US20120216593A1 - Electronic chemical trace detector - Google Patents
Electronic chemical trace detector Download PDFInfo
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- US20120216593A1 US20120216593A1 US13/466,353 US201213466353A US2012216593A1 US 20120216593 A1 US20120216593 A1 US 20120216593A1 US 201213466353 A US201213466353 A US 201213466353A US 2012216593 A1 US2012216593 A1 US 2012216593A1
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- heater element
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
- G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
- G01N27/12—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of a solid body in dependence upon absorption of a fluid; of a solid body in dependence upon reaction with a fluid, for detecting components in the fluid
- G01N27/122—Circuits particularly adapted therefor, e.g. linearising circuits
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
- G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
- G01N27/12—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of a solid body in dependence upon absorption of a fluid; of a solid body in dependence upon reaction with a fluid, for detecting components in the fluid
- G01N27/125—Composition of the body, e.g. the composition of its sensitive layer
- G01N27/126—Composition of the body, e.g. the composition of its sensitive layer comprising organic polymers
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
- G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
- G01N27/14—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of an electrically-heated body in dependence upon change of temperature
- G01N27/18—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of an electrically-heated body in dependence upon change of temperature caused by changes in the thermal conductivity of a surrounding material to be tested
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T436/00—Chemistry: analytical and immunological testing
- Y10T436/10—Composition for standardization, calibration, simulation, stabilization, preparation or preservation; processes of use in preparation for chemical testing
Definitions
- the invention relates to the detection of traces in an environment, in particular, the detection of traces of volatile chemical substances in the air.
- one detection sensor uses micro-hotplate technology, which is a semiconductor sensor on a micro-hotplate where chemical reactions occur of the traces to be detected.
- MOS type detector exploits the variation of electrical resistance of the sensor while, at a certain heating temperature, redox reaction take place on the surface of the sensor.
- the heater resistance is temperature dependent, which implies that current adjustments need to be provided to provide a stable temperature. This can be done by a balancing circuit which balances the heat resistor to a predefined resistor value.
- U.S. Pat. No. 4,847,783 discloses a balancing circuit comprising an adjustable resistor for tuning the heater element to a predefined resistor value.
- the heater element operates a platinum resistance element having a predetermined resistance-temperature characteristic.
- platinum resistance elements may show an almost perfect linear temperature behaviour, the real temperature may vary from sample to sample since the offsets of these elements may vary considerably.
- a repeatable yet unknown precise temperature is provided.
- the invention provides, in a sensor of the above described type, a test circuit for measuring a dissipated power in the heater element and for calculating a real temperature from the dissipated power in the heater element based on the predetermined power-temperature characteristic.
- FIG. 1 shows a typical layout of the gas sensor according to the invention
- FIG. 2 shows a response characteristic of a heatable metal oxide sensor that is exposed to a variety of compositions or chemical substances in varying concentrations
- FIG. 3 shows measured resistance-temperature diagrams of three hotplate sensors
- FIG. 4 shows a preferred embodiment of the inventive concept
- FIG. 5 shows power temperature relationships for the same heater elements as in FIG. 3 .
- FIG. 1 a typical layout is shown for chemical trace detector 1 implementing a heatable conducting plate 2 , also known as hotplate sensor 2 .
- the hotplate sensor 2 is typically provided by a metal oxide sensor element 3 which is sensitive to chemical reactions taking place near the sensor surface area, that is in close spatial relationship with a heater element 4 .
- This sensor element 3 shows in particular a variation in conductance depending on chemical traces reacting near the exposed surface area 5 thereof.
- Various metal oxide sensor elements 3 are known, including but not limited to tin oxide, zinc oxide, iron oxide and tungsten oxide sensors with or without added catalyst, including but not limited to platinum and paladium.
- the hotplate 2 is heated by a heater element 4 which is preferably attached in close vicinity of the sensor element 3 produced by MEMS (micro electrical mechanical systems) technology thus ensuring an identical temperature of the conducting sensor element 3 and the heater element 4 .
- the heater element 4 has a low thermal mass and is controlled by a processor 6 for to provide a stabilized temperature in said sensor element 3 . Typically this is provided by a balancing circuit implementing a Wheatstone bridge as will be further elucidated in FIG. 4 .
- the sensor element 3 is connected to a detection circuit 7 for detecting a change of resistance in the sensor element 3 in accordance with the presence of a chemical trace reacting in the presence of the conducting plate.
- the output of the detection circuit 7 in connection with a preset temperature provided by the processor 6 are stored in an internal memory element 8 of the detector, which can be any type of memory, typically a flash memory.
- a plurality of detected resistance values in the detection circuit relative to a plurality of preset temperatures can be stored to form a footprint of a number of chemical substances 9 which are sensed by the hotplate 2 by exposing the hotplate to a flow of gas 10 .
- the hotplate can be subjected to stagnant air.
- the results are stored in the memory element 8 to be transmitted via a communication terminal 11 to a base station 12 comprising a database for storing footprints of predetermined chemical substances.
- the stored footprints can be communicated to the base station 12 comprising a database 13 , for providing a best match 14 of any of said stored footprints in the memory element 8 to any of footprints stored in the database 13 of known chemical substances.
