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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Phase indicator. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Measuring technology When carrying out electrical work, it is often necessary to identify the phase wire of the network. This cannot be done without a phase indicator. The simplest indicator consists of a neon lamp connected in series and a current-limiting resistor with a resistance of several hundred kilo-ohms. The free output of the lamp is connected to the sensor contact. Holding the contact with your finger, touch the tested circuits with the free terminal of the resistor. If the probe is connected to a phase wire, a small current flows through the elements of the probe and the human body, which is enough to light the lamp. Unfortunately, the glow of the lamp is so weak that it is almost invisible in bright light. The phase indicator, which would be convenient to use in good light, can be made on a liquid crystal display (LCD), which is widely used in electronic watches. Since LCDs are capable of operating at low voltage and current, they can easily replace a neon lamp in a probe. Faulty electronic clocks will always be found, so finding an LCD will not be difficult. LCDs of any size are suitable - both miniature ones from wristwatches, and large ones - from desktop and wall ones. Of course, in the latter version, the indicator will be cumbersome. A diagram of a simple indicator on the LCD is shown in fig. 1. It contains series-connected current-limiting resistor R1 and LCD HG1. When you touch the touch pad and connect the X1 probe to the phase wire, random readings will appear on the LCD. Small-sized LCDs should be protected from voltage overload by a zener diode VD1.
An electronic clock with a serviceable LCD and failed electronics is suitable for the indicator. LCDs are usually placed in the plastic compartment of the watch and connected to the electronic part through a contact gasket made of conductive rubber. In this version, it is convenient to use a plastic case by removing the faulty electronic unit and using printed conductors from the conductive rubber to the microcircuit to connect to the LCD. Which LCD outputs are better to use is determined experimentally so that all or at least part of the segments work. This can be done according to the method described in the selection of reader suggestions "More about checking the LCD" in "Radio", 1998, No. 10, p. 76. It is permissible to use the watch case itself. In this case, the resistor R1 is placed in the probe and connected to the indicator with an insulated wire. Touch contact is strengthened on the watch case if it is plastic. If the body is metal, it will act as a contact. The indicator can also be assembled in any other suitable plastic case - from a used felt-tip pen, from Tick-Tock mint pills, from a toothbrush casing, etc. The external contact will be a piece of foil or wire laid along the body. For the LCD in the case, it is necessary to saw through a window of the appropriate size. One example of such a design is shown in Fig. 2.
To use the indicator conveniently both in bright light and in the dark, you need to add a neon lamp to it (Fig. 3), turning it on in series with the LCD. True, to accommodate the details, you will have to choose a more spacious case.
In both indicators, the limiting resistors are MLT or C233 with a rated power of at least 0,5 W. It is permissible to replace a two-anode zener diode with two low-power zener diodes connected in anti-series with a stabilization voltage of 3,3-6,8 V. The neon lamp in the second device is TN-0,2, TN-0,5, TN-0,95, MN-6 . In conclusion, it should be noted that an LCD indicator is capable of operating in networks with much lower voltage than an indicator with a neon lamp. Author: I. Nechaev, Kursk
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