Method for measuring the electrical conductivity of a fluid and related electronic measuring apparatus
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- SILVER SNC DI RAVAZZONI FLAVIO E PORCELLI MICHELE
- Filing Date
- 2024-06-28
- Publication Date
- 2026-05-13
AI Technical Summary
Existing methods for measuring the electrical conductivity of fluids, such as water, are limited by voltage oscillations affecting signal reliability and the inadequacy of analog-to-digital conversion, leading to compromised measurement accuracy, especially for low conductivity values below 5 pS/cm.
A conductivity measurement method using a sensor with ring-shaped metal electrodes and an electronic module that generates square-wave signals based on fluid conductivity, immune to power supply oscillations and ADC-related disturbances, allowing for accurate conductivity detection down to low values.
The method ensures reliable conductivity measurements across a wide range, including values below 5 pS/cm, by using a sensor with ring-shaped electrodes and an electronic module that processes frequency-based signals, enhancing detection reliability and accuracy.
Smart Images
Figure IB2024056315_09012025_PF_FP_ABST
Abstract
Description
[0001] METHOD FOR MEASURING THE ELECTRICAL CONDUCTIVITY OF A
[0002] FLUID AND RELATED ELECTRONIC MEASURING APPARATUS
[0003] TECHNOLOGICAL BACKGROUND OF THE INVENTION
[0004] Field of application
[0005] The present invention generally relates to systems for checking the electrical conductivity of a fluid . In particular, the invention relates to an innovative method for measuring the electrical conductivity of a fluid, such as water, for example .
[0006] The invention also relates to an electronic measuring apparatus implementing the aforesaid method .
[0007] Prior art
[0008] As is known, a conductivity sensor measures the ability of a fluid or a solution to conduct electric current . It is the presence of ions to make a solution conductive : the greater the concentration of ions , the greater the conductivity . Known conductivity sensors are designed to monitor pure water in chemical processes and pharmaceutical production . These conductivity sensors provide accurate and reliable measurements to ensure process control and conformity .
[0009] The most widespread conductivity sensors provide for the employment of a T- fitting inserted along a conduit in which the fluid flows , e . g . , water . Such a T- fitting comprises two doors which are on the same axis as the conduit in which the fluid flows , and a third door is orthogonal to such a conduit axis . Such a third door is configured to allow the insertion of a probe into the flow of water flowing in the conduit . The aforesaid probe consists of a pair of test electrodes connected to an electronic circuit adapted to detect contaminants in water by measuring the electrical conductivity or resistivity of the water itsel f between the two electrodes . Indeed, the conductivity of water is directly proportional to the amount of ioni zable dissolved solids , such as minerals , normally present in impure water .
[0010] The purity level of water is obtained by comparing the measured conductivity value with a preset reference conductivity value . For example , i f the measured conductivity falls below the reference value , the water has an acceptable purity level and can be employed for the intended purposes . On the other hand, i f the measured conductivity exceeds the reference value , this suggests that water is contaminated to the point of not being usable for the intended purposes .
[0011] However, the known methods for measuring the conductivity of water employing, for example , the above- mentioned conductivity sensors with a T- fitting, have limitations and drawbacks .
[0012] Indeed, the electronic measuring circuit connected to the test electrodes immersed in the flow of water is configured to acquire an analog signal through such electrodes . Such an analog signal is representative of the conductivity of water between the two electrodes . However, the aforesaid analog signal can be highly af fected by oscillations in the voltage supplied to the electronic measuring circuit . Such oscillations can cause signi ficant variations in the amplitude of the measured analog signal , which can compromise the detection reliability for values of conductivity to be measured which are less than 5pS / cm .
[0013] Moreover, the need to process the analog signal acquired requires for such a signal to first be converted into a digital signal through a respective analog-digital conversion block (Analog to Digital Converter or ADC ) . Such an ADC block can introduce further disturbances on the acquired signal caused by di f ferent calibrations between the ADC channels of the logic architectures and by the maximum resolution of the ADC converter employed . Therefore , the maximum resolution obtainable when measuring the conductivity of water with the known methods is often inadequate for many applications .
[0014] SUMMARY OF THE INVENTION
[0015] Therefore , it is the obj ect of the present invention to provide a method for measuring the electrical conductivity of a fluid, such as water, for example , having properties such as to at least partially obviate the drawbacks described with reference to the currently employed conductivity measurement methods of the known type .
[0016] This and other obj ects are achieved by a method for measuring the electrical conductivity of a fluid according to claim 1 .
[0017] The present invention also relates to an electronic measuring apparatus configured to implement the aforesaid method according to claim 10 .
[0018] Preferred and advantageous embodiments of the method for measuring the conductivity of a fluid and the related electronic measuring apparatus are the subj ect of the dependent claims . BRIEF DESCRIPTION OF THE DRAWINGS
[0019] Further features and advantages of the method and apparatus for measuring the electrical conductivity of a fluid according to the invention wil l become apparent from the following description of preferred embodiments thereof , given by way of non-limiting indication, with reference to the accompanying drawings , in which :
[0020] Figure 1 shows an exploded front perspective view of an embodiment of a sensor for measuring the conductivity of a fluid implementing the method of the invention;
[0021] Figure 2 shows an exploded back perspective view of the sensor for measuring the conductivity of a fluid in Figure 1 ;
[0022] Figure 3 shows an exploded enlarged side view of the sensor in Figure 2 ;
[0023] Figure 4 shows an enlarged longitudinal section view of the sensor for measuring the conductivity of a fluid in Figure 1 , in an assembled configuration;
[0024] Figure 5 shows an enlarged side section view of the sensor for measuring the conductivity of a fluid in Figure 1 , in an assembled configuration;
[0025] Figure 6 shows a block diagram o f an example of an electronic apparatus for measuring the electrical conductivity of a fluid implementing the method of the invention;
[0026] Figure 7 shows an example of a circuit diagram of a block for detecting the electrical conductivity of a fluid, included in the electronic apparatus in Figure 6 ;
[0027] Figure 8 shows an example of a circuit diagram of a block for detecting the temperature of a fluid, included in the electronic apparatus in Figure 6 ; Figure 9 shows a circuit diagram of an astable multivibrator with a Schmitt trigger of the known type ;
[0028] Figure 10 shows a trend, as a function of time , of a square-wave signal generated as output from the no- load circuit in Figure 7 , i . e . , in the absence of fluid between the first and second input terminals ;
[0029] Figure 11 shows a trend, as a function of time , of a square-wave signal generated as output from the circuit in Figure 7 when, between the first and second input terminals of the circuit , there is a fluid having electrical conductivity of l .S / cm;
[0030] Figure 12 shows a trend, as a function of time , of a square-wave signal generated as output from the circuit in Figure 7 when, between the first and second input terminals of the circuit , there is a fluid having electrical conductivity of 200 ,S / cm;
[0031] Figure 13 shows , with a flow chart , the operating steps of the general method for measuring the conductivity of a fluid according to the invention .
