WO2006126951A1

WO2006126951A1 - An arrangement and a method for checking the function of a dynamic gas pressure sensor

Info

Publication number: WO2006126951A1
Application number: PCT/SE2006/000616
Authority: WO
Inventors: Nils-Erik Andersson
Original assignee: Siemens Aktiengesellschaft
Priority date: 2005-05-26
Filing date: 2006-05-26
Publication date: 2006-11-30
Also published as: EP1982155A1

Abstract

An arrangement for checking the proper function of a dynamic gas pressure sensor (1) comprises a device (10) connectable to a supply of compressed air for generating pressure pulsations in a path of compressed air. It also has a reference, dynamic gas pressure sensor (30) adapted to measure said pulsations as well as connecting means (15, 29) adapted to connect said path of compressed air to said dynamic gas pressure sensor (1) to be checked. Calculating means (33) are connectable to said sensors and adapted to compare the results of the measurements thereof for determining the status of said dynamic gas pressure sensor.

Description

Applicant: SIEMENS INDUSTRIAL TU RBOMACH I NERY AB

An arrangement and a method for checking the function of a dynamic gas pressure sensor

TECHNICAL FIELD OF THE INVENTION AND PRIOR ART

The present invention relates to an arrangement and a method for checking the proper function of a dynamic gas pressure sensor.

It is directed to all types of dynamic gas pressure sensors, which normally have different types of crystals sensitive to gas pressure variations, which normally have a sine shape character. Such dynamic gas pressure sensors are used in all types of equipment, in which gas pressure variations or pulsations may arise and which may be detrimental to components of such an equipment. Accordingly, such a dynamic gas pressure sensor is then connected to a control unit controlling the function of the equipment for procuring a change of that function, an alarm or a stop of the operation of the equipment would such pulsations measured exceed a predetermined level.

For exemplifying but not in any way limiting the present invention, the use of such a dynamic gas pressure sensor in a gas turbine and the problems associated therewith will hereinafter be discussed.

Such gas turbines may be of very different sizes and used for for example production of electricity in power plants and driving water jets in ferry boats. The application of such a dynamic gas pressure sensor in a gas turbine is schematically illustrated in appended Fig 1 . The output power of such a gas turbine is typically 10-100 MW, but may be outside this range. It is an ongoing aim to reduce the emissions of products resulting from the combustion in the combustion chamber of the gas turbine and being detrimental to the environment. For obtaining this the combustion in the combustion chamber is controlled so that the flames of the burners are close to be extinguished, which results in a risk of an unsteady function and generation of high gas pressure pulsations in the combustion chamber. These pressure pulsations are sounds with high amplitude (for example as high as 100 mbar peak to peak and a sound level of 165 dB, although both higher and lower amplitudes and sound levels are conceivable) and they are at some frequencies harmful to the gas turbine. These pulsations are therefore monitored by a dynamic gas pressure sensor 1 (see Fig 1 ). The temperature inside the combustion chamber 2 may be in the order of 1000⁰C making it impossible to arrange the sensor there. Thus, a waveguide is normally arranged for guiding the gas pressure pulsations to be measured from the combustion chamber to the outside of the gas turbine where the sensor is located. This wave-guide has then a first part 3 leading from the combustion chamber 2 into the central house 4 of the gas turbine and a second part 5 leading to the exterior of the gas turbine to an adapter 6 arranged for holding the sensor. The wave-guide is normally formed by a metal tube. A long damping winding 7 is connected to and prolongs the wave-guide for preventing reflections of pulsations to occur in the wave-guide, which would result in measurement faults. The damping winding may in its turn be connected to the end of the compressor 40 of the gas turbine through a conduit 41 , so that the higher pressure at the end of the compressor will result in a gas flow in the loop thus created in the direction of the arrow 42 preventing hot gases from the combustion chamber from arriving to and damaging the sensor 1. The dynamic gas pressure sensor is adapted to send its signals to a control unit 8 arranged to control the operation of the gas turbine and trigger an alarm and/or stop the gas turbine should gas pressure pulsations detrimental to components in the combustion chamber of the gas turbine arise.

