Indicator Screwdriver

Indicator screwdriver is a multifunctional device, the main purpose of the device is to assess the presence of a voltage phase in this current-carrying section. According to the laws of physics, one wire in a household network is neutral and not dangerous. It is important for an electrician to know where the phase is in order to avoid an accident.

How the indicator screwdriver works

There are many legends about the work of the indicator screwdriver. The most common: when the probe touches the current-carrying part of the bare wire, a circuit is formed consisting of the elements:

  1. Phase.
  2. Internal screwdriver chains.
  3. Man.
  4. Land.


Any unknowing person in electrical engineering can easily be convinced of the insanity of a similar interpretation of the principle of the indicator screwdriver, derived from an elementary reluctance to think and analyze. Modern products do not need contact with the hand to show the proximity of dangerous voltage. But! If touched, the LED lights up brighter. Similar can be seen if you touch a conventional screwdriver under the cross to the metal button on the handle. Wear rubber shoes if in doubt: the product will continue to work.

Not miracles, but laws of physics. The indicator screwdriver works on a single principle, discovered in the XIX century by Heinrich Hertz. Already guessed that we are talking about the radio. The frequency of 50 Hz is actively radiated into space, if you touch the slotted contact button( however, any) with a screwdriver, the size of the transmitting antenna increases, which causes an increase in the brightness of the LED.

The voltage is alternating, a current is generated, even if a discharge lamp with a gap between the electrodes serves as an indicator. Between them, as between the plates of a capacitor, a current arises, the cause of burning. The radiation resistance of the contact button is large, the flow of electrons is not enough to ionize the gap in the light bulb. As soon as the master touches his finger, charge carriers rush to the body.

Many are extinguished in the thick of flesh and blood of the skin, causing a barely noticeable heating of these areas, but a significant portion is radiated into space. The surface of the body rather big, because the power output in the air increased. The phenomenon causes an increase in current through the discharge light bulb. That lights up. What is the reason?

As is well known( see the review on the topic of discharge lamps), the initial ignition of the spark gap occurs due to the potential difference. Suppose readers at least once in their life beat current from the antenna. Wiring has some potential, its difference with the human body is enough to ignite the arc. As for modern indicator screwdrivers, here instead of gas-discharge lamps LEDs are used. Eliminates the need to take up the contact button with your hand - energy is already emitted through a bare platform.

Modern device

The device of the indicator screwdriver

The forums are arguing whether the LED is inside the indicator screwdriver or there is a gas discharge lamp. Formerly, indicator-based screwdrivers used gas-discharge light bulbs for the simple reason that there were no LEDs that were developed only at the end of the 20th century( see the corresponding review on LED lamps, LED lighting, etc.).

Earlier, a light bulb was placed behind the probe, and before reaching the contact button the circuit was protected by resistance from graphite( or similar material).The purpose of resistance is obvious: so that the electrician does not take a bare hand( through the spark gap) for 50 Hz. And taking into account the fact that the resistance of the body is a unit of kOhm, there are no deadly consequences if even the unlucky master took the grounded conductive object with his second hand.

As the experimenters rightly said: directly vanishing the contact pad will probably lead to an explosion. Screwdriver fails immediately, the current will be too large. Vulnerable place - gas discharge light bulb, the first fails. However, skeptics, not without reason, stated that the indicator screwdrivers are made under different voltage.

Automotive probes for 24 or 12 V are supplied in the area of ​​the handle with a clip that fits onto the mass( body).It is easy to guess that the constant voltage is not capable of being radiated on the air, here you need to create a path to the current described above: battery, probe, tap with crocodile, earth. Otherwise the indicator will not light up. If you turn on the car indicator in the AC network of 220 V, the current will exceed the nominal time of 20. It all depends on the designers' forethought.

Separate car probes are supplied with a removable clip( crocodile).Then the device turns into a normal indicator screwdriver for 220 V. It is strongly not recommended to ground the clamp. It must be removed as prescribed by the instruction manual.

Contactless model

Contactless screwdriver-indicators

Today it is not uncommon in the store to see a non-contact voltage indicator. Inside there is a cascade amplifier with transistors, due to which the leakage current( radiation into the ether) is multiplied many times. A pair of batteries serves as the power source of the simplest design. As a result, the mode triggered by the special position of the switch becomes possible, when the screwdriver indicates the presence of voltage at a distance, plus it is able to do this through a thin wall( partition).

