GB2578921A

GB2578921A - Fluid analysis system

Info

Publication number: GB2578921A
Application number: GB1818569.4A
Authority: GB
Inventors: Zhang Zhiyong
Original assignee: Duvas Technologies Ltd
Current assignee: Duvas Technologies Ltd
Priority date: 2018-11-14
Filing date: 2018-11-14
Publication date: 2020-06-03
Also published as: GB201818569D0

Abstract

A fluid analysis system, particularly for use in hazardous environments, determines the presence of compounds by passing light through a sample into a spectrometer 110, via coupling arrangement 120 e.g. a plano-concave lens and parabolic mirror. The sample cell 104 may by a multi-pass absorption cell and the housing may be portable. The lighting arrangement comprises e.g. a UVC, UVB or UVA-band light emitting diode (LED), which may be driven by a constant current power source. This provides light with a stable output intensity, reducing fluctuations, which may provide a more accurate system for analysing dangerous compounds in an explosives environment. UVC LEDs have lower operating voltage, suitable for safety requirements, and are useful for detection of e.g. benzene. A thermal management module (300, figure 3) may control the temperature of the LED with e.g. a thermoelectric cooler, heat-sink and/or fan, using a thermally conductive layer such as aluminium substrate.

Description

FLUID ANALYSIS SYSTEM

FIELD

The invention relates to a fluid analysis system. Particularly, but not exclusively, the invention relates to a fluid analysis system for identifying multiple species in a fluid.

BACKGROUND

It is often required, particularly in hazardous environments, to determine the presence of compounds in gases or fluids.

W02017060853 discloses such a system which employs a multipass absorption cell arranged to receive a sample gas and further arranged to pass light through the sample gas 15 so that the compounds in the gas can be determined by the absorption characteristics of the light which is passed through the absorption cell.

These systems are required to detect species of compounds in gases or fluids at varying sensitivity levels or measurement ranges. For example, for air quality monitoring the sensitivity needs to he of the order of parts per billion. However, the industry process control or continuous emission monitoring application only needs parts per million levels of sensitivity.

The detection of specific compounds is particularly important in explosive atmospheres which can be ignited by particular flammable compounds. These environments arc regulated in Europe under the ATEX regulations which describe the equipment and use of a product to be located in explosive atmospheres. These environments are regulated across large parts of the rest of the world under the IECEX regulations.

Example compounds may include benzene, toluene, ethylbenzene, xylene, styrene, 1,3-butadiene and other acetylides, fulminates, nitrogen-based compounds, nitrates, amines, peroxides, oxides and many others.

However, these systems are often cumbersome, not very mobile and not very configurable for the different compounds they may be required to detect.

Aspects and embodiments are conceived with (he foregoing in mind.

SUMMARY

A fluid analysis system in accordance with the described aspects is configured for the detection of liquids and/or gases and the presence of specific species of liquids or gases in liquids and/or gases.

Viewed from a first aspect, there is a system for analysing a sample of a fluid to determine the presence of compounds in the sample, the system comprising a light source comprising at least one light emitting diode configured to emit light into a sample analysis chamber, wherein the sample analysis chamber is for receipt of a sample, an output optical coupling unit configured to receive the light emitted by the light emitting diode after it has passed through the sample in the sample analysis chamber; and a processing unit configured to spectrally analyse the received light to determine the presence of at least one compound in the sample of fluid.

A system in accordance with the first aspect utilises a light emitting diode as a light source to perform analysis of a sample to determine the presence of compounds within that sample. A light emitting diode is much lighter and less demanding of electrical power when compared to a deuterium or xenon lamp. This means the system can be made more compact.

The sample analysis chamber may he a multipass absorber or a single-pass absorber.

The system may further comprise an input optical coupling unit configured to receive the light emitted by the light emitting diode and to force that light into the sample analysis chamber.

The output optical coupling unit and the processing unit may be distinct in that they may be separate components where the output optical coupling unit directs the light into the 5 processing unit where raw spectrum are generated by a photon detector The system may further comprise a spectrometer configured to receive the light collected by the output optical coupling unit and further configured to generate a spectrum from the light. The output optical coupling unit may be positioned to receive the light after it has 10 passed through the sample in the sample analysis chamber.

The spectrometer may be configured to transmit the spectrum to the processing unit which may be configured to spectrally analyse the spectrum generated by the spectrometer to determine the presence of at least one compound in the sample of fluid.

The processing unit may be configured to process received raw spectrums, extract spectrum absorption signals and analyse the concentration of potential compounds in the sample.

The sample analysis chamber may have an input window and an output window positioned at one end of the chamber, the chamber may he configured to receive the detection light output by the input optical coupling unit at the input window, pass the detection light through the fluid, reflect the detection light to the output optical coupling unit from the output window.

An input optical coupling unit may be configured to receive the detection light emitted by the light emitting diode and output the detection light into the sample analysis chamber The input optical coupling unit may comprise an off-axis parabolic mirror and an air-30 spaced achromatic doublet lens. The output optical coupling unit may comprise a fused silica piano-convex lens and an off-axis parabolic minor.

