FI100739B - Procedure for measuring the relative humidity, especially in radios and humidity sensors for applying the method - Google Patents

Description

100739

Method for measuring relative humidity, in particular in radiosondes, and a humidity sensor applying the method Förfarande för mätning av denatiat fuktigheten, speciellt i radiosonder samt fuktighetsgivare for tillämpning av förfarandet 5

The invention relates to a method for measuring relative humidity using a capacitive sensor assembly, in particular in radiosondes, in which a substance with a permeability as a function of the amount of water absorbed by the substance is used between the capacitor plates and said sensor combination is heated on the sensor surface and / or or to reduce the detrimental effects of condensed moisture, wherein the sensor 15 or part thereof is periodically and / or locally heated periodically with electric current and the sensor capacitance is detected without measuring the sensor temperature after the sensor capacitance or part thereof has cooled substantially to ambient temperature.

The invention also relates to a capacitive humidity sensor, in particular a humidity sensor for carrying out the method of the invention, which comprises a substrate of insulating material. a tin with the necessary '·' contact patterns for forming and switching the sensor capacitance and with an active insulating film between the sensor capacitance electrodes, • · · '• y whose permittivity is a function of the amount of water absorbed by that film and which • · «• · * * ··. · A surface contact is made on the membrane, which is thin, water-permeable and electrically conductive • · · • · · * ”. * 25 surface electrode with a contact pattern attached.

• · · • · · ... Several different types of electrically expressed temperature and humidity sensors are already known • · ♦ *. ···. thighs whose impedance changes as a function of the measurand. Such humidity sensors • ♦ ♦ are known, for example, from U.S. Patents Nos. 3168829 and 3350941 and the applicant's Finnish 30 patents No. 48229.

«· · 2 100739

It is known to use capacitive sensors for measuring temperature, which are generally based on the fact that the permittivity of the insulating material between the capacitor plates is temperature-dependent, whereby the capacitance observed at the terminals of the sensor also depends on temperature.

5

Part of the prior art of the present invention relates to F1 Patent No. 48229, which discloses a capacitive humidity sensor in which the dielectric insulator is a polymer film having a permittivity constant as a function of the amount of water absorbed by the polymer film.

10 The above-mentioned and other impedance-based sensors have undesirable phenomena, such as e.g. sensor freezing and wetting, radiation error, sensor slowness and hysteresis.

Applicant's FI patent application 58402 discloses a method for reducing undesired properties caused by reversible changes in the humidity sensor based on a change in impedance 15, especially in a capacitive humidity sensor with a moisture-sensitive material of an organic polymer heated to . If necessary, the heating power of the sensor can be adjusted to be measured; ' . 20 as a function of humidity. The said FI patent measures the temperature of the humidity sensor and / or • · *! . ' the outdoor temperature and this or these auxiliary variables are used in the calculation of the humidity measurement values. Ko. The FI patent states that the sensor heating can be switched off • · ·; for the duration of the measurement, but it is not specified in what way and for what purpose • ♦ · this switch-off takes place. In any case, the above-mentioned FI patent 58402 always requires • · · 25 measurements of the sensor temperature, on the basis of which the measurement result is corrected. because the sensor "shows" due to its elevated temperature relative humidity • · · too low a reading.

4 4. ···. With regard to the prior art, reference is further made to Applicant's FI patent 58,403 (corresponding GB-30 patent 2,047,431), which discloses a control device in a humidity sensor comprising a bridge connection or the like comprising temperature-dependent resistance elements for detecting a sensor 3 100739. the external temperature and the temperature Ts of the sensor itself and whose bridge differential voltage is used as a feedback signal to control the electrical power heating the sensor. The heating element of the sensor is a resistor element with a positive temperature coefficient, e.g. a platinum resistor, which at the same time acts as a sensor for the temperature Ts of the sensor. As the sensor of the external temperature Ta, a resistor-thermistor arrangement placed opposite the second branch of the bridge connection is used in relation to the position of the latter resistor element, so that a certain function Ts = f (Ta) specific to each sensor type is realized by a control device.

