Analogue front-end reference design for 3-phase power monitoring

April 29, 2014 // By Graham Prophet
Maxim has posted details of its “Petaluma” (MAXREFDES30#) 8-channel subsystem reference design: a cost-optimised, high-speed and high-accuracy analogue measurement solution for three-phase power monitoring applications. Hardware, firmware, design files, and lab measurements are included.

Three-phase power measurement applications require multiple analogue inputs for voltage and current measurements on each line of the three-phase system. A power monitoring system must sample all of the analogue inputs simultaneously to accurately calculate the instantaneous power consumption.

The Petaluma subsystem reference design provides eight high-speed, 250 ksamples/sec, 16-bit simultaneous-sampling analogue input channels that accept ±10V input signals.

The Petaluma design uses two quadruple ultra-precision, ultra-low-noise input buffers (MAX44252); an 8-channel, 16-bit simultaneous-sampling ADC (MAX11046B); an ultra-high precision 4.096V voltage reference (MAX6126); and regulated +10V, -10V, and +5V power rails (MAX1659, MAX765/LM337, MAX8881). In addition to three-phase power measurement applications, this subsystem also performs well in any application that requires multiple simultaneous sampling of analogue inputs, such as multiphase motor control and industrial vibration sensing.

The MAX44252 devices (U1 and U2) are quadruple ultra-precision, low-noise op amps. The op amps attenuate and buffer the ±10V input signals to match the input range of the ADC (MAX11046). The MAX44252 devices are set up in the inverting configuration, so the polarity of the signal is reversed at the input of the ADC. The MAX11046 (U3) is a low-cost, 8-channel, 250 ksamples/sec, 16-bit, single-supply, bipolar, simultaneous-sampling ADC.

Although the MAX11046 ADC has an internal 4.096V voltage reference, Petaluma uses an external MAX6126 (U4) voltage reference to provide the highest possible accuracy. The MAX6126 has an initial accuracy of 0.02% and a 3ppm/°C maximum temperature coefficient. Petaluma connects to FMC-compatible field-programmable gate array (FPGA)/microcontroller development boards.

Maxim Integrated;  www.maximintegrated.com/app-notes/index.mvp/id/5827