The system may be contained in a portable housing. The effect of this is that the system can be carried by hand.

The light emitting diode may be configured to emit light in the UVC-band of wavelengths.

The light emitting diode may be an infrared light emitting diode, visible light emitting diode or an ultraviolet light emitting diode.

The system may comprise a power supply unit configured to supply a constant driving current to the light emitting diode to cause a stable light output of constant intensity to be emitted by the light emitting diode.

A constant driving current will mean the light output by the light emitting diode is of stable 15 intensity which means that a stable sensitivity may be ensured by the system.

The system may be configured to receive an input to select the constant driving current from among a plurality of constant driving currents to cause light of a selected intensity to be emitted by the light emitting diode. This means that the sensitivity and measurement 20 ranges can be selected in accordance with the requirements of the application.

The input may he received from a user of a fluid analytics system or from a component of a fluid analytics system.

The power supply unit may comprise a plurality of constant current sources each corresponding to a constant driving current.

The power supply unit may comprise a plurality of switches operable to enable a constant current from a respective constant current source to be transmitted to the light emitting 30 diode.

The constant current source may be fed by a linear power regulator configured to output a steady voltage to be fed to the constant current source responsive to the selection of the constant current.

The linear power regulator may be fed by a voltage configuration resistor selected by a power supply selection switch responsive to the selection of a corresponding constant current.

The light emitting diode may he mounted to a thermal management module configured to gradiate the operating temperature of the light emitting diode. The effect of the thermal management module is that the operating temperature of the light emitting diode is managed so that if it drops below a defined level, heat may he applied to warm the light emitting diode and if it rises above a defined level, cooling may be applied to cool the light emitting diode.

The thermal management module may he configured to gradiate the temperature of the light emitting diode responsive to an output signal from a thermal control module 15 configured to determine the operating temperature of the light emitting diode.

The thermal detection module may comprise a thermal transducer to convert the temperature of light emitting diode to an electronic signal.

The thermal control module may comprise an analog-to-digital converter to measure the converted electronic signal from thermal detection module.

The thermal control module may comprise a full-bridge driving circuit using MOSFETs to drive the thermoelectric cooler in the thermal management module of light emitting diode.

The thermal control module may comprise a PID (Proportional-integral-derivative) control unit to output a PWM (Pulse Width Modulation) signal to control the full-bridge driving circuit.

The thermal control module may comprise communication circuits to communicate with the control unit 102 to receive related parameters from the control unit 102 and send the temperature and operation data to the control unit.

The thermal management module may comprise a thermoelectric cooler configured to drive heat toward the light emitting diode if the operating temperature drops below a temperature threshold.

The thermal management module may comprise a thermoelectric cooler configured to draw heat away from the light emitting diode if the operating temperature rises above a temperature threshold.

A thermally conductive layer may he disposed between the light emitting diode and the thermoelectric cooler to enable the conductivity of heat between the light emitting diode and the thermoelectric cooler.

The light emitting diode and the thermal management module may be sealed in a housing comprising a window to enable the light emitted from the light emitting diode to pass out of the housing into the fluid analysis system. The effect of the housing is that contamination of the rest of the components of the system due to electromagnetic interference generated by the thermal management module or other hardware system is reduced.

The housing may comprise a first metal enclosure to enclose the light emitting diode and the thermal detection module and a second metal enclosure to enclose the thermoelectric cooler.

The first metal enclosure and the second metal enclosure may be separate in that they are not in contact.

The thermally conductive layer may contact the thermoelectric cooler and the thermoelectric cooler may he attached to a heatsink.

The system may further comprise a fan spaced from the heatsink to draw heat away from the heatsink.

The spacing between the fan and the heatsink will ensure the vibrations generated by the fan do not transfer to the light emitting diode and thereby maintains the stability of the light output.

The thermally conductive layer may comprise an aluminium substrate.

The thermally conductive layer may further comprise aluminium portions disposed underneath the (hernial detection module and the light emitting diode.

DESCRIPTION

An embodiment in accordance with the first aspect will now be described by way of example only and with reference to the accompanying drawings, in which: Figure la schematically illustrates a gas analysis system in accordance with the embodiment; Figure lb schematically illustrates the principle of multipass absorption in a gas analysis system in accordance with the embodiment; Figure lc graphically illustrates the absorption spectra for BTEX gases; Figure ld schematically illustrates the hardware system of a gas analysis system in accordance with the embodiment; Figure 2a schematically illustrates a circuit for driving a light emitting diode to be used on a gas analysis system in accordance with the embodiment; Figure 2h schematically illustrates a circuit for choosing the detection sensitivity & 30 measurement range and driving a light emitting diode to be used on a gas analysis system in accordance with the embodiment; Figure 3 schematically illustrates a thermal management module to manage the heat around a light emitting diode in a gas analysis system in accordance with the embodiment; Figures 4a), 4h) and 4c) illustrate a top side view of a thermal conductor used in a thermal 5 management module in accordance with the embodiment; and Figures 5a), 5b) and 5c) illustrate a side view of a thermal conductor in accordance with the embodiment.

