IE43049B1 - Improvements in or relating to electrical winding and microphone mountings - Google Patents

Abstract

When calibrating mechanical resonators, consisting of a ferromagnetic material, for electromechanical filters by means of a sand blasting or laser erosion device, the resonators are excited into mechanical oscillations via the alternating field of a coil and the frequency of the oscillations of the resonators is measured with the aid of a microphone. To obtain an interference-free microphone output voltage which is as high as possible, the microphone (4) must be arranged in the area of the first anti-node of the air column located between resonator (1) and microphone, and thus closely adjacently to the resonator. To reduce the great wear of the microphone (4) and of the excitation coil (3), which therefore occurs during the calibration process due to reflected sand grains or ejected particles of material, a closed protective housing (9) is provided which exhibits a removable protective plate (5) consisting of insulating material and facing the holder for the resonator (1). Inside the protective housing (9), a sleeve (7) enclosing the microphone (4) and protruding with one end through a hole in the protective plate (5) and displaceable for moving this end close to the resonator (1) is arranged. Two ferrite core pieces (6) are guided through the protective plate (5). The excitation coil can be displaced inside the protective housing (9) so that its core (11) comes to rest against the two core pieces (6).

Description

The present invention relates to electrical winding and microphone mountings.

Although the term microphone transducer will be used hereinafter to describe the invention, it will be understood that by this term is meant any form of electro-acoustic transducer responsive to pressure waves which are in the range from sub-sonic to ultrasonic values of frequency.

When mechanical resonators of magnetic material for electromechanical filters are frequency corrected, these devices are excited by the a.c. field of an electrical winding to perform mechanical vibrations and the frequency of these vibrations is measured with the help of a microphone transducer. j In this context, for example, a method of effecting frequency correction in mechanical resonators is known in which the adjustment of the predetermined resonance frequency is performed by the controlled removal of resonator material using a sand-blaster or a laser beam (German Patent Specification No. 1,929,994). The resonators are excited by the a.c. field of a winding having an iron core in order to perform mechanical vibrations which are converted by a microphone transducer into electrical oscillations corresponding to the actual frequency of the resonators. These electrical oscillations are amplified and are then subjected to a comparison between set-point and actual values and in accordance with the resultant frequency difference, the removal of resonator material by laser or sand blaster is controlled. 43040 In order, in determining the characteristic frequency of the mechanical resonator·, to achieve an adequately large vibrat-ional amplitude, it is preferable for that air gap between the iron core of the excitation winding and the resonator which closes the magnetic circuit to be kept small. The microphone transducer should, in order to furnish the highest possible output voltage, be arranged in the proximity of a vibrational antinode in the air column between resonator and microphone transducer.

In order, furthermore, to exclude the effects of environmental noise during measurement of the characteristic frequency of the resonators, it is preferable to arrange the microphone transducer in the neighbourhood of the first vibrational antinode in the air column. This results in an interval, between resonator and microphone, of only a few tenths of a millimeter. However, because measurement of the characteristic frequency generally takes place in alteration with the step-by-step operation of frequency correction, the excitation winding and the microphone transducer are in the known system, subject to heavy wear either by reflected sand grains or, in the case of laser bombardment, by particles of material knocked out in the course of laser machining.

An object of the invention is to improve upon the known system.

According to the invention, there is provided an electrical winding and microphone mounting, for receiving an electrical excitation winding and a microphone transducer, comprising: an elongate housing - 3 having a detachable protective end plate; a sleeve disposed within the housing for enclosing said microphone transducer, one end of the sleeve extending through said end plate; two magnetic core elements extending through said end plate; and a magnetic core, for said winding, displaceable within the housing and externally of said sleeve in such manner that it can be brought into contact with said core elements.

Preferably said sleeve comprises two cylindrical portions of differing diameters connected together by means of a corresponding tapering tube section, that cylindrical portion having the smaller diameter being detachable from the tapering section and extending through said end plate.

Preferably, the mounting further comprises means for supporting the microphone in such manner that it can be displaced in the direction of the longitudinal axis of the sleeve and comprises means for locking the microphone transducer to prevent it from being thus displaced.

Where the mounting ia in operable combination with an excitation winding of a microphone transducer, the detecting part of the microphone transducer may be arranged at a vibrational antinode of that air column located within said sleeve.

The mounting may be provided with support means for supporting a mechanical resonator adjacent said end plate. There may further be provided holding means for holding a sand blaster and/or a laser in such positions or position that they or it can adjust the resonant frequency.of a mechanical resonator when it is _ 4 supported by said support means.

For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the drawings, in which:— Figure 1 is a schematic view of a frequency correction device of prior art design; Figure 2 is a schematic illustration of an electrical winding microphone mounting; Figure 3 illustrates schematically a vertical section through the mounting of Figure 2, passing through the centre of the microphone; and Figure 4 illustrates schematically a section taken at right angles in relation to that of Figure 3.

Figure 1 illustrates a known frequency correcting device with a laser unit 2 aimed at one end of a resonator 1 of magnetic material which is to be frequency corrected. A frequency measuring unit consisting of an electrical excitation winding 3 and a microphone 4 having a microphone transucer 4', is here disposed at an interval of only a few tenths of a millimeter from the resonator 1 which is to be corrected.

Because of the requisite short interval, both the microphone transducer 4' and winding 3 are subject to heavy wear as a consequence of the particles of material knocked out by laser bombardment. This means that frequent replacement of the winding and the expensive microphone transducer, is necessary. Corresponding conditions apply to the situation in which correction is performed by sand-blasting.

