What Is a Wattmeter?
An instrument that measures electrical power. Generally refers to the power meter that measures power in DC and low frequency technology, also known as wattmeter.
- Chinese name
- dynamometer
- Foreign name
- power meter
- Applied discipline
- Power and communication
- An instrument that measures electrical power. Generally refers to the power meter that measures power in DC and low frequency technology, also known as wattmeter.
- The power meter consists of a power sensor and a power indicator. The power sensor is also called a power meter probe. It converts high-frequency electrical signals into electrical signals that can be directly detected through energy. Power indicators include signal amplification, conversion, and displays. The display shows the power value directly. Connect the power sensor and power indicator with a cable. In order to meet the needs of different frequencies, different power levels and different transmission line structures, a power meter must be equipped with several power meter probes with different functions.
Power meter power introduction
- Power is an important parameter to characterize electrical signals. A power meter is a meter that measures the active power of an electrical signal.
- In the DC and low frequency ranges, power can be calculated by measuring voltage and current. The instantaneous value of power can be expressed by the following formula:
- For a periodic signal with a period T, the average value of the instantaneous power in a period is called active power. The active power is calculated as follows:
- For a sine circuit, the following holds:
- In the above formula, U and I are the effective values of sinusoidal AC power, respectively, and is the phase difference between the voltage and current signals.
- For non-sinusoidal circuits, it is assumed that U and I are the effective values of the nth harmonic component of the AC power, is the phase difference between the nth harmonic component of the voltage and the nth harmonic component of the current, and P is the active power of the nth harmonic component. The above formula still holds. When n = 1, P is the fundamental active power.
- In the UHF and microwave bands, there are TEM and non-TEM waves. In coaxial systems of TEM waves, although voltage and current have exact meanings, it is difficult to measure their absolute values. In waveguide systems, voltage and current lose their uniqueness because of different electromagnetic modes. In individual frequency bands and transmission systems, power is an important method for single-value characterization of signal strength. Measuring power directly in the RF range replaces voltage and current measurements.
Power meter measurement unit
- Power is defined as the work done per unit of time. The basic unit is watts (W). 1W is equivalent to doing 1 Joule of work in 1 second. Commonly used power units are megawatts (1MW = 10 ^ 6W), kilowatts (1KW = 10 ^ 3W), milliwatts (1mW = 10-3W), microwatts (1W = 10-6W), picowatts (1Pw = 10-12W).
- Another commonly used power unit is expressed in decibel milliwatts (dBm). It takes 1 milliwatt as the reference level P0 = 1mW, and the actual power value P (mW) is compared with P0 to take the logarithm. This is the absolute unit of power.
- It can also use decibel watts (dBW) as the power unit. At this time, P0 = 1W, that is, 1 dBW = 30 dBm.
Power meter composition
- The power meter consists of a power sensor and a power indicator. A power sensor is also called a power meter probe. It converts high-frequency electrical signals into electrical signals that can be directly detected through energy. Power indicators include signal amplification, conversion, and displays. The display shows the power value directly. Connect the power sensor and power indicator with a cable. In order to meet the needs of different frequencies, different power levels and different transmission line structures, a power meter must be equipped with several power meter probes with different functions.
Product Categories
- According to the measured signal frequency, the power meter can be divided into: DC power meter, power frequency power meter, variable frequency power meter, RF power meter and microwave power meter.
- Since DC power is equal to the simple product of voltage and current, in practice, voltmeters and ammeters are generally used instead. Power frequency power meters are commonly used power meters, and power meters are often referred to as power frequency power meters. Frequency conversion power meter is the product of the rapid development of frequency conversion speed regulation technology in the 21st century. The measurement object is the variable frequency power, which refers to the AC power used to transmit power and meet one of the following conditions:
- 1. The signal spectrum contains only one frequency component, and the frequency is not limited to the power frequency AC signal.
- Common frequency conversion power waveform and spectrum (5 photos)
- 2. The signal spectrum contains electrical signals of two or more frequency components of interest.
- Frequency conversion power includes voltage, current, and active power, reactive power, apparent power, active energy, and reactive energy derived from voltage and current.
- In addition to the PWM wave output by the inverter, the current waveform input by the inverter rectified by the diode, the voltage waveform output by the DC chopper, and the input current waveform of the transformer without load, all contain large harmonics. Power waveform and related spectrum.
- Due to the complex frequency component of the frequency conversion power, the measurement of the frequency conversion power meter generally includes the fundamental active power (referred to as fundamental power), harmonic active power (referred to as harmonic power), total active power, etc., compared to the power frequency power meter It has more functions and more complicated technology. It is generally called a variable frequency power analyzer or a broadband power analyzer. Some high-precision power analyzers are also suitable for variable frequency power measurement.
- The variable frequency power analyzer can be used as a power frequency power analyzer. In addition, it generally needs to meet the following requirements:
- 1. Meet the necessary bandwidth requirements, and the sampling frequency should be higher than twice the instrument bandwidth.
- 2. It is required that the analyzer can meet certain requirements within a wide frequency range.
- 3. With the Fourier transform function, the fundamental and harmonics of the signal can be separated.
- RF or microwave power meters can be divided into:
- There are two types of terminal and through. The terminal power meter uses the power meter probe as the terminal load of the test system. The power meter absorbs all the power to be measured, and the power indicator directly reads the power value. Through-type power meter, it uses some kind of coupling device, such as directional coupler, coupling ring, probe, etc. to couple out a part of the power from the transmitted power in a certain proportion, and sends it to the power meter for measurement. Multiply the indicator value by the scale factor.
