WO2007065570A1

WO2007065570A1 - Method and device for calibrating a humidity sensor

Info

Publication number: WO2007065570A1
Application number: PCT/EP2006/011317
Authority: WO
Inventors: Walter Knoblach; Jan Zach; Haris Cadordzic
Original assignee: Areva Np Gmbh
Priority date: 2005-12-09
Filing date: 2006-11-25
Publication date: 2007-06-14
Also published as: DE102005059304B3; TW200730818A

Abstract

Disclosed are a method and a device for calibrating a humidity sensor (18), in which a carrier gas having a predefined input steam concentration and a predefined rate of flow (Qv) flows into a mixing chamber (2) communicating with a water reservoir (6) via a steam-permeable partition (4), the temperature (Tw) of the water reservoir (6) being set to a constant value, and steam is admixed to the carrier gas in the mixing chamber (2). A measured value (CM) for the output steam concentration in the steam/carrier gas mixture discharged from the mixing chamber is determined by means of the humidity sensor (18) and is compared to a real value (Cout) of the output steam concentration in the mixture discharged from the mixing chamber (6), said real value (Cout) being defined by a relation depending on the temperature (Tw) of the water reservoir (6), the rate of flow (Qv), and the input steam concentration into the mixing chamber (6).

Description

description

Method and device for calibrating a moisture sensor

The invention relates to a method and a device for calibrating a moisture sensor.

For monitoring a system part containing water or water vapor, for example the primary circuit line of a

Pressure water core reactor, on the occurrence of a leak, it is known from EP 0 175 219 to arrange a manifold on the system part, into which the water emerging from the system part in the event of a leak or the water vapor emerging from the system part can penetrate. The known manifold consists of a tube which is impermeable to water or water vapor and which is provided in its longitudinal direction with a plurality of openings closed with a microporous sintered metal material through which water or water vapor can diffuse into the interior of the tube. Using a method known from DE 24 31 907 C3, the location at which the water or water vapor has penetrated into the collecting line is then determined. This location corresponds to the point at which water or water vapor has escaped from the monitored part of the system. For this purpose, with a pump connected to the collecting line, for example in pressure operation, a compressor at the entrance of the line, the water vapor which has entered the collecting line, together with a carrier gas located in the collecting line, is fed to a moisture sensor which is also connected to the collecting line. With this moisture sensor, the water vapor output concentration is measured as a function of time and monitored for exceeding a threshold value. With known Flow velocity can be determined from the time span between the switching on of the pump and the arrival of the water vapor at the moisture sensor, i.e. the point in time at which the threshold value is exceeded, the place at which water or water vapor enters the collecting line and thus the location of the leak at the system part can be determined.

Especially when using a capacitive humidity sensor, there is the problem that it is unstable during long-term monitoring and drifts away from the working point. In order to obtain reliable measurement results and ensure largely error-free monitoring, regular calibration of these moisture sensors is necessary.

Such a calibration involves considerable effort for the operator of the system. On the one hand, expensive devices such as a regulated moisture generator and a calibrated moisture sensor are required for calibration. On the other hand, the calibration of a moisture sensor is time-consuming, since the entire measuring range of interest has to be covered with a sufficient number of measuring points, which cannot be approached immediately one after the other due to the inevitable hysteresis effects. In addition, it is necessary to interrupt measurement operation at least briefly for the calibration and to remove the moisture sensor to be calibrated and arranged in a sensor module together with the sensor module from the measuring station and to replace it with a calibrated replacement sensor module. For these reasons, such a calibration is carried out relatively rarely in practice, for example once a year. A method for calibrating a moisture sensor is known from WO 94/28410, in which the moisture sensor is introduced into the gas circuit of a calibration device in which a gas circulates, which is saturated with water vapor and whose temperature is known. This temperature corresponds to the dew point, from which the water vapor concentration can be deduced directly. With the known calibration device, it is also possible to calibrate a moisture sensor in situ, ie at the location where it is attached for monitoring the water vapor content of a process gas.

