US 12,304,845 B2
Method to control a process variable
Thomas Alber, Stuttgart (DE); and Christoph Herb, Wiernsheim (DE)
Assigned to Endress+Hauser Conducta GmbH+Co. KG, Gerlingen (DE)
Filed by Endress+Hauser Conducta GmbH+Co. KG, Gerlingen (DE)
Filed on Jul. 29, 2019, as Appl. No. 16/524,851.
Application 16/524,851 is a continuation of application No. 14/968,115, filed on Dec. 14, 2015, granted, now 10,407,328.
Claims priority of application No. 10 2014 118 618.4 (DE), filed on Dec. 15, 2014.
Prior Publication US 2020/0024169 A1, Jan. 23, 2020
This patent is subject to a terminal disclaimer.
Int. Cl. C02F 3/00 (2023.01); C02F 3/12 (2023.01); G05B 19/042 (2006.01); G05D 7/06 (2006.01)
CPC C02F 3/006 (2013.01) [C02F 3/12 (2013.01); G05B 19/042 (2013.01); G05D 7/0617 (2013.01); C02F 2209/005 (2013.01); C02F 2209/38 (2013.01); G05B 2219/15055 (2013.01); G05B 2219/25276 (2013.01)] 18 Claims
OG exemplary drawing
 
1. A method for controlling a process variable representing an air mass flow fed into a liquid volume inside a container including a fluid intake and a fluid discharge and an aerator for introducing said air mass flow into said container in a process for treating the liquid while the liquid is flowing from the fluid intake through the container to the fluid discharge, said process being conducted in the container, said method comprising:
measuring values of a first measurand representing a load of one or several substances found in a volume unit of the liquid in the fluid intake, wherein the volume unit is different than the liquid volume;
sequentially determining values of a reference variable to be supplied to a first control unit based on the values of the first measurand, said reference variable representing a nominal value of the air mass flow to be fed into the liquid volume;
wherein a current value for the reference variable being determined by sequentially saving values of the first measurand in a first FIFO memory having a number K of logically consecutive memory locations (j=i), each location for saving one value of said values of the first measurand, respectively, 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 newest value saved in the first FIFO memory is saved in a final memory location (j=k); 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 than or equal to 1;
the method further comprising:
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 regulating the aerator that serves to supply air into the liquid volume in the container and influencing the air mass flow fed into the liquid volume using the aerator; and
controlling the aerator to supply air into the liquid volume in the container using the values of the regulating variable.