Referring further to the prior art related to the present invention, reference is made to Applicant's F1 Patent 85,770 (corresponding U.S. Patent 5,156,045), which discloses a method for measuring radiosonde impedance sensors, the method measuring the temperature of a sensor or sensors with a thermocouple. in connection with or adjacent to the sensor and having a thermocouple second branch connection 15 placed in the atmosphere surrounding the sensor, wherein said thermocouple detects a difference between the sensor temperature and ambient temperature .

20 • t; With regard to the state of the art related to the invention, reference is also made to Robert Bosch GmbH • 1 EP patent application 89113123.7 (Publication No. 0352682 A3). This publication • · · * .1V sa shows an electrically electrically heated humidity measuring sensor which is

* »I

* ···, intended primarily for use in the passenger compartments of automobiles and which sensor is based on changes in the resistance of • · · 25 active materials.

. ·. 30 · · * · · • ·

It is a general object of the present invention to further develop a prior art relative humidity measurement technique, especially in radiosonde applications, such that. the disadvantages which will be explained in more detail later are avoided.

4,100739

It is an object of the invention to provide a new measuring method and sensors, in particular for radiosonde operation, where the capacitive humidity sensor is exposed to such high humidity that the sensor performance deteriorates and water, frost and / or ice accumulates and condenses on the sensor's active surface or surrounding structures. Once such a disturbance situation is over, it will be a long time before the water or ice has evaporated, during which time the sensor will, of course, give a false message indicating excessive humidity. By heating the capacitive humidity sensor disclosed in the above-mentioned F1 patent 58402, the above-mentioned drawbacks can be avoided, but a satisfactorily unsolved problem remains that in order to obtain a sufficiently accurate humidity measurement, the temperature of the humidity sensor 10 must also be known very accurately. In order to achieve an accuracy of ~ 1-2% relative humidity, the sensor temperature must be measured with an accuracy of ~ 0.1 ° C. There may be more absolute error in the temperature measurement, but the temperature difference from the environment must be known with said accuracy. The main object of the invention is therefore to provide a humidity sensor which can be used to avoid the disadvantages caused by condensation and freezing of water on the surface of the humidity sensor and / or its surrounding structures, for example when the radiosonde flies in a subcooled cloud.

The object of the invention is to provide such a measuring method and sensors in which the relative humidity can be measured with at least the above-mentioned accuracy of ~ 1-2%.

; It is a further object of the invention to provide such a measuring method and sensors, * ♦ * * *. which are particularly well suited for disposable radiosondes, so that using the method and sensors of the invention, the sensor arrangement can be made simple, lightweight and otherwise economical in high-volume production.

• i · 25. The method of the invention is mainly characterized in that the method uses two or more different sensors or a parallel connection of several sub-sensors or the like, that when several different sensors are used, each sensor is heated alternately and that the relative humidity is mainly detected from said heating on the basis of 30 sufficiently cooled sensors or their sub-sensors.

5 100739

The humidity sensor according to the invention is mainly characterized in that the sensor comprises several sub-capacitances connected in parallel to form a measurable sensor capacitance and that each sub-capacitance is provided with its own heating resistor to which heating currents can be separately fed to heat each sub-capacitance.

When applying the method and sensor according to the invention, the step of measuring the temperature of the sensor and the necessary device and calculation arrangements can be omitted altogether, as a result of which the implementation steps and sensor structures and other related systems are substantially simplified and nevertheless the above measurement accuracy is generally achieved.

In particular, the heating energy used in the invention is an electric current, preferably a direct current, which according to the method of the invention is applied to a resistive heating resistor or various combinations of heating resistors connected to the sensor or sensor assembly 15.

The heating of the humidity sensor applied in the invention is needed to remove frost, ice and water from the sensor which are harmful for the humidity measurement. The sensor assembly consists of 20 humidity measuring parts and a heating part. These may be separate '; , structures or humidity measurement any structure can also be used for heating.

»* · * L If necessary, the heating output can also be adjusted in different ways.

• · ♦ • ♦ ♦ • · · · «· • · · • · II. * In the implementation of the heating of the humidity sensor according to the invention, there may be a measurement and • · · 25 control electronics in addition to the usual probe application. If necessary, heating demand. is detected and the heating element can itself act as a sensor for the heating demand so that. · · · ··· ice and / or condensed water cause a change in the heating rate of the element and the deceleration I. I # of the element resistor is measured using electronics. The electronics allow the heating to continue or stop as needed.

