Probe-indicator. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Measuring technology

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When troubleshooting and setting up automation devices and various electrical and radio installations, an electrician has to use two or even three measuring instruments: a current detector, an avometer, a circuit tester (a battery of cells connected in series with an incandescent lamp). This creates certain inconveniences both in movement and at work.

At the same time, in the vast majority of practical cases, the measurement of the exact value of the parameters is not required, only the confirmation of previously known fixed values ​​is needed. Therefore, it is natural to strive to create simple combination probes that meet the requirements of specific operating conditions. It is also obvious that it is impossible to make a simple device that could satisfy all the needs that arise in various fields of technology.

In my sampler, which I offer to the attention of readers, I have combined those types of tests that are most often necessary in practice. The probe, made in the form of a probe, is easy to use, has small dimensions and weight, and is able to work for a long time without changing the power source. The absence of pointer measuring instruments increases its resistance to accidental drops and shocks. The probe allows you to determine the presence in the tested circuit of AC and DC voltage from 60 to 400 V, as well as confirm fixed values ​​of 6,12 and 24 V, indicate resistance within 5 ... 50 Ohm and 50 ... 500 Ohm, check the health of capacitors capacitance of 4 microfarads or more.

The schematic diagram of the device is shown in fig. 1. For all types of tests, it is connected to the circuit under test with probe 1 mounted on the body of the device, and probe 2 connected to the device with a flexible stranded wire. The position of the S81 and SВ2 buttons shown in the diagram corresponds to the voltage indication mode 60 ... 400 V. In the same mode, the VD1, R4, R5 circuit allows you to charge the GB1 battery. By pressing the S82 button, the device operates in the mode of indication of fixed voltage values. If the HL4 LED turns on in the circuit under test, the voltage is at least 6, but not more than 12 V, if HL4 and HL5 are lit at once, then it is in the range from 12 to 24 V, if all three LEDs HL4, HL5, HL6 are more than 24 V.

When measuring DC voltage, probe 1 is connected to the positive wire of the circuit under test. When the button SB1 is pressed (S82 is released), the device operates in the resistance indication mode. The readiness of the device for operation is checked by simultaneously pressing the button SB1 and closing the probes. In this case, the glow of the LEDs HL2 and HL3 is the same and maximum, which corresponds to zero measured resistance. Resistance in the range of 5 ... 50 Ohm indicates the LED HL2, changing the brightness of the glow in inverse proportion; while the brightness of the LED HL3 remains unchanged and maximum.

If a resistance of more than 50 ohms is connected between the probes, the HL2 LED does not light, and the HL3 LED reduces the brightness of the glow with increasing resistance. This makes it possible, with a certain skill, to determine the value of resistance with an accuracy sufficient for practice. In the same mode, the integrity of pn junctions of diodes, transistors, etc. is determined. The serviceability of capacitors of significant capacity is determined by the intensity of the flash of the HL3 LED at the moment the probes touch the capacitor leads. The device is protected against erroneous connection to 220 V voltage in resistance measurement mode or low voltage fixed values. The node on transistors VT2-VT4 during the time required for measurement withstands such an emergency connection, and the node on the transistor VT1 is protected by diodes VD2-VD7 and fuse FU1.

All parts of the probe, with the exception of the GB1 battery and the FU1 fuse, are mounted on two printed circuit boards made of 1 mm thick foil fiberglass. The drawings of both boards are shown in fig. 2. All jumpers and board-to-board connections are also shown here. Both boards are fastened together with four M2,5 screws, while the boards must be located with printed conductors inside. Between the boards it is necessary to lay an insulating gasket made of fiberglass (without foil) 1 mm thick, the dimensions of the gasket are equal to the dimensions of the boards. To the end of the board, on which the LEDs are located, by soldering to the foil pads, marked with the letters A and B, a false panel of foil fiberglass with a thickness of 1 mm is attached. In the false panel, he drills holes for LEDs and a window for a neon lamp.

