WO2007065882A1

WO2007065882A1 - Waveguide test and maintenance device

Info

Publication number: WO2007065882A1
Application number: PCT/EP2006/069286
Authority: WO
Inventors: Otmar Straubhaar
Original assignee: Ericsson Ab
Priority date: 2005-11-25
Filing date: 2006-12-04
Publication date: 2007-06-14
Also published as: DE102005056588A1

Abstract

A test and/or maintenance device for hollow waveguides comprises a source (1, 2, 3, 6) of pressurized dry gas, a first connector (29) for connecting the source to a hollow waveguide (17), a pressure gauge (14) connected to a gas duct (4, 18) extending between the source (2) and the first connector (29) and a first switching valve (8) which in a first position establishes communication between the source and the connector (29) and in a second position establishes communication between a first port (27) of the pressure gauge (14) and the connector (29) and seals the connector (29) from the source (2).

Description

WAVEGUIDE TEST AND MAINTENANCE DEVICE

The present invention relates to a test and/or maintenance device for hollow waveguides.

The interior of a hollow waveguide used for microwave transmission has to be kept free from moisture, since water is a strong absorber of microwave radiation, the presence of which causes considerable attenuation of a microwave propagating in the waveguide and, eventually heating up of the waveguide.

Conventionally, the accumulation of moisture in a hollow waveguide system is prevented by connecting the waveguide system to a pressurised air supply which continuously feeds dry air at a slight positive pressure of a few millibars, so that if a leak exists in the waveguide system, a continuous air current from inside out is maintained in the leak, and no moisture can enter the waveguide through it.

Such a pressurised air supply contributes significantly to the initial and maintenance costs of a microwave system. The object of the present invention is to decrease these costs by eliminating the need for a stationary pressurised air supply.

This object is achieved by a test and/or maintenance device for hollow waveguides comprising a source of pressurized dry gas, a first connector for connecting the source to a hollow waveguide, a pressure gauge connected to a gas duct extending between the source and the first connector and a first switching valve which in a first position establishes communication between the source and the connector and in a second position establishes communication between the pressure gauge and the connector and seals the connector from the source. While the first connector is connected to a hollow waveguide, pressurized dry gas can be administered to the hollow waveguide if the switching valve is in the first position. If it is in the second position, the development of the pressure in the hollow waveguide can be monitored, so that it can be judged whether the waveguide is leaky or not. I.e. if a speed of pressure change above a predetermined limit is observed, it can be said that there is a leak, which might be located in the hollow waveguide or somewhere in the device between the waveguide and the pressure gauge. However, when the speed of pressure change is below the limit, it can be safely judged that the waveguide is airtight, so that the device may be removed from the waveguide and may be used for testing others.

In order to detect pressure changes with high accuracy, the pressure gauge preferably is a differential pressure gauge, a second port of which is also connected to the gas duct, and the device further comprises means for sealing the second port from the gas duct while the first switching valve is in the second position. By allowing the second port to communicate with the gas duct, a pressure sample is admitted to it, so that when the second port is sealed from the gas duct again, a deviation of the pressure reigning in the gas duct from the sample value can be detected with high sensitivity. Preferably, a moisture sensor is connected to the gas duct, thus enabling to determine the degree of humidity of gas circulating in it.

Preferably, the connection of the moisture sensor to the gas duct is via a second switching valve. This second switching valve enables to feed gas from the source selectively either to the moisture sensor, in order to judge whether it is dry enough to be admitted into the hollow waveguide, or to the output port.

Preferably, the moisture sensor is detachably connected to the second switching valve, thus enabling it to be used also on rinsing gas that emerges from the hollow waveguide. According to a first embodiment, the device comprises a first tube, a first end of which is connected to a downstream side of the second switching valve and through a second end of which the moisture sensor is adapted to be inserted. Preferably, the device further comprises a second tube, in which the same moisture sensor is adapted to be inserted, e.g. for measuring the moisture of rinsing gas from the hollow waveguide which is led through this second tube.

According to another embodiment, the detachable connection of the moisture sensor to the second switching valve is by a pair of mating connectors, at least one of which is adapted to mate the first connector. In this case, if the waveguide to be tested has two connectors of a same type, one through which rinsing gas is supplied from the first connector of the device and a second one through which it escapes from the waveguide, the connector of the moisture sensor may fit the second connector of the waveguide.

The pressurized gas source preferably comprises a pump and a desiccant container.

A relief valve may be provided for limiting the pressure in the gas duct. In order to facilitate the use of the device at different locations, it is preferably designed as a portable unit.

Further features and advantages of the invention will become apparent from the subsequent description of embodiments thereof, referring to the appended drawings.

