PROBLEM SOLVING
Mirage technical manual page 55 of 65
Steam boiler temperature controller
The steam boiler temperature controller is a Stork ST25 modified for Kees van der Westen espresso
machines. The ST25 can function both as PID and as thermostat. In the Mirage it is used as a user-
friendly, very precise thermostat. Fast response is obtained by measuring the temperature in the
steam (instead of the water).
Figure P 2. Showing the Stork ST25 temperature controller at operational temperature (left) and in
Eco-mode (right) where control temperature drops to 70 degrees Centigrade (158 °F).
Power to the Temperature controller comes from the Gicar main controller, but only when water in the
steam boiler is above security level.
Temperature information to the controller comes from a Pt100 sensor located in the steam above the
water in the steam boiler. A Pt100 sensor is a so-called PTC sensor which means that with increasing
temperature the electrical resistance of the sensor increases. The resistance value of the sensor is
converted to a temperature value inside the controller.
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Figure P 3. Different dots in the display mean different things.
Left: the lower dot is a decimal point. The display indicates a measured temperature of 12.4 degrees,
control signal to heat is off.
Right: The upper dot is related to the output control signal. The display indicates a measured
temperature of 124 degrees and control signal to heat is on.
Nearly all parameters in the controller can be adjusted by the user, the most likely to change are:
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