ES2381346A1 - Device for measuring oxygen in fluids - Google Patents

Abstract

The device has an excitation signal generator with a block (2) for optoelectronically detecting fluorescent radiation and electronically amplifying the detected fluorescence signal, with a filtering block, with a block (4) for modulating the amplitude of the radiation arriving at the fluorescence sensor, and with an electronic phase detector block (5) connected to a microcontroller (6) with the known method for evaluating the phase shift between the phase of the signal which excites a fluorescence sensor inserted into the fluid and the phase of the emitted fluorescence signal being used in the measurement. Said filtering block is a multiple filter (3) with switchable capacitances, while said excitation signal generator is a generator (1) from which at least one common clock signal is extracted in order to synchronize the sections of said multiple filter.

Description

Fluid oxygen meter.

OBJECT OF THE INVENTION

The present invention, as expressed in the statement of this specification, refers to an oxygen meter in fluids, preferably for liquids but also applicable in gases, whose essential purpose is to obtain accuracies of the order of parts per billion, ppb (10-9), being especially applicable to the control of productive processes based on bioreactors, such as wine production, in the phases in which knowledge of this data is very important; and in order to facilitate better forecasts for the destination and treatment corresponding to the final products; The invention can also be extended to very different fluids, among which different gases can be included. The technical sector of the invention corresponds to the techniques and electronic circuits for measuring oxygen concentrations based on the decrease in fluorescence intensity by increasing the proportion of oxygen, using the technique known as the phase phase evaluation method of the signal that excites a fluorescence sensor inserted in the fluid and the phase of the emitted fluorescence signal, and using circuits such as operational amplifiers, opto-electronic fluorescent radiation detectors with electronic amplification of the detected fluorescence signal, filters , amplitude modulators of the radiation that reaches the corresponding fluorescence sensor and electronic phase detectors equipped with a microcontroller. Therefore, the invention could be framed in the opto-electronics sector with application to the food industry.

BACKGROUND OF THE INVENTION

A large part of the current oxygen concentration meters are based on the principle of decreasing the intensity of fluorescence emitted by a fluorophore in the presence of oxygen, both for gaseous and liquid media (Kaustsky 1939). For this, a fluorescent sensor is used in intimate contact with the medium to which the oxygen concentration is desired, which is excited by a radiation generally of the visible spectrum and which offers in response another radiation, generally also of the visible spectrum but of a wavelength greater than that of the excitation. For an excitation of constant magnitude, the intensity of the fluorescent radiation emitted by the sensor is inversely proportional to the concentration of oxygen in the medium in which it is found, this fact having been quantified using the Stern and Volmer equation in 1919. But this This measure is very inaccurate, since the intensity of the fluorescent radiation emitted by the sensor can change depending on the intensity of the exciting radiation, depending on the opto-mechanical coupling system between the excitation generated and the optical fiber , and depending on the losses introduced by the fiber curvatures from the equipment to the sensor; giving changes also, in addition and among others, by temperature variations.

If the excitation abruptly ceases, the fluorescence emitted by the sensor offers a generally exponential decay with time, the time constant t being proportional to the concentration of oxygen in the medium, and the resulting emitted fluorescence also results in a high degree of independence. regarding the variations of the initial intensity of the fluorescence when the excitation is suddenly interrupted. The direct evaluation of the time constant by measuring the time elapsed from the interruption of the excitation until the fluorescence intensity has decreased by 63%, which is what is usually done, has the disadvantage that the latter Fluorescence intensity level, generally, noise makes the determination of the moment at which the exponential decay of fluorescence reaches it very inaccurate. The measurement of the time constant by using a temporary measurement window improves the measurement for large time constants corresponding to very low concentrations of oxygen, but is insufficient without the elimination of noise. One of the solutions to the noise problem is to carry out a large number of consecutive measurements by means of an excitation in the form of a short-lived pulse train, also averaging the corresponding fluorescence intensities at the same time in each cycle; given here the difficulty of needing a relatively complex system of digitalization and data storage and a very high stability in the rectangular form of the very short duration pulses that are required for the measurement of time constants of the fluorescence decay, often of the order of hundreds of nanoseconds. These requirements for the source of excitation are only possible with the use of lasers; presenting this solution the disadvantage that the cost of the measuring equipment would be excessively raised.

