GB2544997A

GB2544997A - System for checking calibration of a gas analyser

Info

Publication number: GB2544997A
Application number: GB1521279.8A
Authority: GB
Inventors: A T Robinson Jonathan; J Mapes Gary; Barrett Richard
Original assignee: Perkins Engines Co Ltd
Current assignee: Perkins Engines Co Ltd
Priority date: 2015-12-02
Filing date: 2015-12-02
Publication date: 2017-06-07
Also published as: GB201521279D0

Abstract

A system for checking calibration of a gas analyser, includes gas sources 12, gas mixer 16 in fluid communication with the sources, and a gas conduit 18 downstream of the mixer. The mixer prepares a mixture of gases with a predetermined concentration of a gas. The conduit has first 40 and second 42 portions and an elongated section 44, and holds an emitter 46 at the first portion, and a detector 48 at the second, in electrical communication. The conduit receives the mixture of gases proximate to the first portion and expels it proximate to the second portion to atmosphere. A thermocouple 22 is attached to the elongated section to measure temperature of the mixture of gases. An electronic analyser 28 may be connected to the emitter and a control unit 30.

Description

Description SYSTEM FOR CHECKING CALIBRATION OF A GAS ANALYSER Technical Field [0001] The present disclosure relates to calibration of sensors, and more specifically, to a system for checking calibration of a gas analyser.

Background [0002] In order to measure concentration of a gas present in an exhaust gas of an engine, gas analysers are used. A variety of gas analysers are available such as, but not limited to, laser gas analysers, infrared gas analysers etc. In order to measure the concentration of the gas accurately, the gas analysers are periodically calibrated. The calibration is performed to check whether a gas analyser is accurate before an engine emission test can commence.

[0003] Currently, calibration of gas analysers is performed by various techniques, for example, a Siemens LDS6 laser gas analyser is calibrated using calibration cells containing gas of a known concentration and taking measurements from the laser analyser to detect gas concentration. However, the calibration cells are very expensive, and a calibration cell can only provide calibration at the known concentration of the gas contained within it. Therefore, there is a need for a system which is cost effective, and performs accurate calibration of the laser analyser. Also, a system is desired which is not restricted to the known concentration of the calibration cells, and is able to check the performance, in particular a linearity response and an accuracy of the laser analyser at different concentrations.

[0004] US Patent Number 7,152,454 discloses an emission analysis test bench for calibration of exhaust gas analyser. The emission analysis test bench includes a number of analysers such as a flame ionization detector (FID) analyser, a nitrogen oxide (ΝΟχ) analyser, a carbon monoxide (CO) analyser, and a carbon dioxide (C02) analyser, that are connected between an exhaust manifold and a supply manifold. The analysers are calibrated at same time by continuously varying concentration of span gas and zero gas. As an example, the zero gas is preferably nitrogen (N2) gas. The concentration of the span gas and the zero gas is continuously varied by a span gas flow controller and diluent flow controller respectively, as a function of time to achieve a broader range of intermediate values that can be recorded by the analysers. Thus, there is a need for a system which is able to check the calibration or the performance, in particular a linearity response and an accuracy of the laser analyser at different concentrations, and is suitable for laboratory use.

Summary of the Invention [0005] In one aspect of the present disclosure, a system for checking calibration or performance of a gas analyser is provided. The system includes a plurality of gas sources configured to supply a plurality of gases. A gas mixer in fluid communication with the plurality of gas sources, and placed downstream of the plurality of gas sources. The gas mixer configured to prepare a mixture of gases. The mixture of gases includes a predetermined concentration of a gas from the plurality of gases. A gas conduit having a first portion, a second portion, and an elongated section defined between the first portion and the second portion. The gas conduit configured to hold an emitter at the first portion, and a detector at the second portion. The emitter and the detector being in electrical communication. The gas conduit in fluid communication with the gas mixer, and placed downstream of the gas mixer. The gas conduit is configured to allow flow of gases therethrough. The gas conduit is configured to receive the mixture of gases proximate to the first portion, and expel the mixture of gases proximate to the second portion into atmosphere. A thermocouple attached to the elongated section of the gas conduit configured to measure temperature of the mixture of gases present therewithin.