Fig. 1 is a block diagram of a test/maintenance device according to a first embodiment of the invention.

Fig. 2 illustrates a first configuration of the test device connected to a waveguide. Fig. 3 illustrates a second configuration of the test device; Fig. 4 illustrates a third configuration of the test device; Fig. 5 is a block diagram of a second embodiment of the device, connected to a waveguide;

Fig. 6 is a block diagram of a third embodiment; and Fig. 7 is a block diagram of a fourth embodiment of the test device.

Fig. 1 illustrates the general structure of the maintenance and test device according to the present invention. Within a rugged metal casing 15, it comprises an air filter 1, an inlet port of which is open to ambient air. An output port of air filter 1 is connected to a suction port of a pump 2, e.g. a membrane pump. At a gas duct 4 extending from an output port of pump 2 to an output connector 5 mounted in a wall of casing 15, there are located a relief valve 3 through which air is allowed to escape if the pressure at the output side of pump 2 exceeds a threshold which may be set at several millibars above atmospheric pressure, a desiccant container 6 containing a replaceable desiccant cartridge, and two switching valves 7, 8. In the configuration of Fig. 1, air is allowed to flow through the two switching valves 7, 8 to output connector 5. In an alternative position of switching valve 7, the air is supplied to a moisture measuring device 9 via a branch duct 10. Measuring device 9 comprises a moisture sensor 12 and a display 13 for displaying moisture readings to a user. Part of the branch duct 10 is formed of an open- ended tube 11, which has the moisture sensor 12 inserted through its open end.

In an alternative position of switching valve 8, the air duct 4 is blocked, and output connector 5 communicates with a pressure gauge 14. All components of the device mentioned above except the moisture measuring device 9 are fixedly mounted within casing 15.

The moisture measuring device 9 is detachably mounted at or in the casing 15. A second tube 16 and a hose 18 are stored in respective compartments of casing 15. At a first end of hose 18, there is a connector 28 which fits output connector 5; at the other, there is a connector 29 for fitting to a waveguide system to be tested.

Operation of the device of Fig. 1 will now be explained referring to Figs. 2 to 4. In these Figs., a hollow waveguide system to which the device is applied is denoted by reference numeral 17.

In Fig. 2, membrane pump 2 is in operation, and switching valve 7 applies pressurized air from pump 2, which has passed through desiccant container 6, to tube 11, where the moisture sensor 12 is exposed to it. By reading display 13, a user can judge whether the desiccant in container 6 is effective, and whether the pressurized air is fit to be feed into waveguide system 17 through hose 18 which has been mounted between output connector 5 and an input connector 19 of waveguide system 17. The input connector 19 comprises a Schrader valve which is maintained open while the hose 18 is connected to it and closes automatically when hose 18 is removed.

In a second stage shown in Fig. 3, tube 16 has been removed from the casing 15 and has been installed at a second connector 20 of waveguide system 17, which is identical to input connector 19. Connectors 19, 20 are located at opposite ends of waveguide system 17, so that humid air is purged from the entire system 17 when dry air is introduced at connector 19. By connecting the tube 16 to it, the Schrader valve of connector 20 is opened. The moisture sensor 12 has been removed from tube 11 and has been slid into the open end of tube 16. Switching valve 7 is in a position in which air from pump 2 is supplied to the waveguide system 17 via open valve 8 and hose 18. In this configuration, the pump 2 is operated until readings at display 13 indicate that the humidity of the air in the waveguide system 17 has decreased to an admissibly low level.

In a next step, tube 16 is removed from connector 20, whereby its Schrader valve is closed, and a positive pressure is built up inside the waveguide system 17 up to a level defined by relief valve 3.

When this pressure level is reached, switching valve 8 is switched over into the position shown in Fig. 4, in which it seals the waveguide system 17 from pump 2 while establishing communication between waveguide system 17 and pressure gauge 14. The pressure is observed for a predetermined time, and if a pressure decrease of less than a predetermined limit amount is observed, it is decided that the waveguide system is not leaky. The hose 18 is then removed, causing the Schrader valve of input connector 19 to close, and the waveguide system 17 can be expected to hold its positive pressure for a prolonged period of time, at the end of which period inspection by the device of Fig. 1 is repeated.

Fig. 5 illustrates a second embodiment of the test and maintenance device of the invention. Air filter 1, pump 2, relief valve 3, desiccant container 6, switching valve 8 and pressure gauge 14 are the same as in the embodiment of Fig. 1 and are not described here again. Output connector 5 of this embodiment is of the same type as connectors 19, 20 of waveguide system 17, i.e. it is open while hose 18 is connected to it and closed when not. The sensor 12 of moisture measuring device 9 is fixedly installed in a tube 21 which, in the configuration of Fig. 5, is coupled to branch duct 10 by a pair of connectors 22, 30. Connector 22 of the branch duct 10 is of the same type as connectors 5, 19, 20.

