Problem: Many experienced lab technicians are aware of the “sweet spot” in their oven or incubator— the back right-hand corner of the middle shelf where their experiment or process always comes out right. It’s the spot where the temperature in the oven is the same as that on the unit’s temperature display. Of course, what’s really indicated is that temperature accuracy throughout the chamber, the most important factor in oven and incubator performance, is uneven.
Preheating provides uniform airflow within the chamber and consistent temperature for samples. Depicted is the Binder FD Series mechanical convection oven.
Solution: Ovens and incubators that provide uniform and stable temperature control are available, and so the resolution to “sweet spots” and other problems with temperature inconsistency is fairly straightforward. But making a decision as to which oven or incubator is best for a specific process requires an understanding of unit construction and quality control practices.
When incubators and ovens are made, units are randomly subjected to quality control testing. Manufacturers typically use either DIN (German Industrial Standard) or ASTM (American Society for Testing and Materials) standards to document the performance of their apparatus.
A brief comparison of the main criteria in each standard will highlight what they indicate about unit performance. The most important of these is the number and location of the measurement points used in testing. The DIN standard requires a two-hour heat-up to steady state, at which point measurements are taken at 27 points in the chamber (nine points on three levels) and monitored six times a minute.
Using the ASTM standard, a manufacturer will measure 9 points in the chamber (four each top and bottom shelf, one in the middle) without preheating and with no defined sampling time.
Unit controller is important as well. A thermostatic device that turns heating elements off and on as a set point is reached is obviously useful in only basic procedures, such as glassware drying. Simple digital controllers provide quick time to set point, while PID (proportional integral derivative) control provides the best accuracy over time at a single point.
How the apparatus is heated is a key consideration. Mechanical convection provides greater consistency than other methods, and also offers faster recovery after the door is opened when compared to gravity convection, the other common heating method. Furthermore, direct heat and gravity convection ovens suffer from direct contact of the heating coils with the inner chamber wall, creating hot spots, and do not offer preheating.
Other factors relevant to performance include the amount and type of insulation, door closing and gasketing options, and ergonomic features such as the location and design of controllers and displays.
It is worth noting that repair/remodeling existing units is almost always ineffective. A technician can test an inconsistent oven or incubator, but charges for test time alone will bring the cost of an inexpensive unit to a level above that of the most expensive product. Repairing or reconfiguring the oven or incubator to offer the desired performance will add even more cost, if it can be done at all.
If the applications for a given incubator or oven will ever go beyond the most basic requirements, the most well-equipped and validated unit available will offer consistent, reliable results and will cost less over time than inexpensive models.
Incubators and ovens from Binder, Inc. are made to DIN standards, utilize mechanical convection, incorporate PID control, and offer a number of other features to meet demanding temperature stability requirements.
For more information, visit at www.binder-world.com/us.
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