[0032] Similar or equivalent elements in the aforesaid figures are indicated by the same reference numerals .
[0033] DETAILED DESCRIPTION
[0034] With reference to Figures 1 to 5 , an embodiment of a sensor for measuring the electrical conductivity of a fluid, or more simply a sensor, of the present invention is indicated as a whole by reference numeral 100 . In particular, such a conductivity sensor 100 is configured to detect and monitor the purity level of the water employed in chemical processes and / or in those involved in pharmaceutical productions .
[0035] Sensor 100 comprises a tubular body 10 extending along a longitudinal axis X from a first body end 10a to an opposing second body end 10b . Such a tubular body 10 of the sensor is made of insulating material , for example it is manufactured from a thermoplastic polymer selected from the group consisting of : polyether-ether- ketone ( PEEK) , polyacetal POM-C ( Tecaform AH) .
[0036] Such a tubular body 10 comprises a wall 3 adapted to delimit a conduit or cylindrical compartment 2 accessible from outside the sensor through a first la and an opposing second lb door which are associated with the first 10a and second 10b body ends , respectively . The fluid flowing in the tubular body 10 is configured to cross the cylindrical compartment 2 from the first door la to the second door lb, or vice versa .
[0037] Note that the tubular body 10 of sensor 100 i s insertable along a conduit in which the fluid flows , e . g . , water, the purity level of which is to be monitored, so that the flow of such water crosses the compartment 2 of the tubular body 10 . To this end, the first 10a and second 10b body ends are shaped as a ferrule . In a first example , such first 10a and second
[0038] 10b body ends have a threaded inner surface to allow attaching the sensor 100 between two portions of the conduit in which the fluid to be monitored flows . Alternatively, in a di f ferent example , the first 10a and second 10b body ends comprise a watertight bayonet coupling system with the sealing ring ( 0-ring) .
[0039] The aforesaid cylindrical compartment 2 of the tubular body 10 of sensor 100 has a diameter D equal to 8 . 5 mm, for example . Note that such a si ze can vary in relation to the fact that the dimensions of the sensor can be changed to adapt the sensor itsel f to di f ferent operating conditions ( scalability) . The cylindrical compartment 2 is delimited by a first surface 31 of wall 3 of the tubular body 10 facing the aforesaid compartment 2 .
[0040] A second surface 32 of wall 3 of the tubular body 10 of sensor 100 , opposing the first surface 31 , and facing the outside of the tubular body itsel f , is shaped to define a first pair of mutually parallel , opposing flat surfaces S I , S2 orthogonal to a respective second pair of mutually parallel and opposing flat surfaces S3 , S4 . In particular, the first pair of flat surfaces comprises a first S I and a second S2 flat surface . The second pair of flat surfaces comprises a third S3 and a fourth S4 flat surface .
[0041] The sensor 100 further comprises a first 6 and a second 7 ring-shaped metal electrode housed inside the cylindrical compartment 2 of the tubular body 10 , i . e . , housed inside such a cylindrical compartment 2 , in particular entirely housed inside the cylindrical compartment , so as to be aligned and coaxial to each other along the longitudinal axis X and coaxial to such a compartment 2 .
[0042] In particular, such a first 6 and second 7 metal electrodes are similar to each other .
[0043] In an embodiment , the first 6 and second 7 electrodes are made of stainless steel . In greater detail , such electrodes 6 , 7 are embodied by steel bushings .
[0044] The aforesaid first 6 and second 7 metal electrodes comprise an annular wall 61 , 71 having a first electrode surface 61a, 71a configured to be in contact and engage with the first cylindrical surface 31 of wall 3 of the tubular body 10 facing compartment 2 to prevent the first 6 and second 7 metal electrodes from sliding inside compartment 2 .
[0045] Moreover, the annular wall 61 , 71 of the first 6 and second 7 electrodes has an opposing second electrode surface 61b, 71b adapted to delimit a first cylindrical fluid flow compartment 62 , 72 having a first diameter
[0046] DI . For example , such a first diameter DI is 6 mm .
[0047] In particular, such a first diameter DI is smaller than diameter D of the above-mentioned compartment 2 , but in any case , it has such dimensions as not to determine bottlenecks and / or accelerations of the water flow crossing the tubular body 10 of the sensor .
[0048] Moreover, each of such first 6 and second 7 electrodes comprises a median groove 63 , 73 extending circumferentially over the first electrode surface 61a, 71a of the annular wall 61 , 71 and is interposed between two end portions 64 , 74 of the first and second electrodes . At least one of such end portions 64 , 74 is provided with means OR adapted to engage electrode 6 , 7 with the first cylindrical surface 31 of wall 3 of the tubular body 10 facing the compartment 2 .
[0049] In a particular embodiment , such engagement means of each electrode 6 , 7 are sealing engagement means comprising at least one sealing ring OR ( 0-ring) . In the example in Figures 1 , 2 and 4 , the first 6 and second 7 electrodes of sensor 100 comprise two sealing rings each .
