Patent Application
20140036257
The present invention relates to an analyzer instrument and to a method for operating such an analyzer instrument.
The control and optimization of many industrial processes typically involves the online analysis of specific properties of the processed substance, e.g. fluids (gasses, liquids), solids, or solid/fluid mixtures. For many applications, it is advantageous or even necessary to perform this analysis based on optical measurements (e.g. transmission, reflection, scattering of light). Optical measurement has many advantages: It offers non-intrusive in-situ analysis, spectral “fingerprint” analysis, immunity to electromagnetic fields, and intrinsic galvanic insulation between the process and the analyzer.
For some industry segments (e.g. chemical and petrochemical industries), there are special requirements imposed on the electronics of such a device if operated in a hazardous environment. For example, in order to guarantee safe analyzer operation in explosive environments the housing of the electronics of the device has to satisfy certain standards. The energy required for powering electronic circuits may suffice to ignite an explosive gas.
Known are thus optical analyzer devices that are suitable for use in explosive environments by either encasing the instrument in a sealed or purged housing or by the use of optical fibers linking the analyzer electronics to the sensor, such that only the sensor is located in the harsh environment.
WO 2009/146710 A1 discloses a pipe system comprising a remote output system and a gas sensing station that includes a photoacoustic spectroscope. For safety reasons, the remote system, which is part of the analyzer instrument and is located remotely in non-hazardous atmosphere, and the gas sensing station are linked only optically. The light source for the sensing light of the spectroscope is located in the remote part and its light is fed through an optical fiber from the safe atmosphere to the gas sensing station in the sensing area. The system provides a further light source as part of a transducer that is located in the sensitive area. The light of the latter source is used for conversion of the electrical measurement signal into an optical measurement signal that is transmittable through the previously mentioned optical communication link to distant analyzer electronics.
EP 0 289 200 A2 describes an invention that relates to a device for optical investigations of a fluid medium by means of light. Intrinsic safety is achieved by placing the electronics remotely such that only the sensing part is exposed to explosive or harsh environments. Again, the sensing part is linked to the analyzing electronics by means of optical fibers.
The prior art thus comprises devices that separate the energy-intensive electronic parts, in particular the light source for the light for the measurement, from the explosive gas and consequently also from the analyzer head, while providing for an optical link between the components to guarantee the necessary communication in a safe way. Other devices separate the energy-intensive electronics from the hazardous environment by enclosing the electronics in purged or sealed housings.
These strategies impose a significant extra effort and an additional cost burden on the customer of such devices.
It is one of the objects of the present invention to provide an analyzer instrument comprising electronics including a light source for optical measurements, wherein the analyzer instrument is safely operable in a hazardous environment.
This and other objects are achieved by an analyzer instrument according to the claims. Advantageous embodiments are given in the description. Throughout this application, terms like “preferable”, “preferred”, “in particular” or the like denote or relate to embodiments that are optional only.
The present invention specifically provides an analyzer instrument for optically measuring at least one property of a test medium, in particular a fluid, but also any other medium which can be analyzed by using a light beam, said analyzer instrument comprising
Further said analyzer instrument includes and/or is coupled to a power source via a source wiring.
Said power management unit distributes energy from the power source via a buffer wiring to at least said light source, and via a further wiring to at least said light detection unit and/or to said data management unit.
Further, said data management unit is adapted to exchange measurement data measured in said light detection unit via a signal wiring with said light detection unit and directly or indirectly with a receiving unit. In accordance with the invention, said analyzer instrument is adapted to be operated in a potentially hazardous environment, in that at least in the source wiring and/or in said further wiring any current is limited to a current smaller than or equal to 100 milliampere, and any voltage is limited to a voltage smaller than or equal to 30 volt.
The current that the analyzer instrument draws is less than 100 milliampere, and the energy it dissipates is less than 50 milliwatt, preferably less than 35 milliwatt, and more preferably less than 25 milliwatt on average. According to the International Standard IEC 60079-11, these values qualify the analyzer instrument as a simple apparatus. However, since the analyzer instrument stores energy amounts of several millijoules, it is not to be considered as a simple apparatus and protective measures have to be taken in order to ensure intrinsic safety of the device. An explosion in a hazardous environment can occur by thermal ignition or by ignition by sparks.
A hot surface exposed to the hazardous environment can cause thermal ignition by spontaneous combustion. This is why every hazardous area has a temperature classification (see Table 1 for a listing of the temperature classifications according to International Standard IEC 60079-0). Let's take one example of how temperature classification works. A hazardous area classified as T4 risks explosion if any surface gets hotter than 135° C. Faulty motor windings, for example, can create such a high temperature very quickly. Any piece of equipment used inside this particular hazardous area must not be capable of generating a temperature greater than 135° C. Only equipment rated at T4, T5, or T6 would be allowed in this hazardous area.
The surface temperature of any component in analyzer instrument electronics should preferably be smaller than or equal to a maximum surface temperature (see Table 1).
As can be seen from Table 1, there are several temperature classes. The maximum surface temperature may vary, depending on the environment, where the electronics is placed, e.g. ambient temperature and gas species (see International Standard IEC 60079-0). By keeping the surface temperature below said maximum surface temperature, it is ensured that no such surface ignites an explosive gas mixture thermally. Limiting the surface temperature is achieved by having low thermal resistance between electronics and air and by limiting the power and/or by providing corresponding structural cooling and/or dissipation means.
Capacitors store energy in the electrical field between their plates, and this energy can present itself as a spark in the hazardous area. A capacitive circuit supplied by a voltage accumulates energy equal to one-half the capacitance times the square of the voltage. Let us imagine there is a switch connecting the two plates of the capacitor. When the contacts close in a capacitive circuit to discharge a capacitor, a spark can form just before the contacts touch. Because the contacts are almost touching, the size of the spark is small. The switch can also represent field wiring which is accidentally shorted. Thus the maximum capacitance of an intrinsically safe device is limited, depending on the maximum voltage and on the worst-case gas groups (i.e. IIA, IIB and IIC as per IEC 60079-0).
