Voltage tester
A voltage tester is an electrical test device with which the presence, and in some voltage testers also the level, of AC or DC voltage is determined on operationally live parts. A distinction is made between voltage testers for use in the area of low voltage , these are electrical alternating voltages below 1 kV , and in the area above that of high voltage .
Two-pole voltage testers for low voltage are also generally referred to as Duspol (a deonym , since "DUSPOL" is a trademark of the manufacturer Benning ).
High voltage
Voltage testers for alternating voltages from 1 kV to 765 kV used in electrical power engineering are specified in the standards IEC 61243-1 and IEC 61243-2. They are typically designed in the form of an electrically insulated lance up to several meters in length, which is brought up to the high-voltage conductor by hand for testing purposes. The presence of the high voltage is indicated optically and acoustically by a test circuit installed in the lance by means of capacitive voltage division. The area of application of this test equipment is in high-voltage systems such as outdoor switchgear , substations and in the area of high-voltage laboratories , for example in order to check the activation within the scope of the five safety rules before maintenance work .
Low voltage
Two-pole voltage tester according to DIN VDE 0682-401
Voltage testers for low voltage are specified in the standards EN 61243-3 / VDE 06 82 Part 401 and are designed with two poles. Voltage testers are used in low-voltage networks and in electrical installations up to 1000 V for fast, reliable testing. The exact nominal voltage range in which the tester may be used depends on the voltage tester and is noted on the device, for example 12–690 V. In contrast to phase testers , two-pole voltage testers provide reliable test results. Compared to multimeters, they are easier to use, but do not offer the same possibilities.
construction
Voltage testers in the low voltage range consist of a display unit (e.g. measuring mechanism with scale) and two test electrodes (test probes). One of the test electrodes is integrated into the housing of the display unit, the second is permanently connected via a cable with a handle. To protect the voltage tester and the person carrying out the test, there are several series resistors in the device that limit the test current and divide the voltage down to the actual measuring system to a few volts.
For the measurement, two different potentials (for example two lines) are contacted with the test electrodes .
Depending on the voltage tester, the voltage is displayed via a glow lamp , a pointer , LEDs or a digital display . This two-pole test is independent of grounding and provides a reliable test result. Furthermore, voltages between different external conductors in the three-phase three-phase network can also be tested.
display
There are four different ways of displaying voltage detectors:
- Voltage tester with glow lamp or simple LED
- Early voltage testers used a glow lamp with a series resistor as an indicator. Later versions have one or two LEDs that indicate the presence of a voltage and, depending on the version, the polarity: with AC voltage, both LEDs light up, with DC voltage one of the two marked plus or minus.
- Voltage tester with analog display
- In the case of voltage testers with an analog display, the display is made with a pointer that moves over a scale. The test current flows through a moving iron or moving coil measuring mechanism , whereby the pointer gives a deflection. This measuring system has a relatively low resistance of 25–50 kΩ. Two-handed operation is therefore required for safety reasons according to the standard. Due to their immunity to interference, analog voltage testers are preferred by energy suppliers and in industry.
- Voltage tester with step-by-step LED display
- The voltage applied is displayed via several LEDs to which various voltage levels are assigned. The test current flows through an electronic circuit that controls one or more LEDs depending on the size of the voltage to be tested. These voltage testers can only show the approximate level of the applied voltage and are therefore unsuitable for measurements. Because they are easy to use and maintenance-free - as a rule, no battery is required - these testers can be used in a wide range of applications.
- Voltage tester with digital display
- The level of the applied voltage is shown on a digital display. The voltage is evaluated with a microcontroller . The test voltage is divided down to a voltage between 0 V and 3 V by a voltage divider and converted into a digital signal by an analog-digital converter . This digital information is calculated by the microcontroller and shown on the digital display as a numerical value. Digital voltage testers usually have additional functions such as continuity testing for checking ohmic resistances, rotating field measurement or polarity measurement for DC voltage. In addition to the digital display, LEDs are usually also available so that the voltage tester can display voltage even without a battery. Digital voltage testers are often preferred by professional users because of the wide range of possible uses and measurement options.
