Dosing unit and method for dosing a liquid

A dosing unit for dosing liquids, the dosing unit comprising:

• a fluid unit for selectively providing an overpressure and a negative pressure on a working gas, the working gas being accommodated in a fluid channel which is connected at a first end region to the fluid unit, and which comprises a second end region for an accommodation and a discharge of a predetermined volume of liquid;
• a first valve unit connected with the fluid channel for selectively blocking and releasing the fluid channel;
• a second valve unit connected with the fluid channel and arranged spaced apart from the first valve unit along the fluid channel for selectively blocking and releasing the fluid channel, wherein the first valve unit and the second valve unit delimit a fluid reservoir for storing the working gas;
• a control unit for controlling the first valve unit and the second valve unit;
• a first pressure sensor electrically connected to the control unit, the first pressure sensor being assigned to the fluid reservoir for providing a pressure signal as a function of the working gas pressure in the fluid reservoir;
• and
• a second pressure sensor connected between the second valve unit and the second end portion connected to the control unit, wherein the control unit provides an end signal in response to a pressure signal of the second pressure sensor,
• wherein the control unit is configured for performing a method for dosing a liquid comprising the steps:
• opening the first valve unit while the second valve unit is closed;
• providing a negative pressure to the fluid reservoir;
• determining the working gas pressure in the fluid reservoir with the pressure sensor and providing a pressure signal of the pressure sensor to the control unit;
• closing the first valve unit when a predefined first working gas pressure in the fluid reservoir is determined by the control unit to block the fluid reservoir between the first valve unit and the second valve unit and to thereby store the negative pressure in the fluid reservoir;
• opening the second valve unit;
• monitoring a pressure rise in the fluid reservoir during an opening state of the second valve unit and while the second end region of the fluid channel is immersed in the liquid to be metered;
• closing the second valve unit when the control unit determines a predefined second working gas pressure in the fluid reservoir opening the first valve unit;
• providing positive pressure to the fluid reservoir, while the first valve unit is open and while the second valve unit is closed;
• closing the first valve unit as soon as a predefined third working gas pressure is reached in the fluid reservoir;
• opening the second valve unit to achieve a pressure drop in the fluid reservoir during the opening state of the second valve unit;
• and closing the second valve unit when a predefined fourth working gas pressure is reached in the fluid reservoir.

A dosing unit for dosing liquids, the dosing unit comprising:

• a fluid unit for selectively providing an overpressure and a negative pressure on a working gas, the working gas being accommodated in a fluid channel which is connected at a first end region to the fluid unit, and which comprises a second end region for an accommodation and a discharge of a predetermined volume of liquid;
• a first valve unit connected with the fluid channel for selectively blocking and releasing the fluid channel;
• a second valve unit connected with the fluid channel and arranged spaced apart from the first valve unit along the fluid channel for selectively blocking and releasing the fluid channel, wherein the first valve unit and the second valve unit delimit a fluid reservoir for storing the working gas;
• a control unit for controlling the first valve unit and the second valve unit;
• and
• a pressure sensor electrically connected to the control unit, the pressor sensor being assigned to the fluid reservoir for providing a pressure signal as a function of the working gas pressure in the fluid reservoir, wherein the volume of the fluid reservoir is adjustable,
• wherein the control unit is configured for performing a method for dosing a liquid comprising the steps:
• opening the first valve unit while the second valve unit is closed;
• providing a negative pressure to the fluid reservoir;
• determining the working gas pressure in the fluid reservoir with the pressure sensor and providing a pressure signal of the pressure sensor to the control unit;
• closing the first valve unit when a predefined first working gas pressure in the fluid reservoir is determined by the control unit to block the fluid reservoir between the first valve unit and the second valve unit and to thereby store the negative pressure in the fluid reservoir;
• opening the second valve unit;
• monitoring a pressure rise in the fluid reservoir during an opening state of the second valve unit and while the second end region of the fluid channel is immersed in the liquid to be metered;
• closing the second valve unit when the control unit determines a predefined second working gas pressure in the fluid reservoir opening the first valve unit;
• providing positive pressure to the fluid reservoir, while the first valve unit is open and while the second valve unit is closed;
• closing the first valve unit as soon as a predefined third working gas pressure is reached in the fluid reservoir;
• opening the second valve unit to achieve a pressure drop in the fluid reservoir during the opening state of the second valve unit:
• and closing the second valve unit when a predefined fourth working gas pressure is reached in the fluid reservoir.