We now describe a gas analysis system 100 in accordance with the embodiment with reference to Figure la. Although the embodiment is described using the example of a gas analysis system, it will he appreciated that a liquid can be used as the subject of the analysis rather than a gas.

The gas analysis system 100 comprises a hardware system 102 and a sample cell 104. The sample cell 104 comprises a temperature sensor 104a, a pressure sensor 104b and a humidity sensor 104c. The sample cell 104 is configured to receive a sample of gas which is filtered through filter 106 so that it enters the sample cell 104 substantially free of the dust and small particles that may enter the system 100 otherwise. The sample cell 104 further comprises an exhaust 108 configured to enable the sample to he continuously fed out of the sample cell 104.

The sample cell 104 further comprises an entrance window which allows the light to enter the sample cell 104.

The sample cell 104 further comprises an exit window which allows the light to leave the sample cell 104.

The sample cell 104 is configured to receive light from a light emitting diode mounted to a 30 thermal management structure as part of lighting arrangement 112 via input coupling optics 114 which enables the light emitted by the light emitting diode to be reflected into the sample cell 104 via the entrance window. The light emitting diode is powered by driving circuit 116 and uses the temperature control module 118 to control the operating temperature of the light emitting diode. The lighting arrangement 112 and the temperature control module 118 will be described in more detail in Figures 2a, 2b and 3.

The received light is received in the sample cell 104 after it has been emitted by the light emitting diode and it is reflected off reflective surfaces inside the sample cell 104. The path of the light when it is inside the sample cell 104 is illustrated in Figure lb by the dotted line. The light is passed out of the lighting arrangement 112 and is reflected into the sample cell 104 by the input coupling optics 114.

The sample cell 104 guides the light through its interior using reflective surfaces on its walls. After the light has followed a path through the interior of the sample cell 104 the light exits the interior of the sample cell 104 via the exit window where it is reflected onto spectrometer 110 by output coupling optics 120.

Configured in this way, the sample cell 104 becomes a multipass absorber as the light is reflected multiple times in the sample cell and therefore takes multiple paths before it reaches the output coupling optics 120 where it is received by the spectrometer 110. That is to say, spectral components of the light will be absorbed by the sample within the sample cell 104 as the light passes through the sample cell 104.

Input coupling optics 114 may be formed by an off-axis parabolic minor and an achromatic doublet lens which collect and transmit the light emitted by the lighting arrangement 112 into the sample cell 104 through the entrance window 114a of sample cell 104. The function of the input coupling optics 114 is to enable the light to pass into the sample cell 104.

Output coupling optics 120 may he formed by a planoconcavc lens and an off-axis parabolic minor which reflects the light (after it has passed through the sample cell 104 30 and the exit window 120a of sample cell 104) into the spectrometer 110. The function of the output coupling optics 120 is to enable the light to leave the sample cell 104.

The sample cell 104 may be a White cell. This is a multipass absorption cell which consists of multiple mirrors and transducers. The mirrors may be positioned in the cell at positions which reflect the light after it has been reflected into the cell by input coupling optics 114. The multiple positions at which the light is reflected mean the light takes multiple paths through the sample cell 104. In an example of such a cell, one larger spherical concave mirror (Ml) is provided in a space on an inner wall between the entrance window and the exit window and two spherical concave mirrors (M2 and M3) on a wall directly opposing the wall on which mirror M 1 is positioned.

Temperature sensor 104a, a pressure sensor 104b and a humidity sensor 104c may form transducers which are fixed to the internal wall of the White cell. The information gathered by the temperature sensor 104a, pressure sensor 104b and humidity sensor 104c are used to monitor and correct the measurement results obtained by gas analysis system 100 using known algorithms which are programmed into a control unit 102.

Temperature sensor 104a converts a measurement indicative of the internal temperature of the sample cell 104 into an electronic signal and may take the form of a thermistor, thermocouple or a resistive temperature detector. Pressure sensor 104b converts a measurement indicative of the internal pressure of the sample cell 104 into another electronic signal. As temperature and pressure can influence the concentration of the sample in the sample cell 104 it may he necessary to correct the measurement results obtained from the sample cell to correct for the internal temperature and pressure of the interior of the sample cell 104. Humidity sensor 104c also converts a measurement indicative of the internal humidity of the sample cell 104 into an electronic signal. Water vapour or carbon dioxide has strong spectral absorption at infrared wavelengths between 0.7 1.ma to 2.5 p.m and it may necessary to remove this influence if it is suspected that it is influencing the results.

The related electronic signals of indicative of internal temperature, humidity and pressure 30 are measured by the transducers measurement module 117 in real time.

The spectrometer 110 is configured to convert the light received from the output coupling optics 120 into raw spectrum data after it has passed through the output coupling optics 120. The spectrometer 110 may have hundreds or thousands of detection channels each configured to detect light of a specific wavelength as it comes from the output coupling 5 optics. The spectrometer outputs an optical spectrum of the received light for the spectral analysis which is to be performed by the hardware system 102. This is representative of the optical wavelengths which are contained in the received light which is output through the output coupling optics after passing through the sample cell 104. The optical wavelengths which are contained in the received light arc indicative of the compounds which are in the 10 sample contained within the sample cell 104.

