Gas sensor with two switchable filters and method for operating such a gas sensor

Patent metadata

Field	Value
Publication number	US-11892396-B2
Application number	US-201917312843-A
Country	US
Kind code	B2
Filing date	Dec 12, 2019
Priority date	Dec 13, 2018
Publication date	Feb 6, 2024
Grant date	Feb 6, 2024

Abstract

A gas sensor (2) distinguishes between a target gas and a contaminant and includes a light source (8), a measurement volume (4), a detector (22), and an adaptable filter system (20) with a first optical filter and a second optical filter. The filter system switches between a first composite state, with both filters in a reference state, a second composite state, with the first filter in a first reference state and the second filter in a second measurement state, a third composite state with the first filter in a first measurement state and the second filter in a second reference state, and a fourth composite state, with both filters in a measurement state. The gas sensor detects a target gas and makes a determination as to a presence of the contaminant by comparing the respective detector signals, generated during at least three of the composite states, with each other.

First claim

The invention claimed is:

1. A gas sensor configured and arranged to detect at least one target gas, wherein the gas sensor comprises
a light source configured and arranged to emit light,
a measurement volume,
a detector configured and arranged to receive light, and
an adaptable filter system,
wherein the measurement volume and the adaptable filter system are disposed in a light path between the light source and the detector,
wherein the adaptable filter system comprises a first optical filter and a second optical filter,
wherein the first filter is operable to switch between
a first reference state in which the first filter passes light according to a first reference wavelength profile and
a first measurement state in which the first filter passes light according to a first measurement wavelength profile,

wherein the second filter is operable, independently of the first filter, to switch between
a second reference state in which the second filter passes light according to a second reference wavelength profile and
a second measurement state in which the second filter passes light according to a second measurement wavelength profile,

wherein the first reference wavelength profile is different from the second reference wavelength profile, the adaptable filter system thereby being switchable between at least four different composite states, the composite states comprising:
a first composite state in which the first filter is in the first reference state and the second filter is in the second reference state,
a second composite state in which the first filter is in the first reference state and the second filter is in the second measurement state,
a third composite state in which the first filter is in the first measurement state and the second filter is in the second reference state, and
a fourth composite state in which the first filter is in the first measurement state and the second filter is in the second measurement state,

wherein the gas sensor is configured to switch the adaptable filter system between at least three of the composite states,
wherein the detector is configured and arranged to generate one respective detector signal corresponding to light received by the detector for every one of the at least three of the composite states used, and
wherein the gas sensor is configured to determine a presence of a contaminant other than the target gas in the light path between the light source and the detector by comparing with each other the respective detector signals generated during the at least three of the composite states.

2. Gas sensor according to claim 1 , wherein the gas sensor further comprises
at least one object which is arranged in the path of the light between the light source and the detector and
a heating element in thermal connection with the at least one object, wherein the at least one object is positioned such that emitted light passes the at least one object and/or is reflected by the at least one object and wherein the gas sensor is configured and arranged to activate the heating element as a reaction on detecting the contaminant, thereby vaporizing the contaminant on the at least one object in thermal connection with the heating element.

3. Gas sensor according to claim 1 ,
wherein the gas sensor further comprises
at least one object which is arranged in the path of the light between the light source and the detector and
a cleaning device configured and arranged to remove at least partially the contaminant from the at least one object, wherein the at least one object is positioned such that emitted light passes the at least one object and/or is reflected by the at least one object and

wherein the gas sensor is configured and arranged to trigger the cleaning device as a reaction on detecting the contaminant.

4. Gas sensor according to claim 1 , wherein the gas sensor is configured to switch the adaptable filter system
between the first, second, and third composite states or
between the first, second, and fourth composite states.

5. Gas sensor according to claim 4 , wherein the gas sensor is configured to detect that light received during the second composite state has been attenuated differently than light received during the third composite state.

6. Gas sensor according to claim 1 ,
wherein the gas sensor is configured to be selectively operated in a detecting mode in which the adaptable filter system is switched between the first and the fourth composite states or in a distinguishing mode in which the adaptable filter system is switched between at least three of the composite states and
wherein the gas sensor is further configured to switch from the detecting mode into the distinguishing mode if a positive alarm is detected in the detecting mode.

7. Gas sensor according to claim 1 , wherein the first and second filters are arranged on the adaptable filter system in respective regions having respective first and second envelopes, wherein the first and second envelopes overlap.

8. Gas sensor according to claim 1 , wherein the gas sensor is configured
to switch the first filter using a first input signal and
to switch the second filter using a second input signal, wherein the first input signal is a first square wave having a first frequency and wherein the second input signal is a second square wave having a second frequency.

9. Gas sensor according to claim 8 , wherein the gas sensor is configured to switch the first and second filters, using synchronized input signals of the same frequency and to subsequently switch the first and second filters using the first and second input signals.

10. Gas sensor according to claim 1 , wherein the detector is moveable with respect to the adaptable filter system.

11. Adaptable filter system for a gas sensor, wherein the adaptable filter system comprises
a first optical filter and
a second optical filter,
wherein the first filter is operable to switch between a first reference state in which the first filter passes light according to a first reference wavelength profile and a first measurement state in which the first filter passes light according to a first measurement wavelength profile,
wherein the second filter is operable, independently of the first filter, to switch between a second reference state in which the second filter passes light according to a second reference wavelength profile and a second measurement state in which the second filter passes light according to a second measurement wavelength profile,
wherein the first reference wavelength profile is different from the second reference wavelength profile, the first and second filters, thereby being switchable between four different composite states, the four composite states comprising:
a first composite state in which the first and second filters, are in the first and second reference states respectively,
a second composite state in which the first filter is in the first reference state and the second filter is in the second measurement state,
a third composite state in which the first filter is in the first measurement state and the second filter is in the second reference state, and
a fourth composite state in which the first and second filters, are in the first and second measurement states respectively.

12. An adaptable filter system according to claim 11 , in combination with a gas sensor comprising a light source and a detector, wherein the gas sensor is configured and arranged to detect at least one target gas and to detect at least one contaminant.

13. A method of operating a gas sensor configured and arranged to detect at least one target gas, wherein the gas

Assignees

• Draeger Safety Ag & Co Kgaa

Inventors

• Sagberg Håkon
• Greenberg-Fismen Britta
• Hobæk Thor Christian

Classifications

• G01N21/15 Primary

  Preventing contamination of the components of the optical system or obstruction of the light path · CPC title

• G01N21/31

  Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry {(G01N21/72 takes precedence)} · CPC title

• G01N33/0029

  Cleaning of the detector · CPC title

• G01N2021/158

  Eliminating condensation · CPC title

• G01N21/3504 Primary

  for analysing gases, e.g. multi-gas analysis · CPC title