[0050] The sensor 100 further comprises a ring-shaped spacer 8 manufactured from insulating material , for example from polyether-ether-ketone ( PEEK) or of polyacetal POM-C ( Tecaform AH) . Such a ring-shaped spacer 8 is interposed between the first 6 and second 7 metal electrodes . Such a spacer 8 has a first annular wall 80 adapted to delimit a second cylindrical fluid flow compartment 81 having a second diameter D2 equal to the aforesaid first diameter DI of the first cyl indrical compartment 62 , 72 of the electrodes 6 , 7 . Note that the dimension along the axis X of the ring-shaped spacer 8 , i . e . , the distance along axis X between the first 6 and second 7 metal electrodes , can vary based on the resolution in terms of desired conductivity and based on the type of liquid crossing sensor 100 .
[0051] The aforesaid annular wall 80 of spacer 8 comprises a plurality of through holes 82 shaped to receive a temperature probe 9 of sensor 100 . In particular, with reference to Figure 5 , in an assembled configuration of the sensor 100 of the invention, such a temperature probe 9 is configured to engage by insertion one of the aforesaid through holes 82 of spacer 8 .
[0052] The sensor 100 further comprises two mutually similar ring-shaped assembly ferrules 11 made of insulating material . An annular wall of each of such assembly ferrules 11 is adapted to delimit a respective cylindrical fluid flow compartment 12 having a diameter equal to the first diameter DI of the first cylindrical compartment of the electrodes 6 , 7 . Such assembly ferrules 11 are configured to lock in position and electrically isolate the metal electrodes 6 , 7 in an assembled configuration of the sensor 100 of the invention .
[0053] The sensor 100 further comprises an electronic module Ml for measuring the electrical conductivity of the fluid flowing in the cylindrical compartment 2 of the tubular body 10 , operatively associated with the tubular body 10 .
[0054] In particular, such an electronic module Ml for conductivity measurement comprises a microprocessor or microcontroller housed on a first printed circuit ( Printed Circuit Board or PCB ) Cl attached to the tubular body 10 .
[0055] The sensor 100 further comprises a first 13 and a second 14 metal pin housed in a first 4 and a second 5 through hole of wall 3 of the tubular body 10 , in particular made on the first flat surface S I of wal l 3 of the tubular body 10 , to be in contact with the aforesaid first 6 and second 7 metal electrodes , respectively . The first 13 and second 14 pins are configured to electrically connect the first 6 and second 7 metal electrodes to the electronic module Ml for conductivity measurement . In particular, the electronic module Ml of sensor
[0056] 100 is adapted to detect the presence of contaminants in the fluid, e . g . , water, flowing inside the tubular body 10 of the sensor by measuring the electrical conductivity or the resistivity of the water between the first 6 and second 7 electrodes .
[0057] The sensor 100 further comprises the above- mentioned temperature probe 9 connected to the microprocessor Ml of the first printed circuit Cl and configured to engage by insertion a third through hole 4 ' made on the first flat surface S I of wall 3 of the tubular body 10 and one of the aforesaid through holes 82 of the spacer 8 .
[0058] Such a probe 9 has a sensitive end adapted to protrude into the second cylindrical fluid flow compartment 81 to detect the temperature of such a fluid .
[0059] Sensor 100 further comprises a further temperature probe 20 , in particular an NTC (Negative Temperature Coef ficient ) thermistor, connected to the microprocessor Ml of the first printed circuit Cl and configured to engage by insertion a fourth through hole 5 ' made on the first flat surface S I of wall 3 of the tubular body 10 .
[0060] In an embodiment , such a further probe 20 is associated with a pressure transducer connected by means of a double-row serial communication protocol I2C ( inter Integrated Circuit) to microprocessor Ml. Such a pressure transducer is configured to perform two main functions: a first function is that of determining the pressure of the fluid, e.g., water, crossing sensor 100; a second function is that of measuring the amount of fluid crossing the sensor, e.g. how many liters per minute .
[0061] Note that, advantageously, the redundancy of the probes 9, 20 allows obtaining very accurate fluid temperature data. In particular, such fluid temperature data are obtained by averaging, by means of an algorithm, the measurements returned by both probes 9 and 20. Moreover, another advantage associated with the employment of the two temperature probes 9, 20 is that of allowing sensor 100 to detect possible anomalies.
[0062] With reference to Figures 1 to 2, the first flat surface SI of wall 3 of the tubular body 10 is configured to allow attaching a first printed circuit Cl (Printed Circuit Board or PCB) to the tubular body 10. For example, one attachment mode involves gluing the first printed circuit Cl to the first flat surface SI of the tubular body 10.
[0063] The sensor 100 further comprises feeding circuits and / or communication circuits M2 housed on a second printed circuit C2 attached to the tubular body 10. In particular, the second flat surface S2 of wall 3 of the tubular body 10 mentioned above , opposing the first surface S I , is configured to allow attaching the second printed circuit C2 to the tubular body 10 , for example by gluing .
[0064] For example , such a second printed circuit C2 is configured to provide sensor 100 with a direct power supply voltage ( DC ) between 5V and 24V .
[0065] The sensor 100 further comprises one or more radio frequency communication modules M3 operating according to the Bluetooth Low Energy, BLE or Wi Fi standard, for remotely transmitting data representative of the measurements taken, for example for the storage in the Cloud . Such one or more radio frequency communication modules M3 are housed on a third printed circuit C3 attached to the tubular body 10 .
[0066] In particular, the third flat surface S3 of wall 3 of the tubular body 10 is configured to allow attaching the third printed circuit C3 to the tubular body 10 , for example , by gluing .
[0067] The sensor 100 further comprises fluid leak detection devices M4 for detecting the leak of fluid inside or outside sensor 100 , housed on a fourth printed circuit C4 attached to the tubular body 10 .
[0068] The fourth printed circuit C4 further comprises a connector C4c configured to connect sensor 100 to a remote control station .
[0069] In particular, the fourth flat surface S4 of wal l 3 of the tubular body 10 , opposing the third surface S3 , is configured to allow attaching the fourth printed circuit C4 to the tubular body 10 , for example by gluing .
[0070] Once the printed circuits Cl , C2 , C3 and C4 have been attached to the tubular body 10 of sensor 100 , the sensor thus assembled is inserted into a containment and protective casing (not shown in the drawings ) . Such a casing is then filled with a resin adapted to cover and surround sensor 100 and the printed circuits Cl , C2 , C3 and C4 so as to ensure the required sel f-support and insulation .
