阅读说明：本技术 一种阀门内漏泄漏率评价装置及评价等级方法 (Valve internal leakage rate evaluation device and evaluation grade method ) 是由 王琼 魏新明 贾润中 朱亮 肖安山 朱胜杰 于 2020-05-28 设计创作，主要内容包括：本发明公开了一种阀门内漏泄漏率评价装置及评价等级方法,涉及石化企业阀门泄漏检测技术领域。其解决了现有技术中测试装置无法对阀门内漏定级诊断的技术问题。该评价装置包括储气罐、空压机、阀二、流量计及测试阀门,测试阀门上安装有声学传感器,声学传感器通过数据线连接有声学采集设备。评价测试开始后,通过声学采集设备采集声学信号,记录压力值、气体流量值等参数信息,根据内漏流量Q-AErms曲线进行函数拟合,进而得到Q-AErms拟合函数；结合流量等级划分标准,即得测试阀门内漏AErms评价标准。本发明不需停工,即可在线通过声学参数判定阀门内漏泄漏等级,本发明装置及方法可在石化企业推广使用。(The invention discloses a valve internal leakage rate evaluation device and a grade evaluation method, and relates to the technical field of valve leakage detection of petrochemical enterprises. The technical problem that a testing device in the prior art cannot carry out level-setting diagnosis on the internal leakage of the valve is solved. The evaluation device comprises a gas storage tank, an air compressor, a valve II, a flowmeter and a test valve, wherein an acoustic sensor is installed on the test valve, and the acoustic sensor is connected with acoustic acquisition equipment through a data line. After the evaluation test is started, acquiring acoustic signals through acoustic acquisition equipment, recording parameter information such as pressure values and gas flow values, and performing function fitting according to an internal leakage flow Q-AErms curve to further obtain a Q-AErms fitting function; and combining the flow grade division standard to obtain the evaluation standard of the internal leakage AErms of the test valve. The device and the method can judge the leakage grade in the valve on line through the acoustic parameters without shutdown, and can be popularized and used in petrochemical enterprises.)

1. The utility model provides a leak leakage rate evaluation device in valve, its includes gas holder, air compressor machine, valve two, flowmeter and test valve, its characterized in that: the air compressor machine be used for carrying out the punching press to the gas holder, the gas holder with the pipeline of connecting between the flowmeter on set gradually valve two and test valve, test valve on install acoustic sensor, acoustic sensor be connected with acoustics collection equipment through the data line.

2. The apparatus of claim 1, wherein the apparatus comprises: the air storage tank is provided with a pressure gauge, and when the air compressor punches the air storage tank, the pressure value is monitored through the pressure gauge.

3. The apparatus of claim 1, wherein the apparatus comprises: the test valve is a gate valve or a ball valve.

4. The apparatus of claim 3, wherein the apparatus comprises: the ball valve is a floating ball valve, a fixed ball valve, a wafer ball valve, a three-way ball valve or a V-shaped ball valve.

5. The apparatus of claim 3, wherein the apparatus comprises: the gate valve is a rising stem gate valve or a non-rising stem gate valve.

6. The apparatus of claim 3, wherein the apparatus comprises: according to specifications, the ball valve comprises a ball valve specification of 101 and a ball valve specification of 104, wherein the ball valve specification of 101 comprises DN100, DN15, DN20, DN25, DN32, DN40, DN50, DN65 and DN 80.

7. A method for evaluating the grade of the leakage rate of the internal leakage of the valve is characterized in that the device for evaluating the leakage rate of the internal leakage of the valve as claimed in any one of claims 1 to 6 is adopted, acoustic parameters AErms are measured through the acoustic sensor, the internal leakage amount is measured through the flowmeter, a pressure gauge connected to an air storage tank is used for providing test pressure parameters, and function fitting is carried out according to an internal leakage flow Q-AErms curve so as to obtain a Q-AErms fitting function; and then, according to the Q-AErms fitting function, combining with a flow grade division standard to obtain the AErms evaluation standard for testing the internal leakage of the valve.

8. The method for evaluating the leak rate of the valve internal leakage according to claim 7, wherein: the AErms evaluation criteria are:

micro leakage is more than or equal to 0 and less than 54.9 AErms;

small leakage is more than or equal to 54.9, AErms is less than 130.38;

moderate leakage 130.38 is not more than AErms is less than 212.27;

large leakage AErms is greater than or equal to 212.27.

