power transducerIt mainly consists of three-phase isolated sampling circuit, A/D converter, microcontroller, DSP device, D/A converter, calibration amplifier, and dedicated thick film integrated V/I converter.
After the three-phase AC input signal is isolated and sampled by a three-phase isolation sampling circuit, a common ground tracking voltage signal of three-phase current and three-phase voltage signals is formed. Under the control of a microcontroller, it is synchronously sampled by an A/D converter at multiple points. The sampled data is calculated by a DSP device according to electrical principles to obtain the three-phase active power (digital quantity) of the measured signal. Then, the digital signal representing the three-phase power is converted into an analog quantity by a D/A converter, amplified and calibrated by a calibration amplifier to form a DC voltage output VZ. The VZ output is converted into a 0-20mA or 4-20mA DC current output IZ through a dedicated thick film integrated V/I converter.
The key to this series of products is computer software and running speed. In order to ensure the authenticity of power measurement, it is necessary to ensure that all voltage and current signals are sampled simultaneously; In order to ensure the accuracy of power measurement, it is necessary to ensure that there are enough sampling points within a sine wave time interval (generally speaking, the number of sampling points should be greater than 20). The large number of sampling points and data volume require high computing speed, and it is necessary to ensure that the calculation program completes all operations within one sine wave cycle.
Under computer software control, sensors can directly output measured power data,
Three phase three wire circuit: P=UAB × IA × COS φ+UBC × IB × COS φ
Three phase four wire circuit: P=UA × IA × COS φ+UB × IB × COS φ+UC × IC × COS φ
At this point, the output signal is directional, such as the sensor WBP311P71 that outputs a DC voltage of 2.5V ± 2.5V. When the power input is 0, the sensor power output value is 2.5V; when the three-phase current flows forward, the sensor power output value increases from 2.5V, and when the input reaches the rated value, the power output value is 5V; when the three-phase current flows backward, the power output value decreases from 2.5V, and when the input reaches the rated value, the power output value is 0V.
Under the control of computer software, sensors can output the absolute value of measured power data,
Three phase three wire circuit: P=│ UAB × IA × COS φ+UBC × IB × COS φ │
Three phase four wire circuit: P=│ UA × IA × COS │+UB × IB × COS │+UC × IC × COS │
At this point, the output signal is undirected, such as the sensor WBP312P71 that outputs 0-5V DC voltage. When the power input is 0, the sensor power output value is 0V; when the three-phase currents change direction simultaneously, the sensor power output value remains unchanged.
Thick film integrated V/I converter is a specialized device developed by our company, which converts DC voltage signals into 0-20mA DC current output. After adding a highly stable bias circuit, a 4mA to 20mA output can be formed.