WIKA CTD9300 - Handbuch (Seite 10)

9037926 03/2005
10 WIKA Operating Instructions CTD 9300 Rev. 1
Temperature Dry Well Calibrators CTD 9300
2. Device Description
GB Calibrators for Low Temperatures
If the calibrator generates temperatures lower than the ambient
temperature, it must be able to cool actively. In this case, the
isothermal block is made of aluminium and is cooled and heated
through Peltier elements. Depending on the polarity of the voltage,
the Peltier element will heat up on the top side while the opposite
side is cooled. One side of the element always makes contact to the
isothermal block. The other side is connected to a cooling element
that is cooled by a strong fan.
Through reversing the polarity and controlling the voltage at the
Peltier elements, the block can be heated and cooled. For technical
reasons, the max. attainable temperature with Peltier elements is
limited to approx. 165 °C. Depending on the model, the min.
attainable temperature is -50 K to -60 K relative to the ambient
temperature.
Calibrators for High Temperatures
High-temperature calibrators for temperature ranges of from 40 °C
to 650 °C generally work with resistance heating elements.
Depending on the upper limit temperature, different block materials
are used. Brass, bronze or scale-resistant steels.
Due to the low temperatures caused by the permanently decreasing
cooling capacity of the air flow surrounding the block, the control
unit starts working sufficiently fast only at 20 K above the
respective ambient temperature. This limits the lower working
temperature of a device of this kind to approx. 40 °C.
The upper limit is defined through the block material used and the
temperature resistance of the heating elements used.