Temperature uniformity and system accuracy

Temperature uniformity is defined as the maximum temperature deviation in the work space of the furnace. There is a general difference between the furnace chamber and the work space. The furnace chamber is the total volume available in the furnace. The work space is smaller than the furnace chamber and describes the volume which can be used for charging.

SPECIFICATION OF TEMPERATURE UNIFORMITY IN +/− K IN THE STANDARD FURNACE

In the standard design the temperature uniformity is specified in +/− K at a defined set-temperature with the work space of the empty furnace during the dwell time. In order to make a temperature uniformity survey the furnace should be calibrated accordingly. As standard our furnaces are not calibrated upon delivery.

CALIBRATION OF THE TEMPERATURE UNIFORMITY IN +/− K

If an absolute temperature uniformity at a reference temperature or at a defined reference temperature range is required, the furnace must be calibrated appropriately. If, for example, a temperature uniformity of +/− 5 K at a set temperature of 750 °C is required, it means that measured temperatures may range from a minimum of 745 °C to a maximum of 755 °C in the empty work space.

SYSTEM ACCURACY

Tolerances may occur not only in the work space, they also exist with respect to the thermocouple and in the controls. If an absolute temperature uniformity in +/− K at a defined set temperature or within a defined reference working temperature range is required, the following measures have to be taken:

• Measurement of total temperature deviation of the measurement line from the controls to the thermocouple
• Measurement of temperature uniformity within the work space at the reference temperature or within the reference temperature range
• If necessary, an offset is set at the controls to adjust the displayed temperature at the controller to the real temperature in the furnace
• Documentation of the measurement results in a protocol

TEMPERATURE UNIFORMITY IN THE WORK SPACE INCL. PROTOCOL

In standard furnaces, temperature uniformity is guaranteed as +/− K without measurement of temperature uniformity. However, as an additional feature, a temperature uniformity measurement at a target temperature in the work space compliant with DIN 17052-1 can be ordered. Depending on the furnace model, a holding frame which is equivalent in size to the work space is inserted into the furnace. This frame holds thermocouples at up to 11 defined measurement positions. The measurement of the temperature uniformity is performed at a target temperature specified by the customer after a static condition has been reached. If necessary, different target temperatures or a defined target working temperature range can also be calibrated