- a particular detected composition of chemical substances can be identified in the database 13 via per se known pattern recognition and identification software techniques.
- the detector may also be equipped with specific matching routines which can match the detected footprint with one or more predefined chemical substances on board of the detector 1 .
- the detector 1 can be easily modified to provide a detector for detecting specific predetermined chemical substances.
- the detector 1 hence comprises in addition a comparison circuit for comparing a stored footprint with a predetermined set of prestored footprints of predetermined chemical substances, so as to determine a particular detected chemical substance.
- FIG. 2 shows different conductivity responses of the hotplate 2 , in particular, for a concentration of 20 and 80 ppm (line 15 and 16 respectively) of toluene and for a concentration of 50 and 100 ppm (line 17 and 18 respectively) of butyl acetate. Also a blank response 19 is shown, illustrating a detected conductance for varying temperatures.
- the typical detection temperatures vary between 200 and 600° C. It can be shown generally that the metal oxide sensor produces peak conductance values for different chemical substances on different temperature values and for different peak values. For example, the conductance for toluene is generally higher than for butyl acetate.
- the metal oxide sensor 3 is sensitive for oxygen reducible substances.
- components show maximum conductance according to particular temperatures settings.
- a footprint can be obtained of the variety of chemical substances. This footprint can be compared to a number of footprints of known pure substances or mixtures that are stored in a database 13 as referred to in FIG. 1 .
- FIG. 3 shows a measured resistance-temperature diagram of the heater element 4 .
- the heater element 4 can be integrated in a balancing circuit to preset the resistor value thereof to a predetermined value.
- a balancing circuit can provide a preset resistor value of the heater element 4 , giving rise to a predetermined temperature according to the resistance-temperature diagram shown in FIG. 3 .
- the diagram in FIG. 3 clearly shows that the temperatures of the hotplate 2 are varying substantially for a preset resistor value.
- the hotplates W 1 and W 2 are of a same type. This means that the macroscopic dimensions of the heater elements 4 are almost the same. Nonetheless, where the resistance varies only 1.5 Ohm at room temperature, at a preset resistance of 160 Ohm a difference of 25° C. is provided by the heater element. It shows that without individual calibration of the heater element 4 , presetting the heater element 4 to a fixed resistance can give an unacceptable spread in temperatures, which affects the reliability of the detector.
- FIG. 4 shows a preferred embodiment of the inventive concept.
- FIG. 4 shows a processor 6 and a balancing circuit 20 having an adjustable resistor 21 for tuning the heater element 4 to a predefined resistor value.
- the balancing circuit 20 comprises essentially a Wheatstone bridge arrangement of fixed resistors R 5 , R 6 , R 7 , R 8 , in combination with a heatable resistor 4 (also indicated in the drawing as RH) and a tunable digital potentiometer which functions as the adjustable resistor 21 (also indicated in the drawing as U 10 ).
- the digital potentiometer 21 has a very good linearity.
- the resistance in the bridge circuit 20 is determined by the resistor R 8 circuited parallel to the digital potentiometer 21 .
- This resistor R 8 (as well as the other fixed resistors R 5 , R 6 and R 7 ) has a very precise resistive value, typically with a margin of error of less than 0.1%.
- the circuit is balanced by the operational amplifier 22 (U 11 ) which controls the voltage across the heater element 4 .
- the amplifier U 11 will control the Voltage between the + and ⁇ terminals of the amplifier so that there is no voltage difference, i.e. so that the bridge is balanced.
- the Voltage difference is higher, the current through the heater element 4 (RH) will increase.
- the heater element 4 conducting an increased current, will heat up and the resistance will rise accordingly.
- a preset resistive value of the heater element 4 can be controlled, wherein the resistive value of the heater element 4 is known expressed as a ratio of resistive values of the R 5 , R 6 , R 8 , and a fraction of R 7 determined by tunable digital potentiometer 21 (also indicated in the drawing as U 10 )
- FIG. 4 shows a test circuit 23 for the balancing circuit 20 for measuring a dissipated power in the heater element 4 and for calculating a real temperature from the dissipated power in the heater element 4 based on the predetermined power-temperature characteristic which will be further elucidated with reference to FIG. 5 .
- test circuit 23 comprises a pair of test terminals 24 (one being grounded) that directly connect to the terminals of the heater element 4 .
- This arrangement provides a conveniently implementable circuit 21 for calculating the power dissipation in the resistor using the familiar formula VH 2 /RH with VH being a detected voltage difference across the heater element 4 .
- RH indicates a true resistive value of the heater element 4 derived from the balancing circuit 20 .
- the test circuit 23 comprises a calculating circuit 25 to calculate an offset value for the digital potentiometer 21 .
- the test circuit 23 comprises a switch 26 to activate the calculating circuit 25 .
- the test circuit 23 measures a dissipated power in predefined neutral conditions.
- a method of calibrating the hotplate chemical trace detector 1 is carried out.
- a predetermined power level to the hotplate 2 by adjusting the adjustable resistor 21 .
- the predetermined power level can be related to a set temperature using a known power-temperature characteristic of the heater plate.
- a precise set-point for a predetermined number of temperatures can be provided to the processor 6 for the heater element 4 , thus zeroing the adjustable resistor 21 to a preset value relating to the set temperature.