The use of an exciting radiation modulated sinusoidally in amplitude significantly improves the problems related to noise, since in response to this excitation the response of the fluorescent sensor is also sinusoidal, but delayed in phase with respect to the excitation. The corresponding offset angle between the excitation and the emitted fluorescence is proportional to the concentration of oxygen in the medium in which the sensor is located; Its evaluation constitutes an indirect way of measuring the time constant of the fluorescence decay and consequently of the concentration of oxygen in the medium. The measurement of the phase shift between these sinusoidal electrical signals (excitation and detected fluorescence) produces important errors due to the high sensitivity of the phase detectors and the amplitude of the signal, which is critical in the measurement of small concentrations of oxygen. The fluorescence emitted by the sensor is a very loud signal and therefore a strong filter action is always necessary to increase the signal / noise ratio by reducing the signal spectrum. On the other hand, the excitation signal has to be very stable in frequency, since small changes in it can produce large changes in the final value of the offset. Said sinusoidal signal, when the circuits are of low frequency, is usually obtained from a square wave of high frequency stability and a very high selectivity bandpass filter Q, centered on the frequency of the square wave.

In most circuits, the temperature and the drifts of the long-term component values cause unpredictable changes in the lag to be measured, reducing both the repeatability and the reproducibility of the measurement, which leads to significant errors in the appreciation of the concentration of oxygen in the medium. To reduce these negative effects, the following factors must be taken into account: first, the paths for the excitation signal and the detected fluorescence signal must be similar to guarantee very similar phase delays in both, and secondly, the components Passive filters (capacitors and resistors) may have high tolerances and fluctuations in their value with temperature. Thus, the phase shift signal will have unpredictable changes in similar circuits based on independent integrated circuits.

On the other hand, the detection of the phase can be carried out by many circuits, such as tie-down loops (PLL) or by "lock-in" amplifiers of very high cost. The former offer very good results in low profile meters, since their long-term stability and thermal drifts increase the uncertainty of the measurement. In addition, phase detection without feedback is possible with simple electronic circuits, such as zero-crossing detectors and averages, which have very high long-term reliability, high frequency stability, although high frequency frequency stability is required. the signals that are applied to them, with very pure spectral components, which is no problem in the current state of the art.

We also want to indicate in this section of the report that a general meter architecture based on phase shift is described in US patent US6912050 that can be considered a precursor to the oxygen meter of the invention, which provides a means to reach measurements accuracy of concentrations of the order of parts per billion (ppb).

DESCRIPTION OF THE INVENTION

To achieve the objectives and avoid the inconveniences indicated in previous sections, the invention consists of a fluid oxygen meter applicable to the measurement of very small concentrations of dissolved oxygen in fluids, preferably in liquids but also in gases and allowing to measure concentrations of the order of parts per billion (ppb), with an excitation signal generator, with an opto-electronic detector block of fluorescent radiation and electronic amplifier of detected fluorescence signal, with a filtering block, with a block that modulates in amplitude the radiation that reaches the fluorescence sensor, and with an electronic phase detector block connected to a microcontroller. The fluid oxygen meter of the invention employs for measurement the conventional method of evaluation of the phase shift between the phase of the signal that excites a fluorescence sensor inserted in the fluid and the phase of the emitted fluorescence signal.

Novelly, the fluid oxygen meter of the invention has the characteristic that said filtering block is a multiple filter of switchable capacities, while the aforementioned excitation signal generator is a generator from which at least one signal is extracted of common clock for synchronization of the sections comprising said multiple filter.

In a preferred embodiment of the invention each of the aforementioned sections of switchable capacities of the multiple filter consists of a pass-band filter centered on the excitation frequency emitted by the generator and is applied both to the signal corresponding to the excitation, and to the fluorescence signal detected.

