Recommended Solutions for Oven
Validation
A Heating Oven is a device for controlling temperatures in the range of -10°C to +300°C. Simple ovens are insulated boxes with an adjustable heater. More advanced ovens may also include the ability to lower the temperature below ambient (via refrigeration), and/or the ability to control vacuum.
Most ovens provide inner and outer doors often made of glass for transparency. Main controllers include a timer. Some can also be programmed to cycle through different temperatures. Ovens vary in size from tabletop to large floor standing units. Temperature distribution is secured either through gravity or forced convection by fan operation.
Process
Most standard ovens are designed with outside air intake through a filter followed by heating and uniform distribution of the air throughout the chamber in order to secure even impact on the samples placed on (perforated) shelves anywhere in chamber volume. Exhaust air is vented to the outside through a port at the top of the unit. The parameter of interest is temperature and temperature range is typically -10 to +300°C. Samples are often placed in closed containers so cross contamination cannot occur.
Vacuum ovens are more complex in design as temperature along with pressure is monitored and controlled. To decrease pressure levels below normal ambience, a vacuum pump is fitted to the chamber and to secure homogeneity throughout the chamber typically a fan is moving the air. Vacuum ovens are primarily used for drying substances in open containers by forced evaporation.
Typical controlled parameters in ovens are:
• Temperature: -10 to +300°C (+/-2°C)
• Pressure : 10 mBar to 1100 mBar
Challenges
Validation of ovens falls into three main categories.
Standard ovens with a temperature range of -10 to +100°C do not usually pose any special challenges because parameters to be controlled are relatively easy to match. As temperatures are modest and no pressure measurements are needed, the Lab logger series with temperature or temperature and humidity sensors can be used to simplify the operation. The Lab loggers contain an LED light indicator that will provide the operator with instant information on the logger status.
High temperature ovens with a temperature range of +100 to +300°C will require special equipment. When operating wireless loggers, high temperature sensors as well as a thermal barrier to protect the battery will be needed.
For (high temperature) vacuum ovens wireless loggers are practical and therefore the same sensors and protection of the battery applies. In some cases the standard water based thermal barrier cannot be used due to the additional evaporation created by the vacuum.
If loggers are fitted with SKY option, wireless real-time data can be processed but for very small and low volume standard ovens that contain access port(s), the use of thermocouples could be advantageous to reduce impact and chamber volume.
One should consider the amount of time needed to qualify/validate an oven. The logger sample rate will need to be assigned accordingly based on the logger memory capacity.
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Oven
