Improved probe 1-400 volts. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Improved probe 1-400 volts. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Indicators, detectors, metal detectors

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A primitive "control" - an electric cartridge with two wires and a lamp - is far from the best device for "ringing" electrical circuits. Industrially produced testers and avometers are also, as they say, not a gift, especially when you have to deal with modern technology, and they are not cheap. So electricians have to create indicator probes themselves - universal, compact and reliable.

Having made this sampler for himself, developed, by the way, by a talented representative of the rural hinterland, at first he could not get enough of it. The device is indeed a reliable assistant to the fitter, allowing not only to check electrical circuits, but also individual elements - diodes, transistors, capacitors, resistors. Assembled in the body of a toy gun and equipped with probes, it also makes it possible to control AC and DC voltages from 1 to 400 V, detect the phase and "neutral" wires of the network, and evaluate the insulation resistance of electrical equipment.

However, over time, there has been a discrepancy between the real capabilities of the probe-indicator and the requirements that the ever more complex electrical and radio engineering imposes on such devices. In particular, the complexity of detecting voltage in DC circuits and finding out whether the extinguished signal LED indicates a de-energized wire line or a short circuit has ceased to suit. Therefore, the device had to be upgraded. Minimal changes have been made (parts HL2, HL3, R5 and section "a" on the circuit board), but the universal indicator probe is now back in business.

As before, the device is based on a DC amplifier based on transistors VT1 - VT2, the load of which is the HL1 LED. Resistors R1 and R3 limit Ib semiconductor triodes. Capacitor C1 creates a negative feedback circuit for alternating current, excluding false indication from external pickups. Resistor R4 in the VT2 base circuit is used to set the required resistance measurement limit. Resistor R2 limits Imeas when the probe operates in AC and DC circuits. Diode VD1 performs the function of a half-wave rectifier. LEDs HL2 and HL3 are polarity indicators, the current through which limits the resistor R5.

Improved probe 1-400 volts
Circuit Diagram, Circuit Board Topology, and Redesigned Probe Layout

In the initial state, the transistors are closed, and the HL1 indicator is off. But if the probes are connected to each other or connected to a de-energized working circuit with Rc not more than 500 kOhm, then HL1 ignites. The brightness of its glow is inversely proportional to the resistance of the circuit under test.

When the probe is connected to an alternating current circuit, the positive half-waves open the transistors, and the HL1 LED lights up. Additional indicators HL2 and HL3 are also lit at the input of the device. If the voltage is constant, then HL1 and HL3 will light up when there is a “plus” on the X2 probe (with a different voltage polarity in the circuit under test, they will go out, but the HL2 LED will light up).

As when working with the device before modernization, the serviceability of diodes and transistors is checked by comparing pn junctions. The absence of glow indicates a break, but if NI burns constantly, then there is a breakdown in the test junction.

When a healthy capacitor is connected to the probe, the HL1 LED flashes and then goes out. The brightness and duration of the flash depend on the tested electrical capacity. When the capacitor is broken or has a large leak, the indicator light is on constantly.

"Phase" is determined as follows: the X1 probe is taken in hand, and the X2 probe touches the wire under study. If the HL1 LED is on, then the "phase", as they say, is obvious.

The methods of other checks have not changed, but it is still more convenient and faster to work with a modernized probe-indicator than before, because three LED indicators act as informants.

Author: V.Tokar

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Comments on the article:

Rumyantsev V M
As a developer of the device, I can say that for a normal indication of the mains phase, the capacitance C1 must be reduced to 0,01 μF, and with the rating indicated on the diagram, the LED will only emit a short flash. In this circuit, R3 must be reduced to 100 ohms.

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