Energy Meter Reference Design Based on the MAXQ3180/MAXQ3183

The MAXQ3180 and MAXQ3183 are multiphase, multifunction, energy-metering, analog front ends with many advanced power-monitoring features (AFEs). These devices integrate 8 channels of high-precision analog-to-digital converters. A digital signal processor (DSP) processes the ADC samples to provide a rich array of energy and power measurement parameters including, but not limited to: active/reactive/apparent power and energy, power factor, and harmonic content. An SPI™ port provides an interface with a host controller. The MAXQ3180 and MAXQ3183 are two of three multiphase AFE devices from Maxim Integrated Products. The third, the MAXQ3181, is active energy and power only. Table 1 summarizes the key features of the multiphase AFE family.

Table 1. AFE characteristics for multi-phase comparison of measurement equipment

The MAXQ3181 is fully pin-compatible with the MAXQ3180 and its registers are a subset of the registers in the MAXQ3180. Therefore, the same reference design can be used to evaluate the MAXQ3181. The board is changed for the measurement device AFE, but no changes to the application code or PC software are necessary. Please note that when evaluating the reference design, rather than simply the MAXQ3181, some of the metering parameters not provided in the MAXQ3181 will appear random and meaningless.

For simplicity, this application note will refer to the target devices simply as the MAXQ3180 and MAXQ3183, and their unique features will be cited only where necessary. The reference designs for these devices share the same photometric board and use the same host microcontroller (i.e., the MAXQ2000).

About the Reference Design

The MAXQ3180 reference design includes the following:

3-phase energy meter

PC Software

Product Specifications

This reference design supports three-phase four-wire only:

AC conditions: 50Hz/60Hz, 220V, 9A²

Meter constant: 6400

Instrument accuracy: 0.5 second level and 2 level positive response

Serial (PC) communication baud rate: 1200/9600/57600/115200

Display and Communication

The reference design meter automatically starts running when powered up and displays various information on the on-board LCD. The first item displayed is the name of the device (i.e., MAXQ3180 or MAXQ3183), then the RS-232 baud rate, and then various power and energy parameters (voltage and current rms, total power factor, total kilowatt-hours since last power-up). This information automatically rotates continuously with a parameter update rate of one per second. Additional energy and power parameters can be retrieved and displayed by the PC software.

The meter communicates with the PC via an RS-232 serial port, which is hidden inside the meter case. To access the serial port, open the meter case. (See the Communications/JTAG Cable section for connections.) Be sure to turn off AC power before reconnecting. Note that the MAXQ3180 reference design supports infrared communication in hardware, but support for this feature has not been implemented in the firmware (MAXQ2000 code) for this writing.

Figure 1 shows the communication and display elements of the instrument.

Figure 1. Board layout and connection terminals in the energy meter reference design.

AC Terminal Blocks

Refer to Figure 2 when the connection between the reference design meter and a meter tester is communicated

Figure 2. Close-up view of the connector from the energy meter reference design to a meter tester.

The instrument case does not support a neutral current input because there are only three pairs of current inputs (terminals). However, there are also current input nodes for the neutral side. This limitation makes it very inconvenient to demonstrate the four current vector summation capabilities of the MAXQ3183.

The instrument design uses two boards. The "cold board" (i.e., the board that contains the microcontroller and display) is safe to touch as no high voltages exist on this board. The screws and connections underneath the board are not safe to touch, however. The "hot board" below the cold board contains the AC input circuitry and the target device (such as the MAXQ3180/MAXQ3183). This board is connected directly to the AC neutral and, therefore, is not safe to touch.