Any wire that is live at 220 V( 50 Hz) emits. The probe catches a weak wave, and the system is set to resonate with it. Indicator screwdriver does not work from a conventional radio( or cellular network).The wave is amplified by transistors, then reemitted through a contact button. The effect increases when you touch your finger.

The result of such a powerful interaction of science and technology becomes the ability to track the trajectory of the passage of wiring in the wall. The usual cord( PV, etc.) is not shielded, the partitions in the apartment actively radiate energy. In some cases, the reinforcement of a reinforced concrete slab becomes a repeater. And the screwdriver indicator will show the location of the metal part of the wall, and not the wiring.

It is clear that electromagnetic radiation( including frequencies of 50 Hz) is harmful to humans. Causes immense fatigue, the feeling of loss of strength, heats the organs and tissues, increases inflammation. Harmful effect is multiplied if there is a wire under current next to it( a socket with consumers turned on, etc.).Then the wave of radiation on the air is stronger, it is not recommended to equip places of rest, sleep, put a bed.

Find a safe place will help. .. contactless screwdriver indicator. It should be turned on to high sensitivity and find a safe place in the house.

What is radiation resistance

The above stated that modern indicator screwdrivers are able to work without touch. If you touch a metal object or hand, the brightness increases. This is directly related to the concept of radiation resistance. In radio engineering, the term describes the boundary between two media - conductors and ether. Typical antennas are made at 75 and 50 Hz. The directional diagrams and efficiency( Efficiency) of these Hertz vibrators( emitters) are optimal with satisfactory sizes of products.

The characteristic impedance of shielded cables corresponds to the stated values. These are standard values ​​for television and radio reception, respectively. These steps are taken so that a minimum of power is reflected back( to the transmitter).The screwdriver works in the same way. But here the radiation resistance is not chosen according to the radiation pattern. The wizard has little effect on the parameter. The lower the radiation resistance, the higher the current, the brighter the LED.

It is useless to search for a definition of radiation resistance. In our case, it is important that the radiation resistance decreases with the growth of the antenna surface, which leads to an increase in the brightness of the indicator with a simple touch. Man, like metal, becomes a conductor, which makes such specific properties of the body. Clothing affects radiation a little, the wave easily passes through synthetic and natural fabrics.

How to choose an indicator screwdriver

Non-contact screwdrivers are sensitive. The manufacturer promises to give an opportunity with the help of them to detect the presence of grounding, but this is not always possible. Parasitic factors come into play. In the first place - the presence of interference in the neutral from the phase wire. The indicator screwdriver is so powerful that in a sensitive mode it will react to the wires. Despite the fact that the real phase voltage is present in the only one.

Therefore, for the needs of an ordinary electrician, a contactless screwdriver is usually not required. But it will be of great help in checking the quality of cable shielding, the absence of radiation. We should not forget that the product reacts violently only at a frequency of 50 Hz. The cellular network of the screwdriver is unlikely to be able to detect, as well as the energy transferred by operators. In this case, the phone will fit more. It is no secret that the link does not work in the hold of a steel ship. The walls of the hull, the bulkheads are reliably grounded across the water surface.

Checking the product upon purchase is easy in a simple way. For active models( with battery): short the probe through your own body, holding the slot by the hand, and the second by touching the contact button. The LED lights up.

Contactless screwdrivers are checked near the current-carrying conductors. The method of verification is prescribed in the instructions. There is a certain marginal distance at which the product operates. Most screwdrivers have three switch positions. Two are designed for remote action. If in these modes to touch the current-carrying part of the wire, burnout of the electronic part, consisting of transistors and a LED, is possible. Both parts react negatively to any voltage fluctuations.

Professional telecom operators( electricians) is not superfluous to find a route finder for sale. This device works differently. It already has a transmitter that emits a signal. The echo reflected from the screen( or other metal part of the cable) is caught by the receiver. As part of the professional tracker can go a lot of additional useful options:

  • Headphones to work on the noisy streets of the city. The sound detection signal is clearly audible.
  • Ability to determine the status of the telephone line( busy, free, etc.).
  • Convenient case that protects the product during transportation and operation.
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