Single pole voltage tester
In the earthed low-voltage area, the single-pole voltage tester is standardized in DIN VDE 0680-6 with the current edition from April 1977. It is only suitable for dry areas, so it must not be used under wet or damp conditions. Other synonymous terms are colloquially known as "phase tester" or, because of its low reliability, "lying pen".
construction
The single-pole voltage tester mostly resembles a screwdriver in its external shape . The metal tip is used for contact with the conductor to be tested. It is connected via a high-resistance series resistor in the range from 820 kΩ to over 1 MΩ and a small glow lamp with a contact surface that is touched by the person testing. The simple structure leads to very low manufacturing costs.
application
The tip of the phase tester is held against a conductor to be tested (e.g. a socket ) for measurement . The other end of the phase tester is touched with a finger. If the socket contact is the ungrounded outer conductor ("phase"), the glow lamp lights up. The current that flows through the contacting finger is limited by the series resistor and, depending on the grounding, is a maximum of 0.5 mA, so it is not dangerous for healthy people without medical implants (such as pacemakers ).
When the tip of the phase tester makes contact with the neutral conductor or the protective conductor, the glow lamp does not light up because its potential corresponds to the ambient potential .
Reliability and Admissibility
The use as a voltage tester for normal household AC voltage (depending on the model mostly in the range from 100 V to 250 V ) with operational earthing is not permitted according to the current state of the standards for the determination of the absence of voltage . The term “lying pen” is based on the fact that it is often not possible to make a clear statement.
The glow lamp lights up most strongly when the user has a low resistance to earthed objects or the neutral conductor or protective conductor . This can be done by touching earthed metal pipes, sheet metal housings or the damp soil at the same time. If you are in an isolated location (floor covering made of plastic, dry furniture made of wood or plastic, ladders or shoes, lacquered floorboards), the human body only forms a small capacity to the environment, which is predominantly at earth potential . The resulting capacitive reactive current is sufficient to make the glow lamp glow; but it can be seen much weaker. Under no circumstances should one rely on the fact that a line is voltage-free when the glow lamp is very weak and therefore may not be clearly visible, as the current flow also depends on the contact resistance on the finger (e.g. when wearing gloves) and on the local field conditions.
In the case of non-operationally earthed AC voltage networks or those without earthing a conductor from the power network (small IT systems ), no display can be made despite the presence of a possibly high voltage. Conversely, it can happen that the voltage occurring on a disconnected or disconnected conductor is displayed. Such tensions arise in conductors or other metal parts, which run longer distances next to live external conductors, due to capacitive interference .
If the ambient brightness is too strong, the glow lamp lighting up can often not be clearly recognized. Due to capacitive coupling, it is also possible that the glow lamp lights up (although not as brightly) even though the tested lines are safely disconnected from the mains. The user cannot optically see any difference between the capacitive coupling and the weak display due to poor contact with the earth potential (e.g. if the user is standing in a well-insulated location).
As a minimum plausibility check, the phase tester should always be checked on a live conductor before and after use on the actual measurement object. In this way, at least one defective glow lamp can be excluded.
history
On September 22, 1931, Otto Walter Kaschewsky (* December 14, 1902 - † June 19, 1971) first registered a "test rod for determining the polarity of current-carrying lines with alternating current" as a utility model at the Reich Patent Office and registered it on October 30, 1931. This was soon developed into the current shape, which is usually provided with a screwdriver blade, and has hardly changed since then.
Non-contact voltage tester
Non-contact voltage testers are often referred to with the English abbreviation NCV for Non Contact Voltage and are praised as a modern aid, but are difficult to classify as test devices because they are not subject to any special standard. The general standard for the design of measuring and testing devices (EN 61010-1; DIN VDE 0411-1) is applied.
Contactless phase testers use a sensor to detect the electric field strength in the immediate vicinity of the conductor and signal optically via a display, e.g. B. a light emitting diode . A battery is required for operation. Depending on the sensitivity, the existence of voltage can also be determined through the insulation of a cable. An undisputed advantage is that non-contact voltage testers usually come with a high measuring equipment category (often CAT III / 1,000 V and higher). The fundamental problem, however, is the capacitive functioning of these devices, which is only suitable for detecting AC voltage and does not recognize DC voltages of any magnitude. Many devices also lack the essential safety feature of a battery-independent display or display of the battery status. Reliable detection of voltages above 50 V AC (especially since some devices respond at 12 V) is often not possible.
Devices of this type are not suitable for "determining the absence of voltage in electrical systems" and some manufacturers also clearly point this out in the operating instructions. Nevertheless, non-contact voltage testers have their right to exist, e. B. as an aid to find line breaks.