The invention is based on the object of specifying a method and a device for calibrating a moisture sensor which, with high measuring accuracy, is low

Effort can also be carried out in short intervals.

With regard to the method, the object is achieved according to the invention with a method having the features of patent claim 1. According to these features, the method flows to

Calibrating a moisture sensor a carrier gas with a known water vapor inlet concentration and a known volume flow into a mixing chamber which communicates via a water vapor permeable partition with a water reservoir, the temperature of which is set to a constant value, and in which water vapor is added to the carrier gas. The moisture sensor is used to determine a measured value for the initial water vapor concentration in the mixture of water vapor and carrier gas flowing out of the mixing chamber. This measured value is compared with an actual value of the water vapor

Initial concentration in the mixture flowing out of the mixing chamber compared, which is determined by the temperature of the water reservoir, the volume flow and the water vapor Input concentration in the mixing chamber dependent relationship is given.

With such a method, the calibration of a moisture sensor is considerably simplified, since the sensor module does not have to be removed from the measuring station, so that this can be carried out at shorter intervals.

The invention is based on the consideration that the water vapor absorption of the carrier gas flowing through the mixing chamber, for example air, with constant structural conditions of the mixing chamber and the dividing wall is determined exclusively by and through the water vapor inlet concentration, the temperature of the water reservoir and the volume flow the relationship

given is. Here: c _Out [-] mean the water vapor outlet concentration at the outlet of the mixing chamber (actual value)

c _o [-] the water vapor inlet concentration at the inlet of the mixing chamber (actual value)

c _w (T _w ) [-] the water vapor concentration surrounding the mixing chamber (function of the temperature of the water reservoir)

T _W [K] temperature of the water reservoir (measurable)

Qv [m ³ / s] the carrier gas volume flow (given as volume flow) through the mixing chamber (measurable) α _w (T _w ) [m ³ / s] a temperature-dependent parameter of the porous

Partition wall, which the permeability and dimension solutions (will be determined once during commissioning)

To calibrate the moisture sensor, ie to set a known actual value of the water vapor output concentration at the outlet of the mixing chamber, it is sufficient for a given water vapor input concentration C ₀ , which is preferably equal to 0 (dry carrier gas or dry air), the volume flow of Set carrier gas and / or the temperature of the water reservoir to different values. The then resulting actual value of the water vapor output concentration C _out at the output can either be determined by interpolation from a look-up table (characteristic curve field) that was created and stored during a calibration when the device was commissioned, or using the above relationship are calculated if, during the calibration of the device, the parameters describing the properties of the mixing chamber (geometry and vapor permeability of the partition) have been determined experimentally for different temperatures T _w .

If the volume flow of the carrier gas and the temperature of the water reservoir are measured and regulated, the measurement accuracy during calibration is increased.

With regard to the device, the stated object is achieved according to the invention with a device having the features of patent claim 6, the advantages of which, as well as the advantages of the features specified in the subordinate claims of this patent claim 6, correspond analogously to the advantages specified for the associated method claims. If a device according to the invention is integrated in a so-called leakage monitoring system (moisture leakage monitoring system, FLÜS), which contains a sensor line connected to a pump, into which water vapor can penetrate and which comprises a moisture sensor connected to the sensor line to detect the penetrated water vapor, it is possible to remotely calibrate the humidity sensor remotely from a control room at regular intervals and the operational safety of the leakage monitoring system is significantly improved.

To further explain the invention reference is made to the embodiment of the drawing. 1 shows a device according to the invention in a schematic basic illustration,

2 is a diagram in which the water vapor

Initial concentration at the outlet of the mixing chamber for 3 different temperatures of the water reservoir against the flow rate of the carrier gas (air) is plotted in the mixing chamber.