It is of course very important that the dynamic gas pressure sen- sor delivers correct gas pressure pulsation values. Is this not the case gas pressure pulsations harmful to components in the combustions chamber may occur and be allowed to continue reducing the life time of such components or the operation of the gas turbine may be stopped when there is no need to do that, which also would result in considerable unnecessary costs.

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This problem has so far only been addressed by checking the function of such dynamic gas pressure sensors before they are mounted in the monitoring circuit of the gas turbine, but then not any longer. Furthermore, there are normally more than one such dynamic gas pressure sensor, such as three or four circumferentially distributed in the combustion chamber for being able to detect possibly high gas pressure pulsations generated in the combustion chamber, but it is not possible to compare the measurement results of the different sensors for determining whether they function properly or not, since such measurement results should in fact differ.

SUMMARY OF THE INVENTION

The object of the present invention is to provide an arrangement and a method for checking the proper function of a dynamic gas pressure sensor, so that such a dynamic gas pressure sensor may be replaced when it is defect, but only then, resulting in saving of costs and an improved monitoring of the operation of an equipment provided with such a dynamic gas pressure sensor.

This object is according to the invention obtained by providing such an arrangement, which comprises: - a device connectable to a supply of compressed air and when connected to said supply adapted to generate pressure pulsations in a path of compressed air then connected to said supply,

- a reference dynamic gas pressure sensor adapted to measure said pressure pulsations generated by said device,

- connecting means adapted to. connect said path of compressed air to said dynamic gas pressure sensor to be checked, and

- calculating means connectable to said sensors and adapted to compare the results of the measurement by said reference dynamic gas pressure sensor with the results of the measurement by said dynamic gas pressure sensor and on the basis thereof determine the status of said dynamic gas pressure sensor,

as well as a method according to the appended independent method claim.

Such an arrangement may be realized to a cost being low with respect to the costs that may be saved by detecting an improper function of a dynamic gas pressure sensor by using such an arrangement. By in this way using a reference dynamic gas pressure sensor to measure the same pressure pulsations generated by said device as the dynamic gas pressure sensor to be checked the proper function of the latter may be reliably checked.

According to an embodiment of the present invention said de- vice is adapted to generate pressure pulsations having substantially a sine shape, which is advantageous since most dynamic gas pressure sensors are designed to measure pressure pulsation having a sine shape.

According to another embodiment of the invention said device comprises a motor adapted to rotate a member arranged to communicate with said supply of compressed air, and said member is adapted to co-operate with at least one opening in said path of compressed air for alternatively open and close this opening when rotating for alternatively allow and not allow, respectively, air to pass therethrough so as to obtain pressure pulsations in said path of compressed air. It has turned out that gas pressure pulsations of a frequency and amplitude appropriate for checking the proper function of a dynamic gas pressure sensor may be reliably obtained in this way.

According to a another embodiment of the invention said device comprises a cylindrical roller bearing, said opening is formed by a hole substantially radially penetrating the outer ring of the bearing and arranged so as to be closed when a roller rolls on the inner wall of said outer ring over said hole and opened between the passage of the hole by consecutive such rollers. This is an advantageous way of generating said pressure pulsations. Said cylindrical rollers pass such a hole with a much higher frequency than the number of revolutions of the motor, which thereby may be kept rather low and still high frequencies may be obtained. Furthermore, such a hole may very reliably be opened and closed in this way. Another advantage of this embodiment is that a cylindrical roller bearing, is a simple conventional component available to a comparatively low cost.

It is pointed out that "open and close" does not mean that the hole or opening has to be completely exposed or sealed, but it also includes the possibility to never open or close the hole more than to a substantial extent.

According to another embodiment of the invention the width of said hole in the axial direction of the roller bearing firstly increases and then decreases from one end of the hole to the other with respect to the circumferential direction of said outer ring. This results in combination with the cylindrical rollers passing said hole in a generation of gas pressure pulsations having substantially a sine shape, which is preferred, and this is especially obtained when the hole has a substantially square cross- section with one diagonal thereof directed substantially circumferentially and the other diagonal substantially axially with respect to said outer ring. This means that the hole looks like the sign for "diamonds" in play cards when viewed from the outside of the ring. This shape and orientation of the hole results in the generation of pressure pulsations being very close to having a sine shape.

