Holding frame for measurement of tempe- rature uniformity
Temperature uniformity is defined as the maximum temperature deviation in the useful space of the furnace. There is a general difference between the furnace chamber and the useful space. The furnace chamber is the total volume available in the furnace. The useful space is smaller than the furnace chamber and describes the volume which can be used for charging.
Specification of Temperature Uniformity in Δ K in the Standard Furnace
In the standard design the temperature uniformity is specified as the relative, maximum deviation from a defined reference temperature within the useful space in the empty furnace at dwell time. Temperature uniformity is defined as ΔT in K. If, for example, a standard temperature uniformity of ΔT 10 K at 750 °C is specified, it means that the actual temperature in the furnace can vary between 740 °C and 750 °C or between 750 °C and 760 °C.
Specification of the Temperature Uniformity in +/- °C as Additional Feature
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 °C 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 useful space.
Tolerances may occur not only in the useful space, they also exist with respect to the thermocouple and in the controls. If an absolute temperature uniformity in +/- °C at a defined set temperature or within a defined reference 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 useful 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 Useful Space incl. Protocol
In standard furnaces a temperature uniformity is guaranteed as ΔT without measurement of temperature uniformity. However, as additional feature, a temperature uniformity measurement at a reference temperature in the useful space compliant with DIN 17052-1 can be ordered. Depending on the furnace model, a holding frame which is equivalent in size to the charge space is inserted into the furnace. This frame holds thermocouples at 11 defined measurement positions. The measurement of the temperature uniformity is performed at a reference temperature specified by the customer at a pre-defined dwell time. If necessary, different reference temperatures or a defined reference working temperature range can also be calibrated.
For the configuration of furnace and control system to meet specific industry standards such as AMS 2750 E, CQI-9, or FDA, Naber- therm offers adapted solutions. See our catalog „Thermal Process Technology“
Precision of the controls, e.g. +/- 2 °C
Deviation of thermocouple, e.g. +/- 1.5 °C
Deviation from measuring point to the average temperature in the useful chamber +/-3 °C