[0006] Other features and aspects of this disclosure will be apparent from the following description and the accompanying drawings.

Brief Description of the Drawings [0007] FIG. 1 is a system for checking calibration of a gas analyser, in accordance with the concepts of the present disclosure; and [0008] FIG. 2 is a flowchart illustrating a method for checking the calibration of the gas analyser, in accordance with the concepts of the present disclosure.

Detailed Description [0009] FIG. 1 is a system for checking the calibration of a gas analyser 10, in accordance with the concepts of the present disclosure. The system for checking the calibration of the gas analyser 10 includes a number of gas sources 12, a number of valves and regulator assemblies 14, a gas mixer 16, a gas conduit 18, a rotameter 20, a thermocouple 22, a blanket controller 24, a number of flanges 26, an electronic analyser 28, and a control unit 30. The gas sources 12 include a first gas source 32, and a second gas source 34. The valves and the regulator assemblies 14 include a first valve and regulator assembly 36 and a second valve and regulator assembly 38. The gas mixer 16 is placed downstream of the gas sources 12. Similarly, the gas conduit 18 is placed downstream of the gas mixer 16. It should be noted that the system for checking the calibration of the gas analyser 10 include more than two gas sources and more than two corresponding valves and regulator assemblies, without departing from the scope of disclosure. Examples of the gas analyser 10 include, but not limited to, a laser gas analyser, an infrared gas analyser etc.

[0010] The gas sources 12 (i.e., the first gas source 32 and the second gas source 34) are in fluid communication with the gas mixer 16, and are configured to supply a number of gases through the valves and the regulator assembly 14 (i.e., the first valve and regulator assembly 36 and the second valve and regulator assembly 38). In the valves and regulator assembly 14, valves are used for isolation and regulator is used for pressure, and thus the valves and regulator assembly 14 are configured to control the pressure of the gases. Thereafter, the gases are supplied by the gas sources 12 to the gas mixer 16. As an example, the gases are span gases and zero gas. The gas mixer 16 is adapted to prepare a mixture of gases based on the gases supplied by the gas sources 12. The mixture of gases includes a predetermined concentration of a gas with a partial pressure within the gaseous mixture. The mixture of gases is then passed to the gas conduit 18. The gas conduit 18 having a first portion 40, a second portion 42, and an elongated section 44 defined between the first portion 40 and the second portion 42. The gas conduit 18 is adapted to allow flow of gases therethrough. Further, the gas conduit 18 is adapted to hold an emitter 46 of the gas analyzer 10 at the first portion 40, and a detector 48 of the gas analyzer 10 at the second portion 42. The emitter 46 and the detector 48 being in electrical communication through a loop cable 50. The emitter 46 at the first portion 40 of the gas conduit 18 is connected to the electronic analyser 28. The electronic analyser 28 is further connected to the control unit 30 through an Ethemet/LAN cable. The gas analyser 10 includes the electronic analyser 28, the emitter 46, and the detector 48. The control unit 30 includes, but not limited to a laptop, a computer, or PDA.

[0011] The gas conduit 18 is adapted to receive the mixture of gases proximate to the first portion 40. The rotameter 20, which is placed between the gas mixer 16 and the gas conduit 18, is provided to measure flow rate of the mixture of gases. Thereafter, the mixture of gases flows through the gas conduit 18. The thermocouple 22 attached to the elongated section 44 of the gas conduit 18, measures temperature of the mixture of gases present therewithin. Further, the blanket controller 24 attached to the elongated section 44 of the gas conduit 18, is configured to warm walls of the gas conduit 18. Further, the flanges 26 are attached to the elongated section 44 of the gas conduit 18. Thereafter, the mixture of gases proximate to the second portion 42 of the gas conduit 18 is expelled into the atmosphere. Hereinafter, the predetermined concentration is a reference concentration.