The spectrometer 110 then feeds the spectrum data into the hardware system 102. The hardware system 102 is configured to process the received raw spectrum data and match the processed spectrum data with the known optical spectra of gases such as, for example, benzene, toluene, ethylbenzene and xylene. The hardware system 102 may store spectrum data related to many other gases or other compounds or components of the sample in sample cell 104 which can he detected using the gas analysis system 100. The hardware system 102 can retrieve the spectrum data from storage and use known spectroscopy algorithms to process the raw spectrum data to identify components of the light detected using the spectrometer 110.

The spectrometer 110 may be a Czerny-Turner spectrometer which consists of two concave mirrors, a grating and slit as well as a linear or two dimensional image sensor. The image sensor may he a charged coupled device, complementary metal-oxide semiconductor-based device, a negative channel metal oxide-based device or an indium gallium arsenide-based device. The incident light enters the spectrometer through the slit and the sampling time of the image sensor can he configured dynamically.

This enables the gas detection system 100 to indicate the presence of specific gases. Using 30 a UVC-band light emitting diode is particularly useful for benzene, toluene, ethylbenzene and xylene but other light emitting diodes can be used to configure the gas detection system 100 to determine the presence of other species in a sample.

We illustrate, using the graph in Figure lc, the absorption spectrum for benzene, toluene, Ethylbenzene and Xylene which can be used by the gas analysis system 100 to determine the presence of these compounds in a sample gas.

The hardware system 102 may display an output which describes the sample in the sample cell 104 as a spectrum and as components to indicate the presence of species which are identified using the algorithms used by the hardware system 102.

The measured data from sensors 104a, 1046, and 104c may also be displayed as they may be important in being able to determine any anomalies in the results. Each of temperature, pressure and humidity may influence the light intensity in accordance with the formula: 71.

I(A,L)=I0(A.)exp TIL C p j(l))-£ "(A,1)- ,0c11 +N(A) \.o Where: J (A, L) : the light source intensity at the wavelength A at the end of light path 20 ai (A, p,T) : the absorption cross-section of a species j at the wavelength of A p: pressure of sample cell T: temperature of sample cell /0(2): the light source intensity at the wavelength A p,(l): the number concentration at the position 1 along the light path (A, L): Rayleigh extinction e" (A, L): Mie extinction N(A): photon noise Hardware system 102 receives input from each of the spectrometer 110, the lighting arrangement 112, the temperature control module 118, communications module 156 for receiving data from wireless or wired networks, data storage 158, a display unit 160, a battery fuel gauge 162 which measures the available battery capacity for the gas analysis system 100, a battery management system 164, a navigation unit 166 which processes location data for the system 100, the measurement from the pressure, humidity and temperature sensors (104a, 104b and 104c), a sampling pump or fan168 which is configured to pump the sample out of the sample cell 104. The hardware system 102 is illustrated in Figure ld.

The lighting arrangement 112 is configured to receive input from the in hardware system 102 in that the hardware system 102 is used to control the lighting arrangement 112, i.e. input is received to switch the light emitting diode on or off and, as detailed below, at which driving current. The hardware system 102 in turn receives feedback from the lighting arrangement 112 to indicate the light emitting diode is on and emitting light. The lighting arrangement 112 also feeds back information regarding temperature of the light emitting diode to the hardware system 102.

The temperature control module 118 transmits information to the hardware system 102 regarding the temperature of the light emitting diode in the lighting arrangement 112. The temperature control module 118 may also transmit information to the hardware system 20 regarding the ambient temperature surrounding the gas analysis system 100.

The communications module 156 may receive data from a wireless or wired network. This may be in the form of data from another device which may control the gas analysis system, i.e. switch the gas analysis system 100 on or off or even request an update from the gas analysis system 100. A request for an update generates a response which may indicate the ambient temperature, the temperature of the light emitting diode inside the lighting arrangement 112 and the available battery capacity. The communications module 156 may also contain ports for USB devices which can enable data, such as results of analysis performed by the system 100, to be taken from the system 100. An RS232 interface may also be provided. The communications module 156 may also be configured to receive requests from diagnostic devices and software.

The data storage 158 may he in the form of cloud storage or another form of suitable storage which can store data generated by the gas analysis system 100. The hardware system 102 may receive input in the form of data retrieved from data storage responsive to a request for the said data. The hardware system 102 may also issue requests to the data 5 storage 158 for data to be stored. The data storage 158 may also store spectroscopic data regarding compounds which may be of interest to users of the system 100. The system 100 may retrieve the data related to compounds during use of the system to analyse a sample contained in the sample cell 104. This data may then he used to solve the absorption spectra of the received light with compounds that are present in the sample which has been 10 analysed.

