Universal probes-indicators. Encyclopedia of radio electronics and electrical engineering

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With the help of a probe, you can check the presence of voltage in the controlled circuit, determine its type (constant or variable), and also carry out a “diagnostic check” of the circuits for serviceability. The scheme of the device is shown in fig. 1 LED HL2 indicates the presence at the input (plugs XP1 and XP2) of a constant voltage of a certain polarity. If a positive voltage is supplied to the XP1 plug, and a negative voltage is supplied to the XP2 plug, current flows through the current-limiting resistor R2, the VD2 protective diode, the VD3 zener diode and the HL2 LED, so the HL2 LED will shine. Moreover, the brightness of its glow depends on the input voltage. If the polarity of the input voltage is reversed, it will not shine.

Fig. 1

The HL1 LED indicates the presence of AC voltage at the input of the device. It is connected through a current-limiting capacitor C1 and a resistor R3, the VD1 diode protects this LED from the negative half-wave of the alternating voltage. Simultaneously with the HL1 LED, HL2 will also light up. Resistor R1 serves to discharge the capacitor C1. The minimum displayed voltage is 8 V.

A high-capacity ionistor C2 is used as a source of constant voltage for the "dialing" mode of the connecting wires. Before testing, you need to charge it. To do this, the device is connected to a 220 V network for about fifteen minutes. The ionistor is charged through the elements R2, VD2, HL2, the voltage on it is limited by the zener diode VD3. After that, the input of the device is connected to the circuit under test and the SB1 button is pressed. If the wire is good, through it, the contacts of this button, the HL3 LED, the resistors R4, R5 and the FU1 fusible insert, current will flow and the HL3 LED will light up, signaling this. The energy reserve in the ionistor is sufficient for the continuous glow of this LED for about 20 minutes.

The limiting diode VD4 (limiting voltage does not exceed 10,5 V), together with the fusible link FU1, protects the ionistor from high voltage if the SB1 button is accidentally pressed when monitoring the input voltage or charging the ionistor. The fusible link will burn out and will need to be replaced.

The device uses resistors MYAT, C2-23, capacitor C1 - K73-17v, diodes 1 N4007 can be replaced with diodes 1 N4004, 1 N4005, 1N4006, zener diode 1 N4733 - with 1N5338B. All parts are mounted on a breadboard circuit board using wired wiring.

Another probe in the form of a probe is assembled on LEDs and, in addition to "continuity" of the circuits, allows you to determine the type of voltage (DC or AC) and approximately estimate its value in the range from 12 to 380 V. The author of this device is A. GONCHAR from the city of Rudny, Kustanai Region . Kazakhstan. By the nature of his activity, he often has to monitor the performance and repair various devices where different values ​​(36, 100, 220 and 380 V) are used for direct and alternating voltages. To test such circuits, the proposed probe is very convenient, since it is not required to switch at different controlled voltages. When developing this device, a probe was taken as a basis, the description of which was published in Radio No. 4, 2003, p. 57 (Sorokoumov V. "Universal indicator probe"). In order to expand the functionality, it has been finalized.

Fig. 2

The scheme of the upgraded probe is shown in fig. 2. It contains a quenching resistor R1, a scale of two-color LEDs HL1-HL5, a storage capacitor C1 and a phase wire indicator on a neon lamp HL7. The device can operate in three modes: voltage indicator, phase wire indicator and "continuity" - an indicator of the conductivity of the electrical circuit.

To indicate the voltage, the input of the device - the XP1 pin inserted into the XS2 socket, and the XS1 socket (using a flexible insulated wire) is connected to the controlled points. Depending on the potential difference of these points, a different current flows through the resistors R1-R6 and the zener diode VD1. With an increase in the input voltage, the current also increases, which leads to an increase in the voltage across the resistors R2-R6. The HL1-HL5 LEDs light up in turn, signaling the value of the input voltage. The resistors R2-R6 are selected so that at a voltage of 12 V or more, the HL5 LED lights up, 36 V or more - HL4, 127 V or more - HL3, 220 V or more - HL2 and 380 V and more - HL1.

Depending on the polarity of the input voltage, the color of the glow will be different. If on the XP1 pin plus, relative to the XS1 socket, the LEDs are lit in red, if the minus is green. With an alternating input voltage, the color of the glow is yellow. It should be noted that with an alternating or negative input voltage, the HL6 LED may also light up.

In the mode of the phase wire indicator in the network, any of the inputs (XP1 or XS2) is connected to the controlled circuit and the sensor E1 is touched with a finger. The neon indicator lamp will light up if this circuit is connected to the live wire.

To use the device for "diagnosing" circuits, you must first charge the storage capacitor C1. To do this, the input of the device for 15 ... 20 s is connected to a 220 V network or to a constant voltage source of 12 V or more (plus on the XP1 plug). During this time, the capacitor C1 will have time to charge through the VD2 diode to a voltage slightly less than 5 V (it limited by the zener diode VD1). Upon subsequent connection to the controlled circuit, if it is in good condition, the capacitor will be discharged through it, the resistor R7 and the HL6 LED, which will light up. If the test is carried out for a short time, then the charging of the capacitor will be enough for several tests, after which the charging of the capacitor should be repeated.

Fixed resistors R1 - PEV-10 are used, the rest - MYAT, S2-23, capacitor - K50-35 or imported, diode KD102B can be replaced with any diode from the 1N400x series, zener diode KS147A - with KS156A, instead of two-color LEDs, you can use two different glow colors, turning them on in anti-parallel, it is desirable to use the HL6 LED with increased brightness of the glow. It should be noted that LEDs of different glow colors have different forward voltage values, so their turn-on thresholds for different input voltage polarities will not be the same.

Most of the parts are placed on a board made of textolite or getinaks, holes are made for their conclusions and wired wiring is used. LEDs HL1-HL5 are installed in a row. Since a case from a faulty gas piezo lighter was used as a probe case, the board is designed for installation in it (Fig. 3). The hole in the case, designed for the button of the piezo lighter, is covered with plexiglass. All LEDs and a neon lamp are placed on the board so that they can be seen through this hole. Socket XS1 is placed on the side wall of the housing, XS2 - at the end. A screw, also located on the side wall, can be used as a sensor. A plug with a flexible wire and a crocodile clip at the other end is inserted into the XS1 socket, and a metal pin pointed at the end for more convenient connection to small contacts (Fig. 2) into the XS4 socket.

Fig. 4

When assembling, testing and operating the described device, you should remember the safety rules when working with high voltage.

Author: V. Grichko, Krasnodar; Publication: radioradar.net

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