According to another embodiment of the present invention the relationship of the diameter of the rollers of said bearing and the width of said opening in the circumferential direction of said outer ring is 2:1 -1.2:1 , preferably 1.8:1 -1.3:1. It has turned out that this relationship with a somewhat lager diameter of the rollers than the width of said opening in the circumferential direction of said outer ring makes it possible to generate pressure pulsations being close to that normally sensed by a said dynamic gas pressure sensor.

According to another embodiment of the present invention said device comprises a volume in the form of a so called pulsation chamber separated from said supply of compressed air by ^"said opening. This makes it possible to obtain pressure pulsations having a higher amplitude than would the compressed air be allowed to escape on the side of the opening opposite to the supply of compressed air.

According to another embodiment of the present invention the arrangement comprises a regulating member for regulating the speed of the motor for varying the frequency of said pulsations generated by said device. This makes it possible to check the proper function of said dynamic gas pressure sensor with respect to the ability to make correct measurements for different frequencies of gas pressure pulsations. The speed regulating member is advantageously adapted to allow regulation of said frequency at least from 50 Hz to 500 Hz, preferably from 20 Hz to 3 kHz. The pressure pulsations generated in for instance the combustion chamber of a gas turbine and being harmful to components of the combustion chamber may have frequencies within this range, but the acceptable amplitude will be different for different frequencies. According to another embodiment of the present invention the arrangement comprises for that sake a regulating member for controjling the pressure of the compressed air from said supply to said path of compressed air, so that the amplitude of the pressure pulsations generated may be controlled. Said pressure regulating member is according to another embodiment of the invention adapted to regulate said pressure so as to regulate the amplitude of the pressure pulsations generated in said path of compressed air to be between 0 mbar and 200 mbar, in which the lower amplitudes are used for testing the sensor for higher frequencies and higher amplitudes for the lower frequencies.

According to another embodiment of the present invention said reference dynamic gas pressure sensor is arranged to measure pressure pulsations in a part of said path of compressed air forming an inlet to said device. Gas pressure pulsations are not only generated downstream said device, but they are transferred to the inlet side, so that the measurements may take place there, where it is often easier to measure. The arrangement may then comprise connecting means for connecting said dynamic gas pressure sensor to be checked to said inlet to the device, which means that the reference dynamic gas pressure sensor and the dynamic gas pressure sensor to be checked will meas- ure on substantially the same location and should by that deliver substantially the same values, so that it will be easy to check the proper function of the dynamic gas pressure sensor by comparing the signals from these two sensors.

According to another embodiment of the invention, the arrangement comprises connecting means for connecting said path of compressed air to a said dynamic gas pressure sensor to be checked at a substantial distance, such as at least in the order of 0,5 m, to said device, said reference dynamic gas pressure sensor is adapted to be arranged close to said device, and said calculating means is adapted to consider said distance when carrying out said comparison, such as by amplifying the signal from said dynamic gas pressure to be checked. This constitutes another possible way to check the proper function of the dynamic gas pressure sensor, when there is no possibility or diffi- cult to move the gas pressure sensor to be checked and/or the reference dynamic gas pressure sensor to the same place.

According to another embodiment of the invention the arrangement comprises connecting means for connecting said path of compressed air to a dynamic gas pressure sensor to be checked located at a substantial distance, such as at least in the order of 0,5 m, to said device, and the arrangement further comprises an adapter for holding and connecting said reference dynamic gas pressure sensor to said path of compressed air at the location of said dynamic gas pressure sensor to be checked. This possibility to apply the reference dynamic gas pressure sensor close to the dynamic gas pressure sensor to be checked results in the same advantages as when arranging the dynamic gas pressure sensor to be checked on the location of said reference dynamic gas pressure sensor at the inlet of the device as disclosed above.

A further advantage of this embodiment may be a possibility to have said device arranged to generate gas pressure pulsations at one end of a wave-guide connected to the dynamic gas pressure sensor to be checked, so that it may then also be checked that the wave-guide will not distort the measurement results of the sensor. Said adaptor is then advantageously designed to hold both said dynamic gas pressure sensor to be checked and said reference dynamic gas pressure sensor. According to another embodiment of the invention the arrangement comprises a portable briefcase-like casing housing the rest of said arrangement, which makes it easy to transport the arrangement between for instance different power plants for checking the function of dynamic gas pressure sensors on different locations.