[0071] With reference to Figure 6 , described below by way of example is an electronic apparatus 500 for measuring the electrical conductivity of a fluid, e . g . , water, implementing the method of the invention .
[0072] Such an electronic apparatus 500 , or more simply, apparatus , comprises the above-mentioned electronic module Ml for measuring the conductivity of the fluid flowing in the cylindrical compartment or conduit 2 of the tubular body 10 of sensor 100 .
[0073] In particular, such an electronic module Ml for conductivity measurement is housed on the first printed circuit ( Printed Circuit Board or PCB ) Cl attached to the tubular body 10 of sensor 100 .
[0074] The electronic module Ml comprises an electronic processing unit 501 , e . g . , a microprocessor or a microcontroller ( CPU) , operatively associated with a block 502 for detecting the electrical conductivity of the fluid and with a block 503 for detecting the temperature of a fluid . In particular, such an electronic processing unit 501 is configured to control the aforesaid electrical conductivity detection 502 and temperature detection 503 modules so as to receive , from such modules , a first SGI and a second SG2 analog signal , in particular, voltage signals , representative of the electrical conductivity and the temperature of the fluid .
[0075] The electronic apparatus 500 further comprises the above-mentioned first 6 and second 7 metal electrodes of the sensor, connected to the electrical conductivity detection block 502 by means of a first and a second electrical connection . In particular, such first and second electrical connections comprise the above first 13 and second 14 metal pins , respectively .
[0076] The electronic apparatus 500 further comprises the further temperature probe 20 , in particular, the NTC (Negative Temperature Coef ficient ) thermistor, connected to the electronic module Ml of the first printed circuit Cl . In particular, such a temperature probe 20 is connected to the temperature detection block 503 through a third electrical connection 20 ' , e . g . , a metal track .
[0077] A circuit embodiment of the fluid temperature detection block 503 of the present invention is described with reference to Figure 8 .
[0078] Note that the circuit of temperature detection block 503 was developed from the circuit diagram of an astable multivibrator which, as is known, is configured to generate a square-wave output signal the frequency of which is determined by the components of the circuit .
[0079] With reference to Figure 9 , an astable multivibrator with a Schmitt trigger of the known type is indicated by reference numeral 600 . Such an astable multivibrator 600 comprises a low-noise-coefficient operational ampli fier 601 , which operates as voltage comparator to generate a high-voltage or low-voltage output as a function of the input voltage .
[0080] Multivibrator 600 comprises a resistor R connected between an inverting input ( - ) and output OUT of the operational ampli fier 601 . Moreover, multivibrator 600 comprises a capacitor C connected between the inverting input ( - ) itsel f of ampli fier 601 and a ground potential terminal GND of circuit 600.
[0081] The multivibrator 600 further comprises a first R1 and a second R2 resistor: the first resistor R1 is connected between a non-inverting terminal (+) of amplifier 601 and output OUT; the second resistor R2 is connected between the aforesaid non-inverting terminal (+) and the ground terminal GND of the circuit.
[0082] Once circuit 600 is on, capacitor C is completely discharged and output OUT of the operational amplifier 601 takes the value of the positive power supply voltage, i.e., Vout=+Vcc. Then, capacitor C starts charging with the output voltage Vout through resistor R, with a time determined by the time constant i= RC . Since R is the charging and discharging resistor of the capacitor, capacitor C tends to charge completely up to the value of voltage Vout, which in this case is about +V(sat) , i.e., the saturation voltage of circuit 600, within five time constants. However, when the charging voltage of capacitor C to the inverting terminal (-) of the operational amplifier 601 takes a value equal to or greater than the voltage to the non-inverting terminal (+) , which corresponds to the fraction of output voltage of amplifier 601 divided among the resistors R1 and R2, the output voltage Vout of circuit 600 changes status and is switched to the negative power supply level -Vee, i . e . , Vout=-Vee .
[0083] Capacitor C, which was charged at the positive power supply level +V ( sat ) , is now subj ected to a negative input voltage -V ( sat ) on the respective electrode . This inversion of the output voltage discharges the capacitor toward the value of output voltage Vout again with a time constant Rc, which generates , at the output of circuit 600 , a voltage oscillation with a conventional square-waveform, as shown in Figure 9 . Note that the square-waveform in this configuration has a 50% duty cycle , assuming that the charging and discharging time of capacitor C remains constant .
[0084] Again with reference to the example in Figure 8 , the circuit implementing the temperature detection block 503 comprises an astable oscil lator for reading the temperature by means of the NTC probe 20 . Such an astable oscillator 503 includes a respective operational ampli fier OA2 connected between a power supply potential terminal VDD and a ground potential terminal GND .
[0085] In particular, the electrical resistance of fered by the NTC probe 20 corresponds to the charging and discharging resistor R41 of capacitor CH . Such a charging and discharging resistor R41 of capacitor Cn is connected between a respective output terminal OUT2 of circuit 503 and an inverting terminal ( - ) of the operational amplifier 0A2. The circuit block 503 comprises the aforesaid capacitor CH connected between such an inverting terminal (-) and the ground potential terminal GND. The resistance of the NTC probe 20 thus allows affecting the respective time constant i2 = R41C11 of the circuit block 503.
[0086] The circuit block 503 comprises a respective feedback resistor R31 connected between a non-inverting terminal ( + ) of the operational amplifier OA2 and the aforesaid output terminal OUT2, to provide a positive feedback signal on such a terminal. The circuit block 503 further comprises: a respective first resistor Rn connected between the power supply potential terminal VDD of circuit 503 and the non-inverting terminal (+) of the operational amplifier OA2; a second resistor R21 connected between the non-inverting terminal (+) of the operational amplifier OA2 and the aforesaid ground terminal GND.
[0087] The feedback resistor R31 is adapted to act in conjunction with the first Rn and second R21 resistors to generate, on the output terminal OUT2 of the circuit block 503, the above-mentioned second analog signal SG2 representative of the temperature of the fluid.
[0088] Such a second signal SG2 is a periodic analog signal, e.g., a voltage signal. In a preferred embodiment , such a second signal SG2 is a square-wave signal .