The display unit 160 is configured to display data generated by the gas analysis system 100 including data generated by generated by spectrometer 110. The display unit is also configured to generate the output of the gas analysis which is performed by the hardware system to indicate the presence of specific compounds in the sample which is being analysed. The display unit 160 may be a touchscreen which can receive input to configure the parameters of the gas analysis system 100 and may he used to switch the system 100 on or off.

The battery fuel gauge module 162 provides a measurement of the available battery capacity of the batteries used to power gas analysis system 100. The battery management module 164 provides functionality which enables the batteries to be managed. The batteries are lithium ion batteries.

The navigation unit 166 records the position of the gas analysis system 100 in real time and may support GPS (Global Position System), BDS (Bcidou Navigation Satellite System) or any other suitable navigation systems.

The light is provided to the gas analysis system 100 by a light emitting diode as part of 30 lighting arrangement 112. The light emitting diode is configured to emit light in the UVC band, i.e. wavelengths in the range of 200 nanometers to 280 nanometers. However, other light emitting diodes may he used, including infrared light emitting diodes and light emitting diodes which emit light in the UVA and UVB bands.

When compared to a deuterium or xenon lamp, which are typically used in gas detection 5 systems, the operating lifetime of a light emitting diode based light source is extensive. The lifetime of a deuterium lamp is typically about 2000 to 4000 hours. The typical lifetime of a light emitting diode is 10000 hours.

The use of light emitting diodes provides significant technical effects in a gas analysis system. They require significantly lower voltages than Xenon or Deuterium lamps, for example, and also generate substantially less heat. Additionally, light emitting diodes are generally very small compared to a Xenon or Deuterium lamp which means that the overall system 100 can he made to he much smaller or even mobile -enabling it to he used in remote environments where power supply may be a problem. Light emitting diodes also generate significantly lower amounts of heat compared to a xenon or deuterium lamp.

The low operating voltage of light emitting diodes also makes them suitahle for the intrinsic safety requirements of ATEX or IECEx regulation as the requirement for large amounts of electrical power is reduced and the reduced heat generation compared to Xenon 20 or Deuterium lamps reduces the overall thermal footprint of the gas analysis system 100.

Additonally, the use of a light emitting diode which emits light in the UVC band is useful for the detection of benzene, toluene, Ethylbenzene and Xylene and 1, 3 butadiene as they have absorption spectrums in the UVC band as illustrated in Figure 1 c.

That is to say, the lighting arrangement 112 can be configured according to the compounds that are being monitored. A gas analysis system which is configured to determine the presence of compounds with absorption spectra in the UVC hand is particularly suitable for gas analysis systems which are used in explosive environments, such as those specified in the ATEX and IECEx regulations.

We now describe the driving circuit 200 for a light emitting diode which provides light to be used in a gas analysis system 100 as part of lighting arrangement 112 in accordance with the embodiment with reference to Figures 2a and 2b.

Driving circuit 200 may comprise a power source 206, a fixed low dropout linear regulator (LDO) 210, an output voltage configuration resistor 208 and a fixed constant current source 212 to output a fixed constant current for driving the light emitting diode 216, which emits light with the fixed and stable output intensity. The output voltage of the fixed low dropout linear regulator (LDO) 210 is configured by the output voltage configuration resistor 208 to drive the fixed constant current source 212.

Driving circuit 200 may comprise a plurality of power supply selection switches 202A to N. Each power supply selection switch corresponds to a selection which can he made using the input module 204. The input module 204 may be a user interface which receives the selection of a fluid detection sensitivity and measurement range which is required for the environment in which the system 100 is going to be positioned. The input module 204 may also he coupled to another system, such as a third party system, which provides an input which selects the sensitivity for the system 100.

A selection of a particular fluid detection sensitivity and measurement range corresponds to a specific power supply selection switch. This causes the respective power supply selection switch (202A to N) to move into the on position or status from the off position to configure the output voltage of the low dropout (LDO) linear regulator 210 to supply a respective current source which drives the light emitting diode 216 to emit light at a specific level of constant intensity corresponding to the required level of sensitivity by changing the output voltage of the LDO linear regulator 210 to a level required to achieve the selected level of sensitivity when the current supplied from the respective current source is supplied to the light emitting diode 216. A configuration current is conducted through the respective output voltage configuration resistor 208A to N. The power supply selection switch (202A to N) may be any type of relay or transistor.

The respective output voltage configuration resistor (208A to N) provides, as an input to the low dropout (LDO) linear regulator 210, an input configuration voltage which is fed to the low dropout (LDO) lineal-regulator 210 which outputs a constant output voltage The constant output voltage output by the LDO linear regulator 210 is then fed to a respective constant current source 212A to N. A suitable constant current source may be a field-effect transistor but can be any arrangement of circuitry which provides a current output which is constant.

The selection of the particular sensitivity and measurement range also causes the respective constant current selection switch 214A to N to move into an on position from an off position. The constant current switch then delivers the constant current to the light emitting diode 216 from the respective constant current source. The constant current selection switch (214A to N) may be any type of relay or transistor.

The delivery of the constant current to the light emitting diode 216 causes the emission of light from the light emitting diode 216.