The invention also comprises a method for checking the proper function of a dynamic gas pressure sensor according to the em- bodiments defined in the appended dependent method claims. The advantages and advantageous features thereof appear from the discussion above of the different embodiments of the arrangement according to the invention.

The invention also comprises the use of an arrangement according to the invention for checking the proper function of a dynamic gas pressure sensor adapted to measure gas pressure pulsations generated in the combustion chamber of a gas turbine as well as such a use for checking the proper function of a dynamic gas pressure sensor adapted to measure gas pressure pulsations having substantially a sine shape.

Further advantages as well as advantageous features of the invention will appear from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

With reference to the appended drawings, below follows a specific description of preferred embodiments of the invention cited as examples.

In the drawings:

Fig 1 is a simplified view illustrating an equipment in the form of a gas turbine having a dynamic gas pressure sensor to be checked by an arrangement and a method according to the invention,

Fig 2 is a simplified view illustrating an arrangement according to an embodiment of the present invention,

Fig 3 is an enlarged, partially sectioned view of a part of the arrangement of Fig 2,

Fig 4 is a perspective view of a cylindrical roller bearing used in the arrangement of Fig 2 and also shown in Fig 3,

Fig 5 is an enlarged, partially sectioned view of a part of the cylindrical roller bearing of Fig 4,

Fig 6 is a simplified view of a part of the arrangement shown in Fig 2 being slightly modified with respect to -Fig 2, and

Fig 7 is a simplified view illustrating an arrangement of Fig 2 ac- cording to yet another embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

An arrangement for checking the proper function of a dynamic gas pressure sensor as described above according to an embodiment of the present invention is schematically illustrated in Fig 2. This arrangement comprises a briefcase-like casing 9 housing the rest of the arrangement making it easy to carry the arrangement along for carrying out measurements on different locations. Accordingly, this arrangement according to the invention is portable and adapted to be transported between different industrial plants or the like for carrying out measurements on site. The casing contains a device 10 connectable through a first connecting member 11 to a supply of compressed air and when connected to said supply adapted to generate pressure pulsations in a path of compressed air then connected to said supply. How these gas pressure pulsations are generated will now firstly be described. A pressure regulating member 12 is arranged close to the connecting member for regulating the pressure of the compressed air downstream thereof, and this is associated with a manometer 13.

Reference is now also made to Fig 3. The compressed air is led by a hose 14 to a connecting means 15 designed to allow differ- ent connections to the path of compressed air so established. The connecting , means 15 is provided with a channel 16 connecting the compressed air to the exterior of an outer ring 17 of a cylindrical roller bearing (see also Figs 4 and 5). The inner ring 18 of this roller bearing housing the cylindrical rollers 19 is secured to the output shaft 20 of an electrical direct current motor 21 being fed by electricity from a power supply unit 22. The speed of the motor 21 may be controlled by speed regulating members 23, 24. The outer ring 17 of the bearing is provided with an opening 25 in the . form of a through-hole having a substantially square cross-section with a diagonal thereof directed substantially circumferentially and the other diagonal substantially axially with respect to said outer ring. One side of said square is in the present case 2,5 mm, whereas the diameter of a roller 19 is about 5 mm. The volume between the outer and the inner ring of the roller bearing is connected to a volume 26 in the form of a so-called pulsation chamber separated from said supply of compressed air by the opening 25.

The connecting means 15 also comprises a channel 27 for connecting said path of compressed air to the exterior of the casing through a hose 28 and a second connecting member 29.

The function of the device 10 for generating gas pressure pulsations will be as follows: when the inner ring 18 of the cylindrical roller bearing is rotated by the output shaft 20 of the motor 21 , the rollers 19 will pass the hole 25. This means that when a roller 19 is aligned to said opening 25 as shown in Fig 5 this will be substantially closed and then gradually opened before it will be gradually closed through the passage of the next roller 19'. This means that communication of compressed air between the pulsation chamber 26 and the path of compressed air in the connecting means 15 will alternatively be established and interrupted. This results in generation of substantially sine shaped air pressure pulsations, in said pulsation chamber 26 as well as in the path of compressed air at the inlet of the device, such as in the hoses 14 and 28. The frequency of these pulsations will be equal to the frequency of passages of the opening 25 by a cylindrical roller.

