Wattmeter ( watt + dr.-Greek. Μετρεω - “measure”) is a measuring instrument designed to determine the power of an electric current or an electromagnetic signal.
Content
Classification
By purpose and frequency range wattmeters can be divided into three categories - low frequency (and direct current), radio frequency and optical. Radio frequency wattmeters are divided into two types: transmitted power, included in the transmission line break, and absorbed power, connected to the end of the line as a consistent load. Depending on the method of functional conversion of measurement information and its output to an operator, wattmeters are analog (showing and recording) and digital.
Low Frequency and DC Wattmeters
Low-frequency wattmeters are mainly used in power supply networks of industrial frequency for measuring power consumption, can be single-phase and three-phase. A separate subgroup consists of varmeters - reactive power meters. Digital devices usually combine the ability to measure active and reactive power.
Analogue low-frequency wattmeters of an electrodynamic or ferrodynamic system have two coils in the measuring mechanism, one of which is connected in series to the load and the other in parallel. The interaction of the magnetic fields of the coils creates a torque that deflects the instrument arrow, which is proportional to the product of the current, voltage, and cosine or sine of the phase difference (to measure, respectively, active or reactive power ).
- EXAMPLES: Ts301, D8002, D5071
Digital low-frequency wattmeters have two sensors as input circuits - current and voltage, connected in series and parallel to the load, respectively; sensors can be based on instrument transformers , thermistors , thermocouples and others. Information from the sensors through the ADC is transmitted to the computing device, in which the active and reactive power is calculated, then the final information is displayed on a digital display and, if necessary, on external devices (for storage, printing of data, etc.).
- EXAMPLES: MI 2010A, СР3010, ЩВ02
Radio range absorbed power meters
The wattmeters of absorbed power form a very large and widely used subgroup of wattmeters of the radio band. The specific division of this subgroup is mainly associated with the use of various types of primary transducers (receiving heads). In commercially available wattmeters, transducers based on a thermistor , a thermocouple, and a peak detector are used ; much less often, in experimental works, sensors based on other principles — ponderomotive , galvanomagnetic , etc. are used. When working with wattmeters of absorbed power, it should be remembered that due to the non-ideal matching of the input resistance of the receiving heads with the wave impedance of the line, some of the energy is reflected and the wattmeter actually measures not the incident power, but the absorbed power, which differs from the incident power by an amount equal to K P × P pad , where K P is the power reflectance .
Thermistor (bolometric) wattmeters consist of a receiving transducer based on a thermistor (or bolometer ) and a measuring bridge with a low-frequency alternating current source for heating the thermistor. The principle of operation of a thermistor converter consists in the dependence of the resistance of a thermistor on its heating temperature, which, in turn, depends on the power dissipated by the signal supplied to it. The measurement is carried out by comparing the power of the measured signal, dissipated in the thermistor and warming it, with the power of the low frequency current, causing the same heating of the thermistor. In the process of measurement, the total power dissipated on the thermistor (when a simultaneously measured signal and a heating current are applied to it) and, accordingly, the resistance of the thermistor is maintained the same with a measuring bridge, which is balanced by a change in the heating current. In the first models of thermistor wattmeters, balancing was carried out manually; in modern wattmeters, balancing is automatic, readings are displayed in digital form. The disadvantages of thermistor wattmeters are their small dynamic range - the maximum power dissipation - a few milliwatts, this limitation is overcome by the use of attenuators dividing the power, but introducing an additional error.
- EXAMPLES: M3-22A, M3-28
Calorimetric wattmeters differ from thermistor in that a separate load is used to absorb the measured power, from which heat is transferred to a thermistor transducer through a working medium — distilled water or a special liquid. The liquid medium circulates at a strictly defined flow rate, washing in turn the input load, the converter and the cooling heat exchanger.
- EXAMPLES: M3-13, MK3-68, MK3-70
Thermoelectric wattmeters use a thermocouple (or a thermocouple unit) for direct or indirect heating as a primary converter. When measuring, the hot junction of the thermocouple heats up under the influence of the input power of the measured signal, thereby producing thermo-emf. Measuring information in the form of a DC signal is fed to an electronic unit (analog or digital), where it is processed and fed to an indicating device.
- EXAMPLES: M3-51, M3-56, M3-93
Wattmeters with a peak detector are simple in the device, unlike other types of wattmeters capable of measuring not only the power of a continuous signal, but also the peak power of radio pulses , however, due to low measurement accuracy, they are rarely used nowadays. By the principle of operation, such a wattmeter is an alternating current rectifier voltmeter , which has a load at the input with a resistance equal to the cable impedance and with a counting device calibrated in power values.
