GB179566A - Improvements in or relating to microphones - Google Patents

Abstract

179,566. Gardner, J. Oct. 29, 1920. Vibration, indicating.-Relates to microphones for use in detecting faults in connection with moving mechanical parts &c. by responding to vibrations &c. therein, and consists in adapting the microphone to suit the different parts of the detecting system so as to obtain in a telephone, wind indicator or other receiver a faithful reproduction of the noises, knocks, vibrations or other disturbances set up. A suitable microphone compries a body or casing 4 adapted to be rigidly secured to a bearing, guide, or the like 8 and of such proportions as to provide a relatively massive metallic connection of large sectional area therebetween; an electrode 9 mounted in the body or casing and disposed as near as possible to or in alignment with the connection between the body and the bearing; and a second electrode 10 carried by a member 11 detachably secured to the body or casing so as to be readily removable or interchangeable. The electrode 9 is in electrical contact with or insulated from the casing 4 according as the casing is or is not comprised in the electrical circuit, and is preferably formed with a flat face of carbon or other non-oxidizable material. The electrode 10 is carried by and insulated from a bridge 11 which is secured at its ends to the rim of the casing. When used with normally-quiet bearings, the bridge 11 is made thin in the manner of a diaphragm and may be of reed, strip, circular, or other form, the front electrode 10 being of relatively great mass and made, for example, of brass electroplated with gold or platinum. In this case the terminals 9, 10 move relatively to one another in the ordinary microphonic manner. When used in connection with normally noisy bearings, the bridge 11 is made so thick that the distance between the electrodes remains substantially uniform, the microphonic effects, due to the vibrations transmitted by way of the casing 4, being obained mainly or solely from the variation in contact between the particles of the variable-resistance material contained in the cavity 13. The casing may be provided with a water and oil excluding cover 18. Instead of being directly attached, the casing may be secured to the bearing through the medium of a rigid right-angled or other bracket. A number of such microphones may be fitted to a bearing and provided with switching means so that any one may be separately connected to receiving and indicating instruments, the casings being all connected in series with a common return wire. In some cases, the bearings and framework of the machinery may form part of the return path. In addition to ordinary bearings, the microphone may be fitted to the cylinders of reciprocating pumps, or to the cylinders of internal-combustion engines in order to indicate pre-ignition.