ESTUARINE CURRENT METER CONTRACT
1953
Middleton, F. | Kerr, R.
The Y-type position Convectron which was used as a cantilever load detector was replaced by resistance wire strain gages. An 8.5-in.-diam disk and a 2-ft cantilever with 3/8- by 1/16-in. cross section were used in sensing the velocity. The strain produced at the fixed end of the cantilever by a current of 0.1 fps (about 30 x 10 to the minus 6th power in.) could be measured accurately with strain gages. To limit the deflection of the cantilever under high velocities, 3 cantilevers of different stiffnesses were utilized. A servo- balance system is being used instead of an amplifier-meter arrangement. Four gages are connected in series, at the end of the cantilever beam, to produce 1/2 of a Wheatstone bridge circuit. The remainder of the bridge circuit, including a Helipot, is contained in an aluminum box on the side of the assembly. The Helipot shaft extends through the mounting plate and is geared to the servo motor and to the revolution counter. The counter indicates the balance position of the servo system and therefore the deflection of the cantilever beam. A camera will be used to photograph this counter. A compass system will be used to indicate the direction of the current. The programmer will be controlled by a clock starting the equipment every half hour. When the programmer starts the meter, the crystal-controlled oscillator drives the transmitting transducer and the reference channel mixer at 1 mc. A hollow body of revolution with horizontal and vertical stabilizing fins will be used as a support for the instrument.
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