MULTIMETER MOTORIST | MODEL CONSTRUCTION

Owners of digital multimeters offer to acquire a homemade console that will allow you to convert the popular M-830 M-832 and their counterparts in the universal devices, capable to become a reliable assistant and service vehicles. In particular, it will be possible (along with the already mastered many of the health check of the relay-regulator, a current measurement battery power and other electrical parameters on-Board network) to quickly estimate the important performance of the ignition system carburetor of the engine, as the crankshaft rotation and angle, open (easily converted into a corner closed) status breaker contacts.

To work with the prefix multimeter set mode voltmeter with scale 2000 mV. In “N” position of the switch SA1, the instrument measures the pulse frequency of the primary winding of the ignition coil. The feature used here is the technical solution is such that each opening of the breaker contacts, the capacitor C1 is charged through the circuit R3R5VD3R6 to a voltage stabilizing Zener diode VD1, and each circuit is discharged through the resistors R5, R3, coil L1, resistor R1, closed contacts of the interrupter and diode VD2. But that’s not all.

The voltage drop across the resistor R6 in each cycle of charging the capacitor C1 charges the capacitance C2 to a voltage proportional to the frequency of opening (closing) of the breaker contacts.

Indeed, the frequency N of rotation of the crankshaft, measured in rpm, and the frequency f of the opening operation of the contact breaker (unit is Hz) are linked by the dependence N = 120f/z, where z is the number of cylinders of the engine. That is, the reading device is directly proportional to the frequency of disconnection of contacts of the breaker, and hence the rotational speed of the crankshaft. Coil L1 prevents the penetration into the device high-frequency oscillation current of self-induction of the primary winding of the ignition coil, which increases the measurement accuracy.

The printed electric circuit and a printed circuit Board, a homemade console to the digital multimeter, transforming it into a universal device driver

Printed electric circuit and a printed circuit Board, a homemade console to the digital multimeter, transforming it into a universal device driver

In the situation “(Fi)” switch SA1, the instrument measures the angle of the open state of the breaker contacts. More precisely the angle of rotation Cam of the circuit breaker from the moment of disconnection of contacts until subsequent circuit. But in the instructions for adjustment of the interrupter is usually set as a parameter (the angle of the closed state of the contacts). So the recalculation, which is based on the ratio of a + “(Fi)”= 360°/z, where angles are expressed in degrees, a z — number of cylinders of the engine. For 4-cylinder engine a = 90° — (Fi).

By opening and closing the breaker contacts to the input of the device receives the rectangular pulses from the high voltage emissions on the “plus” differential

(at the time of formation of a spark). Zener diode VD1 limits their amplitude.

Leaking chain R2R4R6, the pulse current generates on the resistor R6 a voltage drop, which is averaged by capacitor C2. The resulting Ucp is connected directly proportional almost linear dependence with the value of the angle (Phi) of the circuit breaker. It is fed to a digital voltmeter.

The console is mounted on the circuit Board, somewhat resembling the letter p, Material is 1,5 mm foil glass fiber, in which the depth-coprostasia insulating layer slotted groove of the appropriate shape. The use of two pairs of resistors R2, R4 and R3, R5 dictated only by considerations of convenience of their accurate collection. The same is possible to replace the fixed resistors R4 and R5 trimmer, but larger (by 10-20%) than on the circuit diagram, par. The Capacitor C1 — K73-9, C2 — C50-12. The switch SA1 is acceptable any small toggle switch.

Coil L1 industrial manufacture (for example, taken from the old bell telephone system). But it’ll do, and homemade, wound on a cardboard frame cross-section 12×8 mm, having the cheeks (the size of each — 21×21 mm, the distance between them was 26 mm). In any case, L1 should be 10 000 turns of wire sew-0,08. The resistance of a coil of the DC — about 1700 Ohms.

Before establishing a console switch SA1 is set to “N”. Connect the output with the multimeter included as a voltmeter with a scale of “mV 2000”. Feeding the input of the prefix variable voltage (12-14 V, 50 Hz), the selection of resistors R3 and R5 are seeking intizarova-tion device 1500 mV. Then switch the switch SA1 in position “(Fi)”. The input consoles already served a constant voltage 12-14 In and pick up the resistors R2 and R4 to display a multimeter 360°/z, mV (for 4-cylinder engine — 90 mV). Thus convinced that the reading device in each dimension is numerically equal to the measured value

Now the device can be considered tuned. If in the situation “(Fi)” switch, the instrument shows, for example, 35 mV, there is no doubt — angle open state of the breaker contacts is equal to 35°. Then, the calculated parameter a (angle closed contacts) for 4-TSI-linkagogo engine in this case is 90°-35° = 55°.

N. HERZEN, Berezniki, Perm region.

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