- the test circuit is connectable to a calibration circuit for providing a lookup table to the processor 6 for calculating preset resistor values so as to provide predetermined real temperatures to said heater element.
- the detector 1 in particular, the processor 6 , may be attached to a separate a test circuit 23 , for instance, in a factory setting, indicated by the dotted lines 27 .
- a series of predetermined power settings to the heater element 4 is provided by adjusting the adjustable resistor 21 . Accordingly a series of predetermined temperatures to these power settings is provided using the power-temperature characteristic of the heater plate.
- a series of setpoints for setting a temperature can be provided to form a lookup table to the adjustable resistor 21 for providing preset resistor values so as to provide predetermined real temperatures to said heater element 4 .
- the lookup table is then integrated in the processor 6 , in particular, is provided in a local memory to be accessed when setting the adjustable resistor to a predetermined temperature setting.
- a precise temperature of the heater element 4 can be measured by the test circuit 23 , without having to rely on the resistance-temperature characteristic of the heater element that may vary from sample to sample.
- a precise set point for the heater element can be provided.
- a temperature can be set by adjusting the resistor in the balancing circuit to a real known temperature.
- the amount of power to achieve this temperature can be related to a dissipated reaction energy of the chemical trace.
- the calculating circuit 25 can be arranged to calculate a difference of a measured input power from the test terminals 24 and a calculated input power. This calculated input power can for instance be provided using the known real temperature derived from the preset resistor value 21 after calibration and relating it to a calculated power in the heater element 4 using the power-temperature characteristic of the heater element 4 .
- a dynamic temperature modulation is used of the hotplate 2 .
- the processor 6 is arranged to provide a sliding temperature to the heater element 4 .
- FIG. 5 shows a power-temperature characteristic for two macroscopically identically hotplate sensors 2 .
- the term macroscopically identical indicates a generally identical geometric structure for the hotplate 2 , that is, a generally identical conducting structure for conducting heat from the heater element 4 and the sensor element 3 .
- the power-temperature characteristics for the two heater elements W 1 and W 2 appear to be substantially identical although heater element W 1 shows a resistance of 88.1 Ohm at 22.3° C. and heater element W 3 shows a resistance of 97.4 Ohms at 22.1° C., a difference of more than 10%.
- the power-temperature characteristic is valid in standard conditions, at room temperature in clean air. In non-standard conditions the actual temperature can be measured and used for recalculating the power-temperature characteristic. In this way, the temperature of the heater element 4 Tsensor can be derived for a predetermined number of settings of the digital potentiometer 21 Rpot. This provides a gauge line which can be converted to a function using a linear regression.
- This equation can be implemented in software operating the processor 6 so that a temperature can be preset with a deviation which may be less than 3-5° C.
- test circuit 23 coupled more indirectly to the heater element, for instance a terminal that measures the output voltage of the amplifier U 11 of FIG. 4 .
- test circuit 23 that does not need to use the balancing circuit 20 but could measure the resistance of the heater directly using a preset value of the digital potentiometer 21 .
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Abstract
A hotplate chemical trace detector comprising a heatable conducting plate with a heater element having a predetermined temperature-power characteristic. A balancing circuit comprises an adjustable resistor for tuning the heater element to a predefined resistor value. A processor is provided for adjusting the adjustable resistor so as to provide a stabilized temperature in said heatable conducting plate and a detection circuit is provided for detecting a change of resistance in the heatable conducting plate in accordance with the presence of a chemical trace reacting in the presence of the conducting plate. According to the invention a test circuit is provided for measuring a dissipated power in the heater element and for calculating a real temperature from the dissipated power in the heater element based on the predetermined temperature-power characteristic.
Description
- This application claims the priority benefit of Bos, U.S. patent application Ser. No. 12/094,675, filed on Oct. 6, 2008, entitled “Electronic Chemical Trace Detector,” which is a PCT National Stage, and claims priority benefit, of Bos, International Application Number PCT/NL2006/000591, filed on Nov. 24, 2006, entitled “Electronic Chemical Trace Detector,” and claims priority benefit, of U.S. Provisional Patent Application Ser. No. 60/750,095, filed on Nov. 28, 2005, and European Patent Application No. 05077694.7, filed on Nov. 24, 2005, entitled “Electronic Chemical Trace Detector,” the contents of all referenced patent applications are incorporated herein by reference in their entirety, including any references therein.
- The invention relates to the detection of traces in an environment, in particular, the detection of traces of volatile chemical substances in the air.
- In the art, expensive equipment is used to provide detection instruments, which are also bulky since laboratory like conditions need to be provided in order to provide reliable results. Detectors which are used as field detectors and which are more economically sized exist but do require expensive calibration techniques which prevents straightforward mass production of these items. Therefore, these type of detectors are not as widely used as would be convenient, since most applications are cost prohibitive.
- In the art, one detection sensor uses micro-hotplate technology, which is a semiconductor sensor on a micro-hotplate where chemical reactions occur of the traces to be detected. In particular such MOS type detector exploits the variation of electrical resistance of the sensor while, at a certain heating temperature, redox reaction take place on the surface of the sensor.
