Classifications

• • 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
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
  • G01D3/00—Indicating or recording apparatus with provision for the special purposes referred to in the subgroups
  • G01D3/02—Indicating or recording apparatus with provision for the special purposes referred to in the subgroups with provision for altering or correcting the law of variation

Definitions

• the inventors have made up the first system of measuring chemical and physical variables based on an array of suitable sensors incorporated in a non linear circuit or system.
• the non linear circuit or system mentioned above may be self-oscillating and exhibit chaotic behavior.
• the inventors have made up a method to read out an array of sensors that relies on considering the sensors as elements of dynamic electronic circuits that are operated in non regular regimes, preferrably on the edge-of-the-chaos.
• the measurement procedure and the electronic circuits are designed such that each measure will drive the circuit in a specific regime.
• the object of the invention is to solve the problems mentioned above.
• this is carried out by incorporating the sensor or sensors in a non-linear circuit or system that may be self-oscillating and exhibit chaotic behaviour.
• This invention regards the measurement of physical and chemical variables through an array of suitable sensors.
• the invented method allows the measurands to be measured in real-time and both analog and discrete mode. It provides better measurement results in comparison with the same sensors used in standard read-out configuration.
• Deterministic non-linear dynamic systems have been studied extensively only in the last few years but have nonetheless already found applications in real life.
• the basic characteristic of these systems is that they though apparently random for an external observer do have laws governing their evolution over time.
• the laws are in general recursive, which makes them very sensitive to the initial conditions.
• a small difference in the initial state of two identical systems may give after sufficiently long time a very large difference between the two systems. This is an indicator of the so-called chaotic regime.
• Non-linear systems are often described and characterised by the so-called phase space.
• phase space This is a graph with a state variable of the system on one axis and its delayed versions on the other axes (often only two axes are drawn). Even if only one variable is considered to build this space, a lot of information about the whole system can be obtained due to non-linearity that mixes information among the state variables. Since some variables often cannot be directly observed in a system, the analysis of phase space is therefore of utmost importance in the study of non-linear systems.
• an attractor In phase space, an attractor consists of a number of measurement points that are encountered by the dynamics out of an initial transient. This operative definition can be implemented collecting states in a relatively short period of time. This time depends on the circuitry, but for the intended applications a time of the same order of the sensor reaction time (i.e. to get 10% of the final value) is considered sufficient for mapping the attractor. We call the time necessary to map the attractor the attractor mapping time (tam).
• the sensor signals have so far mainly been used as individual parts in the system.
• the sensors are used in a circuit that exhibit strongly non-linear dynamics and, under certain conditions, chaotic behaviour.
• the attractor of the circuit is studied in real time. If a change in the physical or chemical surroundings causes a change in the shape of the attractor, detection can be made within one or a few tam, i.e. much shorter than the normal response time (i.e. to get 90% of the final value) of a single sensor.
• the assumption we have to make for the second aim to hold is that the system is stable also when the sensors drift, provided that they drift in a similar manner.
• the invention solves one of the most difficult problems for process monitoring in the industry, namely to detect slow changes in the process that may be difficult to separate from drift phenomena in the sensor array.
• the sensor system would then be stable (i.e. have qualitatively the same attractor) also when the sensors drift. It would, however, change if the sensor variations were due to slow changes in the environment.
• the evaluation of the state of the circuit i.e. the type of attractor
• FFT is enough to completely describe the harmonic spectrum in the signal, and this is enough when periodic vs. broadband signal should be distinguished.
• a simple series of filters can also solve the problem still remaining in the analogue processing field.
• the response time is very short (order of seconds to get a stable state for chemical sensors, that are often very slower);
• the dynamic system "probes" the sensor response many times, in a broadband mode, in many different electric regimes and thus obtains a better signal-to-noise ratio.
• the sensor array of interest in a physical and chemical measurement may consist either of a single sensor, if highly selective to a single intended measurand, or of many sensors. This is required when either the measurands are many or the sensors have partially overlapping selectivities. Involved sensors are those with conversion of the measurand into electrical properties.
• a method to read out an array of sensors used for measurement of physical and chemical variables has been invented. The method relies on considering the sensors as elements of dynamic electronic circuits that are operated in non-regular regimes, preferrably on the edge-of-the-chaos. The measurement procedure and the electronic circuits are designed such that each measure will drive the circuit in a specific regime.
• FIG. 1 is a block diagram of the basic configuration of the measurement system, according to the present invention, with one sensor and a Non Linear Dynamic Circuit (NLDC).
• NLDC Non Linear Dynamic Circuit
• NLDC is schematically represented as a two-ports block, one used to connect the sensor, the other to connect a load, whose equivalent resistance is marked as RL.
• An Analogue to Digital converter provides for information on the circuit regime to an analyser that may be analogue as well as digital.
• FIG. 2 is a block diagram of a multi-sensor system, composed of an NLDC connected to two sensors. More sensors are allowed as well.
• FIG. 3 is a block diagram of a multi-sensor system, each sensor being connected to each own