Thus, the device 10 so described and included in the arrange- ment according to the invention may generate pressure pulsations in a path of compressed air over a wide frequency range and with different amplitudes for using these pressure pulsations for checking the status of a dynamic gas pressure sensor.

The arrangement also comprises a reference dynamic gas pressure sensor 30 adapted to measure said pressure pulsations generated by the device 10 by being connected to a further channel 31 of the connecting means 15 and by that to the path of compressed air on the inlet side of the device. The signals from this reference sensor are led to a signal output 32 for connecting them to a calculating means 33 schematically indicated for evaluation of these signals. It is shown how the second connecting member 29 is arranged to connect to an adapter 34 receiving and holding the dynamic gas pressure sensor 1 to be checked. The output of this dynamic gas pressure sensor is also connected to the calculating means 33 adapted to compare the results of the measurement by said reference dynamic gas pressure sensor 30 with the results of the measurement by said dynamic gas pressure sensor 1 and the basis thereof determine the status of said dynamic gas pressure sensor 1. The dynamic gas pressure sensor 1 is in this case located at a distance from the casing 9 and the place (the hole 25) of the generation of the gas pressure pulsations, which is considered by the calculating means 33 by correspondingly amplifying the signal from the sensor 1. The amplifying factor has then to be increased when pulsations of higher frequencies are measured.

The checking of the proper function of the dynamic _. gas pressure sensor 1 may in the practice be carried out in the following way. The casing 9 is opened and the supply of compressed air is con- nected to the first connecting member 11. The adapter 34 is connected to the/ second connecting member 29 and the signal output 32 of the reference dynamic gas pressure sensor as well as the output of the sensor 1 are connected to the calculating means 33. The motor 21 is then started and the speed thereof is controlled to obtain a certain frequency, such as for example 20 Hz, of pressure pulsations generated by the device 10. The pressure regulating member 12 is simultaneously controlled for adjusting the pressure pulsations to have a suitable amplitude for the frequency in question, such as for example 200 mbar. The signals from the two sensors are then compared in the calculating means. The frequency and the amplitude of said pressure pulsations are then changed, in which the amplitude is lowered for higher frequencies, while comparing the signals from the two sensors. The proper function of the dynamic gas pres- sure sensor 1 may in this way be checked.

Fig 6 illustrates an arrangement according to an embodiment of the present invention being slightly modified with respect to the arrangement shown in Fig 2 by a modification of the connecting means 15. This is here shown in the direction of the arrow 35 in Fig 2. The connecting means 15 is here designed to receive the dynamic gas pressure sensor 1 to be checked by a receiving channel being closed in the embodiment shown in Fig 2 by a nut 36. This means that the reference dynamic gas pressure sensor 30 as well as the dynamic gas pressure sensor 1 to be checked are connected to the inlet of the device on substantially the same location, so that the signals therefrom arriving to the calculating means 33 should be substantially identical if the dynamic gas pressure sensor functions properly.

Fig 7 illustrates a further embodiment of the present invention including an adapter 37 arranged to receive both the dynamic gas pressure sensor 1 to be checked as well as said reference dynamic gas pressure sensor. 30, which in this application is removable from the position inserted in the connecting means 15 for sensing gas pressure pulsations on substantially the same location at a substantial distance from the place of generation of the pulsations. This embodiment may be favourable when there is a desire to involve also a wave-guide 38 in said checking. This is also the case for the embodiment shown in Fig 2, but in the embodiment of Fig 7 the measurements of the two sensors are taken place on substantially the same location. The connection between the adapter 34, 37 and the second connecting member 29 may also be established by a tube simulating a wave-guide.

The invention is of course not in any way restricted to the embodiment described above, but many possibilities to modifications thereof would be apparent to a person with ordinary skill in the art without departing from the basic idea of the invention as defined in the appended claims.

The appearance of the dynamic gas pressure sensors are simplified in the figures and may be totally different.

