Voltage frequency meter of synchronous electrical machine

A voltage frequency meter of a synchronous electrical machine, comprising:

• a voltage converter having two outputs;
• a first input voltage measuring channel and a second input voltage measuring channel, their inputs being connected to said outputs of said voltage converter;
• a voltage follower;
• outputs of said frequency measuring channels being connected to an input of the voltage follower;
• a power source;
• a voltage comparator having a first input connected to an output of said voltage follower, and a second input connected to said power source;
• an adjusting resistor having a movable contact;
• each of said input voltage frequency measuring channels containing:
• a zero-crossing detector intended to convert sinusoidal voltage to square-wave voltage;
• two transistor switches, the first having its input connected to an output of said zero-crossing detector;
• a differentiating circuit connected to an input of said second transistor switch;
• a charging resistor;
• an isolating diode;
• a decoupling diode;
• a storage capacitor;
• an output of the first transistor switch being connected to said power source via said charging resistor and via said isolating diode to the output of said second transistor switch and to said storage capacitor;
• said storage capacitor being connected via said decoupling diode to the input of said voltage follower;
• the input of said second transistor switch of said first frequency measuring channel being connected via said differentiating circuit of said first channel to the output of said zero-crossing detector of said second frequency measuring channel;
• the input of said second transistor switch of said second frequency measuring channel being connected via said differentiating circuit of that frequency measuring channel to the output of said zero-crossing detector of said first frequency measuring channel;
• said power source being connected to said adjusting resistor whereof the movable contact is connected to the output of said second transistor switch of each of said frequency measuring channels.