These devices are not subject to a separate standard, and according to the basic standard for the design of measuring and testing devices (DIN EN 61010-1; DIN VDE 0411-1) they are unsuitable for reliable voltage testing.
safety
Voltage testers are subject to special safety requirements according to EN 61243-3 (VDE 0682-401: 2011-02) and are divided into measurement categories (CAT I to IV). Since the new edition of the standard in February 2011, the following most important requirements apply to the test equipment:
- A voltage tester as test equipment must first and foremost detect dangerous voltages reliably (and independently of the ON / OFF switch, any range preselection or battery status).
- Incorrect operation must be ruled out as far as possible, so the voltage tester must be easy and reliable to use.
- A voltage tester must not endanger the operator. It must be constructed in such a way that, when used as intended, no flow through the body or arcing faults can occur.
- A two-pole voltage tester must at least correspond to measuring equipment category III (CAT III).
- The load connection, with which the test current is increased from less than 3.5 mA to a maximum of 200 mA, may only be carried out by simultaneously operating two buttons (operated by both hands).
Voltage testers are divided into measurement categories (CAT I-IV) and since February 2011 have had to correspond to at least Category III in order to ensure safe personal protection. Due to the long transition period until May 1, 2013, it is possible that two-pole CAT II voltage testers will still be offered, which are less well protected against overvoltages and the (possibly resulting) case of a short circuit in the device. They are not universally applicable in house installation, but are only intended for tests beyond a socket.
Two-hand operation under all operating conditions prevents a live test electrode from being touched by hand.
When using voltage testers, it must always be ensured that they are suitable for the operating conditions such as AC or DC voltage, voltage level, temperature, humidity, etc. Voltage testers must not be used for voltages above their nominal voltage or at higher frequencies than intended.
People with medical implants - especially with pacemakers and implanted defibrillator - allowed voltage tester, where the circuit is closed over the body - such as the single-pole voltage tester (phase tester) - not use, since the voltage of the devices as ventricular fibrillation can be interpreted and thereby delivering an electric shock .
Voltage testers must also be tested for function before a voltage test. For this purpose, the device is placed at a point that is definitely live. This function check is important to determine the intended function of the voltage tester in the given context (isolation of the user). A new function test after use - to rule out a defect during the measurement - is recommended, but not mandatory.
Web links
Individual evidence
- ↑ International registration 423199 "DUSPOL" ( register entry at WIPO )
- ^ Website of the manufacturer
- ↑ IEC 61243-1: Voltage detectors - Part 1: Capacitive type to be used for voltages exceeding 1 kV AC , June 1, 2009
- ↑ Data sheet high voltage tester KP (PDF; 475 kB), Pfisterer Kontaktsysteme, accessed on October 6, 2016
- ↑ DIN 57680-6 (VDE 0680-6: 1977-04 protective clothing, protective devices and devices for working on live equipment up to 1000 V; single-pole voltage testers up to 250 V AC )
- ↑ a b Living and dealing with pacemakers and defibrillators. (PDF) Kerckhoff Clinic, p. 2 , accessed on September 26, 2017 .
- ↑ DIN 57680-6 VDE 0680-6: 1977-04 - Standards - VDE VERLAG. Retrieved September 25, 2017 .
- ↑ Dieter Ebner: Technical basics of computer science: Electronics, data processing and process control for natural scientists and engineers . Springer-Verlag, 2013, ISBN 978-3-642-93371-4 , pp. 52 ( limited preview in Google Book Search [accessed December 1, 2016]).
- ↑ Helmut Gente: The glow tube: its physical principles and its use in teaching . Springer-Verlag, 2013, ISBN 978-3-322-98948-2 , pp. 48 ( limited preview in Google Book Search [accessed December 1, 2016]).
- ↑ Douglas C. Giancoli: Physics . Pearson, 2006, ISBN 3-8273-7157-0 , pp. 870 ( limited preview in Google Book Search [accessed December 1, 2016]).
- ^ State of Salzburg - voltage tester. In: www.salzburg.gv.at. Retrieved December 1, 2016 .
- ↑ Utility model roll Reichspatentamt serial no. 1194201
- ↑ Voltage tester - WEKA MEDIA. In: weka.de. Retrieved October 10, 2019 .