Other members than an inner ring having cylindrical rollers of a cylindrical roller bearing may also be rotated by said motor for generating gas pressure pulsations, although that embodiment is particularly advantageous.

The pulsation chamber may be left out and it is theoretically also possible to connect the supply of compressed air to the other side of said opening, i.e. to the volume inside the outer ring of the bearing.

The claims are to be interpreted to also cover the case that the calculating means is a component totally separated from the rest of the arrangement, such as an oscilloscope, and not even carried along with the arrangement. It is well possible that the calculating means does normally not belong to the arrangement, but any type of such means are applied thereto when the arrangement is used for checking the function of a sensor, since the measurements carried out by that sensor and the reference sensor do not make any sense if the results thereof are not compared. This case is also intended to be covered by the claims.

Claims

1. An arrangement for checking the proper function of a dynamic gas pressure sensor, characterized in that it com- prises

- a device (10) connectable to a supply of compressed air and when connected to said supply adapted to generate pressure pulsations in a path of compressed air then connected to said supply, - a reference dynamic gas pressure sensor (30) adapted to measure said pressure pulsations generated by said device,

- connecting means (15, 29) adapted to connect said path of compressed air to said dynamic gas pressure sensor (1 ) to be checked, and - calculating means (33) connectable to said sensors and adapted to compare the results of the measurement by said reference dynamic gas pressure sensor (30) with the results of the measurement by said dynamic gas pressure sensor (1 ) and on the basis thereof determine the status of said dy- namic gas pressure sensor.

2. An arrangement according to claim 1 , characterized in that said device (10) is adapted to generate pressure pulsations having substantially a sine shape.

3. An arrangement according to claim 1 or 2, characterized in that said device (10) comprises a motor (21 ) adapted to rotate a member (18) arranged to communicate with said supply of compressed air, and that said member is adapted to co-operate with at least one opening (25) in said path of compressed air for alternatively open and close this opening when rotating for alternatively allow and not allow, respectively, air to pass therethrough so as to obtain pressure pulsations in said path of compressed air.

4. An arrangement according to claim 3, characterized in that said device comprises a cylindrical roller bearing, that said opening (25) is formed by a hole substantially radially penetrating the outer ring (17) of the bearing and arranged so as to be closed when a roller (19) rolls on the inner wall of said outer ring over said hole and opened between the passage of the hole by consecutive such rollers.

5. An arrangement according to claim 4, characterized in that the width of said hole (25) in the axial direction of the roller bearing firstly increases and then decreases from one end of the hole to the other with respect to the circumferential direction of said outer ring (17).

6. An arrangement according to claim 5, characterized in that said hole (25) has a substantially square cross section with a diagonal thereof directed substantially circumferentially and the other diagonal substantially axially with respect to said outer ring (17).

7. An arrangement according to any of claims 4-6, characterized in that the relationship of the diameter of the rollers (19) of said bearing and the width of said opening (25) in the circumferential direction of said outer ring is 2:1 -1 .2:1 , preferably 1.8:1-1.3: 1.

8. An arrangement according to any of claims 3-7, characterized in that said device comprises a volume (26) in the form of a pulsation chamber separated from said supply of com- pressed air by said opening (25).

9. An arrangement according to any of claims 3-8, characterized in that it comprises a regulating member (23, 24) for regulating the speed of the motor (21 ) for varying the fre- quency of said pulsations generated by said device.

10. An arrangement according to claim 9, characterized in that said speed regulating member (23, 24) is adapted to allow regulation of said frequency at least from 50 Hz to 500 Hz, preferably from 20 Hz to 3 kHz.

1 1. An arrangement according to any of the preceding claims, characterized in that it comprises a regulating, member (12) for controlling the pressure of the compressed air from said supply to said path of compressed air.

12. An arrangement according to claim 1 1 , characterized in that said pressure regulating member (12) is adapted to regulate said pressure so as to regulate the amplitude of the pressure pulsations generated in said path of com- pressed air to be between 0 mbar and 200 mbar.

13. An arrangement according to any of the preceding claims, characterized in that said reference dynamic gas pressure sensor (30) is arranged to measure pressure pulsations in a part of said path of compressed air forming an inlet to said device.