The energy stored in the magnetic field of an inductor can be released in the form of a spark in the hazardous area. An inductor L, fed by a constant current I, stores an energy equal to one-half the inductance times the square of the current. Let us imagine there is a switch that can interrupt the current. When the switch opens, the inductor “tries” to keep current flowing from A to B as it had been before the switch was opened. The voltage which attempts to continue this current flow is determined by the equation V=L(di/dt). The term “di/dt” is the change in current di in the time interval dt. This number can be very large, because the current will change from its previous value to zero when the switch is opened. If the inductance is large, then the voltage developed (which is equal to L*di/dt) is large, and a spark could appear between the two electrodes formed by the switch opening. The switch according to this example can also represent field wiring which is accidentally cut. Thus the maximum inductance of an intrinsically safe device is preferably limited, depending on the maximum current and on the worst-case gas groups (i.e. IIA, IIB and IIC as per IEC 60079-0).
The ability to ignite the hazardous atmosphere also depends on the open circuit voltage (V=VOC), and the short circuit current (ISC=V/R). Energy from the power supply could be released in the form of a spark at the point of the circuit opening or shorting. Thus the maximum current and/or voltage in an intrinsically safe device are limited, depending on the worst-case gas groups (i.e. IIA, IIB and IIC as per IEC 60079-0).
In order to prevent sparking, the current and voltage values related to the analyzer instrument according to invention are restricted. These restrictions also impose constraints on capacitance and inductance of electronic components, which will be discussed further below. Specifically, this means that, in said further wiring (and/or in the source wiring), safe restrictions are imposed on the current, voltage, and/or power which under operation can be reached. The primary limit is directed to the maximum temperature the device can have. It also depends on the gas species in the environment of the application and on the surface temperature and/or sparking risk of the electronics. From this application and layout specific voltage and current limits are deduced. This even under conditions, where the housing of the device is not sealing the interior comprising the electronics from the surrounding hazardous environment, so under conditions where the electronics and the wiring can be exposed to the hazardous environment (however a sealing housing is also possible for double protection). Preferably, the electronic/electric components of the device are further chosen that they internally wherever exposed to the environment never reach the maximum limit values of these quantities.
In the interest of safety, it is desirable to meet a standard that limits the energy at disposal of the instrument to a value that any compliant circuit functions properly under normal operating conditions while it is safe even under fault conditions. Intrinsic safety is such a standard. However, this standard of intrinsic safety has so far never been applied to such optical devices. Intrinsic safety has hitherto been a type of protection based on the restriction of electrical energy for electronics, i.e. within an apparatus and of interconnecting wiring exposed to a potentially explosive atmosphere, to a level below that which can cause ignition by either sparking or heating effects. The requirements for intrinsically safe systems are defined by “The International Electrotechnical Commission” (IEC) and provided in the IEC publication IEC 60079-25.
In this application, preferably, any current I is limited to a current (Imax) smaller than or equal to 100 milliampere, and any voltage U is limited to a voltage (Umax) smaller than or equal to 30 volt. In the following, several embodiments are discussed.
For example, Imax is preferably smaller than or equal to 50 milliampere, more preferably smaller than or equal to 30 milliampere, more preferably smaller than or equal to 25 milliampere, and in particular between 0.01 milliampere and 20 milliampere.
Umax is preferably smaller than or equal to 24 volt, preferably smaller than or equal to 20 volt, more preferably smaller than or equal to 15 volt, and in particular between 0.01 volt and 12 volt.
The total dissipated power Pdiss by the analyzer instrument is in average smaller than or equal to 50 milliwatt, preferably smaller than or equal to 35 milliwatt, more preferably smaller than or equal to 25 milliwatt, more preferably smaller than or equal to 20 milliwatt, and in particular between 0.001 milliwatt and 15 milliwatt.
The maximum overall average power consumption Pmax of the analyzer instrument is preferably smaller than or equal to 200 milliwatt, preferably smaller than or equal to 112.5 milliwatt, more preferably smaller than or equal to 60 milliwatt.
The above stated limits do not necessarily apply for the buffer wiring, but they can also be applied to the buffer wiring.
The maximum capacitance Cmax and the maximum inductance Lmax allowed for any electronic component of an intrinsically safe device depend on Imax and Umax and on the environment (see e.g. International Standard IEC 60079-11).
In the case that Imax=100 milliampere, any capacitor of the analyzer instrument that stores momentarily releasable energy in the analyzer instrument according to invention has a capacitance that is smaller than or equal to Cmax=80 microfarad, preferably smaller than or equal to Cmax=15 microfarad, and more preferably smaller than or equal to Cmax=3 microfarad. These values can be chosen in dependence on the environment as per the International Standard IEC 60079-11.
In the case that Umax=15 volt, any inductor that stores momentarily releasable energy in the analyzer instrument according to invention has a inductance that is smaller than or equal to Lmax=8 millihenry. These values can be chosen in dependence on the environment as per the International Standard IEC 60079-11.
Should any electronic component exceed these upper limits (T1 to T6, Imax, Umax, Cmax, Lmax), special measures have to be taken to ensure intrinsic safety. Such measures can be:
In the context of the present invention, a “property of a test medium” includes a parameter or a property of the test medium that is directly or indirectly accessible to measurement by an optical measurement, for example, a gas concentration, like oxygen or CO2 concentration, a pH value, a refractive index, a turbidity or particle concentration, like suspended solids, such as crystals, biological cells or ash and dust, or combinations thereof, etc. A property of a test medium further includes a level, a distance, proximity, a position, an object ranging, or similar measurement parameters.
The term “test medium” refers preferably to a gas or gas mixture. Test medium can, however, also include solids (e.g. a bulk solid), fluids (e.g. a gas or a liquid of an organic or inorganic chemical, like oil or water, including suspension of particles and/or droplets in gas), or a mixture thereof (e.g. a slurry, an emulsion, or a liquid or gas with suspended particles). The test medium can be opaque or transparent. Preferably, a test medium is substantially fluid, e.g. with a particular refractive index, and, in particular, the test medium is a gas or a liquid. Preferably, the test medium scatters, reflects, and/or transmits light. In particular, the test medium may be a fluid containing particles, e.g. suspended solids, such as crystals, biological cells, ash, dust, or other solids or mixtures thereof. The test medium can also contain an interface between two areas with the same or, in particular, different properties, such a property being in particular a refractive index. The test medium can further be an analyte with absorption-related parameters.
The test medium can be in substantially static state, or it can be in a dynamic state, e.g. a revolving, flowing or a streaming state. It may be a liquid or a solid that evaporates into a gas, or it may be a solid that is partly molten, wherein the molten substance is in a substantially static or a dynamic state.
