From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Technical specification sheet for the Noise Meter Type TF500 and its accessories.
| Identifier | ExFiles\Box 138\1\ scan0310 | |
| Date | 17th August 1938 guessed | |
| NOISE METER. Type TF{T. Fisher}500. DESCRIPTION The instrument measures noise levels in phons over practically the whole range encountered in industry and technology. The measurement is objective, so that there is no possibility of error due to the personal idiosyncrasies of the operator, but phones may be plugged in to listen to the noise being measured. The Meter covers a very wide range of applications, being suitable for the measurement both of steady and impulsive noises. Particular care has been taken to ensure an accurate evaluation of intermittent sounds. Some examples of the application of the Meter are given. APPLICATION OF THE NOISE METER Domestic Appliances. Sewing machines, vacuum cleaners, refrigerators, fans, etc. Transport. Noise from all types of vehicles, including the exhaust noises of internal combustion engines. Industrial. "Steady" sounds, such as transformer hum, noise from motors and alternators from shafting, lathes, milling machines and saws. "Impulsive" sounds, such as noise from rivetters, pneumatic drills, belting, etc. Offices. Persistent sounds, such as noise in general offices, lifts, etc. Impulsive sounds, such as noise from typewriters computing machines, etc. Technological. Determination of the effects of sound proofing and absorbing materials. ACCESSORIES. VIBRATION PICK-UP UNIT This unit replaces the microphone of the Noise Meter for the investigation of mechanical vibration in solid materials. Apart from the simple measurement of vibration, the use of the Vibration Pick-Up makes it possible to locate the source of noises transmitted through the framework of buildings, or to separate a particular mechanically produced noise from the general background. The output of the Vibration Pick-Up is large; a small attenuator unit is available, reducing the output to a level suitable for application to the Noise Meter. ADJUSTABLE TUNING UNIT. This unit can be connected by a plug link to the Noise Meter, and makes the indication of the Meter selective, so that a noise of a particular frequency can be suppressed or emphasised. An example of the application of this unit is the investigation of gear-box noise in motor vehicles, this noise being emphasised by tuning the Unit to its frequency; the exhaust and other noises are largely suppressed. The Unit is completely described on a separate sheet of this catalogue viz.: Page COM. D-7. NOISE METER. Type TF{T. Fisher}500 DESIGN The Noise Meter, Type TF{T. Fisher}500 comprises a microphone, amplifier and calibrated indicator meter. The microphone is of the robust piezo-electric type, having a high sensitivity and flat frequency characteristic. It is very nearly non-directional. Following the microphone is a valve amplifier, the coupling circuits of which include weighting networks giving the instrument three alternative frequency characteristics. An external weighting network can also be used. A crest valve voltmeter is used to operate the indicator meter, the circuit arrangement being chosen to ensure an accurate assessment of intermittent noises. Two attenuators are incorporated in the amplifier circuit, one has six 10 dB{Donald Bastow - Suspensions} steps and the other ten 1 dB{Donald Bastow - Suspensions} steps. These are calibrated to read directly in phons when the meter reading is set to a standard deflection. The power supply is from batteries which are housed inside the instrument in a separate compartment. The Meter gives a reading which is very close to the level of an individual impulse, and which is not seriously affected by the frequency at which the impulses occur; it is, however, equally suitable for measuring steady sounds. Spurious mechanical and electrical pick-up is negligible in the working range. The instrument is housed in a light but rigid metal case and provided with a detachable cover. VIBRATION PICK-UP, Type TF{T. Fisher}481. This accessory comprises a piezo-electric crystal mounted in a small unit fitted with a detachable probe. The crystal element is mounted in its housing at three points only. When Vibration is transmitted by the probe to the housing, the inertia of the crystal causes it to bend, and a voltage is developed. This type of pick-up is very robust compared with those in which the probe is in mechanical contact with the crystal. ADJUSTABLE TUNING UNIT, Type TF{T. Fisher}456. The Unit comprises a tuned circuit including four inductances and a decade condenser. Switching is included so that either a parallel or series tuned circuit may be used. The inductance values are selected so that the circuit may be tuned over nearly the whole audio frequency range. The resonant frequency is made continuously variable by the inclusion of a variable condenser bridging the smallest steps of the decade dials. High stability condensers are employed, and the coils have a satisfactorily low effective resistance over their working ranges. FEATURES The mechanical arrangement of the instrument is designed for maximum convenience in operation. The microphone is mounted on a retractable slide so that it is completely enclosed when not in use. It may also be detached and used on long leads for remote indication. Weighting networks incorporated in the amplifier provide frequency characteristics which correspond with the 40 and 70 phon contours after Fletcher and Munson. A flat characteristic can also be selected. [Text from circuit diagram] MIC, VIBRATION PICK-UP, ATTENUATOR, WEIGHTING NETWORK, VALVE VOLTMETER, PHONES, ADJUSTABLE TUNING UNIT, TYPE T.F. 456, +1 DB{Donald Bastow - Suspensions} STEPS, +10 DB{Donald Bastow - Suspensions} STEPS. | ||