Power Monitoring with PIC Processors

Power monitoring circuits are used in commercial applications such as data centers for two main purposes: monitoring power consumption and sending alerts when the current flow approaches the breaker limit.

Typically data centers have large breaker panels (up to 42, 60, 72 breakers per panel) and use "CT strips" where the current transformers are on a strip in front of the breakers. Each phase power wire goes through the current transformer before it is attached to the breaker. These types of installations are done during the build stage and before main power is applied.

The circuit shown above is used with current transformers that are a "Split Core" type and can be attached to existing power installations.This type of input circuit is ideal for commercial applications such as mechanical rooms in strip malls, etc.

The design is based on a PIC18F46K80 microprocessor with 12 bit A/D resolution.

Here is the design criteria for the above circuit:

  • 6 x 3-phase circuit inputs (Total 18 current monitor channels)
  • Up to 200 Amp Current Transformer input (Solid or Split Core)
  • 18 channel multiplexer to handle mVAC signals
  • High Precision analog front end
  • True RMS AAC software to handle complex AC waveforms
  • Zero Crossing circuit implemented in software
  • Complete read and RMS calculations for all 18 channels in under 3 seconds
  • 3000 VAC Isolation between front end circuitry and interface circuitry
  • Modbus RTU over RS485 interface protocol
  • Wide power input of 9 to 24 VDC

There are other features like dipswitch selection for Modbus ID, lots of LED indicators, baud rate selection via jumper, simple calibration via jumper, plus others.

This design features what can be done with an inexpensive micro like the PIC18F series.



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