- However, such hotplate technology is very sensitive to variations of the temperature and it is therefore important to provide detection of the traces at a prefixed temperature. In particular, the heater resistance is temperature dependent, which implies that current adjustments need to be provided to provide a stable temperature. This can be done by a balancing circuit which balances the heat resistor to a predefined resistor value.
- U.S. Pat. No. 4,847,783 discloses a balancing circuit comprising an adjustable resistor for tuning the heater element to a predefined resistor value. The heater element operates a platinum resistance element having a predetermined resistance-temperature characteristic. However, in practice, although platinum resistance elements may show an almost perfect linear temperature behaviour, the real temperature may vary from sample to sample since the offsets of these elements may vary considerably. Thus, by presetting the heater element to a predetermined value, a repeatable yet unknown precise temperature is provided.
- Hence, for different sensors, a certain chemical substance may be sensed at varying temperatures caused by the differing offsets of the heater elements, which may give rise to a differing detection results for the various sensors. Therefore, to provide a reliable sensor with replicable results, from which sensor results can be coupled to a standardized database comprising footprints of identified chemical compositions or substances, the temperature relation is very critical. However, an individual calibration setup wherein each sensor is 10 tested in conditioned temperature and gas environments is very cumbersome.
- In one aspect it is desirable to provide a sensor which obviates the need for cumbersome individual calibration actions. In another aspect it is desirable to provide a robust and stable sensor which provides reproducible data and which can be produced at relative low costs.
- Accordingly there is provided a sensor according to the features of
claim 1. In particular, the invention provides, in a sensor of the above described type, a test circuit for measuring a dissipated power in the heater element and for calculating a real temperature from the dissipated power in the heater element based on the predetermined power-temperature characteristic. - Accordingly, a deviation of less then 1-1.5° C. from a preset temperature can be attainable using standard components. Thus it is possible to provide a low cost sensor which is easily resettable in neutral conditions. This can be typically done in a factory setting or rather by a user who needs to reset the sensor in a certain conditioned gas ambiance. In this way there is provided an automatic calibration facility on board of the sensor, which by placing it in a neutral ambiance, can easily tune the adjustable resistor to provide a real temperature.
- Further features and benefits will be apparent from the annexed description in conjunction with the drawings.
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FIG. 1 shows a typical layout of the gas sensor according to the invention; -
FIG. 2 shows a response characteristic of a heatable metal oxide sensor that is exposed to a variety of compositions or chemical substances in varying concentrations; -
FIG. 3 shows measured resistance-temperature diagrams of three hotplate sensors; -
FIG. 4 shows a preferred embodiment of the inventive concept; and -
FIG. 5 shows power temperature relationships for the same heater elements as inFIG. 3 . - Turning to
FIG. 1 a typical layout is shown forchemical trace detector 1 implementing a heatable conducting plate 2, also known as hotplate sensor 2. The hotplate sensor 2 is typically provided by a metaloxide sensor element 3 which is sensitive to chemical reactions taking place near the sensor surface area, that is in close spatial relationship with aheater element 4. Thissensor element 3 shows in particular a variation in conductance depending on chemical traces reacting near the exposed surface area 5 thereof. Various metaloxide sensor elements 3 are known, including but not limited to tin oxide, zinc oxide, iron oxide and tungsten oxide sensors with or without added catalyst, including but not limited to platinum and paladium. - The hotplate 2 is heated by a
heater element 4 which is preferably attached in close vicinity of thesensor element 3 produced by MEMS (micro electrical mechanical systems) technology thus ensuring an identical temperature of theconducting sensor element 3 and theheater element 4. Theheater element 4 has a low thermal mass and is controlled by aprocessor 6 for to provide a stabilized temperature in saidsensor element 3. Typically this is provided by a balancing circuit implementing a Wheatstone bridge as will be further elucidated inFIG. 4 . - Furthermore, the
sensor element 3 is connected to adetection circuit 7 for detecting a change of resistance in thesensor element 3 in accordance with the presence of a chemical trace reacting in the presence of the conducting plate. The output of thedetection circuit 7 in connection with a preset temperature provided by theprocessor 6 are stored in aninternal memory element 8 of the detector, which can be any type of memory, typically a flash memory. - In the
memory element 8, among others, a plurality of detected resistance values in the detection circuit relative to a plurality of preset temperatures can be stored to form a footprint of a number of chemical substances 9 which are sensed by the hotplate 2 by exposing the hotplate to a flow ofgas 10. Alternatively, the hotplate can be subjected to stagnant air. - In the embodiment shown, the results are stored in the
memory element 8 to be transmitted via acommunication terminal 11 to abase station 12 comprising a database for storing footprints of predetermined chemical substances. Thus the stored footprints can be communicated to thebase station 12 comprising adatabase 13, for providing abest match 14 of any of said stored footprints in thememory element 8 to any of footprints stored in thedatabase 13 of known chemical substances. In this way a particular detected composition of chemical substances can be identified in thedatabase 13 via per se known pattern recognition and identification software techniques. - Although in this embodiment, the identification of a sensed chemical composition can be done online or offline in an