The term “environment” is to be understood as the volume in which the analyzer instrument is at least partly, preferably completely, located and/or which the instrument can affect directly. The environment may be the test medium itself, part of the test medium, or a medium that at least partly includes or is close to or covers/encloses the test medium. In this context, the term “close” means that the corresponding distance is comparable to the dimensions of the measurement equipment. In particular, the environment can be a volume that contains a potentially explosive gas that may evaporate from a liquid test medium.
The test medium and the environment can be safe (e.g. an inert gas) or hazardous (e.g. an inflammable liquid as the test medium and an explosive gas as the environment of said liquid). For example, the test medium can be safe, while the environment is hazardous.
At least one light source may be any light source that can be operated for the measurement with the available power under these limitations, in particular it can be a semiconductor diode laser, preferably a vertical cavity surface emitting laser (VCSEL), preferably with a feed voltage smaller than or equal to 5 volt, preferably 3 volt, in particular between 0.01 volt and 2 volt. In addition such a laser may be characterized by a supply current smaller than or equal to 200 milliampere, preferably smaller than or equal to 100 milliampere, more preferably smaller than or equal to 50 milliampere, most preferably smaller than or equal to 30 milliampere, and in particular between 0.01 milliampere and 0.5 or 30 milliampere.
A VCSEL device produces light in the infrared region (typically between 670 nm and 2000 nm). An example of a VCSEL is a device that is based on an indium phosphide system, with a buried tunnel junction (BTJ) technology. Such a VCSEL has a wavelength typically in the range from 1300 nanometer to 2050 nanometer and is sold by, for example, the company VERTILAS GmbH in Garching, Germany. VCSELs allow comparatively high modulation rates up to 10 gigahertz and offer optical power levels higher than 1 milliwatt while the electrical feeding power is of the order of a few milliwatt. Other VCSELs available on the market have a wavelength range with a lower limit of 670 nanometers (e.g. from the company Optowell). A typical upper threshold current is below 1.5 milliampere at room temperature (depending on the type of VCSEL), which is very advantageous for low-power application. It is a further advantage of a VCSEL light source that it produces coherent light in a rotational-symmetrical and low-divergence optical beam with high efficiency and reliability. VCSELs have an operation temperature range that extends from less than −40 degree Celsius to over +80 degree Celsius. This is advantageous since the industrial market imposes more stringent constraints on analyzer instruments than the environmental monitoring market (e.g. water and waste water) does. For example, the temperature range of operation of an environmental monitoring device is often 0° C. to +50° C. Due to the low operation voltage and current, the VCSEL is thus advantageous for optical low-power devices and, in particular, for devices that are intended to be operated in hazardous environment and where the light source may be the main load, at least time wise. It is further possible to produce VCSEL arrays, i.e. arrays of light sources, in a compact and efficient manner. Such a light source array may be used to measure several properties of a test medium simultaneously. Moreover, the narrow wavelength of the VCSEL can be tuned over a wide range (typically 5 nm) by changing the temperature of the VCSEL chip or the injection current through the chip. Those measurement concepts allow spectroscopic investigation of the medium or gas temperature and/or gas pressure measurements. For the purpose of changing the temperature of the VCSEL chip, an electronic component may be provided, such as a Peltier element, which can cool or heat said chip and which is preferably provided in a hermetically sealed housing with said chip.
A light management unit is optional; it depends on the specific application and use, whether this component is provided. The light management unit is adapted for receiving at least part of the light from the light source and for guiding at least part of it to the detection space. It can further be adapted to receive at least part of the light that has interacted with the test medium in the detection space and to guide at least part of said interacted light to the light detection unit, if required. The light management unit may contain elements selected from the group consisting of lens systems, splitters, optical filters, dispersive or refractive optics, light guides, optical fibers, light shields, mirrors, etc., as well as combinations thereof. It must be emphasized that the light management unit may be optional; it is conceivable that the light source emits the light directly to the detection space, and at least part of the light that has interacted with the test medium reaches the light detection unit directly.
The term “detection space” has to be understood as the space containing at least a part of the test medium for interaction with light from the light source, wherein said light, after having interacted with the test medium, is subsequently detected by the light detection unit. The actual volume of the detection space may depend on the light, the beam geometry, and also the test medium, or the measurement method.
In the context of the present invention, “interacted with the test medium” has to be understood as transmitted, absorbed, reflected, refracted, and/or scattered by the test medium. It is also possible that the light is incident from a medium different from the test medium onto an interface of the test medium, whereupon it is, for example, back-reflected into said medium different from the test medium.
The power management unit receives power from the power source via the source wiring. Said source wiring is intrinsically safe, preferably through insulation, and further adapted to exchange data. The power from the power source is preferably electrical power; hence the source wiring, but also the buffer wiring and the further wiring are adapted to conduct electrical power. Generally, the transport of electrical energy entails a loss of energy, which has to be considered. The source wiring as well as the signal wiring can be 2-wire connections adapted for transmittal of both data and energy simultaneously. The data transmitted from the analyzer instrument via the source wiring is received by the receiving unit. Preferably, the receiving unit is a standard device that provides measurement data received via a 2-wire connection for further processing or storing, e.g. by a computer. The receiving unit may be integral to the power source or it may be a separate unit. The energy transmittal through the source wiring to the power management unit is preferably achieved with a maximum transmitted voltage of 15 volt and a maximum current of 25 milliampere. Other energy forms are, however, also conceivable, such as light or kinetic energy in form of a flowing fluid or streaming gas, when the corresponding energy conversion means are provided. The energy transfer connections have to then be adapted accordingly. From the power management unit, the power for the operation is further distributed at proper voltage and current levels to the different energy-consuming components via the further wiring. Preferably, the power management unit contains a programmable micro-controller (e.g. from the MSP430 family) that is adapted to turn on/off different parts of the circuit. Advantageously, said micro-controller is also adapted to receive measured data, e.g. a measurement value with a corresponding signal-to-noise ratio, and to control the different parts of the circuit in view of received data. Said further wiring may be adapted to transport data from and to the components, where necessary, and may particularly be a 2-wire connection. It is, however, also possible, to have separate connections for the energy and the data transmission, or, alternatively, to at least partly transmit the data optically, preferably by use of optical links, or even wirelessly by means of known technology.