As described in respect of Figures la to lc, the light emitting diode in gas analysis system 100 is configured for UVC-band emission, i.e. the light emitted by the light emitting diode 216 emits light within the UVC range of wavelengths (between 200 nm and 280 nm). For simplicity and brevity, in this example the light emitting diode 216 is configured for such a system and so emits light within the wavelength range 200 nm to 280 nm responsive to the delivery of the constant current from the selected constant current source.

The constant driving current enables the light emitting diode 216 to maintain a stable light output. The stable light output is achieved as the driving current is maintained at a constant level by the constant current source which reduces the fluctuations in the light output as the operating temperature is kept relatively constant which overcomes the effect on the performance of the light emitting diode 216 from ambient temperature.

The intensity of the light output by light emitting diode is dependent on the driving current. The selection of the driving current using the circuit 200 enables the intensity of the light to be selected and the light to he maintained at a stable intensity during use of the gas analysis system 100.

A specific intensity corresponds to a minimum detection limit for the gas analysis system 5 100. Intensity fluctuations can reduce the reliability of the minimum detection limit as it cannot be guaranteed. Therefore, reducing or even completely alleviating the intensity fluctuations provides a more accurate system for analysing the compounds present in a sample which is fed into the sample cell 104. This is clearly advantageous in an explosives environment where time can he at a premium if benzene or another dangerous compound 10 has escaped into the environment in too high a quantity.

We now describe the thermal management of the light emitting diode 216 used in gas analysis system 100 using thermal management module 300 with reference to Figure 3. This thermal management module 300 may be part of lighting arrangement 112.

Thermal management of a light emitting diode 216 is essential for the stable operation of a gas analysis system 100 which uses the light emitting diode 216 as the light source. Too much heat across the P-N junction in the light emitting diode 216 can cause intensity fluctuations in the light emitted by the light emitting diode 216. Too much heat can also reduce the lifetime of the light emitting diode 216.

That is to say, ineffective thermal management of the light emitting diode 216 can compromise (he lifetime and reliability of the light emitting diode 216. In turn, effective thermal management will extend the lifetime of the light emitting diode and maintain a constant level of reliability and stability in the intensity of the light emitted by the light emitting diode 216.

Thermal management module 300 may comprises a window 302 to enable light emitted by light emitting diode 304 to pass out of the module 300. Light emitting diode 304 is configured to receive a constant driving current in accordance with the light emitting diode 216 described in relation to Figure 2 and to emit light in the UVC band. The driving circuitry 200 may he fed to the light emitting diode 304 between the thermal conductor board 306 and the bottom surface of the light emitting diode 304 in accordance with any known means. Thermal conductor board 306 will be described in more detail below.

A thermal transducer 308 is positioned adjacent and contacts the thermal pad of the light emitting diode 304 through the thermal conductor board 306, and is arranged to measure the operating temperature of the thermal pad of light emitting diode 304 as this is an effective indicator of the temperature across the respective P-N junction. Thermal transducer 308 converts a measurement indicative of the temperature of the thermal pad of light emitting diode 304 into an electric signal, which is further measured by the temperature control module 118 to determine a value of the measured temperature.

The temperature control module 118 is configured to compare the value of the measured temperature with a configured operating temperature which is the temperature at which the light emitting diode 304 is supposed to operate. The configured operating temperature of light emitting diode 304 will be a specific temperature between 5 degrees Celsius and 25 degrees Celsius.

After comparing the measured temperature and the configured operating temperature of light emitting diode 304 in real-time to determine whether the measured temperature is higher or lower than a configured operating temperature, the temperature control module 118 outputs a positive or negative pulse-width modulation (PWM) signal, which is based on the proportional-integral-derivative (PID) control principle. The thermal transducer 308 is attached to the thermal conductor board 306.

In warmer environments where gas analysis system 100 may be exposed to higher ambient temperatures, out in the desert, say, it is ensured that the measured temperature of light emitting diode 304 will be maintained as the configured operating temperature. When ambient temperature is higher than the maximum configured operating temperature of light emitting diode 304, the temperature control module 118 will output a PWM (Pulse Width Modulation) signal with a first polarity to a full-bridge MOSFETs (metal oxide semiconductor field effect transistor). This signal drives the thermoelectric cooler 312 to generate cooling on its upper surface which is directly attached to the thermal conduct board 306. This will cool the thermal conduct board 306 which will cool the light emitting diode 304. This will cause heat to he driven to the lower surface of the thermoelectric cooler 312 which will cause the lower surface to heat up.

As the thermoelectric cooler 312 is attached to a heatsink the heat on the lower surface is removed by the attached heatsink 314 by conduction as the thermoelectric cooler is 5 attached to the heatsink 314.

The heatsink 314 may be any material which causes the transmission of heat away from the thermoelectric cooler 312. The heatsink 314 may comprise a series of fins to assist in the efficient dissipation of heat away from the thermoelectric cooler 312.

In colder environments where gas analysis system 100 may be exposed to colder ambient temperatures, in the Siberian tundra, say, it is ensured that the operating temperate of the light emitting diode 304 will also he maintained as the configured temperature.