external base station 12, the detector may also be equipped with specific matching routines which can match the detected footprint with one or more predefined chemical substances on board of thedetector 1. In this way, thedetector 1 can be easily modified to provide a detector for detecting specific predetermined chemical substances. In this (not shown) embodiment, thedetector 1 hence comprises in addition a comparison circuit for comparing a stored footprint with a predetermined set of prestored footprints of predetermined chemical substances, so as to determine a particular detected chemical substance. -
FIG. 2 shows different conductivity responses of the hotplate 2, in particular, for a concentration of 20 and 80 ppm (line line 17 and 18 respectively) of butyl acetate. Also ablank response 19 is shown, illustrating a detected conductance for varying temperatures. The typical detection temperatures vary between 200 and 600° C. It can be shown generally that the metal oxide sensor produces peak conductance values for different chemical substances on different temperature values and for different peak values. For example, the conductance for toluene is generally higher than for butyl acetate. However, it is clear that when a precise temperature setting is unknown, the discriminatory power between 20 ppm toluene and 100 ppm butyl acetate is poor, even when a test is conducted at various temperatures. Therefore, an accurate setting of the temperature is vital for obtaining reliable test results. - Typically, the
metal oxide sensor 3 is sensitive for oxygen reducible substances. Typically, components show maximum conductance according to particular temperatures settings. By obtaining the detection results at various temperature, a footprint can be obtained of the variety of chemical substances. This footprint can be compared to a number of footprints of known pure substances or mixtures that are stored in adatabase 13 as referred to inFIG. 1 . -
FIG. 3 shows a measured resistance-temperature diagram of theheater element 4. As will be further elucidated with reference toFIG. 4 theheater element 4 can be integrated in a balancing circuit to preset the resistor value thereof to a predetermined value. Thus, a balancing circuit can provide a preset resistor value of theheater element 4, giving rise to a predetermined temperature according to the resistance-temperature diagram shown inFIG. 3 . - However, the diagram in
FIG. 3 clearly shows that the temperatures of the hotplate 2 are varying substantially for a preset resistor value. For three hotplates W1, W2, W3 shown, the hotplates W1 and W2 are of a same type. This means that the macroscopic dimensions of theheater elements 4 are almost the same. Nonetheless, where the resistance varies only 1.5 Ohm at room temperature, at a preset resistance of 160 Ohm a difference of 25° C. is provided by the heater element. It shows that without individual calibration of theheater element 4, presetting theheater element 4 to a fixed resistance can give an unacceptable spread in temperatures, which affects the reliability of the detector. -
FIG. 4 shows a preferred embodiment of the inventive concept. In particular,FIG. 4 shows aprocessor 6 and abalancing circuit 20 having anadjustable resistor 21 for tuning theheater element 4 to a predefined resistor value. - The balancing
circuit 20 comprises essentially a Wheatstone bridge arrangement of fixed resistors R5, R6, R7, R8, in combination with a heatable resistor 4 (also indicated in the drawing as RH) and a tunable digital potentiometer which functions as the adjustable resistor 21 (also indicated in the drawing as U10). Thedigital potentiometer 21 has a very good linearity. The resistance in thebridge circuit 20 is determined by the resistor R8 circuited parallel to thedigital potentiometer 21. This resistor R8 (as well as the other fixed resistors R5, R6 and R7) has a very precise resistive value, typically with a margin of error of less than 0.1%. The circuit is balanced by the operational amplifier 22 (U11) which controls the voltage across theheater element 4. In particular, the amplifier U11 will control the Voltage between the + and − terminals of the amplifier so that there is no voltage difference, i.e. so that the bridge is balanced. When the Voltage difference is higher, the current through the heater element 4 (RH) will increase. Theheater element 4, conducting an increased current, will heat up and the resistance will rise accordingly. Accordingly a preset resistive value of theheater element 4 can be controlled, wherein the resistive value of theheater element 4 is known expressed as a ratio of resistive values of the R5, R6, R8, and a fraction of R7 determined by tunable digital potentiometer 21 (also indicated in the drawing as U10) - In addition,
FIG. 4 shows atest circuit 23 for the balancingcircuit 20 for measuring a dissipated power in theheater element 4 and for calculating a real temperature from the dissipated power in theheater element 4 based on the predetermined power-temperature characteristic which will be further elucidated with reference toFIG. 5 . - In this embodiment the
test circuit 23 comprises a pair of test terminals 24 (one being grounded) that directly connect to the terminals of theheater element 4. This arrangement provides a convenientlyimplementable circuit 21 for calculating the power dissipation in the resistor using the familiar formula VH2/RH with VH being a detected voltage difference across theheater element 4. In addition, RH indicates a true resistive value of theheater element 4 derived from the balancingcircuit 20. - In one embodiment, the
test circuit 23 comprises a calculatingcircuit 25 to calculate an offset value for thedigital potentiometer 21. In particular, thetest circuit 23 comprises aswitch 26 to activate the calculatingcircuit 25. In this embodiment, thetest circuit 23 measures a dissipated power in predefined neutral conditions. - Upon activation, a method of calibrating the hotplate
chemical trace detector 1 is carried out. In particular, using thetest circuit 23 there is provided a predetermined power level to the hotplate 2 by adjusting theadjustable resistor 21. When placing the sensor is placed in a neutral ambiance the predetermined power level can be related to a set temperature using a known power-temperature characteristic of the heater plate. Thus, a precise set-point for a predetermined number of temperatures can be provided to theprocessor 6 for theheater element 4, thus zeroing theadjustable resistor 21 to a preset value relating to the set temperature. - In another embodiment, the test circuit is connectable to a calibration circuit for providing a lookup table to the