The necessary inscriptions can be applied to the false panel by etching foil or paint. Microswitches MP-5 are fixed with brackets made of copper wire 1 mm thick, soldered into the board to the specially provided areas. The fuse is built into probe 2. The body of the probe is glued from sheet opaque polystyrene 3 mm thick. A rectangular window is cut out from the side of the indicators in the case, into which a plate of transparent organic glass of the same size is glued, and holes are drilled for buttons, which are also made of polystyrene.

Two D-0,1 batteries are fixed with a copper wire bracket, the ends of which are fitted with PVC tubes. The ends of the bracket are soldered into a small board made of foil fiberglass. The layout of the probe is shown in fig. 3. The NI neon lamp should be protected with foam pads from damage upon impact. The probes themselves are made of brass. One of them - probe 1 - is screwed to board 1, and the other is screwed into a plastic tube. In the same tube there is also a fuse clamped by a spring.

Transistors KT315B in the probe can be replaced with KT315A, KT315G, and KT816A - with KT816B, KT816G, as well as KT814A, KT814B. Fuse FU1-VGP-1 0,5 A, or, better, 0,25 A. It is better to replace the AL102A and AL307A LEDs with brighter ones AL102B and AL307B. Instead of D-0,1, you can use batteries D-0,06 . Neon pampa INS-1 can be replaced with IN-3.

The adjustment of the device begins with a node on the transistor VT1. A DC milliammeter is connected to the probes. Resistors R2 and RЗ are temporarily replaced with variables with a resistance of 100 ... 300 Ohms, and their sliders are set to maximum resistance.

Reducing the resistance of the resistor R10, set the current to 3 mA on the scale of the microammeter, while the LED HL2 starts to shine. Then the resistance of the resistor R2 is reduced, achieving an equally bright glow of both LEDs HL3 and HLXNUMX. After that, the resistance of variable resistors is measured and constant resistors of the corresponding ratings are soldered in their place.

The node on transistors VT2-VT4 usually does not need to be adjusted if the parts are in good order and their ratings correspond to those indicated in the diagram. The need to recharge the GВ1 battery is indicated by a noticeable difference in the brightness of the HL2 and HL3 LEDs when the probes of the device are closed. For charging, the probes are plugged into a 220 V lighting outlet.

The body of the probe is glued from sheet opaque polystyrene 3 mm thick. A rectangular window is cut out from the side of the indicators in the case, into which a plate of transparent organic glass of the same size is glued, and holes are drilled for buttons, which are also made of polystyrene. Two D-0,1 batteries are fixed with a copper wire bracket, the ends of which are fitted with PVC tubes. The ends of the bracket are soldered into a small board made of foil fiberglass. The layout of the probe is shown in fig. 3. The NI neon lamp should be protected with foam pads from damage upon impact. The probes themselves are made of brass. One of them - probe 1 - is screwed to board 1, and the other is screwed into a plastic tube. In the same tube there is also a fuse clamped by a spring. Transistors KT315B in the probe can be replaced with KT315A, KT315G, and KT816A - with KT816B, KT816G, as well as with KT814A, KT814B. Fuse FU1-VGP-1 0,5 A, or, better, 0,25 A. It is better to replace the AL102A and AL307A LEDs with brighter ones AL102B and AL307B. Instead of D-0,1, you can use batteries D-0,06 . Neon pampa INS-1 can be replaced with IN-3.

The adjustment of the device begins with a node on the transistor VT1. A DC milliammeter is connected to the probes. Resistors R2 and RЗ are temporarily replaced with variables with a resistance of 100 ... 300 Ohms, and their sliders are set to maximum resistance. Reducing the resistance of the resistor R10, set the current to 3 mA on the scale of the microammeter, while the LED HL2 starts to shine. Then the resistance of the resistor R2 is reduced, achieving an equally bright glow of both LEDs HL3 and HLXNUMX. After that, the resistance of variable resistors is measured and constant resistors of the corresponding ratings are soldered in their place.

The node on transistors VT2-VT4 usually does not need to be adjusted if the parts are in good order and their ratings correspond to those indicated in the diagram. The need to recharge the GВ1 battery is indicated by a noticeable difference in the brightness of the HL2 and HL3 LEDs when the probes of the device are closed. For charging, the probes are plugged into a 220 V lighting outlet.

Author: M. Petrunyak, Rostov-on-Don; Publication: cxem.net

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