DC motor reversible speed regulation circuit that changes excitation direction

Reversible speed regulation of a DC motor can be achieved by changing the direction of the excitation current or by changing the direction of the armature current
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    The circuit is shown in Figure 16-87. It is suitable for reversible speed regulation of small and medium-power DC motors , especially in situations where starting is frequent and reversal is infrequent. This circuit can start directly at full speed without causing overcurrent.     Adjust the potentiometer RPi to change the voltage negative feedback amount; adjust RP3 and RP2 to change the current cutoff negative feedback intensity ; adjust the master potentiometer RR to change the motor speed.