DE102005059304B3 - Humidity sensor calibrating method for pressurized water nuclear reactor, involves comparing measuring value with actual value given by relationship that is dependant on temperature of reservoir, mass flow and inlet concentration in chamber - Google Patents

Abstract

The method involves mixing a carrier gas with water vapor in a mixing chamber (2) which communicates with a water reservoir (6). A humidity sensor (18) determines a measuring value for the water vapor outlet concentration in the mixture of water vapor and carrier gas flowing out of the chamber. The measuring value is compared with an actual value of water vapor outlet concentration. The actual value is given by a relationship which is dependant on the temperature of the reservoir, mass flow and the water vapor inlet concentration in the chamber. Independent claims are also included for the following: (1) a mechanism for calibrating a humidity sensor, comprising a compressor (2) a leakage monitoring system with a pump.

Description

The The invention relates to a method and a device for Calibrating a humidity sensor.

For monitoring a water or steam-containing plant part, for example, the primary circuit line of a pressurized water nuclear reactor, the occurrence of leakage, it is from the EP 0 175 219 it is known to arrange a manifold at the plant part into which the water emerging from the plant part in the event of a leak or the water vapor emerging from the plant 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 by a microporous sintered metallic material, through which water or water vapor can diffuse into the interior of the tube. With one from the DE 24 31 907 C3 known method is then determined the place where the water or steam has penetrated into the manifold. This location corresponds to the point at which water or steam escaped from the monitored part of the plant. For this purpose, with a connected to the manifold pump, for example, in the printing operation, a compressor at the entrance of the route, the steam penetrated into the manifold together with a carrier gas in the manifold fed to a also connected to the manifold moisture sensor. With this moisture sensor, the initial water vapor concentration is measured as a function of time and monitored for exceeding a threshold value. At a known flow rate can from the time between switching on the pump and the arrival of water vapor at the moisture sensor, ie the time to exceed the threshold is the place where water or water vapor penetrates into the manifold and thus the leak location are determined on the system part.

Especially when using a capacitive humidity sensor the problem that this is unstable in long-term monitoring and drifts away from the working point. To get reliable results and largely error-free monitoring Therefore, it is a regular calibration of these humidity sensors required.

A Such calibration is a considerable expense for the operator connected to the plant. On the one hand, costly devices for calibration, for example a regulated humidity generator and a calibrated humidity sensor required. On the other hand, the calibration of a humidity sensor time consuming, since the entire measuring range of interest with a a sufficient number of measuring points must be covered because of unavoidable hysteresis effects not immediately one after the other can be approached, each time the transient process is to be awaited. Furthermore it is necessary for the Calibration at least temporarily interrupt the measuring operation and to be calibrated and arranged in a sensor module Moisture sensor together with the sensor module from the measuring station to be removed and replaced with a calibrated replacement sensor module. For these reasons Such calibration becomes relatively rare in practice, for example performed once a year.

Out WO 94/28410 is a method of calibrating a humidity sensor in which the moisture sensor in the gas circulation of a Calibration device is introduced, in which a gas circulates, that saturated with water vapor and whose temperature is known. This temperature corresponds to that Dew point, from which immediately closed to the water vapor concentration can be. It is also with the known calibration device possible, a moisture sensor in situ, i. at the place where he is to monitor the water vapor content of a process gas is mounted to calibrate.

Of the Invention is now based on the object, a method and a Specify means for calibrating a humidity sensor, with high accuracy with low effort in short intervals carried out can be.

Regarding the Method is the object according to the invention solved with a method having the features of claim 1. According to these Characteristics flows in the method of calibrating a humidity sensor Carrier gas with a known water vapor input concentration and a prior art Flow rate in a mixing chamber, which has a water vapor permeable partition wall communicates with a water reservoir whose temperature is at a constant value is set, and in the carrier gas water vapor is added. The humidity sensor becomes a measured value for the Water vapor output concentration in the mixture flowing out of the mixing chamber from water vapor and carrier gas certainly. This measured value is calculated with an actual value of the water vapor initial concentration compared in the mixture flowing out of the mixing chamber, by one of the temperature of the water reservoir, the flow rate and the input water vapor concentration dependent on the mixing chamber Relationship is given.

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

gegeben ist. Dabei bedeuten:

c_out[-]

die Wasserdampf-Ausgangskonzentration am Ausgang der Mischkammer (Istwert)

c₀[-]

die Wasserdampf-Eingangskonzentration am Eingang der Mischkammer (Istwert)

c_W(T_W)[-]

die die Mischkammer umgebende Wasserdampfkonzentration (Funktion der Temperatur des Wasserreservoirs)

T_W[K]

Temperatur des Wasserreservoirs (messbar)

Q_V[m³/s]

der Trägergas-Mengenstrom (angegeben als Volumenstrom) durch die Mischkammer (messbar)

α_W(T_W)[m³/s]

ein temperaturabhängiger Parameter der porösen Trennwand, welcher die Permeabilität und Abmessungen beschreibt (wird einmal bei der Inbetriebnahme bestimmt)