9. The method for evaluating the leak rate of the valve internal leakage according to claim 8, wherein: when the test valve is a dn65 ball valve, the Q-AErms fitting function is as shown in equation (1):

lgQ_g＝3.302*lgAErms-4.642 (1)；

in the formula: q_gIs the gas flow rate in the standard state, m³/h；

AErms is the acoustic parameter measured by the acoustic sensor.

10. The method for evaluating the leak rate of the valve internal leakage according to claim 9, wherein:

when X is less than F_γ·X_τWhen is, Q_g＝0.28(X)^1/2Yp₁K_v

When X is more than or equal to F_γ·X_τWhen is, Q_g＝0.19(X_τ)^1/2p₁K_v

Wherein: q_g- -gas flow rate in standard state, m³/h；

K_v-nominal flow coefficient, dimensionless;

x- - -ratio of differential pressure to absolute inlet pressure (Δ p/p)₁) No dimension;

y- - -expansion coefficient, Y1-X/(3X)_r) (when X > F)_γ·X_τWhen Y is 0.667), no dimension exists;

p₁absolute pressure before valve, kPa;

X_τ-the differential pressure ratio coefficient, dimensionless, of a control valve without an attached pipe under choked flow conditions;

F_γcoefficient of specific heat ratio, F of air in a specified temperature range_γ1, dimensionless.

11. The method for evaluating the leak rate of the valve internal leakage according to claim 10, wherein: said K_vCalculated according to the formulas (2) and (3):

in formula (2): c_v- -flow coefficient, Usgal/min;

k is the flow resistance coefficient and is dimensionless;

d- - -valve drift diameter, inch;

K_v＝C_v/1.156 (3)。

12. the method for evaluating the leak rate of the valve internal leakage according to claim 8, wherein: the values of the parameters in the formulas (2) and (3) refer to a GBT4213-2008 pneumatic regulating valve and a GBT17214.2-2005 industrial process control valve.

13. The method for evaluating the leak rate of the valve internal leakage according to claim 11, wherein: when the test valve is a gate valve, the flow resistance coefficient K-nominal diameter/mm function is:

when the test valve is a ball valve, the flow resistance coefficient K-nominal diameter/mm function is:

Technical Field

The invention relates to the technical field of valve leakage detection of petrochemical enterprises, in particular to a valve internal leakage rate evaluation device and a grade evaluation method.

Background

In the process devices of the petroleum and petrochemical industries, valves are indispensable parts. At present, with the continuous development of equipment manufacturing technology, valves used in petrochemical devices are generally improved in both volume and structural complexity and technical level. Along with the continuous diversification of petrochemical plant production technology and material types, the operating condition of the valve is increasingly complex and severe, the opening and closing operation of the valve is increasingly frequent, and the phenomena of running, overflowing, dripping and leaking of the valve of the petrochemical plant are caused by improper use and maintenance factors. Therefore, in the petrochemical production process, the leakage of the valve can be timely, efficiently and accurately found, the effective leakage grade is judged to be petrochemical production, and the safety maintenance has important significance.

The prior art mainly comprises the following steps:

CN201723983U discloses a low gas leakage measurement and detection device, which mainly comprises a high-level water tank, a low-level water tank, a water pipe, an air pipe, a measuring cylinder, a valve and a controller, and mainly aims to form a back-off vacuum filled with water in the measuring cylinder so as to collect gas by using a 'drainage and gas collection method', measure the leakage amount of gas, the high-level water tank and the measuring cylinder are communicated by using a water pipe, a water outlet of the measuring cylinder is collected by a water collection funnel and flows back to the low-level water tank through a pipeline, the upper part of the high-level water tank is connected with the air pipe, the upper end of the measuring cylinder is connected to the air pipe through a shut-off valve, the lower end of the measuring cylinder is connected to the water pipe through a three-way valve, the air pipe has more than two branch air pipes, one of which extends into the high-level water tank, and the other branch air pipes extend into the measuring cylinder respectively.

