The principle of power sensor involves converting power parameters such as current and voltage into measurable electrical signals, and obtaining the required parameters through processing. The following is a detailed step-by-step description of its working principle:
1. Current measurement principle
Shunt resistor method: By connecting a low-resistance resistor (shunt) in series, the voltage across the resistor is measured. It is applicable to DC or low-frequency AC using Ohm's law, but large current may cause heating.
Hall effect sensor: The magnetic field around the current-carrying conductor is used to make the Hall element generate a voltage proportional to the current to achieve non-contact measurement. It is applicable to AC/DC and has good isolation.
Current transformer (CT): Based on electromagnetic induction, it converts the large current on the primary side into a small current on the secondary side. It is only applicable to AC measurement.
Rogowski coil: A toroidal coil without a magnetic core. It outputs a voltage by inducing the current change rate and obtains the current after integration. It is suitable for high-frequency or high-current AC scenarios and has strong anti-saturation ability.
2. Voltage measurement principle
Resistor voltage divider method: Through a series resistor voltage divider network, the high voltage is scaled down and measured. High-precision, low-temperature drift resistors are required.
Voltage transformer (PT): Similar to CT, it converts high voltage to low voltage and is suitable for AC systems.
Capacitor voltage divider method: High voltage is measured using capacitor voltage divider, which is common in high-frequency or pulse voltage scenarios.
3. Signal conditioning and processing
Amplification and filtering: Use operational amplifiers to amplify weak signals and use low-pass filters to eliminate high-frequency noise.
Analog-to-digital conversion (ADC): Convert analog signals to digital signals, and the sampling rate must meet the Nyquist theorem (at least twice the highest frequency of the signal).
4. Power measurement
Sampling the instantaneous voltage and current at the same time, multiplying them to obtain the instantaneous power, and integrating them to obtain the average active power. In a three-phase system, the two-meter method or the three-meter method can be used to calculate the total power.
5. Isolation and safety
Magnetic isolation: Use mutual inductors or magnetic coupling devices to isolate high and low voltage circuits.
Optical isolation: Transmit signals through optical coupling to block electrical connections.
Fiber optic technology: Use the Faraday effect to measure current, with excellent insulation performance, suitable for high voltage environments.