Another characteristic of the preferred embodiment of the invention is that said filter has inputs for the signal that arrives from said fluorescence sensor, through the opto-electronic radiation detector, and for the signal from the generator, also providing this output filter for the signals that it sends to the electronic phase detector and to said sensor through the amplitude modulator of radiation; This last signal is also carried, which thus reaches said modulator to the electronic phase detector.

Another feature of the preferred embodiment of the invention is that the multiple filter comprises at least a first section to which the generator signal is applied and a second section that receives the fluorescence sensor signal through the opto-electronic detector; while the generator comprises at least one crystal oscillator connected to a programmable frequency divider with adjustable division ratio which in turn connects to a fixed ratio divider.

The fluid oxygen meter of the preferred embodiment of the invention also has the characteristic that the crystal oscillator is a square and high frequency oscillator; while the said fixed ratio corresponds to the ratio between the clock frequency and the center frequency of the filter; while the mentioned microcontroller has an input for temperature data.

With the structure described above, the fluid oxygen meter of the invention has advantages relative to the use of filters with switched, pass-band capabilities, focused on the excitation frequency, both for the excitation signal and for the fluorescence signal detected, and synchronized by a common clock signal that comes from the generator of the excitation signal itself, so that the cost of the components is much lower than in known meters and reliability, as well as the durability of the Meters of the invention are remarkably larger than those given in the prior art. In addition, the use of a synchronous double filter with switched capacities reduces the uncertainty about the uncontrollable magnitude of the phase shift that the required band-pass filter centered on the excitation frequency, for the detected fluorescence signal, introduces. With this, the type of filtering that is used drastically reduces unpredictable and uncontrolled changes in the offset between the signals to be measured. This effect is particularly important when measuring for very small concentrations of oxygen and present for a long time, as is the case, for example, of wine fermenters, in which the required oxygen concentrations are of the order of very few parts per billion, ppb, (10-9).

Next, in order to facilitate a better understanding of this descriptive report and as an integral part thereof, some figures are attached in which the object of the invention has been shown as an illustrative and non-limiting nature.

BRIEF DESCRIPTION OF THE FIGURES

 Figure 1.- Represents a generic functional block diagram of a fluid oxygen meter made according to the present invention.

Figure 2.- Represents the meter of the previous figure 1 by a more detailed functional block diagram, according to a preferred embodiment described in the next section.

DESCRIPTION OF AN EXAMPLE OF EMBODIMENT OF THE INVENTION

Next, a description of an example of the invention is made by referring to the references of the figures.

Thus, the fluid oxygen meter of this example of the invention responds to the generic block diagram of Figure 1, as well as the more detailed diagram of Figure 2, whose references are as follows:

1: Excitation signal generator.

2: Opto-electronic fluorescent radiation detector block and electronic fluorescence signal amplifier detected.

3: Filter block.

4: Modulating block in amplitude of the radiation that reaches the fluorescence sensor.

5: Electronic phase detector block.

6: Microcontroller. 1st: Crystal oscillator. 1b: Programmable frequency divider (with adjustable division ratio). 1c: Frequency divider with fixed division ratio. 3rd: First section of the filter block (to which the generator signal is applied). 3b: Second section of the filter block (receives the signal from the fluorescence sensor through the detector

opto-electronic e1: First entry of the filter block. e2: Second entry of the filter block. s1: First exit of the filter block. s2: Second output of the filter block.

A: Programmable frequency divider input (to apply the division ratio).

CLK: Clock inputs in the sections of the filter block (to apply the common clock signal from the generator).

The oxygen meter of this example responds to the generic scheme of Figure 1, having an excitation signal generator 1, as well as an opto-electronic fluorescent radiation detector block and an detected fluorescence signal electronic amplifier receiving signal from a sensor introduced into the fluid from which the oxygen is to be measured, these blocks 1 and 2 being connected to a filtering block 3, as can be seen in figure 1. In addition, in this generic scheme of figure 1 a modulating block is represented in amplitude of the radiation that reaches the fluorescence sensor, which has been referred to as 4; this block 4 having an exit to the sensor referred to above, as seen in said figure 1. There is also a phase 5 electronic detector block connected to a microcontroller 6, being able to see in figure 1 the generic connection between these blocks 3, 4 and 5, a connection that in addition to generic is functional because it does not necessarily have to be made by cable.

