# US 10,371,678 B2 · Method and measuring apparatus for determining gas properties by correlation

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- Number: US 10,371,678 B2
- Document ID: US10371678B2
- Status: Granted
- Kind: B2
- Application number: 15/379,003
- Filed: 2016-12-14
- Published: 2017-06-22
- Granted: 2019-08-06
- Earliest claimed: 2015-12-19
- Assignees: Mems AG
- Applicants: Mems AG
- Inventors: Philippe Pretre; Andreas Kempe
- Web page: https://patentgrep.com/patent/US10371678B2

## CPC

- G01N 33/0004: {Gaseous mixtures, e.g. polluted air}
- G01F 1/74: Devices for measuring flow of a fluid or flow of a fluent solid material in suspension in another fluid
- G01F 15/022: {using electrical means}
- G01F 15/024: {involving digital counting}
- G01N 33/225: {Gaseous fuels, e.g. natural gas}
- G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q)
- G01F: MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME

## Abstract

A method in which a gas property (Q) is determined by correlation from physical measuring quantities (μj) of the gas mixtures. In the method, the physical measuring quantities are combined into a sensor output (Sout) by making use of a sensor output function (ƒ), wherein the sensor output function is determined in such a way that a group of gas mixtures can be separated from a set of gas mixtures for which the gas property (Q) is determined, within which the correlation between the sensor output (Sout) and the desired gas property (Q) is better than in the entire set.

## Claims

### Claim 1

A method for the determination of gas properties by correlation in which a gas property (Q) is determined by correlation from physical measuring quantities (μj (j=1, . . . , m)) of the gases and/or gas mixtures, and the method comprises:
combining the physical measuring quantities (μj (j=1, . . . , m)) into a sensor output (Sout=ƒ(μ1, . . . , μm)) by making use of a sensor output function (ƒ),
comparing the sensor output (Sout) with a limit value (Soutsep) in order to determine whether the sensor output, within a set (G) of gases and/or gas mixtures to which the method is applied, belongs to a group of gases and/or gas mixtures which is referred to below as gas mixture group (GG), in which a correlation between the sensor output (Sout) and the gas property (Q) to be determined is better than in the entire set (G), and
if the sensor output (Sout) belongs to the gas mixture group (GG), the gas property (Q) is determined from the sensor output with a correlation function (ƒcorr) which is specific to the gas mixture group.

### Claim 2 (depends on 1)

The method according to claim 1, wherein the affiliation with a gas mixture group is checked in two, three, four or more steps,
in that the physical measuring quantities (μj (j=1, . . . , m)) are combined into a further sensor output (Sout,i=ƒi(μ1, . . . , μm)) respectively by making use of a sensor output function (ƒi) which is specific to the gases and/or gas mixtures (Grest,i) of the set that have remained after the separation of the preceding gas mixture group or groups, which are referred to below as the remaining gases and/or gas mixtures (Grest,i), and the further sensor output (Sout,i) is compared with a further limit value (Sout,isep) in order to determine whether the further sensor output belongs within the remaining gases and/or gas mixtures (Grest,i) to a further gas mixture group (GGi) in which the correlation between the further sensor output (Sout,i) and the gas property (Q) to be determined is better than within the remaining gases and/or gas mixtures (Grest,i), and
if the further sensor output (Sout,i) belongs to the further gas mixture group (GGi), the gas property (Q) is determined from the further sensor output with a correlation function (ƒcorr,i) which is specific to the further gas mixture group.

### Claim 3 (depends on 1)

The method according to claim 1, wherein, if the sensor output (Sout, Sout,i) does not belong to one of the gas mixture groups (GG, GGi), the gas property (Q) is determined from the sensor output with a correlation function (ƒcorr,i) which is specific to the remaining gases and/or gas mixtures (Grest, Grest,i).

### Claim 4 (depends on 1)

The method according to claim 1, wherein the sensor output (Sout, Sout,i) is changed before the correlation with a further sensor output function (ƒi) in order to prepare the correlation between the sensor output (S) and the gas property (Q).

### Claim 5 (depends on 1)

The method according to claim 1, wherein the sensor output function (ƒ) and a limit value (Soutsep) for the sensor output are determined in such a way that a gas mixture group (GG) is separated by the limit value from a set (G) of gases and/or gas mixtures for which the gas property (Q) is determined, within which the correlation between the sensor output (Sout) and the desired gas property (Q) is better than in the entire set (G).

### Claim 6 (depends on 1)

The method according to claim 1, wherein the relationship
SoutGG<Soutsep
applies to the gases and/or gas mixtures of the gas mixture group (GG), and the relationship
SoutGrest≥Soutsep,
applies to the remaining gases and/or gas mixtures (Guest) of the set,
or from case to case, instead of the aforementioned relationships, the relationships SoutGG>Soutsep and SoutGrest≤Soutsep apply.