Under the term “2-wire connection” it is understood that a connection uses only two wires to transmit both power and data. If more power and/or more data are to be transmitted, a second pair of wires may be used for feeding the instrument. A possible 2-wire solution is the analogue signaling technology known from prior art as 4-20 mA. Devices using this standard are power constrained per se.
The power source can be located remotely from the analyzer instrument, preferably outside the hazardous environment, particularly in a safe environment, wherein all other elements of the analyzer instrument may be arranged in a compact manner and preferably on one or several platform boards or platform boards assembly with an optional housing for at least part of the components.
The power source may also be located in the vicinity of the analyzer instrument, in this case preferably on one of said platform boards, e.g. in the form of a battery or energy harvester means that is adapted to harvest energy from the test medium and/or the environment. However, special care should be taken when the power source is placed in a hazardous environment. Compliance with intrinsic safety has to be achieved, e.g. by choice of a power source that fulfills respective requirements per se, by means of additional components, or by separating the power source and, if necessary, further elements that may cause harm from the hazardous environment by means of a purged or sealed housing. An analyzer instrument with a mobile source, such as battery or an energy harvester, is particularly advantageous since it allows for construction of a mobile analyzer instrument adapted to analyze a test medium at least temporarily independently from any physical link (e.g. an optical or electrical link) for the purpose of energy supply and/or data communication. A low-power device, like the analyzer instrument according to the invention, may be operated by a battery for hours, days, or even months or years, depending on performance and use. Preferably, such a mobile analyzer instrument comprises data storage means and/or a wireless connection to the data receiving unit, or in general, to marshaling cabinets or control cabinets.
The analyzer instrument may comprise an approved intrinsically safe associated apparatus or unit, by means of which Imax, Umax, and Pdiss are ensured in said wiring. This apparatus is in particular a barrier or interface that guarantees intrinsic safety of the analyzer instrument electronics. The apparatus is preferably located between the source wiring and the power management unit. The barrier defines two sides. The side of the power wiring is referred to as before, the other side as behind the barrier. The approved intrinsically safe associated apparatus may contain current and/or power limiter, diodes, and at least one fuse and may be mounted on one of said platform boards. The apparatus may be an active, or, preferably, a passive device, allowing a safe function of the analyzer instrument under normal conditions. Under fault conditions, however, the approved intrinsically safe associated apparatus protects against harm due to the hazardous environment, i.e. it prevents a current and/or voltage and/or energy build-up or release large enough to ignite e.g. an explosive gas. In particular, excess current and/or voltage that may be generated in the analyzer instrument under fault conditions are transferable safely to the approved intrinsically safe associated apparatus. Excess current and/or voltage are to be understood as the part of the respective value that exceeds over a corresponding limit. The apparatus, for example, uncouples the power source from the power management unit in case of power transfer above the limit, thereby avoiding transmittal of harmful amounts of energy to the intrinsically safe device.
In case that the apparatus is located in the hazardous area, it can be installed in an explosion-proof enclosure and/or with explosion-proof seals for connected wires, which are preferably arranged on the enclosure in an intrinsic safety compliant manner. Preferably, the apparatus may be adapted to ensure that, in the source wiring and in the further wiring, Imax is smaller than or equal to 50 milliampere, preferably 25 milliampere, more preferably 20 milliampere and/or wherein the Umax is smaller than or equal to 24 volt, preferably 15 volt, and/or wherein the dissipated power Pdiss is smaller than or equal to 20 milliwatt, preferably 15 milliwatt.
The power management unit may comprise a direct current to direct current converter and back-end electronics, wherein the back-end electronics include components, e.g. for communication reasons, such as a human-machine-interface and a highway addressable remote transducer. The power management unit may further comprise an energy buffer for storing energy. The approved intrinsically safe associated apparatus is preferentially adapted to guarantee intrinsic safety for the amount of stored energy, i.e. it is adapted to safely receive and dissipate said energy. Preferably, the energy buffer consists of or includes a current limiter, a capacitive buffer, and a direct current to direct current converter. Said current limiter ensures that a predefined current limit is not exceeded. Through said direct current to direct current converter, the energy discharge is managed. Intrinsic safety for the capacitance of the capacitive buffer is ensured as described above.
Preferably, the analyzer instrument is adapted to adjust the energy discharge to the buffer wiring, making an adaptive control of the light source powering possible. The capacitive buffer has a typical capacitance of smaller than or equal to 2 millifarad, preferably smaller than or equal to 1 millifarad, more preferably smaller than or equal to 100 microfarad, and in particular between 0.1 microfarad and 50 microfarad.
Said energy buffer can be adapted to release energy in a pulsed manner via a buffer wiring to the light source, which is operable as a pulsed light source. When the analyzer instrument is measuring in a pulsed mode, there are times, during which the buffer is chargeable and times during which the buffered energy is releasable. Buffer charge times depend on the actual analyzer instrument specifications but are typically smaller than or equal to 200 milliseconds, more preferably smaller than 150 milliseconds, and most preferably smaller than or equal to 100 milliseconds, and in particular between 1 milliseconds and 50 milliseconds. Energy buffer charging currents are typically smaller than or equal to 100 milliampere, preferably smaller than or equal to 50 milliampere, and in particular between 0.1 milliampere and 25 milliampere. The released energy is readily usable for at least one component of the analyzer instrument, preferably for the light source.
It is possible, that the light source is operable primarily by the buffered energy. This is advantageous since the readout electronics require a substantial amount of energy during detection and processing and hence impose a significant load. When the analyzer instrument is operated in pulsed mode, the readout electronics may remain in a low-power standby mode while no light is available and the energy buffer is being charged. This charging process is thus performable with a substantial part from the total power available from the power source. When the buffer is to be discharged, the charging stops and the power that has been used for charging is available to the readout electronics, which is advantageous since they have to become active during the energy release from the buffer and the consequent light emission.