In the configuration depicted in Fig. 5, in which hose 18 is removed from connector 5 and tube 21 is coupled to connector 22, pressurized air from pump 2 can only pass through tube 21, so that its humidity content is measured. This configuration, therefore, corresponds to the one shown in Fig. 2.

In a subsequent stage of the testing procedure, hose 18 is coupled to output connector 5, and tube 21 is removed from connector 22 and is installed at connector 20. In consequence, the Schrader valve of connector 22 will block, whereas those of connectors 5, 19, 20 are open, allowing air to pass through waveguide system 17 and tube 12, corresponding to the configuration of Fig. 3. It is easily recognized that the Schrader valves of connectors 22 and 5 thus assume the function of switching valve 7 of the embodiment of Fig. 1.

For monitoring the pressure in waveguide system 17, switching valve 8 is switched over, just like in the previous embodiment.

A third embodiment of the device illustrated in Fig. 6 differs from the previous ones in that the moisture measuring device 9 is fixedly installed at branch duct 10 which extends from switching valve 7 to a connector 24 mounted in the wall of casing 15. Connectors 5, 24 are always open, regardless of whether a hose 18, 25 is connected to them, as shown in the drawing, or not.

In the configuration shown in the drawing, pressurized air from the pump 2 flows through switching valves 7, 8 and hose 18 into waveguide system 17 and back through hose 25, branch duct 10 and switching valve 7, from where it escapes into the open. In this configuration, moisture in the air returning from waveguide system 17 is measured. In a second position of switching valve 7, air from pump 2 flows through valve 7 and branch duct 10 to connector 24, which should in this case be open so as to let the air escape. It is readily seen that this device can perform the same functions as the previously described embodiments without requiring any detachable members except the hoses 18, 25.

Fig. 7 illustrates a fourth embodiment of the device which differs from that of Fig. 1 by switching valve 8 and pressure gauge 14. Switching valve 8 has four ports, all of which communicate in the configuration shown in Fig. 7. One of these ports is connected to switching valve 7, another to output connector 5, and the remaining two to two ports 26, 27 of differential pressure gauge 14. A buffer volume 23 may be provided between valve 8 and port 26.

In a second position of valve 8, only output connector 5 and port 27 are allowed to communicate through valve 8. Port 26 is sealed from the waveguide system 17, so that the pressure at this port is held constant at the level reigning in the waveguide system 17 at the instant in which valve 8 was switched into the second position. The pressure pressure gauge 14 detects any deviation of the pressure in waveguide system 17 applied to port 27 from that at port 26 with high sensitivity, so that when no substantial pressure difference between the two ports is observed, the waveguide system 17 can safely be judged to be airtight.

Claims

1. Test and/or maintenance device for hollow waveguides comprising a source of pressurized dry gas, a first connector (29) for connecting the source to a hollow waveguide (17), a pressure gauge (14) connected to a gas duct (4, 18) extending between the source (2) and the first connector (29) and a first switching valve (8) which in a first position establishes communication between the source and the connector (29) and in a second position establishes communication between a first port (27) of the pressure gauge (14) and the connector (29) and seals the connector (29) from the source (2).

2. The device of claim 1, wherein the pressure gauge (14) is a differential pressure gauge having a second port (26) connected to the gas duct (4), the device further comprising means (8) for sealing the second port (26) from the gas duct (4) while the first switching valve (8) is in the first position.

3. The device of any of the preceding claims, wherein a moisture sensor (12) is connected to the gas duct (4).

4. The device of claim 3, wherein the connection of the moisture sensor (12) to the gas duct (4) is via a second switching valve (7).

5. The device of claim 4, wherein the moisture sensor (12) is detachably connected to the second switching valve (7).

6. The device of claim 5, comprising a first tube (11), a first end of which is connected to a downstream side of the second switching valve (7) and through a second end of which the moisture sensor (12) is adapted to be inserted.

7. The device of claim 6, further comprising a second tube (16) in which the moisture sensor (12) is adapted to be inserted.

8. The device of claim 5, wherein the detachable connection is by a pair of mating connectors (22, 30), at least one (30) of which is of the same type as the first connector (29).

9. The device of any of the preceding claims, wherein the source comprises a pump (2) and a desiccant container (6).

10. The device of any of the preceding claims, comprising a relief valve (3) for limiting the pressure in the gas duct (4).

11. The device of any of the preceding claims, designed as a portable unit.