• the outputs from the NLDC's are then connected to one or several other NLDC's with a weight g, and thereby influence their dynamic behaviour.
• FIG. 4 shows a multi-sensor system where the sensors influence only the comiectivity strength g between two NLDC's.
• FIG. 5 shows a generalisation of the schemes shown in FIG. 3 and 4 with an interconnected network of several NLDC's (shown as circular nodes) and several sensors included in both the interconnection weights and the nodes.
• FIG. 6 shows an example of synchronization diagram with the locus of the (single) eigenvalue, for two R ⁇ ssler-like circuits coupled as in FIG. 4, with two MOS chemical sensors affecting the connections.
• the measurand that is a gas concentration x, moves the eigenvalue ⁇ along the arrow representing the locus.
• FIG. 7 Example of a bifurcation diagram referred to a circuit like the one shown in FIG. 1.
• the x-axis represents the measurand (e.g. the concentration of a certain gas in air), while the y-axis shows the dynamic pattern of the NLDC as accumulation points in a Poincare section.
• This map shows an edge-of-the chaos regime at the lowest value of the measurand and regular periodic regime above a certain minimum detection limit (mdl). At certain values of the measurand (so-called bifurcation points) the period decreases of one half. Pi marks the range in which there is a period of i length.
• FIG. 8 The R ⁇ ssler-attractor circuit used in a chemical sensing example.
• FIG. 9 The chaotic attractor obtained for zero hydrogen concentration.
• the attractor was forced to be chaotic at zero concentration by varying the voltage V.
• the graph was made by plotting the voltages at X and Y in Fig. 8 on the two axes.
• Fig. 10 The limit cycles (period four) obtained at 156 ppm hydrogen concentration.
• Fig. 11 The limit cycles (period two) obtained at 312 ppm hydrogen concentration.
• Fig. 2 introduces two sensors whose states affect the dynamics.
• the design should consider exactly the same procedure if the intended measurand is only one. In this case the system is redundant for reasons of precision and noise rejection.
• the designer will design a double parameter bifurcation diagram with bifurcations placed in convenient locations of the measurand plane.
• Information extraction in schemes shown in Fig. 1 and 2 may be discrete or continuous. • Discrete means to recognise the order of the bifurcation we are near to and then to estimate a range of the measurand. Taking as an example the case of the bifurcation diagram shown in Fig. 7, this recognition means to know which interval among P16, P8, P4, P2, PI, P0 the measurand belongs to. These intervals are referred to attractor limit cycles of period 16 (or more), 8, 4, 2, 1, 0 (fixed point), respectively. The period of the actual cycle can be easily recognised using a FFT analysis (so we need the A/D converter shown in Fig.
• Discrete is superior to any other existing readout strategy, being very simple and constrained only by the resolution of the measure (i.e. the length of the intervals).
• Continuous means to estimate the parameter value, that is our measurand, from computation instead of a simple recognition. Continuous requires first the discrete estimation to be done, that is to identify the interval; after a refinement takes place measuring the distance between the actual attractor and the one at the next bifurcation (upper bound of the interval). This distance is properly defined according to the bifurcation type and the dynamics type.
• the simplest distance is the ratio of power of the forthcoming sub-harmonic (e.g. period 4) and of the fundamental harmonic (period 1).
• the ratio refers to the presence of the bifurcation point (see Fig. 7).
• a calibration curve can relate the actual ratio to the measurand value in any of the intervals. This approach is much more effective than trying to estimate the standard dynamics parameters, such as generalised Lyapunov exponents and generalised attractor dimensions, as proposed by other authors. The reason is that the double mapping from attractor reconstruction to dynamics parameters then to measurands, is imprecise because difficult to be calibrated and prone to noise and ageing. On the contrary, the design and use of bifurcations is an engineering approach, controllable, precise and repeatable.
• Fig. 6 shows the case of two Rossler-like circuits, with two MOS chemical sensors affecting the connections as in scheme 4.
• the measurand that is a gas concentration, moves the eigenvalue along the arrow representing the locus.
• the occurrence of synchronization means that the concentration is below a value xo.
• & pattern of synchronisation A simulation-based design can be done in order to define many suitable ranges of. measurands, each one occurring in coincidence with a certain synchronisation pattern.
• the read-out technique can be discrete or continuous.
• Discrete means simply to recognise the synchronisation pattern and to associate the ranges of the measurands. Continuous means first discrete estimation, and after a refinement, based on measuring the distance between the actual attractor of the whole network and the one at the neighbouring (according to a suitable distance and induced topology) synchronisation pattern.
• the detection of synchronisation is surely the simplest electronic operation to do: it consists only of a comparator that turns on output high when the inputs' difference is less than a fixed threshold.
• Measurement of physical and chemical variables is something that necessarily occurs in any industrial activities of every field, which incur in technical processes, especially in fabrications ones. Those processes are quite always based on detecting environment changes.
• This invention regards that measurement mentioned above, through an array of suitable sensors.
• the invented method allows the measurands to be measured in real-time and both analog and discrete mode. It provides better measurement results in comparison with die same sensors used in standard read-out configuration.

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• Testing Or Calibration Of Command Recording Devices (AREA)
• Measuring Fluid Pressure (AREA)
• Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)
• Measuring Volume Flow (AREA)

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• 2001
  • 2001-05-11 SE SE0101657A patent/SE524708C2/sv not_active IP Right Cessation
  • 2001-12-21 EP EP01988104A patent/EP1461590A1/de not_active Withdrawn
  • 2001-12-21 WO PCT/IT2001/000650 patent/WO2002093111A1/en not_active Application Discontinuation

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