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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING The generator for the route finder. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Measuring technology When carrying out construction and repair work, it is quite often necessary to look for energy, communication and other cables, pipelines and other utilities hidden in building structures or laid underground. Knowing the exact route and depth of their occurrence is necessary not only to get to the object for repair or replacement, but also to avoid accidental damage during other work. To search for such objects, there are tracing devices, the operation of which is based on the registration of an electromagnetic field created by a well-conductive object located in an environment with poor conductivity, through which an alternating current of a certain frequency flows, created using a special generator. The author offers a relatively cheap, in comparison with industrial designs, self-made multi-mode generator for the locator. It is able to work in conjunction with various search receivers: both industrial and home-made. In various amateur radio literature, descriptions of the simplest "wiring finders" have been published more than once, allowing you to detect wires from a 220 V, 50 Hz household electrical network at a depth of several centimeters in a concrete wall. Unfortunately, by increasing the sensitivity of the receiver of the radiation generated by such wires, it is not possible to significantly increase the depth of detection and the accuracy of determining their path. Interference from other similar cables laid nearby and various devices powered by the network begin to affect, and there are a lot of them today. In order to successfully solve the problem of searching for a cable laid at a depth of several meters, and sometimes several tens of meters, it is necessary to apply a powerful signal to it at a frequency higher than the mains frequency (from hundreds of hertz to several tens of kilohertz) from a special generator. Similarly, an electromagnetic field is created around other search objects, such as metal water pipes. The second terminal of the generator in this case is grounded. The frequency of the search signal is chosen based on the minimum attenuation of the electromagnetic field in the surrounding cable or other communication in the environment (soil, concrete), sufficiently remote from the frequency of possible interference. In addition, various types of signal modulation are used, giving it a "color" that contributes to better recognition by ear or with the help of an automatic detector built into the search receiver. A set of a generator that sends a search signal to the object being searched for and a search receiver is called a locator or cable locator. Today, domestic and foreign industry produces quite a lot of varieties of route finders. Their cost is in the range from 25 thousand to 350 thousand rubles. But those that are cheaper than 100 thousand rubles in most cases do not meet the requirements for them in operation. They are able to operate only at two or three frequencies, their generators are not powerful enough to search for objects located at great depths. The described generator does not have the drawbacks typical for "cheap" devices of a similar purpose. It has been in operation for more than 12 years, and has shown high reliability and efficiency when searching for cable and utility lines at a depth of up to 50 m, as well as when locating cable line damage. The total cost of a set of radio components and materials necessary for its manufacture does not exceed several thousand rubles. The generator is compatible with many receivers of domestic and foreign industrial trace finders designed to search for utilities laid in walls, earth, pipes, channels, mines. High power, wide operating frequency ranges, various combinations of output voltage and current - all this allows you to confidently track communications, even in conditions of strong interference, laid at a depth of up to 50 m at a distance of up to 5 km from the generator. Both a relatively high frequency signal modulated by a low frequency (audio range) and low and high frequency signals can be created separately. It should be noted that when working with the proposed generator, it is necessary to observe electrical safety measures, since the voltage at its output can reach life-threatening values. Main Specifications
*Note. Measured at each of the six outputs of the generator when it is running from a battery at a frequency of 1 kHz with a pointer avometer in the AC voltage measurement mode. The locator generator exciter circuit is shown in fig. 1. A master oscillator is made on the DD1 chip, the frequency of which is stabilized by the ZQ1 quartz resonator. Binary counter DD4 reduces the pulse repetition rate of the master oscillator by 2, 4, 8, 16, 32, 64 and 128 times. Selector-multiplexer DD5 selects a signal from one of the outputs of the counter for further processing. The control codes at the address inputs of the selector are formed, depending on the position of the switch SA2, by an encoder on diodes VD1, VD2, VD4-VD10. In table. 1 shows the correspondence between the position of the switch, the logic levels at the address inputs and the frequency of the signal at the output of the selector and, therefore, at the output of the entire generator.
Table 1
When the SA2 switch is set to position 8, the quartz oscillator is turned off by a low level at pin 13 of the DD1.2 element, and the signal of the low-frequency pulse generator assembled on the DD3 chip with smooth frequency tuning from 500 to 3000 Hz is fed to the selector output. Switch SA1 this generator can be turned off. Chip DD2 controls the operation of the generators described above when selecting modes and frequencies. Chip DD6 performs the functions of a phase inverter and an amplitude modulator. Six of its elements - logical inverters - are connected three in parallel to increase the load capacity. The modulation is performed periodically with the pulse frequency of the generator on the DD3 chip, while simultaneously transferring the outputs of all inverters to a high-impedance state. When the signal of this generator is selected as a search one (switch SA2 in position 8), the passage of its pulses to the EO input of the DD6 chip disables the high level at pin 13 of the DD2.4 element, which disables the modulation. Mutually antiphase signals from the outputs of the first (pins 2, 5, 7) and second (pins 9, 11, 14) groups of inverters of the DD6 microcircuit are fed through interrupters on transistors VT4 and VT5 to the inputs of the shoulders of a push-pull power amplifier on transistors VT3, VT6-VT8, in the collector circuits of which the primary winding of the transformer T1 is included. Both interrupters are synchronously opened and closed by multivibrator pulses on transistors VT1 and VT2, following at a frequency of 0,1 ... 1 Hz. As a result, the oscillator's output signal is switched on and off periodically at this frequency, which helps to identify it by ear among the interference. The signal interruption frequency can be adjusted with a variable resistor R16. The ratio of the duration of the on and off states is changed by a variable resistor R17. The voltage regulator present in the exciter on the integral stabilizer DA1 reduces the voltage U coming from the power supply described below.pit1 (12...14 V) to 11 V and stabilizes it. This voltage feeds all the nodes of the exciter. The signal from the secondary winding of the transformer T1 is fed to the output power amplifier, the circuit of which is shown in fig. 2. It is also push-pull and consists of a pre-terminal amplification stage on transistors VT9 and VT10 and an end stage on transistors VT11-VT16. The output transformer T2 has a secondary winding with taps, which allows you to work on loads of various resistances by connecting them to the appropriate sockets XS1 - XS7. The voltage indicated at these sockets refers to the operation of the generator from a 12 V battery. When operating from a 220 V network, the supply voltage U supplied to the final amplifierpit2 can be adjusted in the range from 5 to 30 V, respectively changing the output voltage of the generator and the maximum power delivered to the load.
The LEDs HL1 and HL2, connected through a limiting resistor R48 to a part of the secondary winding of the transformer T2, serve as indicators of the presence of voltage at the generator output. By the brightness of their glow, you can judge its set level. If desired, one of these LEDs can be replaced with any conventional diode. Author: S. Gubachev
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