In Figure 2, a frequency measuring unit 3049 is shown schematically. An electrical winding 3 and a microphone 4 having a microphone transducer 4* are arranged ' behind- a detachable protective end plate 5 of a housing 9, the plate 5 being of electrically insulating material. Passing through this protective plate 5 are two core elements 6 of magnetic material (e.g. ferrite) which extend the magnetic iron circuit of an excitation winding 3 in such a way that once again a very small air-gap is left between resonator 1 and a core 11 of winding 3. To protect the microphone transducer 4', a cylindrical sleeve 7 is provided into which the microphone transducer 4' projects. The sleeve 7 is tapered at one end and terminates in a tube section 8 of correspondingly smaller diameter which is screwed into the sleeve 7 and projects through the protective plate 5. Section 8 is thus readily detachable from sleeve 7. The end of the tube section 8 is taken up to a point close to the resonator 1. The sleeve 7 cooperates with the tube section 8 to form a resonant column in which an air column vibrating at the frequency of the resonator forms, said air column being little affected by environmental noise. The microphone transducer 4' can therefore, without substantial impairment of the measurement conditions, be arranged at a vibrational antinode in the air column, which is located further away from the resonator 1. Because the protective plate 5, with the core elements 6 in position in it, is screwed on to housing 9, it can readily be replaced in the same way as the tube section 8 screwed on to the sleeve 7. 430 49 It is clear from Figures 3 and 4 how the sleeve 7 enclosing the microphone 4,-and the tube section 8, arc located between the arms of a U-shaped core 11 of the excitation winding 3 and between the core elements 6. The excitation winding 3 which is arranged laterally of sleeve 7 within the protective housing 9, can be displaced, by a screw 10, longitudinally of the housing 9 so that the winding core 11 abuts against the two core elements 6. A-screw 12 is used to lock the winding in position after it has been adjusted.

The sleeve 7 provided to protect the microphone 4 is tapered at that of its ends facing the resonator 1. By means of a tube section 8 screwed on to this end of the sleeve 7 and passing through a bore in the protective plate 5, connection with the resonator 1 is established. The microphetie 4 is housed in electrically insulated fashion in the protective housing 9, within a synthetic plastics material sleeve 13 which can be rotated about its own longitudinal axis, and can be displaced within said sleeve 13 in the direction of its own longitudinal axis, a clamping element 14 being provided to lock it in position as required. One end of the synthetic plastics material sleeve 13 carries a thread 15 on to which the sleeve 7 is screwed. Thus, by rotating the synthetic plastics material sleeve 13, the sleeve 7 can be displaced in the direction of its own longitudinal axis and the interval between the tube section 8 and the resonator 1 adjusted. - 7 049 An arm 16 prevents rotation of sleeve 7 during this adjustment.

The protective housing 9 is closed off at its sides by respective plates 17 so that the only wearing parts are the protective end plate 5 with the two core elements 6 and the tube section 8. These wearing parts can be manufactured quite simply and are easy to replace.

A major advantage of the system thus arises from the fact that microphone and electrical winding are effectively protected and that all components subject to wear are readily exchangeable. Moreover, these wearing parts can be replaced relatively cheaply to that the overall economy is high.

Also, the probability, that sand grains reflected from or particles of material knocked out of the resonator, will reach the microphone transducer is low. The tube element which experiences substantial wear, can be relatively cheap and be readily replaced.

Claims (11)

1. An electrical winding and microphone mounting, for receiving an electrical excitation winding and a microphone transducer/conprising: an elongaCe housing having a detachable protective end plate; a sleeve disposed within the housing for enclosing said microphone transducer one end of the sleeve extending through said end plate; two magnetic core elements extending through said end plate; and a magnetic core, for said winding displaceable within the housing and externally of said sleeve in such manner that it can be brought into contact with z said core elements.

2. A mounting as claimed in Claim 1 wherein said sleeve comprises two cylindrical portions of differing diameters connected together by means of a corresponding tapering tube section, that cylindrical portion having the smaller diameter being detachable from the tapering section and extending through said end plate.

3. A mounting as claimed in Claim 1 or 2, and which further comprises means for supporting the microphone in such manner that it can be displaced in the direction of the longitudinal axis of the sleeve and comprises means for locking the microphone transducer to prevent it from being thus displaced.

4. A mounting an claimed in any one of Claims 1 to 3 wherein said core elements arc of ferrite.

5. A mounting as claimed in any one of Claims 1 to 4 wherein said end plate is of electrically insulating material.

6. A.mounting as claimed in any one of Claims 1 to 5 when in operable combination with an electrical excitation winding and a microphone transducer.

7. A mounting as claimed in Claim 6 wherein'the microphone transducer is arranged at a vibrational antinode of that air column located within said sleeve.

8. A mounting as claimed in any one Of Claims 1 to 7 wherein there is provided support means for supporting a mechanical resonator adjacent said end plate.

9. A mounting as claimed in Claim 8 wherein a mechanical resonator is supported by said support means.

10. A mounting as claimed in Claim 8 or 9 wherein there is provided holding means for holding a sand blaster and/or a laser in such positions or position that they or it can adjust the resonant frequency of a mechanical resonator when it is supported by said support means.

11. A mounting as claimed in Claim 10 in operable combination with a sand blaster and/or a laser.