processor 6 for calculating preset resistor values so as to provide predetermined real temperatures to said heater element. In this embodiment, thedetector 1, in particular, theprocessor 6, may be attached to a separate atest circuit 23, for instance, in a factory setting, indicated by the dotted lines 27. In predefined neutral conditions, a series of predetermined power settings to theheater element 4 is provided by adjusting theadjustable resistor 21. Accordingly a series of predetermined temperatures to these power settings is provided using the power-temperature characteristic of the heater plate. In this way a series of setpoints for setting a temperature can be provided to form a lookup table to theadjustable resistor 21 for providing preset resistor values so as to provide predetermined real temperatures to saidheater element 4. The lookup table is then integrated in theprocessor 6, in particular, is provided in a local memory to be accessed when setting the adjustable resistor to a predetermined temperature setting. - With the hotplate chemical trace detector as hereabove described, a precise temperature of the
heater element 4 can be measured by thetest circuit 23, without having to rely on the resistance-temperature characteristic of the heater element that may vary from sample to sample. In particular, a precise set point for the heater element can be provided. - Thus, when using this setpoint, a temperature can be set by adjusting the resistor in the balancing circuit to a real known temperature. The amount of power to achieve this temperature can be related to a dissipated reaction energy of the chemical trace. Indeed, the calculating
circuit 25 can be arranged to calculate a difference of a measured input power from thetest terminals 24 and a calculated input power. This calculated input power can for instance be provided using the known real temperature derived from thepreset resistor value 21 after calibration and relating it to a calculated power in theheater element 4 using the power-temperature characteristic of theheater element 4. - In this way, a new way of characterizing chemical substances can be provided, whereas, in addition to a measured conductance of the
sensing element 3. - In another embodiment, a dynamic temperature modulation is used of the hotplate 2. In this embodiment, the
processor 6 is arranged to provide a sliding temperature to theheater element 4. Thus, by providing a predefined dynamic temperature profile to theheater element 4 and deriving a sensed conductance of thesensor element 3, more information can be collected from the sensor to provide it to pattern recognition software implemented in thedatabase 13, which for this purpose stores conductance diagrams of predefined chemical substances measured in standard conditions as a function of known real temperature and temperature dynamics. -
FIG. 5 shows a power-temperature characteristic for two macroscopically identically hotplate sensors 2. The term macroscopically identical indicates a generally identical geometric structure for the hotplate 2, that is, a generally identical conducting structure for conducting heat from theheater element 4 and thesensor element 3. The power-temperature characteristics for the two heater elements W1 and W2 appear to be substantially identical although heater element W1 shows a resistance of 88.1 Ohm at 22.3° C. and heater element W3 shows a resistance of 97.4 Ohms at 22.1° C., a difference of more than 10%. The power-temperature characteristic is valid in standard conditions, at room temperature in clean air. In non-standard conditions the actual temperature can be measured and used for recalculating the power-temperature characteristic. In this way, the temperature of theheater element 4 Tsensor can be derived for a predetermined number of settings of thedigital potentiometer 21 Rpot. This provides a gauge line which can be converted to a function using a linear regression. -
Rpot=F(Tsensor) [1] - This equation can be implemented in software operating the
processor 6 so that a temperature can be preset with a deviation which may be less than 3-5° C. - Although the invention has been set forth using a limited number of embodiments the skilled person will appreciate that various modifications and adaptations thereto are possible without departing from the scope of the invention. For instance, it is possible to derive the power dissipated in the heater element by a
test circuit 23 coupled more indirectly to the heater element, for instance a terminal that measures the output voltage of the amplifier U11 ofFIG. 4 . Alternatively, or in addition thetest circuit 23 that does not need to use the balancingcircuit 20 but could measure the resistance of the heater directly using a preset value of thedigital potentiometer 21. - The invention is not limited to the disclosure of the embodiments shown in the description but encompasses variations and modifications thereto and is determined by the scope of the annexed claims and their equivalents.
Claims (6)
1-9. (canceled)
10. A method of calibrating a hotplate chemical trace detector comprising a heater plate tunable by an adjustable resistor, comprising:
placing the sensor in a preconditioned neutral ambiance;
providing a predetermined power to the heater plate;
relating the predetermined power in the heater plate to a set temperature using a temperature-power characteristic of the heater plate; and
zeroing the adjustable resistor to a preset value relating to the set temperature.
11. The method according to claim 10 , wherein the method further comprises using an estimated resistance-temperature characteristic of the heater plate for presetting predetermined resistance values of the adjustable resistor.
12. A method of identifying a chemical substance on a hotplate sensor comprising a adjustable resistance of a heater element heater element having predetermined temperature-power relationship comprising;
presetting a predetermined temperature to a hotplate using an adjustable resistance of a heater element;
measuring a dissipated power in the heater element;
comparing a measured dissipated power to an estimated power using the predetermined temperature-power relationship and relating a measured power difference to a reaction energy of a combination of chemical substances reacting on the hotplate; and
identifying said chemical substance based on said measured power difference.