### Claim 7 (depends on 1)

The method according to claim 1 wherein the steps are carried out automatically.

### Claim 8 (depends on 1)

The method according to claim 1, wherein the sensor output function or sensor output functions (ƒ, ƒi) and/or the limit value or values (Soutsep, Sout,isep) for the sensor output and/or the correlation functions (ƒcorr, ƒcorr,i) are determined in advance, e.g. on the basis of values of the physical measuring quantities and the gas property to be determined from tables and/or technical literature and/or databases and/or measurements.

### Claim 9 (depends on 1)

The method according to claim 1, wherein the sensor output function or the sensor output functions (ƒ, ƒi) and/or the limit value or values (Soutsep, Sout,isep) for the sensor output are determined by a computer program in that:
for each function (fi) in a set of possible sensor output functions the respective functional parameters (pfi) of (fi) such as polynomial coefficients, exponents or constants, are varied within preset limit values for (pfi), e.g. by means of a Monte Carlo selection method,
the sensor output range is subdivided into intervals and the number of ambiguities is counted in particular in each interval, i.e. the number of events for which two or more gas mixtures show different values for the quantity (Q) to be determined or the values for the quantity (Q) to be determined lie outside of a preset value interval for (Q),
the function (fi) and the specific functional parameter set (pfi) are determined for which the fewest of such ambiguity events occur, or the variance (3σ) of the values for the quantity (Q) to be determined is minimal in case of ambiguity events in an interval, or a preset maximum permitted number (nmax) of the ambiguity events or a preset maximum permitted variance (3σmax) of the Q values is not exceeded in case of ambiguity events in an interval, and
in that it is determined in particular from which limit value (Sout,isep) a number (nmax) of the ambiguity events preset for each interval for the determination of the limit value or a variance (3σmax) of the Q values preset for each interval for the determination of the limit value is not exceeded in case of ambiguity events.

### Claim 10 (depends on 1)

The method according to claim 1, wherein at least two or all correlation functions differ from each other, and/or wherein the points of the gases and/or gas mixtures of the gas mixture group or groups each lie on a line described by a distinct correlation function or in tolerance ranges which adjoin such a line on both sides, and which for example are not greater than 0.25% or 0.75% or 2% of the value of the gas property (Q).

### Claim 11 (depends on 1)

The method according to claim 1, wherein the sensor output function (ƒ) or sensor output functions (ƒi) are of the type
Sout,i=μ1p1,i· . . . ·μmpm,i
and p1,i, . . . , pm,i are exponents, and/or
wherein the correlation function (ƒcorr(Sout)) or correlation functions (ƒcorr,i(Sout,i)) are of the type
Q=ƒcorr,i(Sout,i)=a0,i+a1,i·Sout,i+a2,i·Sout,i2
and a0,i, a1,i and a2,i are constants.

### Claim 12 (depends on 1)

The method according to claim 1, wherein the Pearson correlation coefficient (Kor(Sout,Q)) is used as a measure for the precision of the correlation, and wherein a better correlation means that the Pearson correlation coefficient lies closer to the value 1 or −1, in particular that the absolute value of the difference from the value 1 or −1 is less than 0.3 or 0.2 or 0.1.

### Claim 13 (depends on 1)

The method according to claim 1, wherein the physical measuring quantities (μj (j=1, . . . , m)) are detected with one or several sensors, and/or wherein at least two of the measuring quantities thermal conductivity, heat capacity, thermal diffusivity, density, flow velocity, mass flow, sound velocity, dielectric constant, viscosity, infrared absorption, pressure or temperature are detected as physical measuring quantities (μj (j=1, . . . , m)).

### Claim 14 (depends on 1)

A measuring apparatus for determining gas properties with one or several sensors for detecting physical measuring quantities (μj (j=1, . . . , m)) and with an evaluation unit which is set up for carrying out a method according to claim 1.

### Claim 15 (depends on 14)

The measuring apparatus according to claim 14, wherein the evaluation unit forms an assembly together with the sensor or sensors, or wherein the evaluation unit is formed in a separate or superordinate computing unit.

### Claim 16

A method to determine gas properties comprising:
measuring physical quantities (μj (j=1, . . . , m)) of a gas or gas mixture with a sensor;
generating a sensor output (Sout=ƒ(μ1, . . . , μm)) representative of a combination of the measured physical quantities;
comparing the sensor output (Sout=ƒ(μ1, . . . , μm)) to a limit value (Soutsep);
based on the comparison, determining whether the sensor output (Sout=ƒ(μ1, . . . , μm)) corresponds to a gas mixture group (GG), and
if the sensor output (Sout=ƒ(μ1, . . . , μm)) corresponds to the gas mixture group (GG), determining a gas property (Q) for the gas or gas mixture from the sensor output (Soutƒ(μ1, . . . , μm)) and using a correlation function (ƒcorr) which is specific to the gas mixture group (GG).