In the context of the present invention it has to be understood that the above stated limits for the source wiring and the further wiring may also apply for the buffer wiring at least during the charging phase of the energy buffer. Typically, a buffer charge time is longer than a discharge time, i.e. the length of the following light pulse. It may thus be advantageous to place separate limits for the buffer wiring, particularly during the buffer discharge time. Therefore, the limits for the buffer wiring may be higher than the limits for the source wiring and the further wiring. It is, however, for most applications important, that the requirements for intrinsic safety are complied with at any point in time, i.e. the current in the buffer wiring is to be related to the applied approved intrinsically safe associated apparatus, which has to be chosen accordingly, wherein a discharge current is typically smaller than or equal to 250 milliampere, preferably smaller than or equal to 150 milliampere, more preferably smaller than or equal to 100 milliampere, and in particular between 0.01 milliampere and 50 milliampere, and the corresponding voltage is smaller than or equal to 15 volt, preferably smaller than or equal to 10 volt, more preferably smaller than or equal to 5 volt, and in particular between 0.01 volt and 3 volt. These limits may be higher, when additional protection means are provided, e.g. insulation or separation of the buffer wiring and the thereto connected components, such that the requirements of intrinsic safety are fulfilled in spite of higher values.
The light pulses are preferably of a length smaller than or equal to 50 milliseconds, more preferably smaller than 10 milliseconds, and most preferably smaller than or equal to 5 milliseconds, and in particular between 1 nanosecond and 1.5 milliseconds.
The light detection unit may be a photo detector as known in the field. Said light detection unit is preferably adapted to measure stationary or time varying light intensity and/or frequency and/or pulse duration and particularly to provide a first signal based on an incident light pulse of a predefined length. This first signal is transferable via the further wiring and managed by the data management unit. The management unit may also be integrated into the detection unit. The data management unit is adapted to receive signals and to manage received information in exchange with at least the receiving unit, and preferably also with the power management unit, preferably by means of source wiring and/or further wiring, or alternatively by additional wiring and/or wireless means.
Preferably, the analyzer instrument comprises an analyzer unit that is adapted to analyze said first signal. The analyzer unit is adapted to process said first signal and to produce a second signal, i.e. a measurement value, with a corresponding signal-to-noise-ratio. Such analyzers are known from prior art. They may contain an analogue to digital converters (e.g. of the type LTC1865L ADC). The light detection unit and the analyzer unit may also be a single unit, such as a readout unit. The signal provided by the analyzer unit may be available to the data receiving unit and advantageously also to the power management unit via the data management unit, particularly to a micro-controller. The signal-to-noise ratio may be different for different measurement regimes, e.g. for different test medium conditions or for different light intensities. For low light intensity, the performance (i.e. accuracy and detection limit) is typically worse than for operation regimes where the light intensity is high.
The analyzer instrument may thus advantageously be adapted to adjust the light pulse length, i.e. the electronics, for example the power management unit with the micro-controller, shortens or lengthens the pulse length as a function of said signal-to-noise ratio in view of a target signal-to-noise ratio (e.g. larger than or equal to 3:1, preferably 10:1, in particular between 50:1 and 200:1 depending on the measured property) and/or a target accuracy (e.g. smaller than or equal to 10%, preferably 5%, in particular between 0.01% and 2% depending on the measured property) and/or a target time resolution (e.g. larger than or equal to 1/second, preferably 5/second, in particular between 7.5/second and 15/second depending on the measured property). With a longer light pulse, more data is collectable per light pulse due to the longer exposure time and the corresponding signal-to-noise ratio improves. It is emphasized, however, that longer light pulses require the energy buffer to store larger amounts of energy, which may be problematic when the analyzer instrument is to be operated in harsh environment.
The analyzer instrument may further be adapted to average over the first and/or second signals due to subsequent incident light pulses of the pulsed light source. The averaging may be processed, preferably, by the analyzer unit or, alternatively, by the light detection unit directly. This process yields an averaged signal. The analyzer unit may further determine a signal-to-noise ratio of the averaged signal. If the averaging window is long, the response time of the analyzer is degraded. In order to achieve a decent update rate of the measurement value, the averaging window has to be adapted according to the actual value and its rate of change. The analyzer instrument according to the invention is preferably adapted to adjust a number of light pulses used to compute the averaged signal, i.e. the averaging window, as a function of said signal-to-noise ratio of averaged signal in view of a target signal-to-noise ratio of the averaged signal and/or a target accuracy and/or a target time resolution of a measurement of a physical parameter of the test medium addressed by the analyzer instrument. The operation mode using short light pulses and averaging of data collected during the short light pulses is advantageous over collecting data with fewer but longer light pulses, since the required capacity of the energy buffer for the operation of the light source is lower with short light pulses.
The analyzer instrument allows measuring at least one of the properties of the test medium. It can, however, also be adapted to measure several such properties simultaneously or consecutively. Preferably, the analyzer instrument is constructed such that at least parts of its components may easily be exchanged in order to measure further properties. Such further properties may be a gas concentration, like oxygen or CO2 concentration, a pH value, a refractive index, a turbidity or a particle concentration, like suspended solids, such as crystals, biological cells or ash and dust, etc. Such a property of a test medium can further be a level, a distance, proximity, a position, object ranging, or similar measurements property like humidity, dewpoint, pressure, topography, or temperature.
The light management unit may comprise at least one light guiding means. If so, said at least one light guiding means is advantageously protected from movements in order to reduce movement-induced noise. Preferable protection means are rigid housings that fix or enclose the at least one light guiding means at least partially. In order to minimize the effort, and consequently costs, the light source is advantageously located in the vicinity of the detection space.
In a second aspect, the present invention provides a method for measuring at least one property of the test medium by means of the analyzer instrument according to invention for a situation when the analyzer instrument is located in the hazardous environment. Of course, measurements are also possible in safe environments. The analyzer instrument can be located in the vicinity of the test medium, at least partially, or completely in the test medium. The actual location of the analyzer instrument may depend on, for example, the place conditions, the test medium, the environment, the measurement method, or the measured property. The analyzer is operated such that the light source emits light. Said light may be directed or guided to the detection space, e.g. by means of a light guiding means, such as a lens system or optical waveguide, or mirror/splitter systems, where it interacts with the test medium. Interacting means that the light travels through the test medium while it is scattered and/or transmitted or partially absorbed. Interacting may also comprise the case when light does not enter the test medium, but is reflected at an interface of the test medium and an environment, for example, due to an abrupt change of the refractive index at the interface. At least a part of said light that has interacted with the test medium reaches the light detection unit either directly or is guided, e.g. by means of a light guide or a mirror, and subsequently detectable. Depending on the measurement property a stationary and/or a time varying light intensity is evaluated.