13. A method of calibrating a hotplate chemical trace detector comprising:
providing a heatable conducting plate comprising a heater element having a predetermined power-temperature characteristic;
providing a balancing circuit comprising an adjustable resistor for tuning the heater element to a predefined resistor value;
providing a processor for adjusting the adjustable resistor so as to provide a stabilized temperature in said heatable conducting plate;
providing a detection circuit for detecting a change of resistance in the heatable conducting plate in accordance with the presence of a chemical trace reacting in the presence of the conducting plate;
providing a test circuit for measuring a dissipated power in the heater element and for calculating a real temperature from the dissipated power in the heater element based on the predetermined power-temperature characteristic;
placing the trace detector in a preconditioned neutral ambiance;
providing power to the heatable conducting plate having the predetermined power-temperature characteristic;
measuring, via said test circuit, the power provided to the heatable conducting plate;
relating the measured power in the heatable conducting plate to a set temperature using the power-temperature characteristic of the heatable conducting plate; and
zeroing the adjustable resistor of the balancing circuit to a preset value relating to the set temperature.
14. The method according to claim 13 , wherein the method further comprises using an estimated resistance-temperature characteristic of the heatable conducting plate for presetting predetermined resistance values of the adjustable resistor.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US13/466,353 US20120216593A1 (en) | 2005-11-24 | 2012-05-08 | Electronic chemical trace detector |
Applications Claiming Priority (6)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP05077694.7 | 2005-11-24 | ||
EP05077694A EP1790979A1 (en) | 2005-11-24 | 2005-11-24 | Electronic chemical trace detector |
US75009505P | 2005-11-28 | 2005-11-28 | |
PCT/NL2006/000591 WO2007061294A1 (en) | 2005-11-24 | 2006-11-24 | Electronic chemical trace detector |
US9467508A | 2008-10-06 | 2008-10-06 | |
US13/466,353 US20120216593A1 (en) | 2005-11-24 | 2012-05-08 | Electronic chemical trace detector |
Related Parent Applications (2)
Application Number | Title | Priority Date | Filing Date |
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PCT/NL2006/000591 Division WO2007061294A1 (en) | 2005-11-24 | 2006-11-24 | Electronic chemical trace detector |
US9467508A Division | 2005-11-24 | 2008-10-06 |
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Publication Number | Publication Date |
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US20120216593A1 true US20120216593A1 (en) | 2012-08-30 |
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Application Number | Title | Priority Date | Filing Date |
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US12/094,675 Expired - Fee Related US8216519B2 (en) | 2005-11-24 | 2006-11-24 | Electronic chemical trace detector |
US13/466,353 Abandoned US20120216593A1 (en) | 2005-11-24 | 2012-05-08 | Electronic chemical trace detector |
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US12/094,675 Expired - Fee Related US8216519B2 (en) | 2005-11-24 | 2006-11-24 | Electronic chemical trace detector |
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US (2) | US8216519B2 (en) |
EP (2) | EP1790979A1 (en) |
JP (1) | JP5122473B2 (en) |
CN (1) | CN101360991B (en) |
AT (1) | ATE453861T1 (en) |
DE (1) | DE602006011506D1 (en) |
ES (1) | ES2339281T3 (en) |
WO (1) | WO2007061294A1 (en) |
Families Citing this family (14)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP1978087A1 (en) * | 2007-04-02 | 2008-10-08 | Consultatie Implementatie Technisch Beheer B.V. | System and method for detecting micro-organisms |
US20090084160A1 (en) * | 2007-10-01 | 2009-04-02 | Scott Technologies, Inc. | Gas measuring device and method of manufacturing the same |
EP2105728A1 (en) * | 2008-03-27 | 2009-09-30 | Consultatie Implementatie Technisch Beheer B.V. | Detector comprising one catalysed and one uncatalysed metal oxide-sensor and method of detecting |
DE102008043135A1 (en) * | 2008-10-23 | 2010-04-29 | Endress + Hauser Wetzer Gmbh + Co Kg | Device for determining or monitoring process factor, has sensor unit, which has parameter, and control element, which is adjustable |
US20110106476A1 (en) * | 2009-11-04 | 2011-05-05 | Gm Global Technology Operations, Inc. | Methods and systems for thermistor temperature processing |
