capacity for the next DUT, which is almost always larger. A 30–50% volume margin over the current requirement is standard practice for chambers expected to serve a multi-programme laboratory for 10–15 years.

03Ramp rate — rated vs actual under load

The ramp rate figure in a chamber specification — typically stated in °C/min — is almost always the empty-chamber rated value. It is the rate at which the chamber air reaches the new setpoint when the chamber is empty and operating under ideal conditions.

Under load — with a DUT that has thermal mass — the effective ramp rate at the DUT surface is lower. How much lower depends on the ratio of the DUT thermal mass to the chamber's thermal capacity, and the contact between the DUT and the circulating air.

For a JESD22-A104 temperature cycling programme, the relevant ramp rate is at the DUT — not in the air. The standard requires that soak time begins when the DUT reaches the target temperature, not when the air reaches it. A chamber with a rated ramp rate of 5°C/min may deliver 2–3°C/min at a high-thermal-mass DUT. If the test profile requires 3°C/min at the DUT, the chamber's rated 5°C/min may or may not be sufficient — depending on the DUT.

04Temperature range — and why the extremes matter

The temperature range of a reach-in chamber is defined by its refrigeration and heating system. The achievable minimum temperature depends on the refrigeration architecture:

Single-stage refrigeration — typically achieves minimum temperatures of −40°C to −50°C. Suitable for the majority of JEDEC and IEC 60068 qualification programmes, JESD22-A104 Condition G (−40°C / +125°C), and standard automotive qualification requirements.

Cascade refrigeration — two refrigeration stages in series, achieving minimum temperatures of −55°C to −75°C. Required for JESD22-A104 Condition J (−55°C / +125°C), MIL-STD-883 temperature cycling, and certain aerospace qualification programmes. Cascade systems are more expensive, consume more energy, and require more maintenance than single-stage systems.

Specifying a cascade system when a single-stage system would meet the programme requirement adds cost throughout the chamber's life — capital cost, energy cost, and maintenance cost. Specifying a single-stage system when the programme requires −55°C is a test capability gap that cannot be resolved after procurement.

Verify the specific temperature requirements of every standard cited in the test programme before selecting the refrigeration architecture. A single −55°C condition buried in a secondary test standard can drive the need for a cascade system.

05Feed-throughs and DUT access

The feed-through configuration of a reach-in chamber determines how the DUT is connected to external instrumentation, power supplies, and signal analysis equipment during the test. Most test programmes require electrical connections that pass through the chamber wall — and the feed-through specification determines whether the planned test setup is physically achievable.

Standard feed-throughs — gasketed ports in the chamber wall, typically 25–50 mm diameter, through which cables are passed. Most chambers include one or two standard feed-throughs. Additional ports can often be added during manufacture.

Custom feed-throughs — for high-current power connections, fibre-optic cables, fluid lines, or RF coaxial connections, custom-specified feed-throughs are required. These must be defined before manufacture — retrofitting feed-throughs after delivery requires cutting through the chamber wall and resealing the insulation, which affects chamber performance and warranty.

Feed-through location. The position of feed-throughs on the chamber wall determines cable routing inside the chamber and the minimum clearance that can be maintained between cables and the DUT. For temperature cycling programmes where the DUT is instrumented with thermocouples, the feed-through position affects the thermal gradient at the DUT surface.

Define the feed-through requirements in the RFQ — number, diameter, location, and connector type — before procurement. This is the specification element most frequently left to the manufacturer's standard configuration, and the most frequently regretted after delivery.

06Thermal and climatic — choosing the right variant

Reach-in chambers are available in two fundamental variants that determine which tests they can run:

Thermal chambers control temperature only. They have refrigeration and heating but no humidity generation or control system. They are suitable for: IEC 60068-2-1 (cold), IEC 60068-2-2 (dry heat), IEC 60068-2-14 Method Nb (temperature cycling), and any test that specifies only temperature conditions. They are not suitable for any test that requires a defined humidity setpoint.

Climatic chambers control temperature and humidity simultaneously. They include everything a thermal chamber has plus a humidity generation system, a humidity sensor, and a humidity control loop. They are required for: IEC 60068-2-78 (damp heat), JESD22-A101 (temperature-humidity-bias), ICH Q1A stability conditions, and any test requiring defined relative humidity.

A climatic chamber can run all tests that a thermal chamber can run — and more. A thermal chamber cannot run humidity tests. If the test programme includes any humidity-controlled tests now or in the foreseeable future, specifying a climatic chamber avoids a capability gap that cannot be retrofitted.

07What the specification must contain

A reach-in chamber specification stated as performance requirements — not equipment ranges:

Usable workspace volume. Calculated from the DUT envelope plus 100 mm clearance on all sides, plus shelf volume. Not a round number — the calculated minimum volume with margin.

Temperature range at load. The minimum and maximum setpoints achievable with the DUT in place, under operating conditions. Specify the refrigeration architecture (single-stage or cascade) if the minimum temperature requirement dictates it.

Temperature stability at DUT. ±°C deviation from setpoint at the DUT surface during steady-state soak. Not at the controller sensor.

Ramp rate at DUT under representative load. °C/min at the DUT surface with a load representative of the planned test programme. Request this from the manufacturer for your specific DUT thermal mass.

Humidity range and stability. For climatic chambers only: the RH range and ±% RH stability at the operating temperatures required. Confirm capability at the specific temperature/humidity combination — not at each independently.

Feed-through configuration. Number, diameter, and location of feed-throughs. Connector type if standard connectors are required.

Refrigerant compliance. R-449A or CO₂ (R-744) per Regulation (EU) 2024/573. Exclude R-404A.

Acceptance test requirements. Temperature stability and uniformity mapping at minimum, ambient, and maximum setpoints under load, with results documented in a signed commissioning report before acceptance.

08Performance verification after delivery

A reach-in chamber must be verified after delivery and installation — not assumed to perform to specification based on the factory test data. The factory test was conducted at the factory, before transport, under factory conditions.

Verification follows IEC 60068-3-5 (temperature chamber) or IEC 60068-3-6 (temperature and humidity chamber). For a reach-in chamber, the minimum sensor configuration is nine positions — the eight corners of the workspace plus the geometric centre. The verification is conducted without load first (empty), then with a representative load per IEC 60068-3-7.

A signed verification report before the chamber enters service is the minimum documentation standard. For regulated applications — pharmaceutical stability, medical device qualification — the report feeds into the IQ/OQ/PQ qualification record.

Continue reading — Chamber types