Moisture sensor provided with outer coating

Abstract

The invention concerns a moisture sensor (100) for measuring the moisture of materials in the form of dry, liquid or gaseous granulates, or in the form of powders in at least one conduit arranged at least partially along an axis of the sensor through which the materials whose moisture is to be measured flow, the sensor being composed of at least one capacitor through which the material whose moisture is to be measured flows, wherein the aforesaid capacitor comprises rings made of dielectric material and interposed between metal rings mounted coaxially with respect to said axis, all closed by containment flanges, characterized in that the aforesaid sensor comprises an outer coating (10) to said rings that has a layer (30) operating as thermal insulation, interposed between carbon fiber layers operating as a filter against electromagnetic disturbances.

Description

[0001] "MOISTURE SENSOR PROVIDED WITH OUTER COATING"

[0002] FIELD OF THE INVENTION

[0003] The present invention concerns a moisture sensor in the industrial field and, in particular, a sensor for measuring the moisture of products subjected to industrial treatments, such as for example materials in the form of dry, liquid or gaseous granulates, or in the form of powders, wherein the moisture sensor is provided with an outer coating.

[0004] KNOWN ART

[0005] As is known, there are apparatuses for measuring the moisture present in many substance samples and which have many applications, in particular in the food, chemical and pharmaceutical industries.

[0006] In some known devices, moisture measurement does not actually occur in-line during the production process but by sampling and subsequent measuring.

[0007] Such an approach is very complex and requires lengthy times, and the measurement cannot be reliable since many elements can lead to improper sampling.

[0008] Moreover, the sampling itself is not very representative of the production in progress, since the lab systems can only sample a few grams and since it is not possible to collect a sample at the specific point of interest in some production processes, for example in silos or in dryers in nitrogenous environments. Systems in which measurement of the moisture is done in-line are also known.

[0009] For example, document WO 2012 / 004621 illustrates a device for measuring the moisture of materials flowing in the form of dry, liquid or gaseous granulates, or in the form of powders, in at least one conduit arranged at least partially along an axis through which the material flows. The device comprises at least one capacitor through which the material, whose moisture is to be measured, flows. In turn, the capacitor comprises at least two metal rings mounted coaxially to said axis and adjacent to an inner wall of the conduit through which the material, whose moisture is to be measured, flows, and at least one dielectric element having dielectric constant substantially linear with the temperature variation.

[0010] In the case of some types of installation on industrial machines such as injection molding machines, extruders, dryers, etc., a periodic calibration procedure of the equipment, adapted for allowing repeatability and accuracy of measurement, is required.

[0011] In some industrial contexts, calibration also provides for a brief production stoppage since calibration operations are only carried out within certain ambient temperature and moisture values.

[0012] Another problem to be highlighted is that, when the measuring system is subjected to temperatures exceeding 50°c, mainly due to the thermal expansion and permittivity variation of the dielectric material the sensor is composed of, measurement errors are inevitable due to the dimensional and dielectric permittivity variations which affect the proper value of the measurement.

[0013] The total capacitance measurement of the sensor is the resultant of the capacitance value of the empty sensor (capacitor CX) + the permittivity value of the material crossing it (CM) + the permittivity due to the relative humidity of the air (HRU). In other words, the total capacitance (Ctot) is given by the following formula: Ctot = CX + CM + HRU.

[0014] From the formula, it is clear that the value of the empty sensor CX is essential for proper measurement and especially for the repeatability of the measurement. The capacitance drift due to the variation of the dielectric capacitance is neither constant nor linear, since depending on many factors, such as the thermal expansion of all the materials composing it, the peculiarity of some installations, where machinery can affect both thermally and mechanically the structure of the sensor, thus generating a drift or often hysteresis of the capacitance value, forming an even more complex problem to be corrected, even mathematically.

[0015] Due to its structure, the sensor is also subjected to electromagnetic disturbances deriving from interaction with other machines, which can further alter the value of the signal deriving from the sensor. A metal shield eliminates the problem but adds another one which causes a further temperature increase inside the system, with consequent increased drift of the capacitance signal due to thermal expansion of the sensor's components.

[0016] Another problem highlighted is the heating, often over 100°C, of electronic components. The PCB (Electronic Board) of the sensor must be mounted as close as possible to the electrodes of the sensor, this mainly to avoid parasitic capacitances due to contact impedance. The terminal capacitance must fall within a narrow window between 130 fF (femtoFarad) and 170 fF and has a very weak, if possibly negligible, temperature dependence.

[0017] An object of the present invention is therefore to make a system which can protect the moisture sensor against temperature variations.

[0018] Further object of the invention is to make a system which can protect the moisture sensor against electromagnetic disturbances.

[0019] Further object of the invention is to achieve the aforesaid result in a practical and economical way.

