Digital Wattmeter with Data Logger based on Microcontroller

This research is one of the researches of the roadmap “Power Grid Monitoring Based on Microcontroller”. This research has been preceded by the research with title “Measure RMS Voltages and Currents in Power Grid Based on Microcontroller”. In that research, the microcontroller ADC samples the voltage and current grid 64 times per period of the grid voltage with 8 bit data format, so that we obtain 64 instantaneous values of grid voltage and current per period. The result can measure RMS voltage from 25 V to 250 V at frequency from 22 Hz to 80 Hz and current up to 5 A. To expand its ability to measure power and power factor of load, this research must add an algorithm to calculate it.

This research was done by adding three special algorithms. First algorithm will multiply each of instantaneous value of grid voltage and its corresponding current data, so that we obtain instantaneous electric power value. Second algorithm integrates all the instantaneous electric power values so that we obtain electric power value. The last algorithm computes power factor that is a comparison between the value of electric power and the product of RMS voltage and current. All calculation have been done quickly without involving floating point numbers and held on the sidelines of the sampling process.

Product of this research is a digital wattmeter that can measure frequency, RMS voltage and current, power and power factor up to 1 kVA of loads. Maximum measurement error of power and power factor is 2 %. All of those quantities are calculated ten times per second and display is updated once per second by average value of ten existing data. Next research, this microcontroller-based system should be added an algorithm for data reporting to computer, so that we can monitor all values graphically in computer screen.