When the ambient temperature is lower than the configured temperature of the light emitting diode 304 it may cause a cooling effect which will reduce the operating temperature of the light emitting diode 304 to a temperature below a minimum operating temperature. Upon a determination that the operating temperature of the light emitting diode 304 has dropped below a minimum operating temperature the temperature control module 118 is configured to determine the drop in temperature of the light emitting diode 304 below the minimum operating temperature and will output a PWM signal with a second polarity to the MOSPETs of the full-bridge driving circuit, which drives the thermoelectric cooler 312 to generale heat on its upper surface which is attached to the thermal conductor hoard 306. This heat will he transferred to the thermal conductor board 306 which will, in turn, cause the light emitting diode 304 to heat up until it reaches a temperature which is in the acceptable range of operating temperatures for the light emitting diode 304.

Additionally, the temperature control module 118 is not solely limited to driving the heating or cooling of the light emitting diode 304 based on the ambient temperature. The temperature control module 118 may drive the heating or cooling using PWM signals of a first or second polarity based on the operating temperature of the light emitting diode 304 as measured by the thermal transducer 308 using similar principles to those described in relation to the temperature of the ambient environment.

That is to say, the temperature control module 118 is configured to measure the operating 5 temperature of the light emitting diode 304 and to adjust the temperature of the Uhl emitting diode 304 dependent upon the ambient environment or the internal environment of the thermal management module 300. The temperature of the light emitting diode 304 is measured using the thermal transducer 308 and the temperature control module 118 which drive the thermoelectric cooler 312 to cool or heat the thermal conductive board 306 for 10 maintaining a stable operating temperature of the light emitting diode 304 within a range of suitable operating temperatures using the Peltier effect.

A fan 316 is provided which assists in the removal of the heat from the heatsink 314. The fan is spaced from the heatsink 314 and is not in contact with the heatsink 314. This means that the vibration of the fan 316 will not be transmitted to the light emitting diode 304. Contact between the fan 316 and any of the other components of module 300 would cause vibration of the light emitting diode 304 at a frequency substantially equal to the vibration caused by the fan 316. Such vibration would cause instability in the light output as it would he transmitted as a wave with a substantially higher amplitude than necessary, which would compromise the measurements of the spectrometer 110 and the performance of the gas analysis system 100.

The thermal conductor board 306 can he any suitable substrate but some arrangements of 25 the substrate arc more advantageous than others for any type of light emitting diode whether it is packaged as a surface mounted device or a transistor outline device.

Figures 4 a) to c) illustrate three versions of the thermal conductor hoard 306 from a topside view.

Figure 4 a) shows the Mei ial conductor board 306 for a surface mounted device light emitting diode with a so-called large thermal pad. The cathode 402 soldering pad and anode soldering pad 404 are provided on the thermal conductor board to drive the light emitting diode as part of the driving circuitry 200. The contact area 504a is also provided on the thermal conductor board 306 to touch the thermal pad of the light emitting diode 304. The contact area 504h is also provided on the thermal conductor hoard to touch the thermal transducer 308. The contact area 504a and 504b are connected.

Figure 4 b) shows the thermal conductor board 306 for a surface mounted device light emitting diode with a so-called small thermal pad. The cathode soldering pad 402 and soldering pad anode 404 are provided on the thermal conductor board to drive the light emitting diode as part of the driving circuitry 200. The contact area 504a is also provided on the thermal conductor board 306 to touch the small thermal pad of the light emitting diode 304. The contact area 504h is also provided on the thermal conductor board to touch the thermal transducer 308. The contact area 504a and 504h are connected.

Figure 4 c) shows the thermal conductor board 306 for a transistor outline device packaged light emitting diode. The contact area 504a is provided on the thermal conductor board 306 to touch the thermal pad of the light emitting diode 304. The contact area 504h is provided on the thermal conductor board 306 to touch the thermal transducer 308. The contact area 504a and 504b are connected. The circular holes 406 and 408 correspond to the position of the anode pinout 402 and cathode pinout 404 across the thermal conductor hoard 306.

Figure 5 a) to c) illustrates the three versions from a side view of the thermal conductor board 306.

Figure 5 a) shows the cathode soldering pad 402 and anode soldering pad 404. Thermal conductor board 306 comprises a lower portion of aluminium substrate 502 which spans the whole the thermal conductor board 306 and two upper portions 504a and 504h which are positioned respectively underneath the light emitting diode 304 and the thermal transducer 308 -not on the underside of the cathode soldering pad 402 or anode soldering pad 404.

Figure 5 h) shows the cathode soldering pad 402 and anode soldering pad 404. Thermal conductor board 306 comprises a lower portion of aluminium substrate 502 which spans the whole of the thermal conductor board 306 and two upper portions 504a and 504b which are positioned respectively underneath the small thermal pad of the light emitting diode 304 and the surface of the thermal transducer 308 -not on the underside of the cathode soldering pad 402 or anode soldering pad 404.