- EXAMPLES: M3-3A, M3-5A
Radio Band Power Wattmeters
In power transmitting wattmeters, as a primary converter, a directional coupler is usually used, a device that allows a very small amount of energy to be branched from the main transmission path. An abstracted part of the energy is fed to a secondary transducer, for example, a detector or thermistor head, from where the measurement information signal is fed to a functional transducer and then to a indicating device.
At relatively low frequencies (in the DV and SV bands), the use of directional couplers is difficult, in this case, current sensors and line voltage sensors can be used as primary converters, the measurement information from which is further processed in the function converter (multiplication of values taking into account phase difference). Sensors can serve, for example, a voltage transformer and a current transformer . This method of measurement is usually used in specialized devices to control the power delivered to the antenna by a radio transmitter. At ultra-high frequencies, in waveguide paths, for measuring the transmitted power, the ponderomotive method or sensors embedded in the waveguide wall can be used - thermistor, thermoelectric, galvanomagnetic.
- EXAMPLES: M2-23, M2-32, NAS
Optical power meters
- EXAMPLES: OMK3-69, OM3-65
Names and designations
Species Names:
- Power meter is another name for wattmeters of radio and optical ranges
- Kilowattmeter - a device for measuring the power of large values (units of hundreds of kilowatts)
- Milliwattmeter - a device for measuring power of small values (less than 1 watt)
- Varmeter - a device for measuring reactive power
- Wattvarmetr - a device that allows you to measure active and reactive power
To designate types of electrical (low-frequency) wattmeters, an industry-specific notation is traditionally used, in which devices are labeled depending on the system (basic principle of operation):
- Dhh - electrodynamic system devices
- Xxx - devices rectifier system
- Фхх, Шххх - electronic system devices
- Nhh - self-recording devices
Wattmeters of radio and optical ranges are marked according to GOST 15094:
- M1-xx - calibrators, installations or instruments for calibrating wattmeters (radio band)
- M2-xx - wattmeters passing power (radio band)
- M3-xx - wattmeters absorbed power (radio band)
- M5-xx - receiving transmitters (heads) wattmeters
- OM3-xx - optical wattmeters absorbed power
Main standardized characteristics
- Working frequency range
- Measuring range
- Permissible measurement error (for el. Meas. - accuracy class )
- Valid VSFR - for wattmeters of the radio range
See also
- Power
- Radio measuring devices
- Electrical measuring instruments
Literature
- P. Voinarovsky,. Electrical measuring instruments // Encyclopedic dictionary of Brockhaus and Efron : 86 t. (82 t. And 4 add.). - SPb. , 1890-1907.
- Handbook of electrical appliances / Ed. KK Ilyunina - L .: Energoatomizdat, 1983
- Handbook of radio devices. In 3 tons. / Ed. V.S. Nasonov - M .: Owl. radio, 1979
- Meizda F. Electronic Measuring Instruments and Measurement Methods - M .: Mir, 1990
- Handbook of electronic devices. In 2 tons. / Ed. D.P. Linde - M .: Energy, 1978
- Regulatory and Technical Documentation
- GOST 8476-78 Wattmeters and varmeters. General technical conditions
- GOST 8476-93 Direct-acting analog indicating electrical measuring instruments and accessories to them. Part 3. Special Requirements for Wattmeters and Varmeters
- GOST 8.392-80 State system for ensuring the uniformity of measurements. Low-power microwave wattmeters and their primary measuring transducers of the frequency range 0.03-78, 33 GHz. Methods and means of verification
- GOST 8.397-80 State system for ensuring the uniformity of measurements. Low-power pulsed waveguide wattmeters in the frequency range 5.64-37.5 GHz. Methods and means of verification
- GOST 8.497-83 State system for ensuring the uniformity of measurements. Ammeters, voltmeters, wattmeters, varmeters. Method of verification
- GOST 8.569-2000 State system for ensuring the uniformity of measurements. Wattmeters microwave low power frequency range 0.02-178.6 GHz. Method of verification and calibration
- IEC 61315 (1995) Calibration of power meters (wattmeters) of fiber-optic radiation sources
Links
- Wikimedia Commons has media on Wattmeter * Measurement of insertion loss using wattmeters
- Advanced VHF Wattmeter
- HIGH FREQUENCY WATTMETER AND NOISE GENERATOR
- Waveguide wattmeters microwave