Method to control a process variable

A method to control a process variable representing an air volume to be fed into a liquid volume inside a container including a fluid intake and a fluid discharge in a process for treating the liquid, said process being conducted in the container and said method being performed using an air-mass flow controller and comprising the steps:

• measuring values of a first measurand representing a load of one or more substances to be degraded in the process and found in a settable volume unit of the liquid in the fluid intake;
• sequentially determining values of a reference variable to be supplied to the air-mass flow controller based on the values of the first measurand, said reference variable representing a nominal value of the air volume to be fed into the liquid volume;
• sequentially determining values of a regulating variable using both values for the reference variable and sequentially determined values of the process variable, said regulating variable being a variable for an aerator that serves to supply air into the liquid volume in the container and said variable influencing the air volume fed into the liquid volume using the aerator, wherein the regulating variable is a pump capacity or a rotational speed;
• determining a current value for the reference variable by:
• sequentially saving values of the first measurand, or values derived therefrom,
• in a first FIFO memory having a number K of memory locations for saving one value respectively, namely a memory featuring a number K of logically consecutive memory locations (j=i) in such a way that the oldest value saved in the first FIFO memory is saved in a first memory location (j=1) and the value saved last in the first FIFO memory is saved in a final memory location (j=k);
• and
• using only the n oldest values saved in the first FIFO memory to determine the current value for the reference variable, with n being a number of values that is smaller than the number K of the values saved in the memory locations of the first FIFO memory and greater than or equal to 1;
• sequentially measuring values of a third measurand, which represent the remaining quantity of the substance to be degraded in the process and discharged from the container via the fluid discharge, or a dissolved oxygen content found in the liquid in the container;
• using the values of the third measurand for determining the values of the reference variable;
• deriving from the values of the third measurand nominal values by means of a second control unit and using the nominal values in the step of sequentially determining values of the reference variable to be supplied to the air-mass flow controller;
• adjusting the aerator using the air-mass flow controller using the values of the regulating variable.

A method to control a process variable representing an air volume to be fed into a liquid volume inside a container including a fluid intake and a fluid discharge in a process for treating the liquid, said process being conducted in the container and said method being performed using an air-mass flow controller and comprising the steps:

• measuring values of a first measurand representing a load of one or more substances to be degraded in the process and found in a settable volume unit of the liquid in the fluid intake;
• sequentially determining values of a reference variable to be supplied to the air-mass flow controller based on the values of the first measurand, said reference variable representing a nominal value of the air volume to be fed into the liquid volume;
• sequentially determining values of a regulating variable using both values for the reference variable and sequentially determined values of the process variable, said regulating variable being a variable for an aerator that serves to supply air into the liquid volume in the container and said variable influencing the air volume fed into the liquid volume using the aerator;
• determining a current value for the reference variable by:
• sequentially saving values of the first measurand, or values derived therefrom, in a first FIFO memory having a number K of memory locations for saving one value respectively, namely a memory featuring a number K of logically consecutive memory locations (j=i) in such a way that the oldest value saved in the first FIFO memory is saved in a first memory location (j=1) and the value saved last in the first FIFO memory is saved in a final memory location (j=k);
• and
• using only the n oldest values saved in the first FIFO memory to determine the current value for the reference variable, with n being a number of values that is smaller than the number K of the values saved in the memory locations of the first FIFO memory and greater than or equal to 1;
• adjusting the aerator using the air-mass flow controller using the values of the regulating variable;
• deriving air requirement values from at least one value of the first measurand using a proportionality factor, and sequentially saving the air requirement values into the first FIFO memory;
• measuring at least one value of a third measurand in the discharge or downstream of the discharge;
• and
• adapting the proportionality factor based on said at least one value of the third measurand;
• wherein the regulating variable is a pump capacity or a rotational speed.

A device comprising:

• an aerator configured to supply air into a liquid volume in a container, said container having a fluid inlet and a fluid discharge;
• an air mass flow controller configured to control the aerator;
• a first measuring unit serving to measure values of a first measurand representing a load of one or several substances to be degraded in the process and found in a settable volume unit of the liquid in the fluid intake, said first measuring unit being arranged in the fluid intake or upstream from the fluid intake;
• and
• an electronic control unit connected with the first measuring unit to receive the measuring values from the first measuring unit, which comprises an operating software configured to:
• sequentially determine values of a reference variable to be supplied to the first measuring unit based on the values of the first measurand, said reference variable representing a nominal value of the air volume to be fed into the liquid volume;
• sequentially determine values of a regulating variable using both values for the reference variable and sequentially determined values of a process variable, said regulating variable being a variable for the aerator influencing the air volume fed into the liquid volume by means of the aerator, said process variable represents an air volume to be fed into a liquid volume inside a container including a fluid intake and a fluid discharge in a process for treating the liquid;
• with a current value for the reference variable being determined by sequentially saving values of the first measurand, or values derived therefrom, in a first FIFO memory having a number K of memory locations for saving one value respectively, namely a memory featuring a number K of logically consecutive memory locations (j=i) in such a way that the oldest value saved in the first FIFO memory is saved in a first memory location (j=1) and the value saved last in the first FIFO memory is saved in a final memory location (j=1);
• and
• by using only the n oldest values saved in the first FIFO memory to determine the current value for the reference variable, with n being a number of values that is smaller than the number K of the values saved in the memory locations of the first FIFO memory and greater or equal 1, and adjusting the aerator by means of the air-mass flow controller;
• the values of the first measurand or air requirement values derived from at least one value of the first measurand using a proportionality factor are saved sequentially in the first FIFO memory;
• and
• each air requirement value represents an air volume to be fed into the liquid to degrade the substance load represented by the at least one value of the first measurand.

A method to control a process variable in a process using a control unit, the process being conducted in a container, the method comprising the steps of:

• measuring values of a first measurand, wherein the values of the first measurand represent a load of one or more substances to be degraded in the process and found in a settable volume unit of liquid in a fluid intake of the container;
• sequentially determining values of a reference variable to be supplied to the control unit based on the values of the first measurand;
• sequentially determining values of a regulating variable using both values for the reference variable and sequentially determined values of the process variable, wherein the regulating variable represents a variable for an aerator that serves to supply air into the liquid volume of the container and said variable influencing the air volume fed into the liquid volume using the aerator, wherein the process variable represents an air volume to be fed into a liquid volume inside a container including a fluid intake and a fluid discharge in a process for treating the liquid;
• determining of a current value for the reference variable by:
• sequentially saving values of the first measurand, or values derived therefrom, in a first FIFO memory having a number K of memory locations for saving one value respectively, namely a memory featuring a number K of logically consecutive memory locations (j=i) in such a way that the oldest value saved in the first FIFO memory is saved in a first memory location (j=1) and the value saved last in the first FIFO memory is saved in a final memory location (j=k);
• using only the n oldest values saved in the first FIFO memory to determine the current value for the reference variable, with n being a number of values that is smaller than the number K of the values saved in the memory locations of the first FIFO memory and greater than or equal to 1;
• and
• sequentially saving values of a second measurand, or values derived therefrom, in a second FIFO memory having a number N of memory locations for saving one value respectively, namely a memory featuring a number N of logically consecutive memory locations (h=1);
• using all the values saved in the second FIFO memory to determine the current value for the reference variable, with N being a number of values that is equal to the number n of the values saved in the first FIFO memory and used for determining the current value of the reference variable;
• and
• adjusting the aerator using the air-mass flow controller using the values of the regulating variable.