[0089] For example , i f the resistors Rn, R21 and R31 are mutually equal , the non-inverting input voltage ( + ) of the operational ampli fier 0A2 oscillates between VDD / 3 and VDD* 2 / 3 . The charging and di scharging of the network R-C, formed by capacitor resistor R41 and capacitor Cn, is configured to generate a substantially triangular waveform at the inverting input ( - ) of the operational amp 1 i f i e r 0A2 .
[0090] A change in status of the output of the operational ampli fier 0A2 occurs when the level of such a voltage at the inverting input ( - ) exceeds the voltage at the non-inverting input ( + ) of ampli fier 0A2 . The operational ampli fier 0A2 is thus adapted to act as a comparator in a saturated switching mode and the aforesaid second square-wave signal SG2 has a frequency f2 determined by the time constant T=R4iCn .
[0091] When the second analog signal SG2 is provided, following a suitable analog-digital conversion (ADC ) , to the electronic processing unit 501 of apparatus 500 , such an electronic unit 501 is configured to obtain the aforesaid value of frequency f2 of the square wave of the second signal SG2 . Given that the capacitance of capacitor Cn is known, the electronic unit 501 is also configured to obtain the value of res istor R41 associated with the NTC probe 20 .
[0092] Then, from the calculated resistor value , the electronic processing unit 501 is configured to calculate the value of the temperature of the fluid crossing the conduit 2 of the tubular body 10 of sensor 100 , for example by applying the Law of Steinhart-Hart , known to those skilled in the art .
[0093] Based on the above , the respective frequency f2 of the second analog signal SG2 output from the circuit block 503 is variable as the temperature value of the fluid crossing conduit 2 varies .
[0094] In an embodiment (not shown in the drawings ) , the electronic apparatus 500 can comprise the fluid electrical conductivity detection block 502 alone . In this case , the temperature probe 20 is connected directly to the processing unit 501 of the electronic module and the generation of the aforesaid second square-wave analog signal SG2 is not expected .
[0095] In the case of the fluid electrical conductivity detection block 502 , it is the fluid itsel f to act as a charging or discharging resistor of a capacitor, thus determining the variation in the time constant RC and accordingly the oscillation frequency of the first signal SGI . An embodiment of the circuit structure implementing the aforesaid block 502 is described below with reference to Figure 7 .
[0096] The circuit block 502 comprises an astable oscillator configured to provide the first analog signal SGI , which is the signal to be processed, on a respective first output terminal OUT1 ( S IG . OUT ) . Such a block 502 comprises a first operational ampli fier OA1 connected between a power supply terminal VDD and a ground terminal GND . A first T1 and a second T2 input terminal of the circuit block 502 are connected to the electrodes 6 and 7 of the sensitive part , respectively, immersed in the flow of fluid the conductivity of which is to be measured . It is thus assumed that , between the aforesaid terminals Tl , T2 of circuit 501 , there be applied an equivalent resistance R* associated with the fluid representative of the resistivity, or vice versa, of the electrical conductivity of the fluid in which the electrodes 6 , 7 are immersed .
[0097] The circuit block 502 comprises a respective first R1 and a respective second R2 resistor which are resistors adapted to set the saturation voltage value on the first output terminal OUT 1 of the circuit itsel f . In particular, the first resistor R1 is connected between a non-inverting terminal ( + ) of the first operation ampli fier 0A1 of circuit 502 and a ground potential terminal GND . The second resistor R2 is connected between such a non-inverting terminal ( + ) and a power supply potential terminal VDD .
[0098] Circuit 502 further comprises a block resistor R6 connected between an output 01 of the first operation ampli fier 0A1 and the first output terminal OUT1 of circuit 502 to avoid the generation of return signal s from the logic that processes the first signal SGI and which could af fect the oscillation of such a signal .
[0099] Circuit 502 further comprises a respective charging and discharging resistor R5 of a respective capacitor Cl placed at the input to circuit 502 . Such a resistor R5 is connected between the output terminal 01 of the first operational ampli fier OA1 and the second input terminal T2 . The aforesaid capacitor Cl is connected between such a second input terminal T2 and a ground potential terminal GND .
[0100] Note that the charging and discharging resistor R5 is connected to the first input terminal T1 of circuit 501 through a safety resistor R7 . In other words , the equivalent resistance R* of the fluid in which the electrodes 6 , 7 are immersed is substantially connected in parallel to the input resistance Rin of circuit 502 depending on R5 and R7 . A variation in the equivalent resistance R* of the fluid thus determines a variation in an overall input resistance Rtot of the circuit block 502 between the terminals T1 and T2 . Note that the safety resistor R7 , which is connected in series to one of the electrodes of sensor 100 , allows avoiding potential short-circuiting circumstances which could stall the circuit block 502 in the case of the presence of debris with very high conductivity, such as , e . g . , metal fragments , in the fluid .
[0101] Moreover, the charging and discharging resistor R5 serves the function of maintaining the operating stability of circuit 502 in the case of the absence of the fluid to be measured .
[0102] Circuit 502 further comprises an oscillation starting resistor R4 connected between the second input terminal T2 of circuit 502 and the inverting terminal ( - ) of the first operational ampli fier OA1 . Such a resistor R4 aims at starting the oscillation and correcting the waveform as input to the inverting terminal ( - ) of ampli fier OA1 .
[0103] The circuit block 502 further comprises a compensation resistor R3 connected between the output terminal 01 of the first operation ampli fier OA1 and the non-inverting terminal ( + ) of the ampli fier itself . Such a resistor R3 is adapted to compensate for a threshold value set by resistive divider R1-R2 .
[0104] From a functional viewpoint , note that the first signal SGI generated by the circuit block 502 also is a periodic analog signal , in particular a square-wave periodic analog signal , with frequency f l determined by the time constant i=RtotCi .
[0105] When the first analog signal SGI is provided, following a suitable analog-digital conversion (ADC ) , to the electronic processing unit 501 of apparatus 500 , such an electronic unit 501 is configured to obtain the aforesaid value of frequency, or first frequency, f l of the square wave of the first signal SGI . Given that the capacitance of capacitor Cl is known, the electronic unit 501 is also configured to obtain the value of the overall resistance Rtot associated with the input terminals Tl , T2 of circuit 502 . Then, the electronic processing unit 501 is configured to calculate , from the calculated value of resistance Rtot , the value of the equivalent resistance R* associated with the fluid crossing the conduit 2 of the tubular body 10 of sensor 100 , since the values of resistors R5 and R7 are known .