The present example responds to the general feature of the invention in that the filter block is a multiple filter, double in this example, of switchable capacities, while the excitation signal generator is a generator from which at least one Common clock signal for synchronization of the sections comprising the filter.

For this example, each of the sections of switchable capacities of the multiple filter 3, consists of a pass-band filter centered on the excitation frequency emitted by the generator 1 and is applied to both the signal corresponding to the excitation and the signal of the detected fluorescence.

In addition, in the present example the filter 3 has inputs e1, e2, one of them being for the signal arriving from said fluorescence sensor, specifically the one referred to as e1; it can be seen in figure 2 that it does not arrive directly but through the opto-electronic radiation detector 2; and being the other e2 that comes from the generator

1. In addition, the filter 3 has outputs s1 and s2 for, respectively, the signal that is sent to the electronic phase detector 5 exclusively, and that in addition to being sent to said electronic phase detector 5 is sent to the modulator 4 , as can be seen in Figure 2. In the meter of this example, the multiple filter 3 comprises a first section 3a to which the signal from the generator 1 is applied and a second section 3b that receives the signal from the fluorescence sensor through the opto-electronic detector 2; while the generator 1 comprises at least one crystal oscillator 1a connected to a programmable frequency divider 1b with adjustable division ratio R which in turn connects with a fixed ratio divider 1c.

In the meter of this example, the crystal oscillator 1a is a square wave oscillator and high frequency, the said fixed ratio corresponds to the ratio between the clock frequency that is applied at the CLK clock inputs and the filter center frequency ; while the microcontroller has an input for temperature data; All of this can be seen in Figure 2.

Descending to a more concrete level, which would further facilitate the physical realization of the example of the invention, we can say that the crystal stabilized high frequency generator can be, for example, 8MHz offering at its output a square wave that feeds the divider of frequencies 1b at whose input R a division ratio equal to 4 can be applied, so that at the output there would be a square wave of 2MHz usable as a filter clock 3, provided with sections 3a and 3b, for which you can use, for example, an LMF100 from National Semiconductors, operating in step-band mode 1. Simultaneously, the output of the splitter 1b is taken to the splitter 1c with a division factor of 100, whereby the frequency of the square wave at the output is 20kHz. In addition, the sinusoidal output of section 3a of the filter is taken to block 4 to produce the necessary radiation that excites the fluorescence sensor with amplitude modulation, sinusoidally and at the referred frequency of 20kHz. On the other hand, the fluorescent radiation emitted by the fluorescence sensor arrives at the detector block 2 which also incorporates a very broadband amplifier on the basis of photodiode amplifier and operational amplifiers, being able to employ for example an OPA627, taking the electrical output signal to section 3b of the filter, in which a sine wave of 20kHz is obtained, or near values, whose phase offset with respect to the excitation signal is evaluated in the phase 5 detector block, using, for example, zero crossing detectors with a very low threshold, a constant and stable amplitude pulse shaper, for example by means of voltage references, for which an LT1009 circuit, and low-pass filters, with a very high time constant, such as 5 seconds, can be used. The continuous signal that is thus obtained, at the output of the phase detector, is brought to a 10-bit A / D conversion input of the microcontroller 6 which, in turn, receives a temperature continuous signal proportional to the temperature of the medium in which the sensor is inserted, to from this information calculate the value of the dissolved oxygen concentration.

Thus, with the meter of this example, an optimized oxygen meter for measuring very small concentrations of dissolved oxygen in gases and liquids is possible, using a double filter of switched capacities for the generation of the excitation sinusoidal signal of the fluorescent sensor element Oxygen sensitive in one of its sections and the filtering of the fluorescence signal from the sensor detected in the other section, operating in the pass-band mode with the same square wave signal as clock for the circuit that comes from the same oscillator which produces the square wave signal for excitation, a result that had not been obtained so far in the current state of the art.