CN 107462379a discloses an automatic testing device for valve leakage rate, which comprises the following components: the air guide unit is used for discharging the air leaked by the tested valve to the atmosphere or the air storage unit; a gas storage unit for storing gas discharged to the measured valve leakage; a detection unit for detecting the volume of the gas stored in the gas storage unit; and the automatic control unit is electrically connected with the gas guide unit and the detection unit respectively.

In the testing device for detecting the leakage rate of the valve, the former needs manual measurement, and the metering and detection of the valve are more dependent on manual work; the latter, although automated by an automatic control unit, does not allow for a level-specific diagnosis of leaks in the valve.

Disclosure of Invention

One of the purposes of the invention is to provide a valve internal leakage rate evaluation device which can realize online monitoring on valve internal leakage.

The utility model provides a leak leakage rate evaluation device in valve, its includes gas holder, air compressor machine, valve two, flowmeter and test valve, the air compressor machine be used for carrying out the punching press to the gas holder, the gas holder with the flowmeter between set gradually the pipeline of connecting on valve two and test valve, test valve on install acoustic sensor, acoustic sensor be connected with acoustics collection equipment through the data line.

As a preferable scheme of the present invention, a pressure gauge is installed on the air storage tank, and when the air compressor presses the air storage tank, the pressure gauge is used to monitor a pressure value.

In another preferred embodiment of the present invention, the test valve is a gate valve or a ball valve.

The ball valve is a floating ball valve, a fixed ball valve, a wafer ball valve, a three-way ball valve or a V-shaped ball valve.

The gate valve is a rising stem gate valve or a non-rising stem gate valve.

According to specifications, the ball valve comprises a ball valve specification of 101 and a ball valve specification of 104, and the ball valve specification of 101 comprises DN100, DN15, DN20, DN25, DN32, DN40, DN50, DN65 and DN 80.

The second objective of the present invention is to provide a method for evaluating the leak rate of valve inner leakage, which can determine the leak rate of valve inner leakage.

A valve internal leakage rate evaluation grade method adopts the valve internal leakage rate evaluation device, acoustic parameters AErms are measured through an acoustic sensor, internal leakage is measured through a flowmeter, a pressure gauge connected to a gas storage tank is used for providing test pressure parameters, and function fitting is carried out according to an internal leakage flow Q-AErms curve so as to obtain a Q-AErms fitting function; and then, according to the Q-AErms fitting function, combining with a flow grade division standard to obtain the AErms evaluation standard for testing the internal leakage of the valve.

More preferably, the above AErms evaluation criteria are:

further preferably, the Q-AErms fitting function is as shown in equation (1):

lg Q_g＝3.302*lg AErms-4.642 (1)；

in the formula: q_gIs the gas flow rate in the standard state, m³/h；

AErms is the acoustic parameter measured by the acoustic sensor.

Further, when X < F_γ·X_τWhen is, Q_g＝0.28(X)^1/2Y_p1K_v

When X is more than or equal to F_γ·X_τWhen is, Q_g＝0.19(X_τ)^1/2p₁K_v

Wherein: q_g- -gas flow rate in standard state, m³/h；

K_v-nominal flow coefficient, dimensionless;

x- - -ratio of differential pressure to absolute inlet pressure (Δ p/p)₁) No dimension;

y-expansion systemNumber, Y ═ 1-X/(3X)_τ) (when X > F)_γ·X_τWhen Y is 0.667), no dimension exists;

p₁absolute pressure before valve, kPa;

X_τ-the differential pressure ratio coefficient, dimensionless, of a control valve without an attached pipe under choked flow conditions;

F_γcoefficient of specific heat ratio, F of air in a specified temperature range_γ1, dimensionless.

Further preferably, K is as defined above_vCalculated according to the formulas (2) and (3):

in formula (2): c_v- -flow coefficient, Usgal/min;

k is the flow resistance coefficient and is dimensionless;

d- - -valve drift diameter, inch;

K_v＝C_v/1.156 (3)；

further preferably, the values of the parameters in the formulas (2) and (3) refer to GBT4213-2008 pneumatic control valves and GBT17214.2-2005 industrial process control valves.

