GB2386498A

GB2386498A - Alarm microphone with fault indication

Info

Publication number: GB2386498A
Application number: GB0304789A
Authority: GB
Inventors: Roland Bachmann
Original assignee: Sennheiser Electronic GmbH and Co KG
Current assignee: Sennheiser Electronic GmbH and Co KG
Priority date: 2002-03-11
Filing date: 2003-03-03
Publication date: 2003-09-17
Anticipated expiration: 2023-03-03
Also published as: AT414070B; GB2386498B; DE10210497A1; GB0304789D0; ATA2432003A

Abstract

A microphone comprises a first voice coil and a second coil coupled to a pilot tone generator so that a non-audible tone is emitted by the second coil, which induces a voltage at the pilot tone frequency in the voice coil. A detector at the microphone output activates an optical or acoustic indicator when a pilot tone frequency signal is not sensed to alert the user that the microphone is not functioning properly. The pilot tone generator receives supply voltage from the voice coil circuit, preferably from the phantom feed fed in by way of the microphone cable. Preferably the pilot tone is sinusoidal in the range 25 kHz to 50 kHz. The second coil may be the hum-bucking or compensation coil of a dynamic transducer.

Description

Microphone . The invention concerns a microphone, in particular what is

referred to as an alarm microphone.

There are microphones which are used in particular in the security 5 and safety sector, for example in relation to fire brigade services, police or monitoring and surveillance services (atomic power station and so forth), in regard to which it is absolutely essential to be sure that the microphone is also actually operative. In addition it is also necessary to guarantee that, in the event of the microphone being inoperative, that is indicated so that it is 0 possible to carry out a repair as quickly as possible or replace the microphone. DIN 0828 describes in particular such microphones which also have to be continuously monitored for alarm purposes.

Now, the object of the invention is to provide a simple solution for 15 such an alarm microphone which in the event of failure of the microphone also permits simple repair or simple replacement.

In accordance with the invention that object is attained by a microphone according to one of claims 1 and 2.

In the microphone according to the invention (first variant) the 20 microphone contains a pilot tone generator which receives its supply voltage by way of the phantom feed which is fed in by way of the microphone cable. That phantom feed is nowadays regularly also installed in mixing desks. It will be appreciated that the supply of the voltage can also be in the form of a voltage supply.

25 The pilot tone generator now generates a sine tone at a frequency outside the audible range, for example 25 kHz to 50 kHz, or a frequency

range thereabove. That pilot sine tone signal is applied to an air coil (second coil) which is disposed in the proximity of an oscillation or moving coil (first coil). In the case of microphones with a dynamic transducer a hum-bucking or compensation coil is generally installed therein in any case, 5 the hum-bucking coil being arranged in the proximity of the first moving coil and connected in opposite phase relationship with respect to the moving coil. Hum troubles are induced in both coils and as a result cancel each other out.

The microphone according to the invention does not involve hum 10 bucking and instead the pilot tone (sine) is put on to the former 'hum-

bucking coil'.

The signal of the pilot tone coil (compensation coil) is induced in the first moving coil and then a voltage is obtained at the microphone output, at the pilot tone frequency. As long as the signal can be detected at that 15 frequency at the microphone output, the microphone is still functioning.

The pilot tone detector provided in the microphone output is therefore provided with a signal display means (optical or acoustic display device) and the signal display means is activated if the pilot tone frequency can no longer be detected at the microphone output so that the personnel 20 who have to use the microphone according to the invention know immediately that the microphone has failed and they can then also quickly repair or replace it.

All elements for the alarm purpose, which are necessary for the microphone according to the invention, are disposed within the microphone 25 itself and therefore in the event of a possible failure the microphone according to the invention can be directly replaced immediately by another normal microphone.

The microphone according to the invention can be designed not only as a microphone with a dynamic transducer principle but also for 30 electrostatic microphones, the structure of which is then similar, in which case however the pilot tone signal is coupled in electroacoustically.

The Figure shows a block circuit diagram of the alarm microphone according to the invention with a first oscillation or moving coil and a

second coil (compensation coil), wherein both coils are coupled to each other on the air path. The compensation coil receives a sine tone from a pilot tone generator which in turn draws its supply voltage from the circuit of the first moving coil so that, in the event of failure of the supply voltage 5 of the alarm microphone according to the invention, pilot tone generation also fails at the same time and then the absence of the induced pilot tone can be detected at the microphone output. The presence of the pilot tone can be established by way of a pilot tone detector as a display means and, in the event that the pilot tone is no longer detected, suitable signal means, O for example an audible tone by way of a loudspeaker, are activated, so that the personnel who are reliant on proper operability of the alarm microphone can immediately effect replacement of the microphone, but they know at any event that this microphone cannot be further used because it cannot guarantee a sure and certain announcement, because of 15 its inoperability.

Claims

l CLAIMS

1. A microphone comprising a first moving coil and a second coil which is coupled thereto and which is coupled to a pilot tone generator which generates a pilot tone which is emitted in the non-audible range by way of the second coil, wherein the first coil is so excited by the signal of the second coil that a voltage at the pilot tone frequency occurs in the circuit of the first moving coil, there are also provided display means which indicate whether a signal at the pilot tone frequency is fed in the circuit of the first moving coil, wherein the pilot tone generator receives a supply voltage from the circuit of the first moving coli.

2. A microphone comprising a first circuit within which is arranged a first coupling member, wherein the supply voltage of the microphone is fed in within the first circuit, wherein there is provided a second coupling member which is coupled to the first coupling member and the second coupling member is fed with a first signal from a signal generator which receives its supply voltage from the first circuit, the first signal is coupled by coupling of both coupling elements into the first circuit and occurs at the output of the circuit and there are provided display means which display the presence of the signa! which is fed into the circuit.