Claims (6)

1.- FLUX OXYGEN METER, applicable to the measurement of very small concentrations of dissolved oxygen in fluids, with an excitation signal generator, with an opto-electronic detector block of fluorescent radiation and electronic fluorescence signal amplifier detected (2), with a filter block, with a modulating block in amplitude of the radiation that reaches the fluorescence sensor (4), and with an electronic phase detector block (5) connected to a microcontroller (6); using the measurement method of the offset between the phase of the signal that excites a fluorescence sensor inserted in the fluid and the phase of the emitted fluorescence signal; characterized in that said filtering block is a multiple filter of switchable capacities (3), while said excitation signal generator is a generator (1) from which at least one common clock signal is extracted for synchronization of the sections that It comprises said multiple filter. 2. FLUX OXYGEN METER, according to claim 1, characterized in that each of said sections of switchable capacities of the multiple filter (3) consists of a pass-band filter centered on the excitation frequency emitted by the generator (1) and it is applied both to the signal corresponding to the excitation, and to the signal of the detected fluorescence. 3.- FLUX OXYGEN METER, according to claim 1 or 2, characterized in that the filter (3) has inputs (e1, e2) for the signal arriving from said fluorescence sensor (e1), through the optoelectronic detector of radiation (2), and for the signal (e2) from the generator (1), this filter (3) also having outputs (s1, s2) for the signals sent to the electronic phase detector (5) and to said sensor through the radiation amplitude modulator (4); This last signal is also carried, which thus reaches said modulator (4) to the electronic phase detector (5). 4. FLUX OXYGEN METER, according to any one of claims 1 to 3, characterized in that the multiple filter comprises at least a first section (3a) to which the generator signal (1) and a second section ( 3b) that receives the fluorescence sensor signal through the opto-electronic detector (2); while the generator (1) comprises at least one crystal oscillator (1a) connected to a programmable frequency divider (1b) with adjustable division ratio (R) which in turn connects to a fixed ratio divider (1c). 5.- FLUX OXYGEN METER, according to claim 4, characterized in that the crystal oscillator (1a) is a square wave oscillator and high frequency; the said fixed ratio corresponds to the ratio between the clock frequency (CLK) and the center frequency of the filter (3); and said microcontroller (6) has an input (TEMPERATURE) for temperature data. SPANISH OFFICE OF THE PATENTS AND BRAND Application no .: 201031589 SPAIN Date of submission of the application: 29.10.2010 Priority Date: REPORT ON THE STATE OF THE TECHNIQUE 51 Int. Cl.: See Additional Sheet RELEVANT DOCUMENTS

Category

56 Documents cited Claims Affected

X

G.J. GRILLO et al. "Synchronic filter based on switched capacitor filters for high stability phase detectors systems". IMTC 2006 - Instrumentation and Measurement. Technology Conference Sorrento, Italy April 24-27, 2006. 1-5

X

G.J. GRILLO et al. "Amplitude and phase fluorescence-spectroscopy methods for dissolved oxygen concentration evaluation: comparative practical results". IMTC 2005 - Instrumentation and Measurement. Technology Conference Ottawa, Canada May 17-19, 2005. 1-5

TO

US 6815211 B1 (BLAZEWICZ PERRY R et al.) 09.11.2004, column 12, lines 17-65; column 21, line 5 - column 22, line 17. 1-5

TO

US 2003058450 A1 (MOSLEY R MATTHEW et al.) 27.03.2003, paragraphs [0016] - [0020], [0022], [0039] - [0055], [0073] - [0074]. 1-5

TO

US 5498986 A (MANLOVE GREGORY J) 12.03.1996, column 2, lines 15-18; column 3, lines 1 - column 5, line 19. 1-5