[0020] BRIEF SUMMARY OF THE INVENTION

[0021] These and other objects are achieved by means of a moisture sensor for measuring the moisture of materials in the form of dry, liquid or gaseous granulates, or in the form of powders in at least one conduit arranged at least partially along an axis of the sensor through which the materials, whose moisture is to be measured, flow, the sensor being composed of at least one capacitor through which the material whose moisture is to be measured flows, wherein the aforesaid capacitor comprises rings made of dielectric material and interposed between metal rings mounted coaxially with respect to said axis between containment flanges, characterized in that the aforesaid sensor comprises an outer coating to the aforesaid rings that has a layer operating as thermal insulation, interposed between carbon fiber layers operating as a filter against electromagnetic disturbances.

[0022] The advantages of the present invention are countless.

[0023] Firstly, the structure of the sensor and, in particular, the structure of its outer coating is such as to allow to protect the moisture sensor against temperature variations.

[0024] Secondly, the structure of the sensor and, in particular, the structure of its outer coating is such as to protect the moisture sensor against electromagnetic disturbances. Further characteristics of the invention can be deduced from the dependent claims.

[0025] BRIEF DESCRIPTION OF THE FIGURES

[0026] Further characteristics and advantages of the invention will become clearer from the reading of the following description provided by way of example and without limitations, with the aid of the figures depicted in the accompanying tables, in which: figure 1 illustrates a side view of the outer coating for a moisture sensor according to an embodiment of the invention;

[0027] - figure 2 illustrates a view, according to section A- A of figure 1, of the outer coating for a moisture sensor; figure 3 illustrates an enlarged detail of the section of figure 2;

[0028] - figure 4 and 6 illustrate side views of a moisture sensor provided with a holder for an electronic board, according to an embodiment of the invention; figure 5 illustrates an axonometric view of the sensor of figures 4 and 6; figure 7 illustrates an axonometric view of the moisture sensor provided with a holder for an electronic board of figures 4-6, provided with an outer coating of the type illustrated in figures 1-3; and figure 8 illustrates an axonometric view of the outer coating of the type illustrated in figures 1-3.

[0029] DETAILED DESCRIPTION OF THE FIGURES

[0030] The invention will now be described with initial reference to figure 1 which illustrates a side view of the outer coating for a moisture sensor according to an embodiment of the invention, said outer coating being generally denoted by the numerical reference 10. The moisture sensor is illustrated in figures 4, 6 and 7 and is generally denoted by the number of reference 100.

[0031] Moisture sensors, to which the outer coating of the invention can be applied, are known and are generally composed of some metal rings and some rings made of dielectric material, wherein each metal ring is interposed between two rings made of dielectric material so that to form the structure of an electrical capacitor.

[0032] The metal rings and the rings made of dielectric material are assembled between two ring-shaped containment flanges 60,70 (visible in figures 4-7) and by assembly screws.

[0033] The moisture sensor 100 of the invention measures the moisture in-line in the processes in which materials flowing in the form of dry, liquid or gaseous granulates, or in the form of powders, are treated.

[0034] Such moisture sensor is adapted for being positioned in a conduit, not shown, in which it is possible to measure the moisture in-line, i.e. arranged according to an axis along which the material, whose moisture is to be measured, flows.

[0035] In particular, thanks to the structure of the sensor described above, the capacitance of the capacitor is affected the dielectric permittivity of the material between its plates, which permittivity changes depending on its moisture content measured of the material, since water has a much higher permittivity than many solid materials or air, and such phenomenon allows a measurement of the moisture of the material crossing the sensor to be obtained. Figure 2 illustrates a view, according to the section A-A of figure 1, of the outer coating 10 for a moisture sensor 100 according to the present invention.

[0036] Figure 3 illustrates an enlarged detail B of the section A-A of figure 2.

[0037] In the detail in figure 3, it can be seen how the outer coating 10 is similar to a cylindrical shield operating as both a Faraday cage and a thermal shield.

[0038] The outer coating 10 has a layer 30 operating as thermal insulation, interposed between carbon fiber layers 20, 40 operating as a filter against electromagnetic disturbances.

[0039] The intermediate (or central) layer 30 is preferably made of glass fiber.

[0040] In detail, the outer coating 10 therefore provides three layers, i.e. a first outer carbon fiber layer 20, a second intermediate glass fiber layer 30 and a third inner carbon fiber layer 40.

[0041] A sandwich-like structure which allows to achieve two important effects is therefore achieved: the carbon fiber layers 20, 40 (which are electrically conductive) are set at negative potential (grounded) and act as a Faraday cage, therefore resulting in an optimal filter against electromagnetic disturbances.

[0042] The intermediate glass fiber layer 30 acts as thermal insulator, preventing heat due to the passage of the material inside the sensor from spreading outside, with consequent temperature rise of the electronic components of the moisture sensor 100, in particular of its electronic board. This unlike a metal shield generally used in the totality of applications and which instead transmit heat.

