Computer-implemented method for process control of a production plant for continuous production and/or preparation of biopharmaceutical products with at least two units connected together in series for implementation of at least two downstream and/or upstream steps, comprising at least one slave unit connected to at least one buffer volume either in the same unit or in an adjacent unit along the product stream and having one or more sensors for monitoring the buffer volume and actuators for influencing the buffer volume and the sensors for monitoring the buffer volume and one or more actuators for influencing the buffer volume are connected to at least one controller, and wherein the state variable of each buffer volume is controlled by means of the sensor and the actuator connected to at least one controller in a closed action sequence, and at least one master unit which comprises at least one device for conveying the product stream and is characterized in that it is a unit that is crucial in determining a flow rate and its flow rate is controlled not by closed-loop control via the control of the state variable of a buffer volume but by open-loop control, and wherein, if the master unit is adjacent to one or more slave units, it is connected to the buffer volume of each slave unit, wherein: in step a) the values of the state variable of the buffer volumes and the flow rate in the production plant are specified by the following statements: ∘ order of the units along the product stream is stated, ∘ a target value for the flow rate is specified for each master unit, ∘ a target value for the state variable is specified for each buffer volume, ∘ for each closed action sequence, the connection of the controllers to the sensors for monitoring the buffer volume and to the actuators for influencing the buffer volume and if appropriate their connection to one another are specified, ∘ a parameterization of the controllers is carried out, and wherein the method comprises the following further steps for the operation of the production plant: b) The target value for the flow rate of the master units is transmitted by the control system to an actuator for regulating the flow rate in the master unit, with the proviso that in the case of several master units an auxiliary stream - a non-product-laden (or waste product-laden) stream which is conveyed into or out of the product stream - is opened since it is not possible to control two master units with exactly the same flow rate, c) The actual value of the state variable for each buffer volume is determined by the corresponding sensor for monitoring the particular buffer volume, passed on to the controller connected in the respective closed action sequence and there compared with the respective corresponding target value, d) The respective control signals are calculated and transmitted to the respective actuators connected in the closed action sequence for influencing the buffer volumes, e) The actuators for influencing the buffer volume react upon the sensors for monitoring the buffer volume and f) Steps b) to e) are repeated until the production plant is switched off or shut down and wherein the buffer volume in one unit is generated by the use of an expandable hose or a vessel and the state variable of each buffer volume is the fill level or pressure. ∘ order of the units along the product stream is stated, ∘ a target value for the flow rate is specified for each master unit, ∘ a target value for the state variable is specified for each buffer volume, ∘ for each closed action sequence, the connection of the controllers to the sensors for monitoring the buffer volume and to the actuators for influencing the buffer volume and if appropriate their connection to one another are specified, ∘ a parameterization of the controllers is carried out, b) The target value for the flow rate of the master units is transmitted by the control system to an actuator for regulating the flow rate in the master unit, with the proviso that in the case of several master units an auxiliary stream - a non-product-laden (or waste product-laden) stream which is conveyed into or out of the product stream - is opened since it is not possible to control two master units with exactly the same flow rate, c) The actual value of the state variable for each buffer volume is determined by the corresponding sensor for monitoring the particular buffer volume, passed on to the controller connected in the respective closed action sequence and there compared with the respective corresponding target value, d) The respective control signals are calculated and transmitted to the respective actuators connected in the closed action sequence for influencing the buffer volumes, e) The actuators for influencing the buffer volume react upon the sensors for monitoring the buffer volume and f) Steps b) to e) are repeated until the production plant is switched off or shut down and