Further preferably, when the test valve is a gate valve, the flow resistance K-nominal diameter/mm function is:

when the test valve is a ball valve, the flow resistance coefficient K-nominal diameter/mm function is:

compared with the prior art, the invention has the following beneficial technical effects:

(1) acoustic parameters are obtained through equipment such as an acoustic sensor, and the acoustic emission detection means can effectively perform online detection on the internal leakage of the valve, so that economic loss caused by shutdown is avoided;

(2) the method for evaluating the grade of the leakage rate of the internal leakage of the valve can grade the severity of the internal leakage, and fills the gap that no clear standard exists in the evaluation of the leakage rate of the internal leakage of the valve at present;

(3) the testing valve can be a ball valve or a gate valve, and the type and the caliber of the valve are not limited by the method;

(4) the invention can judge the leakage grade in the valve on line through the acoustic parameters without shutdown. The invention can effectively perform online detection of the internal leakage of the valve by using an acoustic emission detection means, thereby avoiding economic loss caused by shutdown; at present, no clear standard exists for evaluating the size of the leakage rate of the internal leakage of the valve on site, and the evaluation method for the grade of the leakage rate of the internal leakage of the valve can grade the severity of the internal leakage.

(5) The device and the method are safe to use, convenient to implement and capable of being popularized and used in petrochemical enterprises.

Drawings

The invention is further described below with reference to the accompanying drawings:

FIG. 1 is a schematic structural diagram of an apparatus for evaluating an internal leakage rate of a valve according to the present invention;

fig. 2 is a schematic view of valve internal leakage classification.

Detailed Description

The invention provides a device and a method for evaluating the leakage rate of valve internal leakage, and the invention is described in detail with reference to specific embodiments in order to make the advantages and technical scheme of the invention clearer and clearer.

Throughout the specification and claims, unless explicitly stated otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element or component but not the exclusion of any other element or component.

Spatially relative terms, such as "below," "lower," "upper," "above," "upper," and the like, may be used herein for ease of description to describe one element or feature's relationship to another element or feature in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the object in use or operation in addition to the orientation depicted in the figures. For example, if the items in the figures are turned over, elements described as "below" or "beneath" other elements or features would then be oriented "above" the elements or features. Thus, the exemplary term "below" can encompass both an orientation of below and above. Other orientations of the components are possible (rotated 90 degrees or at other orientations) and the spatially relative terms used herein should be interpreted accordingly.

The term "air compressor" as used herein refers to an air compressor.

As shown in fig. 1, the valve internal leakage rate evaluation device comprises an air storage tank, an air compressor, a first valve, a second valve, a flowmeter, a test valve and an acoustic sensor, wherein the air compressor is connected with the air storage tank and used for stamping the air storage tank, a pressure gauge is mounted on the air storage tank, when the air compressor stamps the air storage tank, the pressure value is monitored through the pressure gauge, when the index of the pressure gauge reaches the test pressure, the air compressor is stopped, the first valve is closed, and the test is prepared.

The gas storage tank is a device specially used for storing gas, plays a role in stabilizing the pressure of the system, and can be divided into a high-pressure gas storage tank, a low-pressure gas storage tank and a normal-pressure gas storage tank according to different bearing pressures of the gas storage tank. The gas storage tank can be divided into a carbon steel gas storage tank, a low alloy steel gas storage tank and a stainless steel gas storage tank according to different materials of the gas storage tank. In particular, the present invention allows for the conditions that meet the gas phase conditions of different petrochemical scenarios, and therefore prefers a high pressure gas tank that can meet a wide pressure range.

The air compressor is an air compressor, which is a device for compressing air, and has a structure similar to a water pump, and those skilled in the art can realize the air compressor by using the prior art, and the detailed description is omitted here.

The acoustic sensor described above functions by converting acoustic pressure waves into vibrations of a mechanical element and qualitatively detecting these vibrations by changes in the piezoelectric, resistivity, permeability or capacitance.

And a second valve and a test valve are sequentially arranged on a pipeline connected between the gas storage tank and the flowmeter, an acoustic sensor is installed on the test valve, and the acoustic sensor is connected with acoustic acquisition equipment through a data line.

The flowmeter is arranged behind the test valve, the valve II is opened, different flow tests are carried out by adjusting the opening of the test valve, acoustic signals are collected after the test is started, and parameter information such as pressure values, gas flow values and the like is recorded.

The specific structure of the acoustic sensor and the monitoring method thereof are not described in detail, and can be realized by referring to the prior art.