In a method according to the invention the light source may be operated in pulsed mode, a continuous light emission may, however, also be possible, depending on the actual measurement.
According to the method of invention, the analyzer instrument according to invention may also average over measurement results due to single light pulses and/or adjust a light pulse length in dependence of a predefined measurement requirement, such as a target signal-to-noise ratio, a target accuracy, or a target time resolution.
The analyzer instrument is particularly advantageous when used for measuring at least one property of test medium in a potentially hazardous environment due to its comparably low price, due to its high energy efficiency, and due to its compliance with intrinsic safety.
The following important elements of the invention shall be summarized, wherein these elements can be taken alone or in any possible combination as preferred embodiments:
Low-Power Architecture:
Realize intrinsic safety of an optical analyzer platform by using energy limited sources, such as battery or power limited sources, such as energy harvesting or low-power 2-wire transmitter architecture. In the latter approach, the power for all analyzer components is delivered by the 2-wire loop (available power typically: P=9 volt·3.5 milliampere=31.5 milliwatt).
Laser Light Source:
The analyzer instrument preferably uses a new light source which is based on stimulated emission (laser). Vertical-cavity emitting lasers (VCSEL) are even suited since they consume a factor of 10 less electrical power as compared e.g. with LEDs. Since the light source is normally the main load, it should be operated intermittently. The energy for the light pulses can be accumulated in a charging buffer. The repetition rate of light pulses can limit the best achievable response time and through the signal-to-noise ratio also the accuracy. Since the signal-to-noise ratio is dependent on the working regime of the sensor (low light intensity versus high light intensity), an adaptive signal processing control is proposed.
Adaptive Control:
It is proposed to use the information from the sensor reading to adjust the averaging window of the data analysis depending on the measurement regime of the sensor, i.e. depending on a low/medium/high signal: A first idea is to average the measurement points over several pulses in case of insufficient signal-to-noise ratio. A second idea is to adjust the pulse length of the laser light and the connected measurement window. These adaptive methods allow for achieving an optimal sensor performance with respect to accuracy and resolution. Furthermore, the control can be adapted to the signal dynamics. If the analyzer detects a large rate of change in the measured light intensity, it adapts the number of pulses used to compute the average (resp. the length of the averaging window). This enables the analyzer to quickly give a response to abrupt changes of the fluid parameter, albeit with a reduced accuracy, while achieving a high accuracy on steady-state measurements.
Platform Concept:
It is further proposed to apply the optical analyzer as a platform device which can address more than one fluid parameter. The optical interrogation then determines fluid properties such as turbidity, suspended solids, refractive index, dissolved oxygen, chlorine, pH, CO2 etc. Various embodiments for signal evaluation are foreseen, e.g., in which either stationary or time varying light intensity is evaluated. The latter is important for fluorescence decay measurements after an excitation pulse.
Architectural Setup:
The transmitter electronics is arranged in a way that all optical light guiding means (e.g. lens systems, optical waveguides) are protected by housings and thus cannot be moved. Thus, error readings due to signal variations which are caused by a change in an open optical link (e.g. fiber bending, connector geometry) are avoided. A usual precondition for this is to be able to arrange the transmitter directly in the vicinity of the analyzer head in the explosive atmosphere and this is only possible, in a cost-effective manner, when the realization is compliant with intrinsic safety. Furthermore, a low-power local analyzer enables the realization of a battery-powered or energy-harvester-powered instrument with wireless connection to marshaling cabinets or control cabinets. In other words, any kind of physical link (be it optical or electrical) is avoided.
Preferred embodiments of the invention are described in the following with reference to the drawings, which are for the purpose of illustrating the present preferred embodiments of the invention and not for the purpose of limiting the same. An identical reference sign refers to the same feature. In the drawings,
Said light management unit 22 comprises a first light guiding means that is adapted to receive light from the light source 20 and to guide at least part of it to a detection space 30. Preferably, any light guiding means comprised in the analyzer instrument is enclosed in a rigid housing in order to avoid movement-induced noise. In order to reduce noise and to save effort and related costs, the light source 20 and the light detection unit 24 are in the vicinity of the detection space 30, i.e. the length of any light guiding means is preferably minimized, most preferably there are no light guiding means. The light management unit 22 is adapted to emit at least part of the light that subsequently enters the detection space 30 on a first side. The light detection unit 24 is located at a second side of the detection space 30, opposite to said first side, and is adapted to directly receive the light that has passed through detection space 30, thereby avoiding additional light management components.
During a measurement, the platform board 8 is located e.g. in a hazardous environment 5, at least partly in a test medium 4, in such a way that particularly the detection space 30 is within the test medium 4. The power source 10 is located remotely from the platform board 8, in this case outside the test medium 4. The power source 10 comprises here the receiving unit 19 and transmits power, compliant with the above stated limits, to the power management unit 13 via source wiring 7. From the power management unit 13, the received power is distributable to the light source 20 by means of the buffer wiring 18, to the light detection unit 24, and to the data management unit 28 by means of the further wiring 9, 11.
The light source 20 is a low-power and highly efficient vertical cavity emitting laser, as described above. It is adapted to produce light, part of which is guided to the detection space 30 in the above described manner; at least part of said light subsequently travels through the detection space 30 while it interacts with the test medium 4. The light detection unit 24 is adapted to receive at least part of said light. The light detection unit 24 is adapted to detect at least part of the incident light and to produce and provide a first signal, which is a processed signal, an analogue or preferably already a digital signal. The data management unit 28 is adapted to receive said first signal via the signal wiring 11. Preferably, the signal wiring 11, as well as the source wiring 7 are 2-wire connections as described above. The data management unit 28 is adapted to acquire said signals, preferably to store them, and particularly to transmit them to the data receiving unit by means of the signal wiring 11 and the source wiring 7 via the power management unit 13.
Another example of an analyzer instrument 1 is illustrated in
The platform board 8 is located in the hazardous environment 5, while the power source 10 including the receiving unit 19 are located in a safe environment 6, wherein there is an interface 35 between said environments. The interface 35 may also be an interface region. The power wiring 7 is crossing the interface 35 and is connected to the approved intrinsically safe associated apparatus 12.