[0012] FIG. 2 is a flowchart illustrating a method for checking the calibration of the gas analyser 10, in accordance with the concepts of the present disclosure. The method is described in conjunction with FIG. 1.

[0013] At step 52, the gas mixer 16 receives the gases from the gas sources 12. The gas sources 12 (i.e., the first gas source 32 and the second gas source 34) are adapted to supply the gases through the valves and regulator assembly 14 (i.e., the first valve and regulator assembly 36 and the second valve and regulator assembly 38). The gases may be span gases and zero gases. For example, the first gas source 32 is nitrogen (.¾) cylinder. Similarly, the second gas source 34 is an ammonia/nitrogen (NH3/ .¾) blended gas cylinder. As an example, the first gas source 32 and the second gas source 34 are adapted to contain the gases at a pressure of 1.5 bar, which is supplied through the first valve and regulator assembly 36 and the second valve and regulator assembly 38 respectively, to the gas mixer 16. It will be apparent to one skilled in the art that the gas sources 12 mentioned above have been provided only for illustration purposes. In an embodiment, the gas sources 12 may be ammonia/nitrogen (NH3/1¾) blended gas cylinder, nitrogen (N2) cylinder etc., without departing from the scope of the disclosure.

[0014] At step 54, the gas mixer 16 prepares the mixture of gases from the received gases. The mixture of gases includes a reference concentration of a gas. For example, the reference concentration of the gas such as ammonia is 4ppm with the balance gas being a non-reactive gas.

[0015] At step 56, the gas conduit 18 recei ves the mixture of gases proximate to the first portion 40. Similarly, the gas conduit 18 expels the mixture of gases proximate to the second portion 42 into atmosphere. As discussed above, the gas conduit 18 is adapted to hold the emitter 46 at the first portion 40, and the detector 48 at the second portion 42.

[0016] At step 58, a first concentration of the gas from the gases is measured. For example, the gas analyser 10 (i.e., a laser gas analyser) is used to measure the first concentration of the gas (for example, ammonia). The gas analyser 10 (i.e., the laser gas analyser) transmits a laser beam of a predetermined intensity through the emitter 46 at the first portion 40 in order to measure the first concentration of the gas. Based on the transmission, the detector 48 at the second portion 42 of the gas conduit 18 detects an intensity of the laser beam. Thereafter, based on the detection, the concentration of the gas is measured. For example, the first measured concentration of the gas is 4.1 ppm when the reference concentration of the gas in the mixture of gases is 4ppm.

[0017] After measuring the first concentration of the gas, the second concentration of the gas is measured in the same manner as discussed above by varying the reference concentration of the gas present in the mixture of gases. Thereafter, the second measured concentration of the gas is utilized to flush out the mixture of gases present inside the gas conduit 18. For example, the second measured concentration of the gas is 8.3ppm when the reference concentration of the gas in the mixture of gases is 8.2ppm. It will be apparent to one skilled in the art that the first measured concentration and the second measured concentration of the gas mentioned above have been provided only for illustration purposes. In an embodiment, more number of concentrations of the gas such as a third concentration, a fourth concentration etc. is measured in a similar maimer as discussed above, without departing from the scope of the disclosure, in alternative embodiment, an average value of the first measured concentration is determined by taking multiple measurements. Thereafter, the electronic analyser 28 attached to the emitter 46 at the first portion 40 of the gas conduit 18, captures and displays different concentration of the gas on the control unit 30. The control unit 30 is utilized for storing different concentration of the gas.