[0106] The processing unit 501 is configured to obtain, from the calculated value of equivalent resistance R* , the electrical conductivity of the fluid .
[0107] Based on the above, the aforesaid first frequency fl of the first analog signal SGI is variable as the value of the equivalent resistance R* associated with the fluid between the first 6 and second 7 metal electrodes varies .
[0108] Since the electrical conductivity of a solution i s normally expressed in pS / cm, it is possible to deduce that IpS / cm is equivalent to l * 10~6S / cm . Also knowing that Siemens , i . e . , the unit of measurement of conductivity, is the reciprocal of the resistance measured in Ohm, it is possible to af firm that l * 10~6S / cm is equivalent to about 106Ohm .
[0109] From this it is apparent that as the electrical conductivity of a fluid nears zero , the resistance of such a fluid tends to the infinite . Since it is one of the obj ects of the electronic measuring apparatus 500 to ensure the accuracy of the reading of the conductivity of fluids in solution, especially in very pure water, the equivalent resistance R* at the input of circuit 502 can take very high values .
[0110] The time-dependent diagram in Figure 10 shows , by way of example, the first square-wave signal SGI generated as output by the no-load circuit 502 in Figure 7 , i . e . , in the absence of fluid between the first T1 and second T2 input terminals .
[0111] The oscillogram shows signal SGI at a base frequency of 77Hz . By varying the value of the charging and discharging resistor R5 or the capacitance of capacitor Cl , it is possible to change the time constant and thus increase or decrease the no-load frequency of signal SGI as needed .
[0112] The time-dependent diagram in Figure 11 shows , by way of example, the first square-wave signal SGI generated as output by the circuit 502 in Figure 7 i f there is a fluid having conductivity of IpS / cm between the first T1 and second T2 input terminals of circuit 502 .
[0113] The time-dependent diagram in Figure 12 shows , by way of example, the first square-wave signal SGI generated as output by the circuit 502 in Figure 7 i f there is a fluid having a conductance of 200pS / cm between the first T1 and second T2 input terminals of circuit 502 .
[0114] In this latter case , as shown by the oscillogram, it is possible to note a very stable relationship between the high and low levels of the first signal T1 without any spikes or noise . Moreover, the leading and tail fronts of the square wave are sharp and have no distortion .
[0115] With reference to Figure 13 , a general embodiment of a method 700 for measuring the electrical conductivity of a fluid crossing a conduit 2 according to the invention is shown with a flow chart . The method begins with a symbolic starting step STR and ends with a symbolic ending step ED .
[0116] Such a method 700 is implemented by an electronic apparatus 500 for conductivity measurement described with reference to Figure 6 . In the most general embodiment , such an apparatus 500 comprises :
[0117] - an electronic module Ml comprising :
[0118] - an electronic processing unit 501 ;
[0119] - a fluid electrical conductivity detection block 502 operatively associated with the electronic processing unit 501 ;
[0120] - a first 6 and a second 7 metal electrode connected to block 502 for detecting the electrical fluid conductivity through a first 13 and a second 14 electrical connection, respectively; such first 6 and second 7 electrodes are insertable into conduit 2 to be in contact with the fluid;
[0121] - a temperature probe 20 connected to the electronic module Ml through a third electrical connection 20 ' to provide the electronic processing unit 501 with temperature information SG2 associated with the fluid crossing conduit 2 .
[0122] The method 700 of the invention comprises a step 701 of applying a measurement potential di f ference between the first 6 and second 7 electrodes in contact with the fluid to generate a current signal I I to be provided as input to the electrical conductivity detection block 502 .
[0123] In particular, note that such a measurement potential di f ference applied between the electrodes 6 , 7 is constantly variable between a first (V+ ) and a second (V- ) input voltage threshold value of block 502 configured to switch the output status of the first operation ampli fier OA1 .
[0124] Moreover, there is included a step 702 of generating, by the electrical conductivity detection block 502 , a first analog signal SGI representative of the conductivity of the fluid crossing the conduit 2 ; such a first analog signal SGI is a periodic signal having a first frequency f l .
[0125] As mentioned above , such a first frequency f l is variable as the value of the equivalent resistance R* associated with the fluid flowing between the first 6 and second 7 metal electrodes varies . Under static conditions , such a first frequency f l is constant .
[0126] The method 700 further includes a step 703 of providing the first analog signal SGI to the electronic processing unit 501 . Such an electronic unit 501 is adapted to proces s
[0127] 704 the first analog signal SGI to obtain the value of the first frequency f l of the periodic signal .
[0128] Moreover, the electronic processing unit 501 is configured to calculate 705 a value of equivalent resistance R* associated with the fluid between the first 6 and second 7 electrodes from the first frequency f l obtained .
[0129] The method 700 further includes the step 706 o f providing, by the temperature probe 20 , the electronic processing unit 501 with such temperature information SG2 of the fluid crossing conduit 2 .
[0130] The method further includes the step 707 of calculating, by the electronic processing unit 501 , a value of electrical conductivity of the fluid based on the aforesaid calculated value of equivalent resistance R* and the temperature information SG2 .
[0131] In a particularly advantageous embodiment , the electronic module Ml of apparatus 500 further comprises a fluid temperature detection block 503 connected to the temperature probe 20 and operatively associated with the electronic processing unit 501 .
[0132] According to such an embodiment , the step of the method 700 of providing 706 temperature information on the fluid comprises the further steps of : generating, by such a temperature detection block 503 , a second analog signal SG2 representative of the temperature of the fluid crossing conduit 2 ; such a second analog signal SG2 is a periodic signal having a second frequency f2 ;
[0133] - providing the electronic processing unit 501 with the second analog signal SG2 .
[0134] In a further embodiment , the provision step 703 of the method 700 of the invention comprises a step of performing an analog-digital conversion of the first analog signal SGI to generate a first digital signal to be provided to the electronic processing unit 501 .
