The topic of the work is the design and manufacture of a controller, used to control a water pump system. The system is heat insulated and placed into an environment in which the temperature can drop below the freezing point of water. For the system to function correctly a control of two process variables (water pressure and air temperature in the system) is mandatory. The controller consists of a microcontroller and output relays. The microcontroller measures instantaneous values of the process variables and controls of the output relays. Relays control the operation of an electric motor (used to drive the water pump) and an electric heater (used to control the temperature inside the system). Goal specifications of the system are user-friendly process parameter reference value setup (buttons and LCD user interface), reliable operation, and a safe mode operation if a fault in the system is detected. Pressure reference value adjustment is discrete (step size of 100 kPa) in the interval form 200 to 400 kPa. Temperature reference value adjustment is discrete (step size of 1 °C) in the interval form 0 to 25 °C.
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