30 The warm - up period may be performed once per test cycle of the probe or; The heating output can be adjusted if required. If necessary, the magnitude of the power can be measured, for example by means of a heating resistor simultaneously with the heating. This information can also be used as a measure of freezing efficiency or supersaturation.

The humidity sensor according to a preferred embodiment of the invention is characterized by its small size and structure so that a short-term thermal pulse propagates only to and in the vicinity of the surface electrode. In this case, the thermal and humidity time constants of the sensor are very short and allow the sensor to be used for humidity measurement directly without correcting errors caused by heating in probe operation, where the humidity measurement takes place once in approx. 1.5 s. Heating removes ice and water from the surface of the humidity sensor and / or its surroundings that interfere with the measurement. The small size of the sensor makes it unnecessary to use radiation protection. The manufacturing cost of the sensor can also be made lower than with previously known sensors.

In the invention, two physically separate sensors or an integrated thermally isolated pair of sensors can be used so that one sensor is heated while the other is measuring relative humidity and vice versa. Heating removes ice and water harmful to the sensor for moisture measurement. The rotation principle avoids the use of a sensor that is heated but not yet sufficiently cooled; "20 humidity measurements and eliminates cumbersome sensor temperature measurements and the difficulty of compensation calculation. In addition, there is a wide range of •« · * * heating timing and power control. The sensor does not have to be as extremely fast as a single sensor pulse heater, although this can also be used • · · '·. · * The sensor best suited for this use is a sensor heated by a base electrode, which has the advantage of providing integrated heating resistance during the manufacture of the humidity sensor, so that the thermal and humidity time constant is sufficiently short. , M · good heat transfer and correct application of heating power Small size integration brings cost savings in manufacturing Changes are needed in electronics compared to the previously known probe electronics, as the sensors are connected in turn for heating or humidity 30 If necessary, the heating can also be adjusted I · I ♦ «· in different ways. Electronics that measure both humidity sensors 7 100739 all the time are also possible. In this case, only the heating is alternated, and the correct humidity is separated by data processing based on the fact that the warm sensor shows a lower reading. It is also possible to use one sensor by heating it in between and discarding the erroneous data and placing the interpolated "correct" data in place of the discarded one.

The humidity sensor according to the invention is implemented in such a way that several humidity measuring sub-sensors are connected in parallel. The measurement of relative humidity takes place in parallel, preferably across all capacitive humidity sensors, continuously. Each sub-sensor 10 is heated separately at a time. The error caused by heating always goes to N parts when N sub-sensors are connected in parallel compared to the error of one sub-sensor. The error is further reduced when the sensor assembly is calibrated. with the heating normally operating. Electronics are needed to perform the heating and perform the measurement. Such parallel connection of the sensors 15 can be realized with sensors based on surface or bottom electrode heating. The known structure of the applicant's "Humicap" ™ is also possible with the addition of a heating resistor which is vaporized on the substrate or a combustion resistor. Humidity sensors can be integrated on one or more substrates.

; The invention also realizes the advantage that the electric current used for heating does not; the various electrical phenomena associated with it interfere with the measurement of the sensor capacitance, which is also important in that the sensor capacitances used in the relative humidity measurements are quite small and their capacitance time is usually in the range of 1-100 pF.

The invention will now be described in detail with reference to the accompanying drawings. to some of the preferred embodiments of the invention shown in the figures, in which the invention is in no way narrowly limited.

«·» • · ···. Figure 1A is a top view of a first embodiment of a sensor according to the invention.

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Figure 1B is the same as Figure 1A seen from the side.

Fig. 1C shows a substitute connection of the sensor according to Figs. 1A and 1B.

Figure 2A shows another embodiment of a sensor according to the invention.

Figure 2B shows the same as Figure 2A seen from the side.

Fig. 2C shows a surrogate connection of the sensor of Figs. 2A and 2B.

10

Figure 3A shows a top view of a third embodiment of a sensor according to the invention.

Figure 3B shows the same as Figure 3A seen from the side.

15

Fig. 4A shows a side view of a humidity sensor according to the invention, the heating resistor of which is wrapped around the sensor.

Figure 4B shows the same as Figure 4A seen from above.

