Electronic tachometer

Abstract

Abstract AN ELECTRONIC TACHOMETER SUITABLE FOR PRODUCING INDICATIONS OF ENGINE R.P.M BY CONNECTING TWO LEADS FROM THE TACHOMETER ACROSS A PAIR OF TERMINALS (E.G. IN THE IGNITION SYSTEM OF THE ENGINE) BETWEEN WHICH THERE IS GENERATED A SERISES OF VOLTAGE PULSE RECURRENT AT A RATE PROPORTIONAL TO ENGINE SPEED. A ZENER-DIODE CLAMPING CIRCUIT DERIVES, FROM THE ENGINE-SYNCHRONIZED VOLTAGE PULSES, A CORRESPONDING SERIES OR CONTROL PULSES HAVING PREDETERMINED FIXED AMPLITUDES AND APPLIES THEM TO THE BASE CIRCUIT OF A TRANSISTOR CONNECTED IN THE COMMON-EMITTER CIRCUIT CONFIGURATION. THE EMITTER LOAD FOR THE TRANSISTOR IS A CAPACITOR, WHICH IS CHARGED TO A PREDETERMINED VOLTAGE IN RESPONSE TO EACH ENGINESYNCHRONIZED PULSE. BETWEEN SUCH PULSES THE CAPACITOR IS DISCHARGED BY WAY OF A DIODE CONNECTED BETWEEN THE CAPACI- TOR AND THE BASE OF THE TRANSISTOR, SO THAT THE DISCHARGE PATH IS EFFECTIVELY OPENED DURING CHARGING BUT CLOSED DURING THE DISCHARGING INTERVAL. A CURRENT METER IS CONNECTED IN THE CHARGING PATH FOR THE CAPACITOR, AND PRODUCES A NEEDLE DEFLECTION PROPORTIONAL TO THE AVERAGE CURRENT THROUGH IT AND HENCE PROPORTIONAL TO THE RATE OF OPERATION OF THE ENGINE. TO CHANGE THE SCALE FACTOR OF THE METER, ONE OR MORE CAPACITORS MAY BE CONNECTED IN PARALLEL WITH THE ORIGINAL CAPACITOR WHEN LOWER RATES OF ENGINE OPERATION ARE TO BE INDICATED. A RECTIFIER IN THE INPUT LEAD ENABLES EASY CALIBRATION BY CONNECTION TO A POWER LINE.

Inventors

• 👤 Joel N Ashcraft

Bibliographic Details