A device for finding a break in a cable. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Measuring technology
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In the note "Probe from an electronic-mechanical clock" ("Radio", 2013, No. 4, p. 53), G. Guzenkov spoke about how to use an alarm sounder as an indicator when checking the health of various electrical and radio elements. I suggest another application of such a signaling device - in a device for localizing a wire break in a cable or bundle.
Fig. 1
The scheme of the proposed device is shown in fig. 1. The field-effect transistor VT1, together with the sensor E1 connected to the output of its gate, performs the function of an electric field strength sensor. In the absence of a field, the voltage between the gate and source of the transistor is zero, therefore it is open and shunts the emitter junction of the transistor VT2 with a low channel resistance, which is why it is closed. an alternating voltage will appear at the source of the transistor and the channel resistance will increase so much that, under the influence of a current through the resistor R1, the transistor VT220 will open and the low resistance of the emitter-collector section will connect the “k” point of the alarm sounder A1 to the negative power wire, as a result of which it will give a signal.
Capacitor C1 improves the sound quality (without it, it turns out to be "rattling"). The sensitivity of the device increases if you touch the battery G1 with your finger.
Fig. 2
The details of the device are mounted on a printed circuit board made of one-sided foil fiberglass 1 mm thick, the drawing of which is shown in Fig. 2. Resistor - any small-sized (MLT, S2-23, S2-33), capacitor - ceramic or film is also small-sized. Transistors VT1 and VT2 - any of the series indicated on the diagram. The first of them lies on the board on its side and is glued to it with Moment glue.
Sensor E1 is a spiral of seven turns of single-core copper wire (possibly insulated) with a diameter of 0,5 mm, wound on a mandrel with a diameter of 4 mm. The spiral is slightly stretched and then glued to the board with the same glue. The output of the gate of the field-effect transistor is soldered to it after the glue has dried. A power switch is not provided. With serviceable parts and no errors in installation, the device starts working immediately and does not need to be adjusted.
Refinement of the watch itself comes down to the careful removal of all parts of the mechanism and finding the point of connection of the device to the signaling device. After inserting the battery, they check the operation of the signaling device, and then the movable contact coming from the negative power bus is bent up, noticing at the same time which contact pad it was connected to. This will be the point "k" of the signaling device, indicated in fig. 1.
The location of a broken wire in an unshielded cable is found by connecting this wire to the "phase" of the mains outlet. For example, you need to find a break in the cord of a lamp with a switch in one of its wires. Turning on this switch, insert the plug into the mains socket and lead the device along the cord from the plug to the lamp. If an alarm sounds along the entire length, then the wire of this cord, connected to the phase wire of the network, is working. We turn the plug in the socket 180 ° (that is, we connect another wire of the cord to the phase wire of the network) and again we lead the device from the plug to the lamp. In the place of the break, the signal will be lost. In the same way, they find a break in the power cable of any electrical or radio device.
In all work carried out with cables connected to a mains socket, electrical safety regulations must be observed.
Author: N. Abramov
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