US8646306B2 (en) * | 2009-12-14 | 2014-02-11 | Ngk Insulators, Ltd. | Method for manufacturing sensor element for gas sensor |
NL2008632C2 (en) * | 2012-04-12 | 2013-10-16 | Consultatie Implementatie Tech Beheer B V | MOBILE DEVICE AND METHOD FOR ANALYZING BREATH SAMPLES. |
NL2008737C2 (en) | 2012-05-01 | 2013-11-04 | Consultatie Implementatie Tech Beheer B V | CLOSING ELEMENT FOR CLOSING A SAMPLE HOLDER. |
EP2762867B1 (en) * | 2013-01-31 | 2018-11-21 | Sensirion AG | Gas sensor with temperature control |
CN105404324A (en) * | 2015-11-26 | 2016-03-16 | 重庆晟初科技有限公司 | Temperature control method and system applied to specific electromagnetic spectrum therapeutic apparatus |
JP6701956B2 (en) * | 2016-05-23 | 2020-05-27 | 株式会社島津製作所 | Thermal conductivity detector and gas chromatograph |
TWI633046B (en) * | 2016-12-29 | 2018-08-21 | 財團法人工業技術研究院 | Micro-electromechanical apparatus for heating energy control |
US10393718B2 (en) | 2016-12-29 | 2019-08-27 | Industrial Technology Research Institute | Micro-electromechanical apparatus for thermal energy control |
CN112585455A (en) * | 2018-08-10 | 2021-03-30 | Tdk株式会社 | Gas sensor |
Citations (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP1182439A1 (en) * | 2000-08-23 | 2002-02-27 | TA Instruments - Waters LLC | Power compensation differential scanning calorimeter |
Family Cites Families (16)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB802372A (en) * | 1955-07-01 | 1958-10-01 | Simplex Electric Co Ltd | Improvements relating to means for controlling the power dissipation in electric heaters |
US4847783A (en) * | 1987-05-27 | 1989-07-11 | Richard Grace | Gas sensing instrument |
US4947057A (en) * | 1987-09-09 | 1990-08-07 | Motorola, Inc. | Adjustable temperature variable output signal circuit |
JPH09152417A (en) * | 1995-11-30 | 1997-06-10 | Toyota Motor Corp | Heater electric energization control method for oxygen sensor |
IT1285863B1 (en) * | 1996-05-08 | 1998-06-24 | Magneti Marelli Spa | CONTROL CIRCUIT FOR A VARIABLE RESISTANCE HEATER ASSOCIATED WITH AN EXHAUST GAS OXYGEN SENSOR. |
JP2963871B2 (en) * | 1996-05-20 | 1999-10-18 | ビージー ピーエルシー | Internal combustion engine |
JP3764800B2 (en) * | 1997-05-23 | 2006-04-12 | 株式会社リケン | Heating control circuit |
JP3700379B2 (en) * | 1998-03-04 | 2005-09-28 | 富士電機機器制御株式会社 | Gas detection alarm |
JP4033575B2 (en) * | 1999-03-19 | 2008-01-16 | ホーチキ株式会社 | Sensor and humidity gas detection method |
JP3715162B2 (en) * | 1999-12-17 | 2005-11-09 | 矢崎総業株式会社 | Gas detection device and gas detection method |
US20040075140A1 (en) * | 2000-12-20 | 2004-04-22 | Henry Baltes | Microsensor and single chip integrated microsensor system |
CN1453578A (en) * | 2002-04-23 | 2003-11-05 | 马立文 | Temperature compensating circuit for gas-sensing sensor |
DE10218834A1 (en) * | 2002-04-26 | 2003-12-04 | Siemens Ag | Thermal conductivity gas analyzer |
JP3985720B2 (en) * | 2003-04-21 | 2007-10-03 | 株式会社日立製作所 | Hydrogen gas sensor |
JP2005156161A (en) * | 2003-11-20 | 2005-06-16 | Yazaki Corp | Heater control circuit |
JP4540992B2 (en) * | 2004-01-13 | 2010-09-08 | 矢崎総業株式会社 | Gas detector |
-
2005
- 2005-11-24 EP EP05077694A patent/EP1790979A1/en not_active Withdrawn
-
2006
- 2006-11-24 JP JP2008542260A patent/JP5122473B2/en not_active Expired - Fee Related
- 2006-11-24 ES ES06824281T patent/ES2339281T3/en active Active
- 2006-11-24 AT AT06824281T patent/ATE453861T1/en not_active IP Right Cessation
- 2006-11-24 US US12/094,675 patent/US8216519B2/en not_active Expired - Fee Related
- 2006-11-24 CN CN2006800515942A patent/CN101360991B/en not_active Expired - Fee Related
- 2006-11-24 WO PCT/NL2006/000591 patent/WO2007061294A1/en active Application Filing
- 2006-11-24 EP EP06824281A patent/EP1960764B1/en not_active Not-in-force
- 2006-11-24 DE DE602006011506T patent/DE602006011506D1/en active Active
-
2012
- 2012-05-08 US US13/466,353 patent/US20120216593A1/en not_active Abandoned
Patent Citations (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP1182439A1 (en) * | 2000-08-23 | 2002-02-27 | TA Instruments - Waters LLC | Power compensation differential scanning calorimeter |
Also Published As
Publication number | Publication date |
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US20090215180A1 (en) | 2009-08-27 |
ES2339281T3 (en) | 2010-05-18 |
EP1960764B1 (en) | 2009-12-30 |
JP2009517658A (en) | 2009-04-30 |
CN101360991B (en) | 2012-02-01 |
EP1960764A1 (en) | 2008-08-27 |
WO2007061294A1 (en) | 2007-05-31 |
EP1790979A1 (en) | 2007-05-30 |
ATE453861T1 (en) | 2010-01-15 |
CN101360991A (en) | 2009-02-04 |
DE602006011506D1 (en) | 2010-02-11 |
US8216519B2 (en) | 2012-07-10 |
JP5122473B2 (en) | 2013-01-16 |
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