A Tachomotor uses a servo amplifier with a speed processor The speed processor circuit get a differential input and outputs a inphase or out of phase voltage to the servo amplifier My question is what causes or controls the tachomotor speed? 1.) is it the phase degree? 2.) Is it the amplitude? 3.) Is it the differential voltage? The larger the differential voltage , the faster the tachomotor speed is? The small the differential voltage , the slower the tachomoter speed is?