Maintaining optimal conditions in chambers and incubators

1st April 2013

Some of the most demanding applications for environmental measurement equipment are environmental chambers and incubators, where operating parameters are highly defined and failure to meet those exact specifications puts product quality, production schedules, and patient health at risk.

From stability evaluation chambers for pharmaceuticals to incubators used for tissue growth, maintaining optimal conditions can be achieved with a good preventative maintenance programme.

Fixed measurement instruments in the chambers and incubators may be exposed to conditions outside of their operating specifications, contamination, or other factors that cause incremental degradation of performance.

For example, humidity sensor performance can degrade if the probe is exposed to strong chemical vapours for long periods. Over time, these subtle factors can cause the measurements to vary from the actual conditions - known as sensor drift - ultimately resulting in the chamber operating out of specification. However, since these subtle changes are part of the chamber's control system, there are no alarms as with detected failures.

To address health, safety, and environmental risks that can result from undetected measurement inaccuracies, internationally-recognised quality management systems each state minimum requirements for maintenance of measurement devices. These requirements are included in ISO 9001, Good Manufacturing Practice (GMP), and Good Laboratory Practice (GLP). ISO 10012 Measurement Management Systems is specifically designed for measurement equipment maintenance.

In some areas, compliance with these regulations is legally mandated and in other areas it is voluntary. But the common-sense business case is clear: in pharma and bio testing and manufacturing, preventative maintenance of measurement equipment optimises uniform quality standards and yields - and can save money and lives (Fig. 1).

Calibration is important

Each lab manager or quality assurance manager needs to develop a calibration process that meets their legal and voluntary requirements, is easiest to implement and sustain, and is cost effective. Since each application is unique, there is no universal maintenance and calibration schedule that is effective in all situations.

The first step is to identify the equipment that requires calibration. Next, the allowable tolerances need to be identified to determine if calibration should be completed in a calibration laboratory or if field calibrations are sufficient.

Calibration laboratories are preferred when parameters require the highest accuracy and where multi-point calibration is needed to validate a wide range of defined characteristics. Accredited calibration labs offer the highest level of one-point and multi-point calibration, typically at premium service rates.

Many calibration labs offer accurate, non-accredited calibration services at more cost-effective rates. Field calibrations have the advantage of being reliable, quick and easy since the measurement equipment does not need to be taken out of production. Field calibration is ideal for one-point, in-situ calibration.

Each lab and chamber environment is unique and each lab manager must develop a calibration interval that meets their requirements. There are however, some guidelines for developing and refining a schedule. A metrologist's approach is to develop a history for the measurement equipment by calibrating it - without adjustment - regularly until the measured drift exceeds allowable performance. The time between the 'in service' date and the last acceptable calibration becomes the calibration interval. This interval can be monitored with less frequent calibrations until an acceptable pattern of performance is demonstrated.

Accuracy and long-term stability of the measurement are two of the most important performance requirements for any fixed or portable instrument. The more highly defined the conditions, the more accuracy and long-term stability matter. These performance requirements can both be achieved by an informed specification process that addresses the accuracy, reliability, ease of use, maintenance, and installation of fixed instruments - combined with a good preventative maintenance programme that addresses the same qualities for the portable instruments used for calibration.

Field calibration is relatively low cost because the measurement equipment does not need to be removed from production and qualified in-house personnel using hand-held devices specifically designed for calibration can perform the calibration service. Also, it is more convenient and less costly to send a hand-held calibrator than a fixed measurement device to a calibration lab.

In pharma and bio applications, there are three parameters that are the commonly controlled and monitored in chambers and incubators: temperature, humidity, and carbon dioxide. One or more of these parameters has defined qualities or at least a defined operating range in every chamber and incubator.

Manufacturers that have experience in developing and improving measurement instruments over many generations of technology have the advantage in delivering instruments that are accurate and reliable in the most challenging real-world applications.

One of these manufacturers is Vaisala, which started environmental measurements with the development and launch of the first radiosonde in 1931.

From this start in meteorology, the company has evolved to become a world leader in many measurement fields, including temperature, humidity, and carbon dioxide. Vaisala provides a full suite of fixed and hand-held instruments for chambers and incubators that accurately measure these variables and more. The company extends its measurement expertise by providing accredited laboratory calibration services and calibration resources to help develop in-house good measurement practices.

Its suite of field calibrators is led by the Vaisala HUMICAP hand-held humidity and temperature meter HM70. The HM70 is designed for on-site calibrations and uses Vaisala HUMICAP sensor technology, which measures humidity by detecting the change in capacitance of a thin polymer film.

This technology is proven in testing and commercial use over decades as the benchmark of accuracy and long-term stability in humidity measurement. The HM70 is designed to reduce or eliminate factors that can cause sensor drift such as preventing condensation on the probe by preheating the sensor and chemical purge options that reduce damage from harsh chemical vapors.

Vaisala's field calibrators include the Vaisala CARBOCAP hand-held carbon dioxide meter GM70. The GM70 is a hand-held carbon dioxide meter already considered by many professionals to be indispensable for accurate carbon dioxide measurements in the field. The MI70 is a convenient multiple measurement indicator device that uses humidity and temperature probes from the HM70 and carbon dioxide probes from the GM70. It also has extensive memory for data logging that can be easily transferred to a Windows PC for further data analysis.

Whether using field calibrations or an accredited calibration lab, calibration of measurement equipment is a necessary part of a preventative maintenance program that maintains optimal environmental conditions in chambers and incubators. Accuracy and long-term stability of the field calibrators is as important as it is for the fixed instruments for quality measurement systems.

Jan Grönblad is with Vaisala, Helsinki, Finland,


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