20 * · l '; Fig. 5A shows a modification of the sensor shown therein in accordance with Fig. 4A.

• · · • · «I« 9 100739

Fig. 8 is a block diagram of a measuring system according to a first preferred embodiment of the invention, in which two sensor capacitances which are heated alternately are used.

Figure 9 shows the measurement cycles and sequences of the measurement system of Figure 8.

Fig. 10 shows an example of such an electronic connection, by means of which it can be detected whether, for example, the sensor according to Figs. 4A, 4B or 5A, 5B contains ice or moisture.

10

The humidity sensor shown in Figs. 1A and 1B is constructed on a stable glass substrate 10 on one surface surface of which a sensor capacitance electrode 13a is provided, on which a plastic film 12 is arranged, the permittivity of which is a function of the amount of water absorbed by the film 12. A water-permeable, yet electrically conductive surface electrode film 14 is made on the film 12, which is in galvanic contact with the surface contact 13b. The capacitance CM to be measured is detected between the terminals ct and c2 connected to the contacts 13a and 13b. The sensor 10 according to Figs. 1A and 1B is provided with an electric heating resistor 15, the conductor pattern of which is made on the same surface of the substrate 11 as the base electrode 13a. A heating electric current I, preferably ', can be applied to the heating resistor 15; 1 20 direct current through terminals rt and r2 connected to contact patterns 15a and 15b.

•; The electrical substitute connection of the humidity sensor 10 according to Figs. 1A and 1B is shown in Fig. 1C. The heating current I supplied to the heating resistor R provides the heating power

1 8 S

'11 / W = I2 x R, which heats the active film 12 of the capacitance to be measured, melts any ice or frost on top of it S · · 25 and evaporates the excess from the surface of the film 12. moisture.

* »1 • ·« • 1 · · · • f · 4 «· •

Figures 2A and 2B show another humidity sensor 10 according to the invention, in which a separate heating resistor R is not used, but the heating resistor R is formed by an electrically conductive surface electrode 14. Connected to opposite edges of the surface electrode 14: conductor patterns 13b and 15a to which terminals rj and r2 are connected. a heating current 10 100739 I is supplied, which, when passing through the conductive resistive material of the surface electrode 14, produces the intended heating effect W = I2 x R, where R = the resistance measured from the poles 13a, 15b of the surface electrode. The surface electrode 14 is a very thin moisture-permeable "perforated" film, e.g. gold, which, however, is electrically uniform and thus also conductive.

The electrical substitute connection of the humidity sensor 10 according to Figs. 2A and 2B is shown in Fig. 2C, which shows that the capacitance CM to be measured and the heating resistor R formed from the surface electrode have a common pole c2 = r2.

10

Figures 3A and 3B show the sensor 10 otherwise shown in Figures 1A and 1B, except that the heating resistor 15 is located on a surface opposite to the electrodes 13a, 14 and the active film 12 of the glass substrate 11. The surrogate connection of the humidity sensor according to Figs. 3A and 3B is as shown in Fig. 1C. In order to achieve the objects of the invention, the dimensions 1 x m x s of the sensors shown in Figures 1, 2 and 3 are relatively small, so that the sensor is small in size and thermal mass and thus heats and cools sufficiently quickly. Typically, the above dimensions 1 x m x s are <4 mm x 1.5 mm x 0.2 mm.

Figures 4A and 4B show a sensor 10 according to the invention attached to support strips 16a and 16b which are insulating material. Support strips 16a, 16b • «*; around and at the same time around the active sensor 10 a resistor wire 15 is wound, from which »i» * · f * '*. * a sensor heating resistor R is formed, to the terminals rj and r2 of which a heating * · · V, /' current I is applied. and 5B show a heated sensor structure otherwise as shown in Figures 4A and 4B except that the active sensor 10 is attached to the unit. . ·, To a strip 16 around which, as well as the sensor 10, a resistance wire 15 is wound, which • · # ·· *. forms the heating resistor R of the sensor 10. The electrical substitute connection of the sensors of Figures 4 and 5 is as shown in Figure 1C. Thus, Figures 4 and 5 • | In accordance with i!.! §, the actual sensor 10 and the heating resistor 15 and its possible support structures 16a, 16b are, in contrast to Figures 1-3, a separate structure manufactured at different stages of manufacture. An advantage in the structures according to Figures 4 and 5 is that> t t i 11 100739 humidity sensors 10 can be used with sensors of the known nature, e.g. sensors marketed under the trademark "Humicup" by the applicant. However, the structures according to Figures 1-3 have the particular advantage of their small size and low thermal mass, which has a substantial advantage in various applications of the invention, as will be explained in more detail later.

