MCP3909 3-Phase Energy Meter Reference Design Using PIC18F2520 (MCP3909RD-3PH1)
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The MCP3909 3-Phase Energy Meter Reference Design is a fully functional Flash MCU based 3-phase energy meter. The meter comes populated with components for a 220V, 5(10)A system complete with plastic IEC compliant energy meter case. The case contains high voltage line and load screw terminals for direct connection to mains voltage or to energy meter calibration equipment. The 3-phase energy meter calculations are Flash based using 7K of PIC18F2520 program memory. The calculations include active energy pulse output, active power, apparent power, RMS current, and RMS voltage. There are over 100 serially accessible output registers containing power quantities, in Flash. For calibration, there are registers including offset, gain, phase, and LSB correction for all power and energy quantities, in Flash. All registers are accessible through RS-232 and USB.
The calibration and correction registers can easily be moved from Flash to EEPROM using a simple ‘store’ command for end user configurable write cycle times.
The analog conversion uses the wide dynamic range 16-bit ADCs MCP3909, which are sampled at 128 times per line cycle. The calculations are all interrupt driven to ensure ‘Zero-Blind’ measurements for all power quantities per line cycle.
The system also includes a Phase Lock Loop circuit for line cycle sample lock.
The system is easy to use, command driven, and offers ‘mode’ registers for features such as positive only energy accumulation mode or no-load threshold mode. A 64-bit wide active energy register is used for long term energy accumulation. Phase calibration for CT non-linearity correction is included.
In addition to the power calculation engine using MCP3909 + PIC18F2520, a second communications module is included with the system. The included communications module is the PIC18F4550 USB Interface Module, which allows for meter evaluation and calibration using the “3-Phase Energy Meter Software” running on Windows XP or Windows 2000. The PIC18F4550 USB interface module also includes an LCD for additional energy meter firmware design.
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