1, a device according to the invention comprises a mixing chamber 2, which communicates with a water reservoir 6 via a partially permeable partition 4. The partially permeable partition, for example made of a sintered metal material, is permeable to water vapor, but impermeable to water. The partition 4 can directly adjoin the water in the water reservoir 6 on its flat side facing the water reservoir 6. In principle, however, there can also be a gas cushion saturated with water vapor, usually air saturated with water vapor, between the water in the water reservoir 6 and the membrane, since the diffusion speed of the water vapor through the partition 4 is essentially determined only by the difference in the partial pressures of water vapor in the mixing chamber 2 and in the water reservoir 6. The water reservoir 6 is connected to the ambient atmosphere via a pressure compensation line 7 in order to avoid excess pressure when the water reservoir 6 is being heated.

The mixing chamber 2 has an inlet 8 and an outlet 10 for a carrier gas, usually air, flowing through it. The input 8 is connected via an input line 12 to a compressor 14 which, as carrier gas, sucks in air from the environment and conveys it to the mixing chamber 2, through which it flows and in which it absorbs water vapor, so that at the outlet 10 a mixture of water vapor and carrier gas (Air) is present, its water vapor output concentration by the volume flow Q _v , the water vapor input concentration C ₀ in the carrier gas at the inlet 8, the geometric conditions of the mixing chamber 3 and the physical properties of the partition 4 and the temperature T _{w of} the water reservoir 6 according to given above relationship.

An output line 16 is connected to the output 10, to which a moisture sensor 18 to be calibrated is connected, with which a measured value of the water vapor

Initial concentration c _out is determined in the carrier gas flowing in the outlet line 16.

The water reservoir 6 is heated with a heating device 20 so that its temperature T _w can be set to predeterminable values. For this purpose, the heating device 20 is connected to a control device 22, which uses control signals S1 to either adjust the heating power to a predeterminable value and thus controls the temperature T _{w of} the water reservoir 6 or regulates the temperature T _{w of} the water reservoir 6. For this purpose, a temperature sensor 23 is arranged in the water reservoir 6, the measured values of which are fed to the control device 22, so that the temperature T _{w of} the water reservoir can be regulated to a predetermined value.

The control device 22 also controls or regulates the compressor. In order to enable regulation, a flow sensor 24 is arranged in the input line 12, with which the mass flow Qv, for example the volume flow, is measured through the input line 12. The corresponding measured values are then also processed in the control device 22 for generating control signals S2 for regulating the compressor 14.

With the help of the control device 22, different temperatures T _{w of} the water reservoir 6 and different volume flows Q _{v of} the carrier gas are now set, each of which includes a previously known water vapor output concentration at the outlet 10 of the mixing chamber 2, which are in the form of a characteristic field which at commissioning was measured by a single calibration. 3-way valves are connected into the input line 12 and into the output line 16, which are controlled by the control device 22 with the aid of control signals S3, S4 and are connected to a bypass line 30 which carries the carrier gas flowing in the input line 12 past the mixing chamber 2 directly to the moisture sensor 18. If the carrier gas fed into the input line 12 is dry, ie has a water vapor output concentration which is practically equal to 0, the zero point of the moisture sensor 18 can be calibrated in this operating mode of the device. The ones from Humidity sensor 18 for various known actual values of C d _out ^he steam outlet concentration measured measurement values c _M can then be used to calibrate the moisture sensor 18th

In the exemplary embodiment, the bypass line 30 is also connected via a three-way valve 32 to a sensor line 34 of a moisture leakage monitoring system, through which carrier gas, generally air, is conveyed to the moisture sensor 18 at constant time intervals by a compressor 36. Water vapor can penetrate into the sensor line 34 either along the entire line or at predetermined line positions. The sensor line 34 is arranged on a system part carrying water or water vapor. In the event of a leak in the system part, a measurement value c _M for the water vapor concentration is then measured with the moisture sensor 18, to which an actual value c _{τ is} assigned on the basis of the previous calibration and which can be compared in the control device with a predetermined threshold value c _s . The occurrence of a leak is indicated when the actual value c _τ exceeds the threshold value c _s . The three-way valve 32 is also controlled by the control device 22 via control signals S5, so that an automatic switchover from the monitoring mode to the calibration mode is possible.