The invention is based on the consideration that the water vapor uptake of the carrier gas flowing through the mixing chamber, for example air, is determined solely by the incoming water vapor concentration, the temperature of the water reservoir and the mass flow, and by the relationship given constant structural conditions of the mixing chamber and the dividing wall

given is. Where:

c _out [-]

the water vapor output concentration at the outlet of the mixing chamber (actual value)

c ₀ [-]

the water vapor input concentration at the input 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)

Q _V [m ³ / s]

the carrier gas flow rate (expressed as volume flow) through the mixing chamber (measurable)

α _W (T _W ) [m ³ / s]

a temperature-dependent parameter of the porous partition, which describes the permeability and dimensions (determined once during commissioning)

For calibration of the humidity sensor, ie for setting a known actual value of the water vapor output concentration at the outlet of the mixing chamber, it is thus sufficient for a given water vapor input concentration c ₀ , which is preferably equal to 0 (dry carrier gas or dry air), the mass flow of the carrier gas and / or to adjust the temperature of the water reservoir to different values. The resulting actual value of the water vapor output concentration c _out at the output can be determined either by interpolation from a look-up table (characteristic field) that has been created and stored during a calibration during the commissioning of the device, or with the aid of the above relationship calculated when the calibration of the device, the parameters describing the properties of the mixing chamber (geometry and vapor permeability of the partition wall) has been experimentally determined for different temperatures T _W.

If the mass flow of the carrier gas and the temperature of the water reservoir is measured and regulated, the measuring accuracy is increased during the calibration.

Regarding the Device, the object is achieved according to the invention with a Device with the features of claim 6, the advantages as well as the advantages of the subordinate to this claim 6 dependent claims indicated features mutatis mutandis to the respective associated Specified method claims To match advantages.

If a device according to the invention in a so-called leakage monitoring system (moisture leakage monitoring system, FLÜS) integrated is that contains a connected to a pump sensor line in the Water vapor can penetrate and one connected to the sensor line Moisture sensor for detecting the penetrated water vapor includes, it is possible remotely controlled the humidity sensor without modification from a control room at regular intervals too calibrate and the operational safety of the leakage monitoring system is significantly improved.

to further explanation The invention is based on the embodiment refer to the drawing. Show it:

1 a device according to the invention in a schematic schematic diagram,

2 a diagram in which the water vapor output 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.

According to 1 For example, a device according to the invention comprises a mixing chamber 2 , which have a semi-permeable partition wall 4 with a water reservoir 6 communicated. The partially permeable partition, for example of a sintered metallic material, is permeable to water vapor, but impermeable to water. The partition 4 Can do it on your water reservoir 6 facing flat side directly adjacent to the water. Basically, but also between the water reservoir 6 water and the membrane is a water vapor saturated gas cushion, usually saturated with water vapor, as the diffusion rate of water vapor through the partition wall 4 essentially only by the difference of the partial pressures of Water vapor in the mixing chamber 2 and in the water reservoir 6 is determined. The water reservoir 6 is via a pressure equalization line 7 connected to the ambient atmosphere by an overpressure during heating of the water reservoir 6 to avoid.

The mixing chamber 2 has an entrance 8th and an exit 10 for a carrier gas flowing through them, usually air. The entrance 8th is via an input line 12 to a compressor 14 connected, which sucks air as a carrier gas from the environment and to the mixing chamber 2 through which it flows and in which it absorbs water vapor, so that at the exit 10 a mixture of water vapor and carrier gas (air) is present, whose water vapor output concentration by the flow rate Q _V , the water vapor input concentration c ₀ in the carrier gas at the entrance 8th , the geometric relationships 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 the relationship explained above.

At the exit 10 is an output line 16 connected to the one to be calibrated humidity sensor 18 is connected, with which a measured value of the water vapor output concentration c _out in the output line 16 flowing carrier gas is determined.

The water reservoir 6 comes with a heater 20 heated, so that its temperature T _W can be set to predetermined values. The heater 20 is for this purpose to a control device 22 connected to the control signals S1 either the heating power to a predetermined value and thus the temperature T _{W of} the water reservoir 6 controls or the temperature T _{W of} the water reservoir 6 regulates. This is in the water reservoir 6 a temperature sensor 23 arranged, the measured values of the control device 22 be fed so that the temperature T _{W of} the water reservoir can be controlled to a predetermined value.

The control device 22 also controls or regulates the compressor. To allow a regulation is in the input line 12 a flow sensor 24 arranged, with the mass flow Q _V , for example, the volume flow through the input line 12 is measured. The corresponding measured values are then also in the control device 22 for generating control signals S2 for the control of the compressor 14 processed.

With the help of the control device 22 now different temperatures T _{W of} the water reservoir 6 and set different flow rates Q _{V of} the carrier gas, to each of which a previously known water vapor output concentration at the output 10 the mixing chamber 2 belongs, which are in the form of a characteristic field, which has been measured during commissioning by a one-time calibration. In the entrance line 12 and in the output line 16 are each 3-way valves connected by means of control signals S3, S4 from the controller 22 be controlled and connected to a bypass line 30 connected in the input line 12 flowing carrier gas at the mixing chamber 2 passing directly to the humidity sensor 18 passes. If that is in the input line 12 Injected carrier gas is dry, ie has a water vapor output concentration which is practically equal to 0, in this mode of operation of the device, the zero point of the humidity sensor 18 be calibrated. The from the humidity sensor 18 for various previously known actual values c _{out of} the water vapor output concentration measured values c _M can then be used to calibrate the moisture sensor 18 be used.