[0135] In yet a further embodiment , the provision step comprises a step a performing also an analog-digital conversion of the second analog signal SG2 to provide a second digital signal to the electronic processing unit 501 .
[0136] In a particular embodiment , the first analog signal SGI and / or the second analog signal SG2 are square-wave signals .
[0137] With reference to the circuit example in Figure 7 , the fluid electrical conductivity detection block 502 comprises a circuit block having a respective input resistance Rin and an input capacitance Cl connected to said equivalent resistance R* of the fluid through the aforesaid first 13 and second 14 electrical connections of the first 6 and second 7 metal electrodes , respectively . In this case , the step 705 of calculating the value of equivalent resistance R* of the method 700 of the invention is performed based on the equation : Rtot*Cl = l / 2nf l ( 1 ) where : Cl is the value of the input capacitance of the electrical conductivity detection block 502 ; Rtot is the value of overall resistance obtained from the connection in parallel between the equivalent resistance R* of the fluid and the input resistance Rin of the electrical conductivity detection block 502 ; f l is the first frequency of the first analog signal SGI .
[0138] In an advantageous embodiment of the method 700 of the invention, the step 707 of calculating a value of electrical conductivity of the fluid comprises a step of compensating for the calculated conductivity value based on the di f ference between the value of temperature of the fluid crossing conduit 2 associated with the temperature information SG2 , i . e . , the second analog signal SG2 , provided by the temperature probe 20 and a standard temperature value .
[0139] Indeed, the measured fluids usually are at di f ferent temperatures from the standard one and the conductivity value is generally expressed in pS / cm at 25 ° C . For example , i f we consider the water extracted from the subsoil and measured immediately after extraction, it could have a conductivity of 100 pS / cm at 15 ° C . Once brought to the standard temperature of 25 ° C, the conductivity value will instead be 119 pS / cm .
[0140] Therefore , with such a functionality, i f the fluid temperature measured through probe 20 and the related temperature detection block 503 is known, the method 700 of the invention allows making a correction even before the fluid reaches the standard temperature .
[0141] The method 700 for measuring the conductivity of a fluid, e . g . , water, of the present invention and the related electronic measuring apparatus 500 have several advantages and achieve the preset obj ects .
[0142] Indeed, since the water conductivity values are calculated from the first constant frequency f l of the first , in particular square-wave , periodic analog signal SGI generated by the first electronic block 502 connected to the electrodes 6 , 7 and not by the amplitude of such a signal SGI , such a conductivity measurement performed by the apparatus 500 of the invention is substantially immune against the oscillations of the power supply voltage of the electronic measuring circuit . In other words , the electronic apparatus 500 implementing the method 700 of the invention ensures reliability in the conductivity detection even for values of conductivity to be measured less than 5pS / cm .
[0143] Moreover, the first frequency f l of the first signal SGI is not even af fected by the successive processing operations performed by a respective analogdigital conversion block (Analog to Digital Converter or ADC - not shown in the drawings ) on the first analog signal SGI to convert it into a digital signal . Indeed, such a first frequency f l is not af fected by the disturbances introduced by the ADC block on the amplitude of the acquired signal SGI caused by di f ferent calibrations between the ADC channels of the logical architectures and by the maximum resolution of the ADC converter employed .
[0144] Moreover, since the water temperature values are also calculated from the second constant frequency f2 of the second, in particular square-wave , analog signal SG2 generated by the second electronic block 503 connected to the NTC probe 20 and not by the amplitude of such a signal SG2 , the temperature measurement performed by apparatus 500 is also substantially immune against the oscillations of the power supply voltage of the electronic measuring circuit . In other words , the present invention also ensures increased reliability in the detection of the water temperature .
[0145] In order to meet contingent needs , those skilled in the art may make changes and adaptations to the embodiments of the method for measuring the electrical conductivity of a fluid described above or may replace elements with others which are functionally equivalent, without departing from the scope of the following claims . Each of the features described as belonging to a possible embodiment can be made irrespective of the other embodiments described .
[0146] -k 'k 'k
Claims
CLAIMS1. A method (700) for measuring the electrical conductivity of a fluid crossing a conduit (2) by means of an electronic measuring apparatus (500) , said electronic measuring apparatus (500) comprising:- an electronic module (Ml) comprising:- an electronic processing unit (501) ,- a block (502) for detecting the electrical fluid conductivity operatively associated with the electronic processing unit (501) ;- a first (6) and a second (7) metal electrode connected to said block (502) for detecting the electrical fluid conductivity through a first (13) and a second (14) electrical connection, respectively, said first (6) and second (7) electrodes being insertable into said conduit (2) to be in contact with the fluid;- a temperature probe (20) connected to the electronic module (Ml) through a third electrical connection (20' ) to provide said electronic processing unit (501) with temperature information (SG2) associated with the fluid crossing the conduit (2) , said method (700) comprising the steps of: applying (701) a measurement potential difference between said first (6) and second (7) electrodes in contact with said fluid to generate a current signal(II) to be provided at the input of the electrical conductivity detection block (502) ; generating (702) , by said electrical conductivity detection block (502) , a first analog signal (SGI) representative of the conductivity of the fluid crossing the conduit (2) , said first analog signal (SGI) being a periodic signal having a first frequency (fl) ; providing (703) said electronic processing unit (501) with said first analog signal (SGI) ; processing (704) , by the electronic processing unit (501) , said first analog signal (SGI) to obtain the value of said first frequency (fl) of the periodic signal ; calculating (705) , by the electronic processing unit (501) , a value of equivalent resistance (R*) associated with the fluid between the first (6) and second (7) electrodes from the first frequency (fl) obtained; providing (706) , by said temperature probe (20) , the electronic processing unit (501) with said temperature information (SG2) of the fluid crossing the conduit ( 2 ) ; calculating (707) , by the electronic processing unit (501) , a value of electrical fluid conductivity based on said calculated value of equivalent resistance(R*) and said temperature information (SG2) .
