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How to Select an Environmental Control Chamber CONSIDERATIONS WHEN PURCHASING A CONTROLLED ENVIRONMENT CHAMBER by Brian E. Hohman Electro-Tech Systems, Inc. (ETS) The combination of chamber, controller and operating systems determines the performance of the environment. Selecting the correct components can be the difference between years of trouble free service and limited performance. Understanding how these components interact allows the end user to make informed decisions when designing an environment. Selecting The Correct Chamber Standard chambers are always less expensive than custom boxes. The chamber you select should be large enough to accommodate the samples, equipment or desired process along with any internally mounted systems (heater, fan, etc.). Sufficient space must also be given to allow proper airflow. When specifying a chamber size, please take into account that the internal dimensions will typically be ½” to ¾” less than the outer dimensions due to material thickness. Ports, circulating fans, doors, power outlets, gloves, operating systems, etc. will also utilize a portion of the internal space. Chambers can be ordered with or without glove ports. All ETS chambers include an access door along with system and cable pass-through ports. Standard chambers can be modified to meet a specific requirement and custom chambers of virtually any size can be fabricated. Please note that any size environment can be configured to perform virtually any controlled function. To assist the user in selecting a system, ETS offers Option Packages based on typical user applications. ETS currently offers four standard and two custom chamber series. Series 5503 4.75 cu. ft. Series 5506 9.00 cu. ft. Series 5518 13.0 cu. ft. Series 5532 13.0 cu. ft. Series 5538 Custom Desiccator Boxes. Series 5500-8000 Custom Chambers Selecting a Controller The controller determines the range and accuracy of the environment. Controller pricing, functions and features vary widely. When making a selection, first determine the functions needed at the present time along with those you may require over the next few years. Single function controllers can be user adjustable or factory preset to a single level and are usually not expandable. Dual function controllers, which control both humidity and temperature, offer the best combination of features and price. Purchasing a controller with additional capabilities such as temperature control or communication boards allows future expansion by simply adding the required operating system when needed. Microprocessor PID controllers offer the greatest accuracy and can be used with or without software. All ETS controllers include a sensor. ETS currently offers the following controller types: Comparator Type Single-Point Dehumidification Factory set at 5% RH. (not adjustable) Adjustable Dehumidification User Adjustable (ambient and below) Microprocessor Type Single Function Controller PID Control (Incr. & Dec.) Humidity or Temp Dual Function Controller PID Control (Incr. & Dec.) Humidity and Temp Dual Function/Display PID - Displays Levels & Set Points. Selecting Operating Systems (Heating, Cooling, Humidification & Dehumidification) Operating systems determine the performance of the environment. Several choices are usually available for each function with each system having benefits and limitations. Standard operating systems from ETS include humidification, dehumidification, heating, cooling and oxygen monitoring. System selection should be based on your conditioning time requirement (long term, short term), desired operational range and the range of multiple systems used at the same time (what humidity level needs to be maintained at what temperature and for how long). Please note that the specific range of each system is independent of what can be achieved when used in combination with other systems. Ultimately, the level that can be achieved depends on the system selected, size of the environment, conditioning time, ambient conditions and dew point. The operational range is always specified at ambient conditions unless otherwise noted. While an environment may be able to maintain 5 to 98% RH at ambient laboratory conditions, when the temperature is elevated to 55ºC it may only be able to maintain 60-70% RH. Before selecting a system, it is critical to know the highest humidity/temperature and the lowest humidity/temperature combination required. This will allow the appropriate systems to be recommended or selected. Accuracy and stability are important factors which can vary greatly from system to system. When cooling, liquid CO2 offers the user a low cost, short-term solution but sacrifices stability and humidity control. Thermoelectric cooling systems offer unmatched stability and precision but are expensive and provide limited cooling capability. Users often ask, “How long will the desiccant, deionized water, etc. last”. The length of time varies greatly for each location and application. It is influenced by the ambient conditions, test material placed inside the chamber, length of conditioning time, how frequently and for how long the door is opened, sealing of the ports and other factors. Most systems require periodic maintenance (filling, changing or cleaning) to maintain peak performance. Before selecting an operating system, it is a good idea to check and see if you have access to any systems at your facility. Dry nitrogen, if available, is an excellent choice for lowering humidity levels to less than 2% RH. Renewable desiccant, dry house air or self-regenerating molecular sieve systems may also be available. Computer Control Software can be a very useful addition to your environmental control capabilities and is available as an option for all ETS microprocessor controllers. Adding computer control gives the end user the ability to monitor environmental stability over virtually any period of time and to remotely change the parameters. For some applications such as ramping and soaking it is a must. Computer control requires the installation of communications boards, software, and depending upon the setup, RS485/RS232 converter, gender changer, computer interface and y-cable. A single function controller has one communication board and a dual controller two. The user must decide between an RS232 or an RS485 style communication boards. ETS recommends RS485 boards be used in most instances. This board allows multiple modules to be linked together. An RS232 board may be used when a single microprocessor module is used and there are no plans to expand in the future. ETS currently offers three software versions: Calcomm, Calgraphix and CalOPC Server. Each version is designed for use with a different application and offers a unique set of features. Air Filtering Although ETS acrylic chambers are not intended for use as mini-cleanrooms, some applications such as filter weighing and powder analysis require chamber air to be as clean as possible. Many operating systems utilize outside air to achieve the required parameters. Filters are available to trap micro-particles at input, vent and/or recirculated air. In-line units with replaceable filters prevent desiccant dust from entering the dried air stream. These can also be used in venting if exhaust assist is used. HEPA media filters with gaskets can trap particles as small as 0.3 microns and generally are used in recirculation and venting applications. Filtering is not needed for most applications but should be reviewed before purchasing a system. Chamber Construction ETS uses clear and white acrylic as our material of choice. Alternate materials such as static dissipative acrylic, polycarbonate, steel or other material can also be provided. Acrylic has excellent visual characteristics and can be easily fabricated into virtually any form needed. Standard chambers are fabricated using PS30 (a welded seam) construction. This is the highest quality joint available and is commonly referred to as “museum quality”. At ETS, we are still using some chambers with this type of joint that were fabricated in the 1970’s. Poron gaskets, which are resistant to a permanent set, are used for all door and hinged access port openings. Stainless steel latches are used to seal the doors and a variety of fittings are used to interface with the various systems. Conclusions Environmental chamber manufacturing companies such as ETS focus on high-quality products and are typically more receptive to requests for modifications and customization. Detailed product information can now be found online. This information can be supplemented with an e-mail or call to the manufacturer. By reviewing your requirements in detail and understanding the advantages and limitations of each system, the user can design a system to meet their needs today and long into the future. www.electrotechsystems.com |
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ets, electro-tech systems, inc 3101 Mt. Carmel Avenue, Glenside, PA 19038 Tel 215-887-2196 | Fax 215-887-0131 Home | Products | ESD Testing Services | ESD Consulting Services | Articles of Interest | Manuals | FAQs | About ETS Links | Directions | Sitemap | Request Information Copyright © 2004 electro-tech systems, inc. Website by Advance Design |
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