Figure 5 c) shows the cathode pinout hole 406 and anode pinout hole 408. Thermal conductor hoard 306 comprises the lower portion of aluminium substrate 502 which spans the whole the thermal conductor board 306 but does have two upper portions 504a and 504b which are positioned respectively underneath the light emitting diode 304 and the thermal transducer 308. -The aluminium substrate 502 or the upper portion 504a is not on the underside of the cathode pinout hole 406 or anode pinout hole 408.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be capable of designing many alternative embodiments without departing from the scope of the invention as defined by the appended claims. In the claims, any reference signs placed in parentheses shall not be construed as limiting the claims. The word "comprising" and "comprises", and the like, does not exclude the presence of elements or steps other than those listed in any claim or the specification as a whole. In the present specification, "comprises" means "includes or consists of and "comprising" means "including or consisting of'. The singular reference of an element does not exclude the plural reference of such elements and vice-versa. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

CLAIMS 1. 2. 3. 4. 5. 6. 7.A system for analysing a sample of a fluid to determine the presence of compounds in the sample, the system comprising: a light source comprising at least one light emitting diode configured to emit light into a sample analysis chamber, wherein the sample analysis chamber is for receipt of a sample, an output optical coupling unit configured to receive the light output by the sample analysis chamber after the light has passed through the fluid in the sample analysis chamber; and a processing unit configured to spectrally analyse the received light to determine the presence of at least one compound in the sample of fluid.
System according to Claim I wherein the sample analysis chamber is a multi-pass optical absorption cell.
System according to any preceding Claim wherein the system is contained in a portable housing.
System according to any preceding Claim wherein the light emitting diode is configured to emit light in the UVC-band, UVB-band or UVA-band of wavelengths.
System according to any of Claims 1 to 4 wherein the light emitting diode is an infrared light emitting diode.
System according to any of Claims I to 4 wherein the light emitting diode is an ultraviolet light emitting diode.
System according to any preceding claim wherein the system comprises a power supply unit configured to supply a constant driving current to the light emitting diode to cause a stable light output of constant intensity to be emitted by the light emitting diode.
8. System according to any preceding claim, wherein the system is configured to receive an input to select the constant driving current from among a plurality of constant driving currents to cause light of a selected intensity to be emitted by the light emitting diode.
9. System according to Claim 8, wherein the input is received from a user of a fluid analytics system.
10. System according to Claim 8, wherein the input is received from a component of a fluid analytics system.
11. System according to any of Claims 7 to 10, wherein the power supply unit comprises a plurality of constant cut-rent sources each corresponding to a constant driving current.
12. System according to any of Claims 7 to 10, wherein the power supply unit comprises a plurality of switches operable to enable a constant current from a respective constant current source to be transmitted to the light emitting diode.
13. System according to Claim 11 or Claim 12 wherein the constant current source is fed by a linear power regulator configured to output a steady voltage to be fed to the constant current source responsive to the selection of the constant current.
14. System according to Claim 13 wherein the linear power regulator is fed by a voltage configuration resistor selected by a power supply selection switch responsive to the selection of a corresponding constant current.
15. System according to any preceding claim, wherein the light emitting diode is mounted to a thermal management module configured to gradiate the operating temperature of the light emitting diode.
16. System according to Claim 15, wherein the thermal management module is configured to gradiate the temperature of the light emitting diode responsive to a driving signal from a thermal control module configured to determine the operating temperature of the light emitting diode.
17. System according to Claim 16, wherein the thermal detection module comprises a thermal transducer mounted on the thermally conductive layer to measure the temperature of light emitting diode.
18. System according to Claim 15 wherein the thermal management module comprises a thermoelectric cooler configured to drive heat toward the light emitting diode if the operating temperature drops below a temperature threshold.
19. System according to Claim 16 wherein the thermal management module comprises a thermoelectric cooler configured to draw heat away from the light emitting diode if the operating temperature rises above a temperature threshold.
20. System according to Claim 18 or 19 wherein a thermally conductive layer is disposed between the light emitting diode and the thermoelectric cooler to enable the conductivity of heat between the light emitting diode and the thermoelectric cooler.
21. System according to any of Claims 16 to 20 wherein the light emitting diode and the thermal management module arc scaled in a housing comprising a window to enable the light emitted from the light emitting diode to pass out of the housing into the fluid analysis system.
22. System according to Claim 21 wherein the housing comprises a first metal enclosure to enclose the light emitting diode and the thermal detection module and a second metal enclosure to enclose the thermoelectric cooler.
23. System according to Claim 22 wherein the first metal enclosure and the second metal enclosure are separate.
24. System according to Claim 20 wherein the thermally conductive layer contacts the thermoelectric cooler.
25. System according to any of Claims 20 to 24 wherein the thermoelectric cooler is attached to a heatsink.
26. System according to Claim 25 wherein the arrangement further comprises a fan spaced from the heatsink to draw heat away from the heatsink.
27. System according to Claim 20 wherein the thermally conductive layer comprises an aluminium substrate.
28. System according to Claim 20 wherein the thermally conductive layer further comprises aluminium portions disposed underneath the thermal detection module and the light emitting diode.