Method to control a process variable

Patent metadata

Field	Value
Publication number	US-10407328-B2
Application number	US-201514968115-A
Country	US
Kind code	B2
Filing date	Dec 14, 2015
Priority date	Dec 15, 2014
Publication date	Sep 10, 2019
Grant date	Sep 10, 2019

Abstract

A method to control a process variable in a process by means of a control unit comprises: sequential determination of values of a reference variable to be supplied to the first control unit based on the values of a first measurand; sequential determination of values of a regulating variable using both values for the reference variable and sequentially determined values for the process variable; 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 of the values 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 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.

First claim

The invention claimed is:

1. 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; and
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);
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
adjusting the aerator using the air-mass flow controller using the values of the regulating variable;

wherein 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.

2. The method according to claim 1 , wherein:
sequentially determining values of the reference variable to be provided to the air-mass flow controller further comprises measuring values of a second measurand that differs from the first measurand, said values being used to determine the reference variable.

3. The method according to claim 2 , further comprising:
determining the current value for the reference variable by sequentially saving values for the 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=I), and by 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.

4. The method according to claim 1 , wherein:
the regulating variable is a pump capacity or a rotational speed.

5. The method according to claim 4 , further comprising:
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.

6. The method according to claim 5 , further comprising:
using the values of the third measurand for determining the values of the reference variable.

7. The method according to claim 1 , wherein:
several values for the first measurand and a throughput of the liquid are measured sequentially to determine each air requirement value;
with the sequentially measured values for the first measurand or values derived therefrom being accumulated until the throughput reaches a settable throughput threshold value; and
the air requirement value is determined by the accumulation value resulting from the accumulation of values of the first measurand using the proportionality factor.

8. The method according to claim 7 , wherein:
with the respective air requirement value determined most recently being saved to a memory location in the first FIFO memory, the oldest air requirement value saved in the first FIFO memory is simultaneously deleted or overwritten.

9. The method according to claim 7 , wherein:
the values of the first measurand are measured at a measuring point arranged in the fluid intake, and wherein the settable throughput threshold value equals the quotient of the volume taken up by the liquid found between the measuring point and the fluid discharge, and the number K of the memory locations of the first FIFO memory, so that each memory location corresponds to a liquid volume unit flowing into the container by the way of the fluid intake, and the air requirement value saved in that memory location represents the air volume to be supplied into the liquid in order to degrade the load contained in this liquid volume unit.

10. The method according to claim 9 , wherein:
to obtain the current value of the reference variable to be supplied to the air-mass flow controller, the n oldest requirement values saved in the first FIFO memory are added to obtain a total air requirement value; and
the number n of the air requirement values being used for the total air requirement value is selected in such a way that the sum of the liquid volume units corresponding to the respective memory locations is equal to the volume of the container comprising the liquid.

11. The method according to claim 7 , wherein:
the second measurand represents an air volume introduced into the liquid in the container using the aerator; and
the method further comprises determining air introduction values from several sequentially captured values of the second measurand by accumulating the sequentially captured values of the second measurand or values derived therefrom until the liquid throughput detected for the simultaneous determination of an air requirement value has reached the settable throughput threshold values, and the air introduction values are determined by accumulation values obtained by the accumulation of the values of the second measurand or the values derived therefrom.

12. The method according to claim 11 , wherein:
at the same time that a newly determined air requirement value is saved, and the oldest air requirement value in the first FIFO memory is deleted, the air introduction value saved in the second FIFO memory at a first memory location according to the logical sequence of the memory locations (h=1) is deleted as well.

13. The method according to claim 12 , wherein:
to obtain the current value of the reference variable to be supplied to the air-mass flow controller, all air introduction values saved in the second FIFO memory are added to obtain a total air introduction value.

14. The method according to claim 13 , wherein:
in order to determine the current value for the reference variable, a deviation value representing the deviation of the total air requirement value from the total air introduction val

Assignees

• Endress Hauser Conducta Ges Fuer Mess Und Regeltechnik Mbh Co Kg
• Endress Hauser Conducta Gmbh Co Kg

Inventors

• Alber Thomas
• Herb Christoph

Classifications

• C02F2209/38

  Gas flow rate · CPC title

• C02F2209/005

  Processes using a programmable logic controller [PLC] · CPC title

• C02F3/006 Primary

  Regulation methods for biological treatment · CPC title

• C02F2209/40

  Liquid flow rate · CPC title

• C02F2209/22

  O2 · CPC title