Apparatus 12, as described above, has the function of a barrier that guarantees intrinsic safety. Under normal conditions, it is adapted to limit current and voltage transmitted from the power source 10 to values as stated above and to decouple the power source 10, if the transferred power does not comply with said limits. Thereby it ensures the above stated limits for the further wiring 9, 11 of the analyzer instrument 1. Particularly, any excess current or voltage that occurs under fault conditions behind the barrier, i.e. on the platform board 8, is safely transferable to the apparatus 12. Importantly, the source wiring 7 before the barrier is intrinsically safe, preferably through insulation, and connected to the apparatus 12 by means of explosion proof seals that guarantee compliance with intrinsic safety. Preferably, also the wiring attached to the barrier from the side after the barrier is connected with such seals.
The direct current to direct current converter 14 belongs to the power management unit 13 and is adapted to distribute the power received from the power source to the back-end electronics 15 and front-end electronics 16. Typically, it is adapted to provide about 40% or less of the available power to the back-end electronics 15 and the rest to the front-end electronics 16 and/or the energy buffer 17.
The energy buffer 17 is supplied by power source 10 through the power management unit 13 and via the further wiring 9, 11 and adapted to transfer the buffered energy via the buffer wiring 18 to the light source 20. Through the energy buffer 17 the light source 20 is particularly operable in a pulsed mode. The apparatus 12 is adapted to ensure intrinsic safety for the buffer wiring, i.e. excess energy is safely transferable to it, as described above. The light emitted during a light pulse is at least partly guided by the light management unit 22 to the detection space 30, interacts at least partly with the test medium 4 in the detection space 30. The light detection unit 24 is adapted to at least partly detect said light and to provide a first signal that is transferable to the analyzer unit 26 via the signal wiring 11.
The analyzer unit 26 is located between the light detection unit 24 and the data management unit 28. It is connected to the light detection unit 24 and the data management unit 28 by means of signal wiring 11. There is a further connection to the power management unit 13 via the wiring 9, through which the analyzer unit 26 is powered. Alternatively, it may also be powered via signal wiring 11. The analyzer unit 26 is adapted to produce a second signal from said first signal and a corresponding signal-to-noise ratio.
The analyzer instrument 1 is adapted to adjust a length of a light pulse emitted by the pulsed light source 20. The pulse length is adjustable via the power management unit 13, preferably via a programmable micro-controller that is adapted to receive the second signal and the corresponding signal-to-noise ratio. The length is adjustable particularly as a function of said signal-to-noise ratio in view of a target signal-to-noise ratio and/or a target accuracy and/or a target time resolution of measurement of a physical parameter of the test medium 4. The analyzer instrument 1 is further adapted to average over the second signals due to subsequent incident light pulses of the pulsed light source 20. The averaging is preferably processed by the analyzer unit 26 that is adapted to provide an averaged signal including a signal-to-noise ratio of the averaged signal. Alternatively, the analyzer instrument may be adapted to average over the first signals. Advantageously, the analyzer instrument 1 may be further adapted to adjust a number of light pulses used to compute the averaged signal as a function of said signal-to-noise ratio of the averaged signal in view of a target signal-to-noise ratio and/or a target accuracy and/or a target time resolution of measurement of a physical parameter of the test medium 4 addressed by the analyzer instrument 1.
Several variations of analyzer instrument design are possible. For example, the light detection unit 24 may be located at another, e.g. the same first side of the detection space 30. In general, the different components of the analyzer instrument 1 shall be chosen according to requirements. Also the design is to be adapted to the purpose of the analyzer instrument 1, e.g. the mutual position of the light source 20 and the detection unit 24 may be adjusted depending on given requirements, such as space conditions or measurement property of the test medium 4.
In a preferred method for measuring at least one property of the test medium 4, the analyzer instrument 1 is placed in the hazardous environment 5 with a predefined location with respect to test medium 4, see
In a further preferred method according to the present invention, an analyzer instrument according to invention is employed, wherein the power from the power source 10 is transferred by the power management unit 13 to the light source 20 via the energy buffer 17, wherein said energy buffer 17 is continuously charged via the further wiring 9, 11 with power from the power management unit 13 and discharged via the buffer wiring 18. The discharge energy is released to the light source 20 in a pulsed manner. The light source 20 is thus operated such that it emits light pulses. The light path is as described above. The light detection unit 24 is adapted to detect light from subsequent light pulses and to produce and provide the subsequent first signals. The data management unit 24 receives said first signals and exchanges it with the receiving unit 19.
Preferably, the analyzer instrument 1 comprises an analyzer unit 26 that receives the first signals and produces and provides the second signals with the corresponding signal-to-noise ratios. The analyzer unit 26 preferably also computes average signals from said first and/or second signals including the signal-to-noise ratio of the averaged signal. The signals provided by the analyzer unit 26 are exchanged with the receiving unit 19 by means of the data management unit 28 via signal wiring 11 and source wiring 7. The data management system may also provide signals and signal-to-noise ratios to the power management unit, particularly to the micro-controller, which uses the received information for adaptive control of the analyzer instrument 1. The analyzer instrument 1 preferably adapts the pulse length of the light pulse and/or the number of signals from which the average signal is computed as a function of said signal-to-noise ratio of the averaged signal in view of a target signal-to-noise ratio and/or a target accuracy and/or a target time resolution of measurement of a physical parameter of the test medium 4 addressed by the analyzer instrument 1. It is also conceivable that the light intensity or the beam geometry is adapted by suitable means, as known from prior art.
The analyzer instrument of the present invention may be used for measuring at least one property of test medium 4 in a potentially hazardous environment 5 by means of the following measurement methods. It has to be understood that the methods discussed below are only examples of a large variety of experimental analyses, which are possible using a low-power high efficiency light source equipped analyzer instrument complying with intrinsic safety.
Property: Gas Concentration, e.g. Oxygen:
Method 1: Luminescence Characteristics of Excited Chemical Complex (Intensity, Decay, Phase Delay)
Oxygen sensors based on optical measurement principles use the effect of dynamic fluorescence quenching. Typically, a specially designed chemical complex, distributed in a thin oxygen permeable matrix (such as polymer, sol-gel material or silica gel), is excited by light of appropriate wavelength range and emits a red-shifted luminescence light. The presence of oxygen in the vicinity of the complex leads to a change of the emission characteristics due to non-radiative energy transfer by collisions with oxygen molecules (luminescence quenching). Besides oxygen, also other molecules can be detected using this method, e.g., CO2 and pH (see www.polestartech.com).