The shape, specification and type of the test valve are not limited, and the test valve is a gate valve or a ball valve. Specifically, the ball valve may be classified into a floating ball valve, a fixed ball valve, a wafer ball valve, a three-way ball valve or a V-shaped ball valve, a stainless steel ball valve, etc. according to its kind.

Specifically, the gate valve may be a rising stem gate valve or a non-rising stem gate valve.

The stainless steel ball valve has the specification such as a 101 ball valve, a 104 ball valve, a 201 ball valve, a 206 flange ball valve, a 216 ball valve and the like. Such as for each of the specifications of the ball valve:

101 ball valves comprise DN100, DN15, DN20, DN25, DN32, DN40, DN50, DN65 and DN 80;

104 the ball valve specifications include: DN10, DN100, DN15, DN20, DN25, DN32, DN40, DN50, DN65, DN8, DN 80;

201 ball valve specification: DN10, DN100, DN15, DN20, DN25, DN32, DN40, DN50, DN65, DN8, DN 80;

specification of 206 flange ball valve: DN100, DN25, DN32, DN40, DN50, DN65, DN 80;

216 ball valve specification: DN15, DN15, DN20, DN20, DN25, DN25, DN32, DN32, DN40, DN40, DN50, and the like.

The types and specifications of the ball valve or the gate valve are not described in detail, and those skilled in the art can reasonably select the type and specification according to actual needs.

The evaluation method of the present invention will be described in detail with reference to specific examples.

Example 1:

a valve internal leakage rate evaluation grade method is characterized in that a valve internal leakage rate evaluation device comprises an air storage tank, an air compressor, a second valve, a flowmeter and a test valve, wherein the air compressor is used for stamping the air storage tank, the second valve and the test valve are sequentially arranged on a pipeline connected between the air storage tank and the flowmeter, an acoustic sensor is mounted on the test valve, and the acoustic sensor is connected with acoustic acquisition equipment through a data line; the air storage tank is provided with a pressure gauge, and when the air compressor punches the air storage tank, the pressure value is monitored through the pressure gauge.

The method for evaluating the grade of the internal leakage rate of the valve specifically comprises the following steps:

firstly, measuring an acoustic parameter AErms through an acoustic sensor, and measuring internal leakage through a flowmeter;

secondly, providing a test pressure parameter through a pressure gauge connected to a gas storage tank, and performing function fitting according to an internal leakage flow Q-AErms curve to further obtain a Q-AErms fitting function;

and thirdly, combining flow grade division standards according to a Q-AErms fitting function to obtain the AErms evaluation standard for testing the internal leakage of the valve.

Example 2:

the valve internal leakage rate evaluation device comprises a gas storage tank, an air compressor, a second valve, a flowmeter and a test valve, wherein the air compressor is used for stamping the gas storage tank, the second valve and the test valve are sequentially arranged on a pipeline connected between the gas storage tank and the flowmeter, an acoustic sensor is mounted on the test valve, and the acoustic sensor is connected with acoustic acquisition equipment through a data line; the air storage tank is provided with a pressure gauge, and when the air compressor punches the air storage tank, the pressure value is monitored through the pressure gauge.

The formula in the calculation standard for the rated capacity of the valve according to GBT4213-2008 pneumatic control valve and GBT17214.2-2005 industrial process control valve part 5-1 is shown in the following table.

TABLE 1 calculation formula for rated capacity of valve

Wherein Q is_g- -gas flow rate in standard state, m³/h；

K_v-nominal flow coefficient, dimensionless;

x- - -ratio of differential pressure to absolute inlet pressure (Δ p/p)₁) No dimension;

y- - -expansion coefficient, Y1-X/(3X)_τ) (when X > F)_γ·X_τWhen Y is 0.667), no dimension exists;

p₁absolute pressure before valve, kPa;

X_τ-the differential pressure ratio coefficient, dimensionless, of a control valve without an attached pipe under choked flow conditions;

F_γcoefficient of specific heat ratio, F of air in a specified temperature range_γ1, dimensionless;

calculating the rated capacity of the valve according to the formula, wherein the rated flow coefficient K_vThe calculation is carried out according to the following formula, wherein the values of all parameters in the formula refer to GBT4213-2008 pneumatic regulating valve and GBT17214.2-2005 industrial process control valve.