2. A method (700) for measuring the conductivity of a fluid according to claim 1, wherein said electronic module (Ml) further comprises a fluid temperature detection block (503) connected to said temperature probe (20) and operatively associated with the electronic processing unit (501) , said step (706) of providing a temperature information (SG2) of the fluid comprising the further steps of: generating, by said temperature detection block (503) , a second analog signal (SG2) representative of the temperature of the fluid crossing the conduit (2) , said second analog signal (SG2) being a periodic signal having a second frequency (f2) ; providing said electronic processing unit (501) with said second analog signal (SG2) .
3. A method (100) for measuring the conductivity of a fluid according to claim 1 or 2, wherein said provision step (703) comprises a step of performing an analogdigital conversion of said first analog signal (SGI) to generate a first digital signal to be provided to the electronic processing unit (501) .
4. A method (100) for measuring the conductivity of a fluid according to claim 2 or 3, wherein said provision step comprises a step of performing an analog-digitalconversion of said second analog signal (SG2) to provide a second digital signal to the electronic processing unit (501) .
5. A method (100) for measuring the conductivity of a fluid according to any one of the preceding claims, wherein said first analog signal (SGI) and / or said second analog signal (SG2) are square wave signals.
6. A method (100) for measuring the conductivity of a fluid according to any one of the preceding claims, wherein said first frequency (fl) of the first analog signal (SGI) varies as the value of said equivalent resistance (R*) associated with the fluid between the first (6) and second (7) metal electrodes varies.
7. A method (100) for measuring the conductivity of a fluid according to the preceding claim, wherein said block (502) for detecting the electrical fluid conductivity comprises a circuit block having a respective input resistance (Rin) and an input capacitance (Cl) connected to said equivalent resistance (R*) of the fluid through said first (13) and second (14) electrical connections of the first (6) and second (7) metal electrodes, said step (705) of calculating the value of equivalent resistance (R*) is performed according to the equation:Rtot*Cl l / 2nflwhere: Cl is the value of the input capacitance of the electrical conductivity detection block (502) ; Rtot is the value of overall resistance obtained from the connection in parallel between the equivalent resistance (R*) of the fluid and said input resistance (Rin) of the electrical conductivity detection block (502) ; fl is the first frequency of the first analog signal (SGI) .
8. A method (100) for measuring the conductivity of a fluid according to any one of claims 2, 4-5, wherein said second frequency (f2) of the second analog signal (SG2) varies as the temperature value of the fluid crossing the conduit (2) varies.
9. A method (100) for measuring the conductivity of a fluid according to any one of the preceding claims, wherein said step (707) of calculating an electrical fluid conductivity value comprises a step of compensating for the calculated conductivity value based on the difference between the temperature value of the fluid crossing the conduit (2) associated with said temperature information (SG2) provided by the temperature probe (20) and a standard temperature value.
10. An electronic apparatus (500) for measuring the electrical conductivity of a fluid crossing a conduit (2) , comprising: an electronic module (Ml) comprising:an electronic processing unit (501) ,- a block (502) for detecting the electrical fluid conductivity operatively associated with the electronic processing unit (501) ;- a first (6) and a second (7) metal electrode connected to said block (502) for detecting the electrical fluid conductivity through a first (13) and a second (14) electrical connection, respectively, said first (6) and second (7) electrodes being insertable into said conduit (2) in contact with the fluid;- a temperature probe (20) connected to the electronic module (Ml) through a third electrical connection (20' ) to provide said electronic processing unit (501) with temperature information (SG2) associated with the fluid crossing the conduit (2) , said apparatus (500) being configured to carry out the method (700) according to any one of claims 1 to 9.
11. An electronic apparatus (500) according to claim 10, wherein said electronic module (Ml) further comprises a fluid temperature detection block (503) connected to said temperature probe (20) and operatively associated with the electronic processing unit (501) .
12. An electronic apparatus (500) according to claim 10 or 11, wherein said block (502) for detecting the electrical fluid conductivity comprises:- a first operational amplifier (0A1) connected between a power supply potential terminal (VDD) and a ground potential terminal (GND) ; a first (Tl) and a second (T2) input terminal connected to said first (6) and second (7) metal electrodes, respectively, and a first output terminal (OUT1) ;- a first (Rl) and a second (R2) resistor, wherein said first resistor (Rl) is connected between a non-inverting terminal (+) of the first operational amplifier (0A1) and the ground potential terminal (GND) , and the second resistor (R2) is connected between said non-inverting terminal and the power supply potential terminal (VDD) ;- a block resistor (R6) connected between an output (01) of the first operational amplifier (0A1) and the first output terminal (0UT1) ; a resistor (R5) for charging and discharging a capacitor (Cl) placed at the input of said block (502) , said charging and discharging resistor (R5) being connected between the output terminal (01) of the first operational amplifier (0A1) and the second input terminal (T2) , said capacitor (Cl) being connected between the second input terminal (T2) and the ground potential terminal (GND) ; a safety resistor (R7) connected between the chargingand discharging resistor (R5) and the first input terminal (Tl) of the block (502) ;- a start oscillation resistor (R4) connected between the second input terminal (T2) and the inverting terminal (-) of the first operational amplifier (OA1) ; a compensation resistor (R3) connected between the output terminal (01) of the first operational amplifier (OA1) and the non-inverting terminal ( + ) of said amp 1 i f i e r .
13. An electronic apparatus (500) according to claim 11 or 12, wherein said fluid temperature detection block (503) comprises:- a second operational amplifier (OA2) connected between a power supply potential terminal (VDD) and a ground potential terminal (GND) ;- an additional charging and discharging resistor (R41) of an additional capacitor (CH) , said charging and discharging resistor (R41) being connected between an output terminal (OUT2) of the block (503) and an inverting terminal (-) of the second operational amp 1 i f i e r ( OA2 ) ;- said additional capacitor (Cn) connected between the inverting terminal (-) of the second operational amplifier (OA2) and the ground potential terminal (GND) ; a feedback resistor (R31) connected between a non-inverting terminal (+) of the second operational amplifier (0A2) and said output terminal (OUT2) ;- an additional first resistor (Rn) connected between the power supply terminal (VDD) of the block (503) and the non-inverting terminal (+) of the second operational amp 1 i f i e r ( OA2 ) ;- an additional second resistor (R21) connected between the non-inverting terminal (+) of the second operational amplifier (OA2) and said ground terminal (GND) .