Object StatementPortable tachometer, Frahm vibrating-reed type, aluminium / steel / glass, made by Biddle Instruments, Philadelphia, Pennsylvania, United States of America, 1960-1990, used at Caltex Lubricating Oil Refinery, Kurnell, New South Wales, Australia, 1960-2011
Physical DescriptionThe tachometer consists of a grey cast aluminium box containing an array of tuned steel reeds which differ in length and thus in natural vibration frequency. Two linear scales sit on the top face of the box, alongside the square white tops of the reeds and under a flat glass cover. When the device is held against the casing of a vibrating machine, the reed that matches its vibration frequency will be observed to vibrate much more than the others, as it resonates with the machine. The frequency, in hundreds of revolutions per minute, can be read from one of the scales. The top scale runs from 2000 to 3500 revolutions per minute (rpm) and the lower scale from 3500 to 5000 rpm. Two groups of five raised lines run down the long sides of the box to provide grip, while the shorter sides and base are plain.
MarksAbove the scales: RESONANT REED FRAHM TACHOMETER. Each letter of the name FRAHM is enclosed in a box, and there are short horizontal lines above and below the R and H, and two horizontal lines above and below the A; all these elements form a logo that suggests vibrating reeds. Below the scales: BIDDLE INSTRUMENTS X100 RPM MADE IN USA. Above the lower scale: CAT. 312236 / PAT. NO. 188,345.