Fig. 6 shows a sensor assembly 10P according to the invention with N sensor sub-capacitances Cj ... CN connected in parallel. Each partial capacitance Cj ... CN is equipped with its own heating resistor Rj ... Rn, to which 10 heating currents Ij ... IN (usually li = I2 ... = In) can be alternated separately · Measured capacitance CM = Cj -I- C2 ... + CN. The measurable capacitance CM can be detected all the time. The heating of the different sub-capacitances Cj ... CN is performed alternately so that always one sub-capacitance Cj ... CN is heated while the other capacitances cool down. The heating error thus drops to the N part and yet frost is obtained from the active surface of each sub-capacitance and remains alternately melted and the excess moisture evaporated. The error caused by the heating can be further reduced by calibrating the sensor while that alternating heating is in normal operation. When the sensor capacitance CM is measured continuously or almost continuously, the partial capacitances Cj.-.Cn are heated in a certain reproducible cycle T0 '20 alternately for the time t0 and the above times are chosen so that t0 «T0 / N, where N is the partial capacitances Cj.- .Cn number. If no continuous measurement is required, rest periods and / or periods in which all sub-capacitances * · · i · · "V Ci ... CN are heated simultaneously may be used between measurement cycles T0 I I 1.

Fig. 7 shows in principle a measuring system of a radiosonde according to the invention and a measuring system applying the two humidity sensors 10j and 102 according to the invention • · ·, ···. as a block diagram. The ice system according to Fig. 7 comprises a sensor element 30, an electric source I. I f tea 31, sensors 10j, 102, a heating level controller 32 and a heating current distributor 33.

«I«!,! The system includes a measurement and heating control unit 34, a probe data processing unit 35 (optional), a telemetry transmitter 36 and sensor measurement electronics »» I * <• ;; / 40. The system also includes physical quantities measured by the radiosonde, «, 4 · 12 100739 such as pressure and temperature sensors 101,102 and 103 ... 100n and humidity sensors 10j and 102 according to the invention. The above-mentioned units are on a gas balloon in a rising radiosonde and via wireless telemetry link TE in radio communication with ground radio receivers 37 and data processing units 38. Unit 38 5 processes, indicates and displays with sensors 101 ... 100n, 10! and 102 observed physical quantities of the atmosphere. The unit 33 controls the heater units 20i, 202, which heat the humidity sensors 10j and 102, preferably alternately, so that in each heating step ice or frost on the surface of the respective sensor 10t and 102 is melted and the moisture evaporated, so that the sensor capacitance CM 10 to cool sufficiently close to the ambient temperature without the need to measure the temperature CM of the sensor capacitance and to perform a compensation calculation of the measurement results based on it. However, the system shown in Fig. 7 can also be used in connection with the sensor according to Fig. 6, modified in such a way that the heating is alternated for each of the N sub-sensors Cj ... CN and the capacitance CM is measured from the sensor terminals Cj and c2 shown in Fig. 15.

In the ice system of Figure 7, the humidity sensors 10! and 102 act alternately as measuring sensors. The system can also operate such that the electronics 40 measure both of the humidity sensors 10! and 102 the capacitances CM at all times and only the heating of the sensors by means of the units' 20 20j and 202 is alternated. In this case, the correct humidity observation (cooled sensor 10! ^ '': 102) is separated by data processing based on the fact that the sensor 10 is too warm! ^ 1¾ t «·’ · * · / shows a lower reading that is discarded.

