How to Select an Isolator for Variable-Condition Studies

What do rodent inhalation studies and circuit board solderability testing have in common? Both require a well-designed, multiplexed isolation chamber that offers the flexibility of running concurrent exposure tests under a carefully controlled range of conditions.

In the former case, differing concentrations of a test substance—an aerosolized pharmaceutical, for instance—are introduced into chambers containing infected mice to study drug efficacy. In the latter case, oxidation-prone microelectronic components are stored at varying concentrations of dry nitrogen, measured in terms of relative humidity, to assess their susceptibility to failure during subsequent solder reflow operations.

Similar test requirements are faced in many other industries. Compatibility testing of medical devices gauges their operational reliability under varying humidities and temperatures, as well as tissue exposure to outgassed substances. Drug shelf-life testing following prolonged exposure to varying environmental conditions is yet another example.

click the image to enlarge Multi-chamber Mini-environments often use multiplexed nitrogen purging to maintain multiple sub-ambient humidity levels. (Photo: Terra Universal)

Multi-chamber Mini-environments

These studies are effectively conducted in a Multi-chamber Mini-environment (MCM) with an automated monitor/control system that regulates the flow of a conditioned process gas to maintain critical humidity, temperature, or other environmental conditions. A multi-chamber configuration with adjustable, multiplexed controls allows the researcher to establish a different critical environmental set point value in each chamber, allowing multiple tests to be run concurrently.

A separate high-accuracy, miniaturized sensor and control module in each chamber provides this independent monitor/ control capability. Each module is programmed to maintain a distinct level of humidity, temperature, gas concentration, or other test variable. The gas purge controller directs conditioned process gas (generally nitrogen, in controlled humidity applications) only to the chamber where it is needed to keep the controlled environment within the set-point range.

During pharmaceutical shelf-life studies, for example, a multi-chamber cabinet is purged with humidified air to simulate varying storage conditions between ambient and 100% RH. Chambers with higher-humidity set points receive more frequent purging with the humidified process gas, allowing time/potency studies at many humidity levels.
In microelectronics solderability studies, chambers are purged with nitrogen-enriched air to create very dry storage conditions, allowing researchers to determine the optimal low-humidity storage conditions for oxidation-prone materials. The use of various sensors, including bio-sensors, allows accelerated life testing at varying temperatures, or inhalation studies using multiple concentrations of spores or other bio-contaminants.

A well-designed system incorporates easy-to-read displays and capabilities for remote or local set-point control. Alarms alert researchers when access doors are open or chamber readings exceed set points. The chambers themselves can be insulated, equipped with UV or other special lighting, or otherwise optimized for the particular test being performed.
A PLC-based control system allows data to be downloaded to a remote PC for display and analysis, providing complete documentation of chamber access, measured conditions, and set points in each chamber. This traceable storage history is an invaluable tool in R&D experiments and an indispensable support for certification of medical devices and other regulated products.

Michael Buckwalter
Publications Director, Terra Universal