Tachometer generator

The shaft seals preventing gas leaks, the brush-contact unit and the electric drive tachometer generator attachment unit have been also modified. Owing to the actions taken the failures of the pumps causing the abnormal operating conditions have been avoided since the 15th cycle (since December, 1985). 

Over a total period of power plant operation 2 failures of the pumps have occurred both leading to the power reduction of the plant with a loop disconnection, i.e. in 1980 the motor and tachometer generator shaft coupling failed and in 1985 the electric motor brush unit failed. 

Transducer - dii-s9r (1924) n. A device that transforms the value of a physical variable into an electrical signal, usually voltage or current. Examples are thermocouple, pressure transducer, linear variable differential transformer (a motion transducer), tachometer generator, and force cell. 

A tachometer generator is, as the name implies, a small AC or DC generator whose output voltage is directly proportional to the angular velocity of its rotor, which is driven by the controlled output shaft. Tachometer generators are available for shaft speeds of 5000 r/min, or greater, but the output may be nonlinear and there may be an unacceptable output voltage ripple at low speeds. 

AC tachometer generators are less expensive and easier to maintain than DC tachometer generators, but DC tachometer generators are directly compatible with analog controllers and the polarity of the output is a direct indication of the direction of rotation. The output of an AC tachometer generator must be demodulated (i.e., rectified and filtered), and the demodulator must be phase sensitive in order to indicate direction of rotation. 

Olson and Alway [1] described a method to record the first-order derivative. The authors used a recorder with a tachometer generator, coupled with the driving gear of the y-axis, and a lock-in amplifier followed by a filter. For wavelength scanning, the rate of movement of the recorder in the ordinate direction is proportional to the first derivative. 

Klein and Dratz [2] produced a 60-Hz signal with a tachometer generator, the amplitude of which was proportional to the ordinate component amplified with a lock-in amplifier, the signal was rectified, smoothed, and filtered. Only the first derivative could be generated with this method. 

Velocity encoders Both velocity (speed) of solid objects and liquid flow rates can be measured. One way is to use an optical encoder and measure time between position changes to give the differential of position, i.e., velocity. Tachometers use an AC or DC generator to give a voltage proportional to angular velocity. Flow rate transducers can use the differential pressure in a pipe to measure a flow rate if pipe diameters are known. Alternatively, a small turbine blade can be inserted into the flow and its rotation velocity used to measure flow rate. 

Standard accessories should be available along with the DG Set instrumentation for engine/generator tachometer, engine temperature, indication for electrical power drawn in kilowatts, voltage, ammeter, KWH meter, frequency meter, start up batteries, and battery charger. 

Another simple method is to use an electrical tachometer. The small DC generator is coupled to the rotating shaft. The output voltage of the generator is fed to a voltmeter. The generator output voltage is directly proportional to the rotational speed of the shaft. Thus, the measured voltage can be directly converted into rpm. 

Phase-lock servo A digital control system in which the output of an optical tachometer is compared to a reference square wave to generate a system error signal proportional to both shaft velocity and position. 

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