[0018] At step 60, the measured concentration of the gas is compared with the reference concentration of the gas. The reference concentration of the gas is determined by either a traceable gas divider or by sampling after the mixture of the material is formed. For example, the reference concentration of the gas is 4ppm which is compared with the first measured concentration of the gas i.e., 4.1ppm. Similarly, the reference concentration of the gas is 8.2ppm which is compared with the second measured concentration of the gas i.e., 8.3ppm. It should be noted that the comparison is performed for each concentration (i.e., the first measured concentration and the measured second concentration) measured above with a corresponding reference concentration for checking the calibration or the performance of the gas analyser 10 across a range of concentrations, without departing from the scope of the disclosure.

[0019] At step 62, die calibration or the performance of the gas analyser 10 is checked based on the comparison. The comparison is performed between the reference concentration of the gas and the corresponding measured concentration (i.e., the first measured concentration and the second measured concentration) of the gas as discussed above.

Industrial Applicability [0020] Gas analysers are used for measuring concentration of a gas present in an exhaust gas of an engine. In order to measure the concentration of the gas accurately, the gas analysers are periodically calibrated. The calibration is performed to check whether a gas analyser is accurate before an engine emission test can commence. Currently, calibration of the gas analysers is performed by various techniques, for example, a Siemens LDS6 laser analyser is calibrated using calibration cells containing gas of a known concentration and taking measurements from the laser analyser to detect gas concentration. However, the calibration cells are very expensive, and a calibration cell can only provide calibration at the known concentration of the gas contained within it. Therefore, there is a need for a system which is cost effective, and is not restricted to the known concentration of the calibration cells, and is able to check the performance, in particular a linearity response and an accuracy of the laser analyser at different concentrations.

[0021] The present disclosure provides the system for checking the calibration the gas analyser 10. The system discloses the gas sources 12 in fluid communication with the gas mixer 16. The gas mixer 16 is in fluid communication with the gas conduit 18. The gas conduit 18 is adapted to hold the emitter 46 at the first portion 40, and the detector 48 at the second portion 42. The emitter 46 and the detector 48 being in electrical communication. Further, the thermocouple 22 attached to the elongated section 44 of the gas conduit 18, measures temperature of the mixture of gases present therewithin. Such type of the gas conduit 18 is utilized for checking the calibration or the performance of the gas analyser 10 at a range of different concentrations, for example, the system is used for performing linearity verification test for the Siemens LDS6 laser gas analyser. The system does not require expensive calibration cell, and therefore, is cost effective, and performs accurate traceable calibration/performance check of the gas analyser 10.

[0022] While aspects of the present disclosure have been particularly shown and described with reference to the embodiments above, it will be understood by those skilled in the art that various additional embodiments may be contemplated by the modification of the disclosed machines, systems and methods without departing from the spirit and scope of what is disclosed. Such embodiments should be understood to fall within the scope of the present disclosure as determined based upon the claims and any equivalents thereof.

Claims

Claims What is claimed is:

1. A system for checking calibration of a gas analyser, the system comprising: a plurality of gas sources configured to supply a plurality of gases; a gas mixer in fluid communication with the plurality of gas sources, and placed downstream of the plurality of gas sources, the gas mixer configured to prepare a mixture of gases, wherein the mixture of gases includes a predetermined concentration of a gas from the plurality of gases; a gas conduit having a first portion, a second portion, and an elongated section defined between the first portion and the second portion, the gas conduit configured to hold an emitter at the first portion, and a detector at the second portion, the emitter and the detector being in electrical communication, the gas conduit in fluid communication with the gas mixer, and placed downstream of the gas mixer, wherein the gas conduit is configured to allow flow of gases therethrough, wherein the gas conduit is configured to receive the mixture of gases proximate to the first portion, and expel the mixture of gases proximate to the second portion into atmosphere; and a thermocouple attached to the elongated section of the gas conduit configured to measure temperature of the mixture of gases present there within.

2. The system of claim 1 further including an electronic analyser connected to the emitter at the first portion of the gas conduit of claim 1 and a control unit.