Fig. 8 shows a more detailed implementation example of the system according to Fig. 7. As shown in Figure 8, the system comprises a measurement sequence unit 43 which controls. multiplexer 41 and sensors 10! And 1¾ heating control unit 22, to which • · * heating power is supplied from unit 21. Humidity sensors 10 and 102 have • · · l £ * • heating resistors 15! And 152, to which the heating current and I2 (usually Ij = I2) are alternately supplied under the control of the unit 21. The multiplexer 41 connects to the measurement and to the telemetry connection TE alternately all the different sensors of the probe, which in Fig. 8 are • · ·:; ; denoted s, p, k2, T, ux = 10 !, u2 = 1 ^ 2 And ^ ι · Sensor s represents e.g. the temperature sensor 13 100739 of the pressure sensor, the sensor p the pressure sensor, the sensor T the temperature sensor and the sensors kj and k2 accurately known reference and calibration sensors. Through the multiplexer 41, the above-mentioned sensors, which are generally capacitive sensors, are connected to the frequency-determining capacitance part of the RC oscillator 42, whereby the frequency fM> 5 is obtained from the oscillator 42, which is proportional to the measured quantity. At the frequency fM, the radio transmitter 36 is modulated.

The upper part of Fig. 9 shows successively repeated measurement cycles, each cycle comprising a successive reading of the sensors s, p, k2, T, u1, u2 and kj. The lower part 10 of Fig. 9 shows a pulse diagram of the heating, stabilization and measurement sequences of the sensors ^ = 10t and u2 = 102, so that when the pulse is high, the function mentioned on the left side of Fig. 9 is to be performed.

The so-called only one sensor can be used in a low pulse application. In these 15 applications, erroneous data is detected programmatically and interpolation is performed.

A feature can be included in the invention to detect freezing, fogging or the presence of condensed water on the active surface of the sensor or its surroundings. This feature can be realized, for example, by a circuit as shown in Fig. 10, the operation of which is characterized by measuring the heating rise rate or the like of the heating resistor 15 in the structures shown in Figs.

The circuit shown in Fig. 10 comprises a heating power supply unit 21, a heating detection unit 23. The heating unit 15 indicates the resistance of the heating resistor 15. based on the rate of change, the heating demand based on the input signal Uc of the unit 23.

· · ^ • · · ΙΥί 'Unit 23 provides heating power to control unit 22 and / or heating pulse period • · ·

for control unit 24 (optional) control signals Cj and c2. The operation of the unit 23 is based on the fact that if the heating resistor 15 and the associated sensor capacitance CM

• 1 30 condensed water, frost or ice is present, after the heating pulse is switched on, the rate of increase of the resistance of the heating resistor 15 is substantially

M

100739 is slower compared to the situation where there is no condensed water, frost or ice on or around the active surface of the heating resistor 15 and the sensor capacitance CM, since the latter contribute to the heating-retarding thermal mass of the sensor resistor 15. When, at the beginning of the heating phase, the sun speed of the sensor resistor 15, which can be expressed e.g. as a constant current I, is increased above a certain threshold value, the heating is stopped under the control of signals Cj and / or C2 of unit 23. If, on the other hand, the rate of increase of heating and resistance of the resistor 15 is less than said threshold value, the periodic heating of the sensor resistor 15 according to the invention is continued under the control signal C1 and / or c2 of the unit 23 until said threshold value is exceeded and / or according to a preset sequence.

The following are claims which, within the scope of the inventive idea defined by it, the various details of the invention may vary and differ only from those exemplified above.

• · * · * · • »* •« • · · • · • · · · · · · · · · · · · · · · · · · · · · · · · · · • • * * · • · · M · • · · • · · ·

Claims (13)

