The universal device of the motorist. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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The universal device of the motorist. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Automobile. Electronic devices

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The figure shows a schematic diagram of a universal measuring device for a motorist. Depending on the position of the type of operation switch, they can check the voltage of the built-in autonomous power source, the serviceability of electrolytic capacitors, the voltage of batteries, the ignition timing, the crankshaft speed of four-cylinder and six-cylinder engines.

In addition, at any position of the type of operation switch S1, it is possible to check low-resistance electrical circuits.

(click to enlarge)

As can be seen from the figure, to improve the stability and accuracy of the measurement results, the electronic part of the device is powered by a galvanic battery G1 through a voltage stabilizer on transistors V12, V13. A parametric diode stabilizer (V14 - V16) is used as a reference voltage source. The value of the stabilized voltage of 3,5 V can be smoothly adjusted with a variable resistor R33. When measuring constant voltages (switch S1 in position 1 or 3), a milliammeter together with resistors R25 and R20, R29 forms a constant voltage voltmeter. When checking the health of external circuits, instead of a milliammeter, the indicator is the V11 LED, which is connected in series with the G1 battery through the R34 resistor. An open circuit under test is connected to the "Circuit" and "0" terminals.

The principle of measuring the ignition timing and engine speed is to measure the time characteristics of the pulse voltage acting on the terminals of the engine ignition system interrupter. So, the frequency of appearance of pulses is directly proportional to the speed of the engine crankshaft and inversely proportional to the number of cylinders, and the angle of rotation of the shaft at which the chopper is in the closed state is directly proportional to the ratio of the pulse duration to its repetition period.

When connecting the breaker contacts to the terminals "To the breaker" and "0" (fourth position S1), the impulse voltage is filtered from additional high-frequency interference by a low-pass filter (R1, R2, C1, C2). limited by a diode limiter (V1 - V3) and then goes to the input of the Schmitt trigger (V4 - V5). In this case, the duration of the output pulses of the trigger corresponds quite accurately to the time of rotation of the motor shaft when the chopper contacts are closed, and the pulse repetition period corresponds to the time between the occurrence of a spark in each cylinder. Since the amplitude of the pulses at the output of the trigger is constant, the average value of the current at the output of the emitter follower (V7) will be directly proportional to the angle of rotation of the shaft at which the breaker contacts are closed.

When measuring the crankshaft speed of a four-cylinder engine (position 5 of switch S1), a single vibrator (V8, V9) is used, which is triggered by pulses from the output of the Schmitt trigger through the differentiating circuit C3R10 V7R11. The output pulses of a single vibrator are stable in amplitude and duration, and their repetition period is inversely proportional to the rotation speed. Therefore, the average current passing through the milliammeter and resistors R22, R31 will be directly proportional to the number of revolutions per minute. To measure the speed of a six-cylinder engine, switch S1 must be set to position 6 ..

The scale of the milliammeter is calibrated directly in the measured values: direct voltage - 0 ... 15 V; angle of rotation - 0... 100°: speed - 0... 3000 rpm. The milliammeter scale is linear for all measurements. To set up the device, it is necessary to apply an alternating voltage of 24 V to the "To the breaker" terminals. For this, you can use a suitable step-down transformer. mains powered.

Trimmer resistor R30 sets the milliammeter needle at 45 ° on the angle scale. Then, with resistor R31 in position 5 of switch S1, an arrow is set on the engine speed scale at 1500 for a four-cylinder engine and 1000 for a six-cylinder engine.

Checking the performance (serviceability) of capacitors is carried out according to the readings of a milliammeter when the capacitor is connected to sockets "C". If the capacitor is good. then the arrow of the device will first deviate and then slowly return to its original position.

From the editor. Transistors V4, V5, V9, V13 can be types KT312B. KT315B; V6, V8 - KT608B; V10 - MP114; -V12 - GT403V; LED V11 - AL102A, the rest are diodes of the KD521 type.

Literature

"Antenna" (Brazil), 1978, No. 1. No. 2
Radio No. 1, 1979, c.61

Publication: N. Bolshakov, rf.atnn.ru

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