In the diagram according to FIG. 2, the actual value c _{τ of} the initial water vapor concentration in air is plotted for a device explained with reference to FIG. 1 against the speed of air in the mixing chamber, which in the exemplary embodiment has an inner diameter of 6 mm. The diamonds represent measurement points that were obtained at a temperature T _{w of} the water reservoir of 25 °. Triangles represent measured values that for different volume flows at a temperature T _w = 30 ° have been obtained, and points correspond to measured values at a temperature T _w = 40 °. The solid lines are calculated values which have been obtained using the above-mentioned model. It can be seen from the measurement points and the curves shown in the diagram that the model describes the water vapor output concentration generated at the outlet of the mixing chamber with high accuracy. With the help of the model, it is therefore possible to considerably reduce the number of measurements to be carried out when the device is calibrated for the first time, since in principle only one measuring point is required for each temperature T _w in order to determine the parameter α _w (T _w ) can.

15

Reference list

2 mixing chamber

4 partition

6 water reservoir

8 entrance

10 exit

12 input line

14 compressor

16 Output line

18 humidity sensor

20 heating device

22 control device

23 temperature sensor

24 flow sensor

26,28,32 three-way valve

30 bypass line

34 sensor cable

36 compressor

Sl - S5 control signals

Claims

11

Claims 1. Method for calibrating a moisture sensor (18), in which a carrier gas with a known water vapor inlet concentration and a known volume flow (Q _v ) flows into a mixing chamber (2) which is connected to a water reservoir (4) by a water vapor permeable partition (4). 6) communicates, the temperature (T _w ) of which is set to a constant value, and in which water vapor is added to the carrier gas, and in which the moisture sensor (18) is used to make a measurement (c _M ) for the initial water vapor concentration the mixture of water vapor and carrier gas flowing out of the mixing chamber is determined and compared with an actual value (c _ou t) of the initial water vapor concentration in the mixture flowing out of the mixing chamber (6), which is determined by a temperature (T _w ) of the water reservoir (6) , the mass flow (Q _v ) and the water vapor input concentration in the mixing chamber (6) dependent relationship.

2. The method according to claim 1, wherein the mass flow (Q _v ) of the carrier gas is controlled.

3. The method according to claim 1 or 2, wherein the mass flow (Qv) is measured and controlled.

4. The method of claim 1, 2 or 3, wherein the temperature (T _w ) of the water reservoir (6) is measured and controlled.

5. The method according to any one of the preceding claims, wherein the water vapor input concentration is at least approximately zero. 12th

6.Device for calibrating a moisture sensor (18), with a compressor (14) for generating a carrier gas flow with a known volume flow (Q _v ), and with a mixing chamber (2) connected to it for admixing water vapor, which is separated by a partition permeable to water vapor (4 ) communicates with a water reservoir (6) which can be heated with a heating device (20), and which is provided with an outlet line (16) for the mixture of carrier gas and water vapor generated in the mixing chamber (2), to which the moisture sensor (18) is connected , and with a control device (22) for controlling the heating device (20) and for setting the temperature (T _w ) of the water reservoir (6) to a predeterminable value.

7. Device according to claim 6, wherein the control device (22) for regulating the temperature (T _w ) comprises a temperature sensor (23).

8. Device according to one of claims 6 or 7, wherein the control device (22) for regulating the flow rate (Qv) of the carrier gas comprises a transducer (24) for measuring the flow rate (Qv).

9. Device according to one of claims 6 to 8, wherein the mixing chamber (2) is assigned a bypass line (30).

10. Leakage monitoring system with a sensor line (34) connected to a pump (36) into which water vapor can penetrate and with a moisture sensor (18) connected to the sensor line (34) for detecting the water vapor, and with a between the sensor line (34 ) and 13

Moisture sensor (18) switched device according to claim 9.