The analysis of the luminescence light can be done in three different ways: i) measurement of the luminescence intensity in a specific spectral range, ii) measurement of the phase delay with respect to the sinusoidally modulated excitation light, or iii) measurement of the lifetime of the luminescence decay when pulsed excitation is used. The two latter concepts are favorable due to their immunity to measurement artifacts from light source aging or transmission changes in the optical link. Concept (iii) is especially favorable regarding this invention, since it complies well with low-power pulse mode operation of the excitation light source. Using these concepts the absolute concentration of oxygen in the medium can be determined.
Method 2: Tunable Diode Laser Absorption Spectroscopy (TDLAS)
An experimental setup for TDLAS requires a scanning laser diode, some transmission optics, a container for the investigated medium containing the analyte, receiving optics, and a detection unit. The basic idea is to tune the laser frequency (temperature or current tuning) over a spectral range of characteristic absorption line(s) of the analyte. This leads to a decrease of signal intensity in the detection path, which can be detected by a photodiode and which is used to determine the analyte concentration (Lambert-Beer law) or other absorption-related parameters (e.g. gas temperature, gas flow velocity). In order to increase signal-to-noise ratio, often modulation techniques are applied. Also, pulse-mode wavelength scanning schemes are conceivable for compliance with low power requirements.
Property: Turbidity or Particle Concentration, e.g. Suspended Solids, Such as Crystals, Biological Cells or Ash and Dust, Etc.:
Method 1: Light Scattering Off Particles Using Propagating Waves
The turbidity of a sample can be measured by analyzing the diffusely scattered light from particles present in the sample medium (gas, liquid, or solid). In a typical experimental configuration, light of a specific spectral range is shone through a window onto the particles in the sample, and the light intensity of the scattered light is measured. One or more detection channels can be applied either for the analysis under different angles (forward, backward, side scattering) or for the analysis in different spectral ranges or for both. Normally, the light source is modulated (e.g. sinusoidally or in a pulsed way), in order to enhance signal-to-noise ratio and to permit for immunity against stray light from other sources. The pulse mode operation is especially favorable with respect to this invention, since it meets the requirements of an intrinsically safe low-power electronics platform including light source.
Method 2: Light Scattering Off Particles Using Evanescent Waves
See below “Refractive Index”.
Parameter “Level, Distance, Proximity, Position, Object Ranging etc.”:
Method: Reflection, e.g., Time-of-Flight Measurement of Reflected Light Pulses
Designed for bulk solids, slurries, and opaque liquids, laser ranging can be used to measure the position of a reflective surface, i.e., filling level of a vessel. The principle is very similar to that of ultrasonic level sensors. Instead of using the speed of sound to find the level, however, the speed of light is used. A laser transmitter at the top of a vessel fires a short pulse of light down to the process liquid surface, which reflects it back to the detector. A timing circuit measures the elapsed time (time-of-flight) and calculates the distance. The key is that lasers have virtually no divergence and no false echoes. Since this measurement technique relies on pulsed operation, it is particularly well-suited for low-power operation.
Parameter “Refractive Index”:
Method: Detection of Angle of Total Internal Reflection of Divergent Light Beam
The refractive index of a process fluid can be measured by determining the critical angle at which a light beam undergoes total internal reflection at an interface. This can be accomplished by using a diverging light beam (e.g. as emitted from an illuminated optical fiber) and a prism, one surface of which is in contact with the process medium of interest. Two opposite surfaces of the prism act as mirrors bending the light rays such that the diverging rays meet the interface at different angles. The rays that are subject to total internal reflection are reflected again internally to produce an image on a position-sensitive detector (e.g. a CCD chip). The position of the shadow edge is a function of the difference in refractive index between the prism and the process medium. This scheme lends itself to pulsed operation, the accuracy being limited by the spatial resolution of the chip.
Property “Concentration”:
Method: Attenuated Total Internal Reflection—Light Scattering/Absorption Using Evanescent Waves
Upon total internal reflection of a light ray (typically IR) at an interface between an optical medium (e.g. a window) and a process medium of lower refractive index, an evanescent wave forms that extends into the process medium (typically between 0.5 and 2 micrometer). The reflected light intensity depends on the attenuation of the evanescent wave specific to the medium. This effect can be amplified by using multiple internal reflections. The attenuation of the beam is a direct measure of the concentration of a component of the process medium absorbing or scattering at the chosen wavelength. By modulating the light source, the change in intensity can be measured with a high signal-to-noise ratio. In addition, a second light source emitting in a spectral range in which the component of the medium does not absorb, can be used as a reference.
Method: Raman Scattering
Raman spectroscopy is a powerful tool for classifying unknown chemicals by their vibrational spectra. Laser light in the visible or near infrared parts of the spectrum is directed into the sample, and the scattered light is detected in an optical arrangement similar to that used for turbidity measurements. Raman spectroscopy can be used to detect a wide variety of organic and inorganic chemicals. The frequency-shifted, scattered laser light is collected, transmitted via fiber optic cable, and filtered to separate Rayleigh- from the Stokes-scattering associated with the sample component of interest. The intensity of the Stokes signal is proportional to that component's concentration in the sample. As Raman scattering is a process of low efficiency, pulsed operation with higher peak powers or multi-pass optical layouts are preferred. The advantage of Raman over IR spectroscopy is that bands are sharper, and there is no interference with water or CO2 absorptions.
An analyzer instrument according to the present invention, i.e. an instrument that cannot, even under severe fault conditions, generate a heat discharge with sufficient energy to ignite the explosive gas, is consequently advantageous in that it allows for a compactly constructed device for analyzing a test medium in a potentially hazardous environment. Importantly, there is no need to place energy-intensive electronics remotely while establishing additional physical links or to provide for sealed or purged housings that shield potentially igniting sparks or hot spots from the explosive medium. The additional and costly commissioning required for the previously mentioned measures are thus not required. A further advantage of the analyzer instrument according to invention is that, by default, the power consumption is low, which is favorable for an instrument design relying on a mobile power source intended for time-wise self-sustaining operation.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2011/005541 | Apr 2011 | US |
| Child | 14048960 | US |