[0043] The intermediate layer 30, preferably made of glass fiber, has a thickness greater than that of the carbon fiber layers 20, 40. The thickness of the intermediate layer 30 is preferably at least twice and less than seven times greater than the thickness of the carbon fiber layers 20, 40.

[0044] In a particularly preferred embodiment, the thickness of the layer 30 operating as thermal insulation has a value between about 0.40 mm and about 0.60 mm, preferably equal to 0.50 mm, and the thickness of the carbon fiber layers 20, 40 operating as a filter against electromagnetic disturbances have a value between 0.20 mm and 0.30 mm, preferably equal to 0.25 mm. Figures 4 and 6 illustrate side views of a moisture sensor 100 provided with a holder 50 for an electronic board according to an embodiment of the invention, and figure 5 illustrates an axonometric view of the sensor of figures 4 and 6. Naturally, the holder 50 for the electronic board is optional and a moisture sensor 100 provided with an outer coating 10 and devoid of the holder 50 falls within the protection scope of the present invention.

[0045] The sensor 100, as stated, provides for metal rings among which rings made of dielectric material are interposed, all assembled between two ring-shaped containment flanges 60,70 and by assembly screws.

[0046] A holder 50, made of thermally insulating material, for an electronic board controlling the sensor 100 is further connected to the ring-shaped containment flanges 60,70.

[0047] Figure 7 illustrates an axonometric view of the holder for an electronic board of figures 4-6, provided with an outer coating 10 of the type illustrated in figures 1-3.

[0048] Figure 8 illustrates an axonometric view of the outer coating 10 of the type illustrated in figures 1-3, from which it can be seen how said outer coating 10 has a substantially cylindrical conformation and a substantially rectangular hole 12 for housing the holder 50 for the electronic board.

[0049] The cylindrical shape of the outer coating 10 is open at the ends for containing the moisture sensor 100.

[0050] The outer coating 10 also has holes 14 for inserting screws 15 to secure the holder 50 for the electronic board to the moisture sensor 100.

[0051] Obviously, a technician of the field can make further changes and variations to the present invention, all thereby comprised in the protection scope of the invention, as defined by the following claims, for the purpose of meeting contingent and specific needs.

Claims

CLAIMS1. Moisture sensor (100) for measuring the moisture of materials in the form of dry, liquid or gaseous granulates, or in the form of powders in at least one conduit arranged at least partially along an axis of the sensor through which the materials whose moisture is to be measured flow, the moisture sensor (100) being composed of at least one capacitor through which the material whose moisture is to be measured flows, wherein the aforesaid capacitor comprises rings made of dielectric material and interposed between metal rings mounted coaxially with respect to said axis between containment flanges, characterized in that the aforesaid sensor (100) comprises an outer coating (10) to the aforesaid rings that has a layer (30) operating as thermal insulation, interposed between carbon fiber layers (20, 40) operating as a filter against electromagnetic disturbances.

2. Moisture sensor (100) according to claim 1, wherein the layer (30) operating as thermal insulation has a thickness greater than that of the carbon fiber layers (20, 40) operating as a filter against electromagnetic disturbances.

3. Moisture sensor (100) according to claim 2, wherein the thickness of the layer (30) operating as thermal insulation is at least twice and less than seven times greater than the thickness of the carbon fiber layers (20, 40) operating as a filter against electromagneticdisturbances.

4. Moisture sensor (100) according to claims 2 and 3, wherein the thickness of the layer (30) operating as thermal insulation has a value of about between 0.40 mm and about 0.60 mm, preferably equal to 0.50 mm, and the thickness of the carbon fiber layers (20, 40) operating as a filter against electromagnetic disturbances has a value between 0.20 mm and 0.30 mm, preferably equal to 0.25 mm.

5. Moisture sensor (100) according to any one of the preceding claims, wherein the layer (30) operating as thermal insulation is configured for preventing a temperature rise of the electronic components of the sensor as a result of material passing through it, while the carbon fiber layers (20, 40) act as a Faraday cage for shielding against electromagnetic disturbances.

6. Moisture sensor (100) according to any one of the preceding claims, wherein the layer (30) operating as thermal insulation is constituted of glass fiber.

7. Moisture sensor (100) according to the preceding claims, wherein the outer coating (10) has a cylindrical conformation surrounding the sensor.

8. Moisture sensor (100) according to the preceding claims, wherein the outer coating (10) has a rectangular hole (12) for housing a holder (50) made of a thermally insulating material for an electronic control board of the moisture sensor.

9. Moisture sensor (100) according to the precedingclaims, wherein the outer coating (10) includes holes (14) for inserting screws (15) to secure the holder (50) of the electronic board to the moisture sensor.

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