Universal probe-indicator. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Universal probe-indicator. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur

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When repairing and installing electrical wiring, it often becomes necessary to measure the mains voltage, determine the phase and neutral wires, and “ring out” the circuits for breaks or short circuits. An indicator - a phase indicator will not always be at hand, and the use of an avometer for these purposes is inconvenient due to the need to switch its operating modes.

The way out is to build the proposed device (see figure), consisting of an LED voltage scale, a control unit for the conductivity of electrical circuits ("continuity"), an AC voltage indicator and a phase wire indicator.

Universal probe-indicator

The LED scale is made on LEDs HL1-HL5 and resistors R2-R6, shunting the LEDs, and has five gradations of standard voltages. The operation of the scale is based on the ignition of a certain LED when the voltage across its shunt resistor is about 1.7 V. The VD3HL7 circuit serves to indicate the alternating voltage on the probe probes, as well as the reverse, compared to that indicated in the diagram, the polarity of the constant voltage on them.

The conductivity control unit consists of a storage capacitor C1 of a relatively large capacity, a VD1VD2 charging circuit and an R7HL6 indication circuit. When the probes are connected to a constant voltage source for a few seconds, the capacitor is charged through the diode VD2 from the voltage falling on the zener diode VD1. The probe is ready to "diagnose" the circuits. If the probes touch a working circuit, the capacitor discharge current will flow through it, resistor R1, LED HL6 and resistor R7. The LED will light up. As the capacitor discharges, the brightness of the LED will decrease. From one charge of the capacitor it is possible to make 8-12 checks.

The phase wire indicator is assembled according to the relaxation generator circuit. Touching the E1 sensor with your finger, connect any of the probes to the phase wire. The voltage rectified by the diodes VD4, VD5 charges the capacitor C2. When the voltage on it reaches a certain value, the HL8 neon lamp will flash. The capacitor is discharged through it, the process is repeated.

LEDs - indicated on the diagram or their foreign counterparts, for example, L-63IT It is desirable that they be close in parameters, and HL6 - with maximum light output at low current. Instead of the zener diode indicated on the diagram, it can be KS156A or D814B. Capacitor C1 - K50-35 or its foreign analogue (say, manufactured by Jamicon). Resistors R2-R9 - MLT of the corresponding power R1 - PEV, C5-37 with a power of at least 8 W (in extreme cases, you can install six series-connected MLT-2 resistors with a resistance of 1,3 kOhm).

The device is mounted in two cases made of dielectric material in the form of probes of the same size. Resistor R1 is placed in one probe, the rest of the device is in the other. The probes have pointed tips with a diameter of 3 and a length of 20 mm. The probes are interconnected by a flexible wire in double insulation, designed for a voltage of at least 380 V.

When adjusting the probe and working with it, precautions must be taken, since parts of the probe may be under high voltage!

If all parts are in good condition and mounted correctly, the probe can be used immediately. True, you may have to choose a resistor R7 in order to achieve a clear burning of the HL6 LED (when connected between the probes of a resistor with a resistance of 300 ... 400 Ohms). But its resistance should not be significantly reduced, since this will cause a rapid discharge of the storage capacitor. And in order to achieve clearly distinguishable flashes of a neon lamp, it is enough to choose a resistor R8.

Author: V.Sorokoumov, Sergiev Posad, Moscow region

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