1. A method for measuring relative humidity by using a capacitive humidity sensor combination (10 µ, 102; 10 P), especially in radio probes, in which sensors using a blank (12) between the capacitor discs whose permittivity is a function of the amount of water absorbed by the substance (12) and in which process said sensor combination is heated to reduce harmful effects caused by ice, frost and / or condensed moisture collected on the surface of the sensor and / or in the environment, and at which method the capacitor capacitance (CM) or a portion (C ^-Cj ^) thereof is heated in a timely manner and / or locally periodically with electric current (I), and the observation of the capacitor capacitance (CM) is performed without measuring the sensor temperature where the sensor capacitance or a portion (Cj ... CN) of this is cooled by substantially to ambient temperature, characterized in that two (10L, 10- parallel coupling of several sensors (Cj ... CN) or the equivalent, that when using several separate sensors (10 ^ 10 10j, 102) or its donor (C C - C. C) cooled by sufficient. 20 2. A method according to claim 1, characterized in that in the process ::: several parallel coupled capacitances ((^ ... (^)) are used, whereby a heating circuit (I) is connected to each of these in a circulating sequence in turns and that • ·: the capacitance (CM) to be measured is observed from the poles (^, ¾) of the parallel-coupled encoder combination, whereby using N pieces of encoder (¢ ^ ... (¾) 25, the proportion of the heated sensor is only an Nth part of the sensor's total capacitance • (CM) (Figure 6). A method according to claim 2, characterized in that the capacitance (CM) is measured substantially continuously and that the partial capacitances (Cj ... CN) are successively heated in a repeated cycle (T0) the time where tQ / N. 19 100739 Method according to any one of claims 1-3, characterized in that before the actual point coupling of the heating of the sensor is observed in the process the presence of ice, frost and / or condensed moisture collected at the sensor (10). 5 Method according to claim 4, characterized in that the observation of the icing, frosting and / or dewatering of said sensor (10) is carried out on the basis of the measurement of the change in the heating rate and / or the resistance of the resistor (15) at the sensor (Figure). 14). 10 A capacitive humidifier, especially a humidifier (10) for carrying out the method according to any of claims 1-5, which humidifier comprises a substrate (11) of insulating material for which necessary contact figures have been made for the design and coupling of the sensor capacitance and where there is a active insulating film (12) between the sensor capacitance electrodes, whose permittivity is a function of the amount of water absorbed by the film (12) and on which film (12) a surface contact (14) is made, which is a thin, water-permeable and conductive surface electrode (14), to which is connected a contact figure (13b), characterized in that the encoder comprises several subcapacitances (C1, C2 ... CN) which are connected in parallel to form the encoder capacitance: \: 20 (CM) to be measured and that each subcapacitance (Cj, C2 ... CN) is provided with its own heat resistance (Rj ... Rn), to which one can separately conduct heating • ·: currents (Ij ... IN) for is to heat each partial capacitance (Cj ... CN) separately for • ·: itself. • «« ♦ ♦ «♦ · · Humidity sensor according to claim 6, characterized in that the contact figures (13b, 15a) have been connected to said surface electrode (14) in such a way that via an electric current they can conduct an electric current. (I) to said surface electrode (14) which heats the sensor (10) (Figures 2A, 2B, 2C). : ·]: 30 Humidity sensor according to claim 6 or 7, characterized in that the one pole (¾¾ of the surface electrode heating resistor (R) and of the capacitance (CM) to be measured is common in the sensor (10)) (Figures (2A, 2B) , 2C) Humidity sensor according to any of claims 6-8, characterized in that the heat resistance (15) of the sensor (10) is arranged on opposite surfaces of the sensor substrate (11) relative to the active insulating film (12) (Figures 3A, 3B ). Humidity sensor according to claim 6, characterized in that a resistance tree or piece (15) which is special in relation to the actual sensor structure (10) has been connected to the humidity sensor (10), which resistance tree is arranged to function. as heat resistance (R) for the humidity sensor (Figures 4A, 4B, 5A, 5B). 10 Humidity sensor according to claim 10, characterized in that, in connection with the actual humidity sensor (10), a support part (16) or support parts (16a, 16b), supported by winding (15) of resistance trees or an resistor piece (s) is attached, which (s) form a heat resistance for the humidifier (10) (Figures 4A, 4B, 5A, 5B). Humidity sensor according to any of claims 6-11, characterized in that in the sensor there is a group of N connected in parallel capacitances and that N «2 ... 20,. · · ·. most preferably N = 5 ... 10. 20: Y; Humidity sensor according to any of claims 6-12, characterized in that: a unit (23) is coupled to the humidity sensor, with which it is observed the rate of change of resistance of the heat resistance (Rj ... Rn) in conjunction with transducer capacity: T: tansema (Cj ... CN) or a quantity derived from this when supplying electric current (I) to the transducer resistor, on the basis of which one can express about heating requirements for • · • * ·· The humidity sensor is provided, in which purpose said unit (23) is arranged to with its · ·· V · output signals (Cj and / or control a control unit (22) for the heating current ·; ”· belonging to the system and / or a control unit (24) for the period of heating current: the impulse (Figure 10). «I * 30