- RF or microwave power meters by sensitivity and measurement range
- Thermistor type power meter uses thermal resistance as the power sensing element. The temperature coefficient of the thermal resistance value is large. The power of the measured signal is absorbed by the thermal resistance to generate heat, which causes its own temperature to rise, and the resistance value changes significantly. The change in resistance value is measured using a resistance bridge to display the power value.
- Thermocouple type power meter The thermocouple junction in a thermocouple type power meter directly absorbs high-frequency signal power, the junction temperature rises, and a temperature difference potential is generated. The magnitude of the potential is proportional to the absorbed high-frequency power value.
- Calorimetric power meter A typical thermal effect power meter uses a heat-insulated load to absorb high-frequency signal power to increase the temperature of the load, and then uses a thermocouple element to measure the temperature change of the load and calculate the high-frequency power value based on the heat generated.
- The crystal detector power meter crystal diode detector converts high frequency signals into low frequency or direct current signals. Select the working point appropriately so that the amplitude of the output signal of the detector is proportional to the power of the high-frequency signal.
- Classification by measured signal
- There are continuous wave power meters and pulse peak power meters.
Power meter technical indicators
Power meter frequency conversion
- Power meter for variable frequency power measurement (3 photos)
- Bandwidth: 50kHz ~ 100kHz;
- Sampling frequency: more than twice the bandwidth;
- Voltage and current accuracy: 0.02, 0.05, 0.1, 0.2, 0.5;
- Power accuracy level: 0.05 level, 0.1 level, 0.2 level, 0.5 level, 1 level;
- Accuracy level applicable fundamental frequency range: DC, 0.1Hz ~ 400Hz;
- Applicable voltage range of accuracy level: 0.75% Un ~ 150% Un;
- Accuracy level applicable current range: 1% In ~ 200% In;
- Accuracy class applicable power factor range: 0.05 ~ 1.
RF power meter
- The following are typical technical indicators of RF power meters
- Power range
- Maximum and minimum range of measurable power to ensure measurement accuracy. The power range of the power meter is determined by the power probe.
- Maximum allowable power
- The maximum input power value that the probe will not be damaged is usually the average power. When measuring high-power peak signals, pay attention that the peak voltage cannot exceed a certain value, otherwise it will cause voltage breakdown. Never use a power meter to measure a signal that is greater than the allowable power value, otherwise the power probe will burn out.
- Frequency Range
- The frequency range of the signal being measured can ensure measurement accuracy and performance indicators.
- measurement accuracy
- Refers to the accuracy of power probe calibration. Does not include test system mismatch errors.
- stability
- The stability of the power meter depends on the stability of the power probe and the zero drift and noise interference of the indicator.
- Response time
- Also called the time constant of the power sensing element. Usually refers to the time required for the power indicator to rise to 64% of the stable value.
- Probe model and impedance
- When selecting a power meter probe, the frequency and power range of the power probe must be consistent with the measured signal, and the structure and impedance of the probe transmission line should match the measured transmission line.
- Technical Parameters
- Frequency range 9KHz 110GHz (depending on the sensor)
- Power range -70 + 44dBm
- Measurement accuracy Absolute accuracy: (logarithmic) ± 0.02dB; (linear) ± 0.5%
- Relative accuracy: (logarithmic) ± 0.04dB; (linear) ± 1.0%
- Logarithmic resolution: 1.0; 0.1; 0.01 and 0.001 dB (default setting: 0.01 dB)
- Linear mode: 1 to 4 digits (default setting: 3 digits)
- SWR 1.06 max (option 003 can go to 1.08)
- Applicable sensors: E series sensors, 8480 series sensors
- Common application field average power measurement (such as on-site repair service)
- Warranty and calibration standard configuration: Global 3-year warranty and 2-year calibration cycle
- Steps
- Connect the probe and the host with a cable
- Connect the probe to the host calibration source after warming up, press the calibration key to calibrate
- After calibration, remove the probe and measure at the test point frequency.
- Precautions
- Pay attention to the common ground of the power meter and the measured signal before use
- Pay attention to the choice of probe direction and range
- Do not connect the antenna port of the power meter to the RF transmitting end of the device, it is easy to burn the power meter.
- Take care to calibrate with a calibration source before measuring
- Use power timing frequency and measured frequency should be the same
- When the measurement power is less than -50dBm, it should be zeroed before the test. [1]
Power Meter Product Application
Power meter optical power measurement
- It is used to measure the absolute optical power or the relative loss of optical power through a fiber. In fiber optic systems, measuring optical power is the most basic, much like a multimeter in electronics. In optical fiber measurement, the optical power meter is a commonly used meter for heavy loads. By measuring the absolute power of the transmitting terminal or optical network, an optical power meter can evaluate the performance of the optical terminal equipment. Using an optical power meter in combination with a stable light source can measure connection loss, verify continuity, and help evaluate fiber link transmission quality. According to the specific application of the user, to select a suitable optical power meter, the following points should be paid attention to:
- 1.Select the optimal probe type and interface type
- 2. Evaluate calibration accuracy and manufacturing calibration procedures to match your fiber and connector requirements.
- 3. Make sure these models are consistent with your measurement range and display resolution.
- 4. With dB function for direct insertion loss measurement.
Power meter electrical test
- Application of variable frequency power analyzer (7 photos)