Category of the documents cited X: of particular relevance Y: of particular relevance combined with other / s of the same category A: reflects the state of the art O: refers to unwritten disclosure P: published between the priority date and the date of priority submission of the application E: previous document, but published after the date of submission of the application

This report has been prepared • for all claims • for claims no:

Date of realization of the report 29.02.2012

Examiner B. Weaver Miralles Page 1/4

REPORT OF THE STATE OF THE TECHNIQUE Application number: 201031589 CLASSIFICATION OBJECT OF THE APPLICATION G01N21 / 64 (2006.01) H03G5 / 24 (2006.01) H03H7 / 12 (2006.01) Minimum documentation sought (classification system followed by classification symbols) G01N, H03G, H03H Electronic databases consulted during the search (name of the database and, if possible, terms of search used) INVENES, EPODOC, WPI, NPL, INTERNET State of the Art Report Page 2/4  WRITTEN OPINION Application number: 201031589 Date of Written Opinion: 29.02.2012 Statement

Novelty (Art. 6.1 LP 11/1986)

Claims Claims 1-5 IF NOT

Inventive activity (Art. 8.1 LP11 / 1986)

Claims Claims 1-5 IF NOT

The application is considered to comply with the industrial application requirement. This requirement was evaluated during the formal and technical examination phase of the application (Article 31.2 Law 11/1986).  Opinion Base.- This opinion has been made on the basis of the patent application as published. State of the Art Report Page 3/4  WRITTEN OPINION Application number: 201031589  1. Documents considered.- The documents belonging to the state of the art taken into consideration for the realization of this opinion are listed below.

Document

Publication or Identification Number publication date

D01

G.J. GRILLO et al. 04/27/2006

D02

G.J. GRILLO et al. 05/19/2005

D03

US 6815211 B1 (BLAZEWICZ PERRY R et al.) 09.11.2004

D04

US 2003058450 A1 (MOSLEY R MATTHEW et al.) 03/27/2003

D05

US 5498986 A (MANLOVE GREGORY J) 12.03.1996

 2. Statement motivated according to articles 29.6 and 29.7 of the Regulations for the execution of Law 11/1986, of March 20, on Patents on novelty and inventive activity; quotes and explanations in support of this statement Claim 1: Document D01 is considered as the closest state of the art. Said document identically discloses the object of the invention set forth in claim 1, that is: a fluid oxygen meter consisting of an excitation signal generator from which at least one clock signal for synchronization of the sections comprising is extracted. the multiple filter, an opto-electronic detector block and an amplifier of the detected fluorescence signal, a filtering block consisting of a multiple filter of switchable capacities, with a modulator block in amplitude of the radiation that reaches the fluorescence sensor , an electronic phase detector block connected to a microcontroller; using the measurement method of the offset between the phase of the signal that excites a fluorescence sensor in the fluid and the phase of the emitted signal. Therefore, said claim is not new according to article 6.1 of patent law 11/1986. Document D02 also discloses the features of claim 1. Therefore, said claims is not new in view of the known state of the art, according to article 6.1 of patent law 11/1986. Claims 2-5: Both document D01 and D02 disclose the technical characteristics of the dependent claims; whereby said claims 2 to 5 are not new according to article 6.1 of patent law 11/1986. Other documents: Document D03 discloses an oxygen monitoring device that uses the method described in the first claim of the application, which consists of a circuit that generates a square wave by a clock generator at a fixed frequency that is amplified and in turn modulated by a LED and which serves as a reference for a lock-in amplifier that only detects signals of the same frequency as the reference (column 12, lines 17-65; column 21, line 5 - column 22, line 17; D03). Document D04 discloses a meter of different characteristics of a fluid, among which is the concentration of oxygen, using a device consisting of some of the basic elements mentioned in the first claim of the application, as well as a filter of multiple capacities (paragraphs [0016] - [0020], [0022], [0039] - [0055], [0073] - [0074]; D04). Document D05 discloses an engine oxygen meter that includes a multiple filter of switchable capacities (column 2, lines 15-18; column 3, lines 1-column 5, line 19; D05). State of the Art Report Page 4/4