Anti-hunting system for valve operator circuit

A pulse rate comparison system for comparing two input pulse trains to control a stepping motor and having means for preventing hunting action, and comprising:

• a. a J-K flip-flop circuit, said J-K flip-flop comprising,
• i. a flip-flop circuit with a set terminal, a reset terminal and a clock terminal as input terminals and Q and Q output terminals,
• ii. a first AND gate having one input terminal designated as the J input terminal and a second input terminal connected to the Q output terminal, the output of said first AND gate being connected to the set input terminal of the flip-flop circuit, and
• iii. a second AND gate having one input terminal designated as the K input terminal and a second input terminal connected to the Q output terminal, the output of said second AND gate being connected to the reset input terminal of the flip-flop circuit;
• b. means for applying one of two input pulse trains to be compared to the J input terminal of the J-K flip-flop circuit;
• c. means for applying the remaining or second pulse train to the K input terminal of the J-K flip-flop circuit;
• d. means for combining the two input pulse trains to form a third pulse train having an absolute time relationship with the input pulse trains;
• e. means for applying the third pulse train to the clock pulse terminal of the J-K flip-flop circuit;
• and
• f. means, responsive to the state of the input and output terminals of the J-K flip-flop circuit, for controlling the energizing of the stepping motor so that the motor is moved into the correct position without hunting, whereby a control pulse for energizing the stepping motor is produced only when a pulse is received by either the J or K input terminals of the J-K flip-flop circuit which does not change the state of the output of the J-K flip-flop circuit.