C_v- -flow coefficient, Usgal/min;

k is the flow resistance coefficient and is dimensionless;

d- - -valve drift diameter, inch;

K_v＝C_v/1.156

the flow coefficients K for the different size and type valves are shown in table 2 below.

TABLE 2 flow resistance coefficient K of different size and type valves

According to the data, the flow resistance coefficient of the ball valve is constant 0.1, while the flow resistance coefficients of the gate valve and the stop valve are not fixed, and the nominal diameter and the flow resistance coefficient of the gate valve and the stop valve are fitted to obtain a flow resistance coefficient K-nominal diameter function, as shown in Table 3.

TABLE 3 flow resistance coefficient K-nominal diameter (mm) function of gate valve and stop valve

The calculation formula of the rated capacity of the stop valve is as follows:

(Usgal/min)

K_v＝101.9÷1.156＝88.12m³/h

due to the fact thatThus using the formulaCalculating Q_g。

Q_g＝18389L/min

According to the algorithm, the rated capacity of the valve is calculated respectively. According to the provisions of GBT4213-2008 pneumatic control valve and GBT17214.2-2005 Industrial Process control valve, Q_g×10^-4For minor leakage, Q_g×10^-3For small leakage, Q_g×5×10^-3In the case of a medium leak,Q_g×10^-2is a large leak.

Example 3:

the valve internal leakage rate evaluation device comprises a gas storage tank, an air compressor, a second valve, a flowmeter and a test valve, wherein the air compressor is used for stamping the gas storage tank, the second valve and the test valve are sequentially arranged on a pipeline connected between the gas storage tank and the flowmeter, an acoustic sensor is mounted on the test valve, and the acoustic sensor is connected with acoustic acquisition equipment through a data line; the air storage tank is provided with a pressure gauge, and when the air compressor punches the air storage tank, the pressure value is monitored through the pressure gauge.

On the basis of example 2, the test valve is a gate valve under 0.1 MPa.

The pressurization is performed using a compressor. The testing pressure is 0.1MPa, the testing adopts a DN65 gate valve, the leakage flow is adjusted by adjusting the opening of the gate valve, the testing is carried out by a flowmeter, and the leakage rate is tested from 6L/min to 120L/min by a difference value of 6L/min. And acquiring acoustic emission signal data under various working conditions to provide data support for the diagnosis method. And detecting by adopting acoustic emission acquisition equipment, wherein a 30kHz resonance sensor is selected as the sensor.

And performing function fitting according to an internal leakage flow Q-AErms curve to obtain a Q-AErms fitting function.

The gate valve Q-AErms function fitting coefficient R-square of DN65 is 0.8404, accords with the application requirement of engineering R-square >0.9, and the fitting function is lg Q-3.302 lg A Erms-4.642.

And (4) obtaining DN65 gate valve internal leakage AErms evaluation standard by combining the flow grade division standard according to a Q-AErms fitting function, wherein the evaluation standard is shown in a table 4.

TABLE 4 DN65 ball valve internal leakage AErms evaluation criteria

As shown in fig. 2, the AErms evaluation criteria is scaled down by 5% according to engineering criteria, and if the in-valve leak signal AErms is above the micro-leak criterion 95%, the valve is evaluated as a small leak, and if the in-valve leak AErms is below the micro-leak criterion 95%, the valve is evaluated as a small leak.

In conclusion, the method for evaluating the grade of the leakage rate of the valve inner leakage provided by the invention comprises various valve types and valve calibers and meets the measurement requirements of different leakage amounts. The evaluation device for the internal leakage rate of the valve can judge the internal leakage grade of the valve on line through the acoustic parameters without shutdown, and can be popularized and used in petrochemical enterprises.

The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited thereto.

Although terms such as air reservoir, air compressor, flow meter, test valve, etc. are used more often herein, the possibility of using other terms is not excluded, and these terms are used only for the purpose of more conveniently describing and explaining the essence of the present invention; they are to be construed as being without limitation to any additional limitations that may be imposed by the spirit of the present invention.

It is further understood that the specific embodiments described herein are merely illustrative of the spirit of the invention. Various modifications or additions may be made to the described embodiments or alternatives may be employed by those skilled in the art without departing from the spirit or ambit of the invention as defined in the appended claims.