Liquid treatment device and method of treating a liquid

A liquid treatment device, comprising:

• a tank for receiving and further processing liquid through biological and/or chemical processes taking place in the liquid,
• a tempering jacket which surrounds the tank and is arranged in a fluid circuit in which a tempering fluid circulates, and via which the liquid in the tank is tempered to control biological processes in the liquid,
• a control valve which is located in the fluid circuit and via which the liquid flow in the tempering jacket can be closed-loop controlled to adjust the temperature of the liquid in the tank,
• a first temperature sensor which measures the actual temperature of the liquid received in the tank,
• a second temperature sensor which measures the actual temperature of the tempering fluid present in the tempering jacket, and
• an electronic closed-loop control unit for the closed-loop control of a temperature of the tempering fluid present in the tempering jacket,
• wherein the closed-loop control unit includes a primary loop of closed-loop controlling and a secondary loop of closed-loop controlling,
• wherein a first electronic closed-loop controller is included in the primary loop of closed-loop controlling and a second electronic closed-loop controller being included in the secondary loop of closed-loop controlling,
• wherein the closed-loop control unit is configured such that the reference variable of the first closed-loop controller is the desired temperature of the liquid contained in the tank and the actual temperature of the liquid is fed into the first closed-loop controller as a closed-loop control variable, and that the controlled variable of the first closed-loop controller is a desired value for a difference between the temperature of the liquid received in the tank and the temperature of the tempering fluid in the tempering jacket which is necessary to achieve the desired temperature, and the actual temperature of the liquid is additionally offset against the controlled variable of the first closed-loop controller to form a desired value of the temperature for the tempering fluid contained in the tempering jacket, and
• wherein the desired value for the temperature of the tempering fluid contained in the tempering jacket forms the reference variable for the second closed-loop controller and the actual temperature of the tempering fluid contained in the tempering jacket is fed as a closed-loop control variable into the second closed-loop controller, the second closed-loop controller determining a controlled variable by means of which it drives the control valve.