In the exemplary embodiment, the bypass line 30 also via a three-way valve 32 to a sensor line 34 a moisture leakage monitoring system connected by a compressor 36 at constant intervals carrier gas, usually air, to the moisture sensor 18 to get promoted. In the sensor line 34 can penetrate either along the entire line or at predetermined line positions water vapor. The sensor line 34 is arranged on a water or steam leading plant part. In case of a leak in the system part is then with the humidity sensor 18 a measured value c _M for the water vapor concentration is measured, to which an actual value c _{T is} assigned on the basis of the preceding calibration, 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 _T exceeds the threshold value c _s . The three-way valve 32 is also via control signals S5 from the controller 22 controlled, so that an automatic switchover from the monitoring mode to the calibration mode is possible.

In the diagram according to 2 is the actual value c _{T of} the initial water vapor concentration in air for a by 1 explained device against the speed of air in the mixing chamber, which has an inner diameter of 6 mm in the embodiment applied. The diamonds represent measuring points which have been obtained at a temperature T _{W of} the water reservoir of 25 °. Triangles represent measured values that have been obtained for different volume flows at a temperature T _W = 30 ° and correspond to points Readings at a temperature T _W = 40 °. The solid lines are calculated values obtained from the above-mentioned model. It can be seen from the measuring points and the curves shown in the diagram that the model describes the water vapor output concentration produced at the outlet of the mixing chamber with high accuracy. With the aid of the model, it is therefore possible to considerably reduce the number of measurements to be made during the first calibration of the device, since basically only one measuring point is necessary for each temperature T _W in order to be able to determine the parameter α _W (T _W ).

2

mixing chamber

4

partition wall

6

water reservoir

8th

entrance

10

output

12

input line

14

compressor

16

output line

18

humidity sensor

20

heater

22

control device

23

temperature sensor

24

Flow Sensor

26 28, 32

Three-way valve

30

Bypass line

34

sensor line

36

compressor

S1-S5

control signals

Claims (10)

Method for calibrating a humidity sensor ( 18 ), in which a carrier gas having a known water vapor input concentration and a known mass flow (Q _V ) into a mixing chamber ( 2 ) flows through a water vapor permeable partition wall ( 4 ) with a water reservoir ( 6 ), whose temperature (T _W ) is set to a constant value, and in which the carrier gas is admixed with steam, and in which with the moisture sensor ( 18 ) a measured value (c _M ) for the starting water vapor concentration in the mixture of water vapor and carrier gas flowing out of the mixing chamber is determined and with an actual value (c _out ) of the starting water vapor concentration from the mixing chamber ( 6 ) flowing through one of the temperature (T _W ) of the water reservoir ( 6 ), the mass flow (Q _V ) and the water vapor input concentration into the mixing chamber ( 6 ) dependent relationship is given. The method of claim 1, wherein the mass flow (Q _V ) of the carrier gas is controlled. The method of claim 1 or 2, wherein the flow rate (Q _V ) is measured and regulated. Method according to Claim 1, 2 or 3, in which the temperature (T _W ) of the water reservoir ( 6 ) is measured and regulated. Method according to one of the preceding claims, in the incoming water vapor concentration at least approximately zero is. Device for calibrating a humidity sensor ( 18 ), with a compressor ( 14 ) for generating a carrier gas flow with a known mass flow (Q _V ), and with a mixing chamber connected thereto ( 2 ) for admixing water vapor, which via a water vapor permeable partition wall ( 4 ) with a heating device ( 20 ) heatable water reservoir ( 6 ) and that with an output line ( 16 ) for that in the mixing chamber ( 2 ) is provided mixture of carrier gas and water vapor to which the moisture sensor ( 18 ) is connected, as well as with a control device ( 22 ) for controlling the heating device ( 20 ) and for adjusting the temperature (T _W ) of the water reservoir ( 6 ) to a predefinable value. Device according to Claim 6, in which the control device ( 22 ) for controlling the temperature (T _W ) a temperature sensor ( 23 ). Device according to one of Claims 6 or 7, in which the control device ( 22 ) for controlling the mass flow (Q _V ) of the carrier gas, a transducer ( 24 ) for measuring the mass flow (Q _V ). Device according to one of claims 6 to 8, wherein the mixing chamber ( 2 ) a bypass line ( 30 ) assigned. Leakage monitoring system with one connected to a pump ( 36 ) connected sensor line ( 34 ) into which water vapor can penetrate and with one to the sensor line ( 34 ) connected humidity sensor ( 18 ) for detecting the water vapor, as well as with a between sensor line ( 34 ) and humidity sensor ( 18 ) connected device according to claim 9.