Test & Inspection: Flash Forward to Today's Environmental Test Chambers
Remember back, maybe 20 years ago, when you were the newbie, sent down to the test lab for the first time? As simple as your boss made an environmental test chamber sound-it’s just a pizza oven with humidity or it’s just a freezer that goes hot too-actually using a chamber was much more trouble.
Lucky for you it was in the lab, and you didn’t have to purchase or maintain the equipment at that point in your career. You did have to deal with the lab manager, who closely guarded his chambers. The controller was confusing, failures were mysterious and data collection was a chore.
Flash forward to today, where you are the boss and that lab manager is long gone, but that same test chamber is there. Now is a great time to replace that aging chamber in your lab. Not only will you have a more reliable machine, you will benefit from improvements in technology.
Controllers give access to dataThe first digital controllers for test chambers were about as easy to use as MS-DOS, but without the keyboard. It took an expert just to set a single temperature point to run. Data collection was done by strip chart or circular recorders on paper. Most of these controllers have been retrofitted on older chambers with generic process controllers such as a Watlow F4, which also have serial interfaces for data collection.
New chambers now include their own integrated controller, with extended features and benefits suited specifically to temperature and humidity control. While one should not select a chamber based solely on its controller, each manufacturer’s proprietary interface and fixed capabilities will leave you scrambling to come up with new operation plans once you get your new machine.
Data collection to a computer is de rigor, for example, but variations in interface types, file access and storage, as well as the data itself, may leave the operator happy or frustrated. Remote Web-based access is the current trend and has taken chamber use to an even higher level of user-friendliness. Also, control and recording based on sample temperature-not air temperature-is commonplace.
Refrigeration gets fasterBack in the day, compressor failures and refrigerant leaks were expected troubles with test chambers. Larger and faster chambers had bulky refrigeration systems that were expensive to maintain. The refrigeration on today’s temperature chambers is rock-solid reliable and high performance is an accessible choice.
All chamber manufacturers now offer mid-size models with fast temperature change rates (5 to 20 C per minute) that have a reasonably small footprint. A new scroll type of compressor that is compact, powerful and reliable has made this possible, thus making fast temperature cycling a more realistic choice when shopping for a new chamber.
Some companies have been replacing laboratories full of liquid-nitrogen cooled chambers for new units with advanced refrigeration and control.
Humidity: still a mysteryHumidity systems on older chambers were always mysterious and fussy. Today, manufacturers have each refined their own technology for generating and controlling humidity. Humidity may be generated by an in-chamber water bath, an external steam boiler or an atomizer.
Humidity detection and control may be via an electronic sensor or wet-bulb method. All are valid methods, but each has different operation and maintenance requirements, keeping them somewhat mysterious.
Often the most trouble comes from end-users who do not understand the details of the system they own.
Consider Thermal ShockIf you are like most test professionals, a thermal shock chamber has been on your wish list for some time. The extreme temperature change caused by suddenly switching from a hot to a cold exposure zone is a tempting expansion of any lab’s capability. Operation costs and facility requirements have improved, but such a machine still remains a significant investment.
Savings for thermal shock can be accomplished by reducing the number of defrost cycles. Running the cold zone at extremes such as -65 C constantly, it attracts moisture from the room, freezing on the cooling coil. The expansion and shrinking of the air volume due to the temperature shock also draws in moisture. In old thermal shock chambers, defrosting as frequent as every 10 temperature cycles was necessary.
Improved sealing of the chambers, as well as added systems to purge the zones with nitrogen or dried air, has extended defrosting periods to 100 cycles. One new innovation is a bellows-type component that allows the volume of air in the chamber to change without sucking in room air, so that defrosting may be required only every 500 cycles.
The latest integrated controllers can automatically manage operation to save energy and boost performance, taking advantage that one zone is always in standby mode. If the controller has the capability to temporarily turn off the standby zone, energy savings of up to 45% have been recorded.
For improved performance, the standby zone can be temporarily set to a more extreme temperature than the desired final condition, helping ensure a fast recovery. If a test calls for a -40 C cold cycle, for example, the chamber could run the air at -55 C in anticipation of a transfer from the hot zone. After the transfer, the temperature is controlled to ensure the product recovers to the desired -40 C temperature, albeit more quickly. This control feature can reduce the size of refrigeration needed, thus saving capital, facilities and energy costs.
New industries bring new technologyThe products you test may be more or less the same as they were 20 years ago, but equipment manufacturers have to respond to new trends in technology and their unique test needs, altering and improving their products for everyone. In the past decade, networking equipment for the Internet and cell phones drove test chamber sales, but today the new demand is from solar panels and lithium-ion battery products.
Photovoltaic solar panels are being tested to simulate the stress of extreme outdoor conditions-environmental extremes unlike nearly any other product, except some aerospace and automotive applications. Humidity testing at 85 C/85% for six weeks or more requires large vault-like solid chambers. The sheer volume of chambers that has been sold to this industry in the past few years has drastically improved the design of these large walk-in chambers, forcing manufacturers to move them from the custom world into the standard world.
The rapid progression of lithium-ion battery applications from cell phones and laptops to automobiles also has forced changes in temperature chambers. While these batteries are inherently safe when sold to consumers, the environmental testing is geared toward ensuring that safety. And when testing for safety, accidents can and will happen. A battery leaking, venting or exploding in a standard chamber is a significant danger. A myriad of special safety options and design features are now being offered, such as low-temperature heaters and explosion vents.
As an interesting example, one company needing to test a new hand sanitizer dispenser knew they had a problem with the alcohol-based product being in a chamber. Years ago, chamber salespeople would have struggled with finding the right solution. In this case, the salesperson was able to quickly apply the some of the same safety features as might be used on a chamber for batteries. Q
David Jung is marketing manager at ESPEC North America (Hudsonville, MI). For more information, call (616) 896-6100, e-mail email@example.com or visit www.espec.com .
BenefitsNew chambers include their own integrated controller with extended features and benefits suited specifically to temperature and humidity control.
All chamber manufacturers now offer mid-size models with fast temperature change rates that have a reasonably small footprint.
In the past decade, networking equipment for the Internet and cell phones drove test chamber sales, but today the new demand is from solar panels and lithium-ion battery products.