Environmental Monitoring Using a Systems Integration Approach
Using a modular data acquisition system for measuring critical environmental parameters can make managing a clean environment much easier.
By Jack Kelley, Perry Pollins, Dave Rizzo
In the field of process measurement, control, alarming and documentation are solutions to the critical problems that arise in managing the environment within cleanrooms and anti-contamination rooms. Small, moderately priced cleanrooms and anti-contamination rooms demand as much attention in maintaining the quality of their environment as the larger, more complex systems. While there are hand-held solutions and some fixed instrumentation for monitoring individual parameters, all-inclusive data gathering, alarm and off-site monitoring systems are, in fact, often economical and relatively easy to implement. Also, since sensor positions are fixed, a consistency of measurement is established over time.
Major considerations in the management of a cleanroom include keeping it free of particulate and foreign matter; ensuring that the room`s pressure is conducive to keeping debris out or preventing biological media from escaping; controlling humidity at a level that will inhibit electrostatic discharge (ESD); making sure that temperature requirements are met; and that laminar air flow is consistent with adequate filtration and also meets good manufacturing practices (GMP).
Other parameters, such as fire protection, vibration, process gas concentrations, and enter/exit integrity, can be made readily available at any time in the future. This approach provides the ability to make changes to improve procedures and controls over time. Ever-present monitoring, analysis, alarms and the periodic production of hardcopy documentation assure compliance with regulatory agency demands and GMP. In addition, there may be provisions for interrogating the cleanroom from a remote location, and for calling the outside world from the cleanroom if its environment should break down while the room is unattended.
Advantages of an Integrated Modular System
Paramount in an integrated modular system are the measurement of critical environmental parameters, the storing of this analog data, and the ability to change system configuration if the process or testing procedure must be modified. Also, the system should be simple and inexpensive to implement and sustain. Modular data acquisitions systems (DAS), whose signal-conditioning configurations can be conveniently altered to meet these demands, are a readily available solution. In addition, a DAS can provide changes in data timing, PC communications, call-up to or interrogation by a remote location, as well as supporting software.
Many times, the heart of a process control system is a data acquisition system, whose sole purpose is to gather sensed analog information, signal-condition it, digitize it precisely, and export the required data to a PC. While numerous types of sensors can be utilized with the data acquisition system, only those that meet basic cleanroom needs should be installed initially. Expansion of the system`s mission can easily be carried out in the future by the use of other sensors; but it must be remembered that any signal, regardless of its origin, should, as an effect of its magnitude or timing, provide (1) an accurate measurement (2) a reasonable order of stability (3) an alarm signifying a fault condition (4) documented evidence of the cleanroom`s performance over time, and (5) the ability to notify someone off-site of an impending environmental failure.
Compatible Sensors
Of prime interest in most cleanrooms is particulate, laminar air flow, temperature, pressure and relative humidity. An added feature–low in cost because of its digital nature–is enter/exit integrity. All sensors that service this need can be handled by a DAS.
While all manufacturers of sensors in these categories cannot be listed, a few who are known to have sensors or subsystems that can provide outputs compatible with several DASs are presented as a starting point (see “Sensor Manufacturers”). Output from a sensor detecting particulate, for example, can be either analog or TTL pulses. DAS should be capable of processing either type of signal.
Small- to moderate-size cleanrooms that process microbiological substances, semiconductors, or complex electromechanical assemblies such as CD drives need not want for an uncomplicated, inexpensive way to continually measure, observe and alarm sensitive environments. The use of a DAS provides the conversion of critical sensor data and supporting software to satisfy industry`s need for quality products, safe working conditions and compliance with regulatory requirements at low cost and with minimal complexity. n
John Kelley is president of Cyborg/ Manufacturing Technology (Newton, MA).
Perry Pollins is vice president of marketing and sales at Cyborg/Manufacturing Technology.
Dave Rizzo is vice president of engineering for Cyborg/Manufacturing Technology. He has also worked as an engineer at Cyborg and a test engineer at Data Translation.
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Cyborg/Manufacturing Technology`s RoomWatch system is capable of monitoring all parameters of a cleanroom environment. It monitors, analyzes, and provides constant examination of temperature, humidity, laminar air flow, back-pressure, and cleanroom access.