Environmental test chambers feature precise control of appropriate parameters to create repeatable environmental conditions. Test chambers are suitable for numerous applications: product shelf life, stability and package testing, light exposure and temperature evaluation studies, electronic component burn-in, plant growth, and many more.
Environmental testing chambers come in various designs and sizes, ranging from a few liters (chamber) up to several thousand cubic meters (room) and feature a wide temperature and relative humidity (RH) range. Most modern test chambers offers microprocessor based controllers with computer communications, autotune, solid state RH sensor, and stainless steel temperature probes. LED displays show both process and set point values.
Tests are performed according to the HALT or HASS testing principles:
- HALT - Highly Accelerated Life Test
- HASS - Highly Accelerated Stress Screen
HALT and HASS, also known as Accelerated Stress Testing (AST), subject a product to a series of overstresses, effectively forcing product weak links to emerge by accelerating fatigue. In other words tests are unique. Accelerated product reliability test methods focus on finding defects in products so they can be fixed before becoming expensive field issues. Stresses are applied in a controlled, incremental fashion while the unit under test is continuously monitored for failures. Once the weaknesses of the product are detected the limits of the product are clearly defined.
Considering today’s consumers and businesses expect totally fault-free operation and uninterrupted service, tests must be designed to guarantee performance. Environmental testing is conducted to determine a component’s ability to perform during or after exposure to a specific environment. These tests are designed to assess the basic design of the device and the fabrication methods and materials used. Passing these tests is an indicator that the device will be robust enough to provide long-term reliability. In addition, environmental tests assist in determining a device’s safe and proper operation and also ensure its operational limits.
Examples of different test chambers:
- Humidity Test Chambers
- Temperature Only Chambers
- CO2/LN2 Test Chambers
- Salt Spray/Fog Chambers
- Thermal Shock Chambers
- Vibration Chambers
- Vacuum Chambers
Most common tests are performed using temperature cycling tests. Mismatches in thermal coefficients of expansion of materials used in electronic and optoelectronic components are among the leading contributors to the failure of equipment exposed to extreme temperature variations. Repeated exposure to cyclic temperature variations can fatigue joints of different materials, and cause them to fail. Conducting temperature cycling tests on these components will assist in determining the existence of thermal coefficient mismatches, and the sensitivity of these mismatches to repeated temperature excursions. Temperature cycling is performed in chambers that control the number of cycles, dwell times, transfer times or ramp rates, and temperature extremes.
The exact nature of validation will depend on type of environmental chamber. Testing parameters can vary but will be defined based on the type of chamber. Ellab offers a variety of validation equipment. The TrackSense® logger system along with its interchangeable sensors are an ideal solution. The parameters covered are temperature, pressure, humidity, conductivity and vacuum. For extreme temperatures the use of a thermal barrier at the higher temperatures may be required. For lower temperatures, the Pro X, Pro XL, Compact Ultra X or Frigo loggers are required. The SKY option can be used to process data in real time. When using thermocouples, having access ports on small chambers could be advantageous to reduce impact and to keep chamber integrity. In this case, high temperature measurements are covered by using Kapton or fiber glass thermocouples.
When using TrackSense® wireless loggers one should keep in mind that validation takes long time and the sample rate will need to be matched with total logger memory capacity.
For the approval of performed tests, numerous steps must be taken to ensure that the environmental test chamber functions correctly, ex. fluctuations in temperature and humidity remain within the stipulated range and this occurs over relatively long periods of time. Validation must be carried out regularly to ensure that an environmental room or cabinet is capable of accurate and repeatable performance.
Validation of an environmental chamber consists of various steps regarding Installation Qualification (IQ), Operational Qualifications (OQ) and Performance Qualifications (PQ).
The IQ is conducted to demonstrate that the chamber is inspected and contains all the required parts for its proper functioning.
During the OQ, the performance of the chamber and its operational procedure are verified. The OQ consists of parameter mapping of the empty chamber and is performed to confirm that the empty chamber works within the specified limits throughout the chamber. The OQ also contains information about the calibration of measuring equipment and defines the location of the thermocouples/data loggers in the stability chamber.
The PQ verifies that the loaded environmental chamber is capable of reaching and maintaining the target parameter and confirms that the loaded chamber works within the specified limits.
The typical number of temperature measuring points in a small to medium sized chamber is (corners + center) on lower and top shelf during OQ. They are typically fixed directly on the shelves in the empty chamber and during the PQ they are placed into loaded samples. For larger chambers it is recommended to place 5 measuring points on a minimum of 3 layers or on each layer with sample readings every 1- 5 minutes during 24, 48 or 72 hour studies.
Wireless loggers are recommended because even with most standard environmental chambers that provide access port(s), the integrity of the chamber can be compromised (leak) if cables are used.
In the pharma and medical device industry, validation of environmental chambers require the use of advanced software such as ValSuite™ Pro due to its 21 CFR Part 11 compliance, sophisticated reports and features. For industries where electronic records are not required, ValSuite Basic will provide the appropriate functionality.
For validation purposes, creating a Unit with exact positions of each measuring point documented by pictures is advantageous when handling many sample points. The addition of a Profile including Limit Report as well as Statistical Report is useful and time saving.
At the end of each study report(s) can be signed by Electronic Signature(s), stored, printed and distributed in a secure and locked PDF format.
Using the built-in calibration functionality, users can calibrate the Ellab sensors at regular intervals. The ValSuite™ Pro software generates an easy to read calibration report that includes all measurements and tolerances that are defined by the user. It is recommended that Ellab sensors and probes are sent in at least once a year for factory calibration (which includes a traceable calibration certificate).