14. An arrangement according to claim 13, characterized in that it comprises connecting means (15) for connecting said dynamic gas pressure sensor (1 ) to be checked to said inlet to the device.

15. An arrangement according to any of claims 1 -13, characterized in that it comprises connecting means (29) for connect- ing said path of compressed air to a said dynamic gas pressure sensor to be checked at a substantial distance, such as at least in the order of 0.5 meter, to said device, that said reference dynamic gas pressure (30) sensor is adapted to be arranged close to said device, and that said calculat- ing means (33) is adapted to consider said distance when carrying out said comparison, such as by amplifying the sig- nal from said dynamic gas pressure sensor (1 ) to be checked.

16. An arrangement according to any of claims 1-13, character- ized in that it comprises connecting means (29) for connecting said path of compressed air to a dynamic gas pressure sensor (1 ) to be checked located at a substantial distance, such as at least in the order of 0.5 meter, to said device, and that it further comprises an adapter (37) for holding and connecting said reference dynamic gas pressure sensor

(30) to said -path of compressed air at the location of said dynamic gas pressure sensor to be checked.

17. An arrangement according to claim 16, characterized in that said adapter (37) is designed to hold both said dynamic gas pressure sensor (1) to be checked and said reference dynamic gas pressure sensor (30).

18. An arrangement according to any of the preceding claims, characterized in that it comprises a portable briefcase-like casing (9) housing the rest of said arrangement.

19. Use of an arrangement according to any of the preceding claims for checking the proper function of a dynamic gas pressure sensor adapted to measure gas pressure pulsations generated in the combustion chamber of a gas turbine.

20. Use in accordance with claim 19 for checking the proper function of a dynamic gas pressure sensor adapted to measure gas pressure pulsations having substantially a sine shape.

21. A method for checking the proper function of a dynamic gas pressure sensor (1 ) adapted to measure gas pressure pulsations generated in the combustion chamber of a gas turbine, characterized by the steps of a) generating pressure pulsations in a path of compressed air, b) measuring said pressure pulsations by a reference dy- namic gas pressure sensor (30), c) measuring said pressure pulsations by said dynamic gas pressure sensor (1 ) to be checked, and d) comparing the results of said measurements for determining the status of said dynamic gas pressure sensor.

22. A method according to claim 21 , characterized in that said pressure pulsations are generated by rotating a member (18) arranged to communicate with a supply of compressed air so as to alternatively open and close an opening (25) in said path of compressed air for alternatively allow and not allow, respectively, air to pass therethrough so as to obtain pressure pulsations in said path of compressed air.

23. A method according to claim 22, characterized in that the speed of said rotating member (18) is regulated for varying the frequency of said pulsations generated.

24. A method according to any of claims 21 -23, characterized in that the pressure of compressed air from a supply of compressed air to said path of compressed air is regulated for controlling the amplitude of said pressure pulsations generated.

25. A method according to any of claims 22, 23 or 22 and 24, characterized in that said measurement of pressure pulsations by said reference dynamic gas pressure sensor (30) is carried out in a part of said path of compressed air forming an inlet from said supply of compressed air with respect to said opening (25).

26. A method according to claim 25, characterized in that said dynamic gas pressure sensor (1 ) to be checked is connected to said inlet for measuring said pressure pulsations on that location.

27. A method according to any of claims 21-25, characterized in that said path of compressed air is connected to a said dynamic gas pressure sensor to be checked at a substantial distance, such as at least in the order of 0.5 meter, to the place of said generation of pressure pulsations, that measurement of said pressure pulsations by said reference dynamic gas pressure sensor (30) is carried out close to a location of said generation of pressure pulsations, and that said distance is considered when carrying out said compari- son, such as by amplifying the signal from said dynamic gas pressure sensor to be checked.

28. A method according to any of claims 21 -25, characterized in that said path of compressed air is connected to a dy- namic gas pressure sensor to be checked at a substantial distance, such as at least in the order of 0.5 meter, to the place of said generation of pressure pulsations, and that said pressure pulsations are measured by said reference dynamic gas pressure sensor (30) in said path of com- pressed air at the location of said dynamic pressure sensor

(1 ) to be checked.