Remotely Monitoring Electrical Power Signals with a Single-Board RIO

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"The combination of the sbRIO off-the-shelf platform and the custom RIO mezzanine card (RMC) for I/O makes a powerful, cost-effective, and yet configurable solution for measurements of AC power signals."

- Jim Campbell, Viewpoint Systems

The Challenge:
Local power analysis systems typically have constraints in equipment cost, size, and power usage balanced against the need for simultaneous sampling front-end circuitry and custom data processing algorithms on the back-end. Furthermore, many of these systems are presently deployed as prototypes or short-run productions, requiring a combination of off-the-shelf and custom-designed components.

The Solution:
The customer needed 8 channels of simultaneously-sampled analog inputs (AI), each capable of sampling at least 50 kHz. These AI channels sample the voltage and current of the neutral and three phase power lines. Furthermore, to coordinate power and load fluctuations across many measurement locations, a world-wide synchronization signal is needed.

Author(s):
Jim Campbell - Viewpoint Systems

Electronics Design for sbRIO Mezzanine Card Combines Custom Needs with Flexibility

The Single-Board RIO (sbRIO) platform offers an excellent balance between off-the-shelf capability and custom design needs in a reasonably small package. The sbRIO provides the processor, memory, and connectivity while the RIO Mezzanine Card (RMC) provides the I/O and signal conditioning needs. See this white paper, Developing Embedded Systems: Comparing Off-the-Shelf to Custom Designs, for a discussion of the benefits of using this approach.

The RMC was designed with simultaneously-sampled analog inputs and a GPS receiver. The RMC was mounted to a sbRIO-9606. Some of the design specifications are as follows:

  • 8 analog input cannels: simultaneous sampling at 50 kHz, ±10 V range, 16-bit resolution
  • GPS receiver with Pulse Per Second (PPS) timing signal with 60 ns accuracy
  • SMA Connector for external GPS active antenna
  • 20 position terminal block for analog inputs and shields, removable for wiring
  • Operates inside an enclosure with internal conditions -40 to 55 °C temperature

An image of the designed RMC and the sbRIO-9606 is shown below.

Power Line Data Acquisition sbRIO RMC Module with GPS Timing

 

Since the A/Ds reside on the RMC, the data bytes are accessed by sbRIO FPGA VIs code communicating through an SPI data bus designed into the RMC.  The internal real time clock coupled with the GPS PPS signal allowed for timing accuracy within a GPS region well under +/- 1uS of accuracy for all data sampled no matter the location, internally or from unit to unit within feet or 1000s of miles away.

System Benefits

The key benefits to this system are:

  • The combination of the sbRIO off-the-shelf platform and the custom RIO mezzanine card (RMC) for I/O makes a powerful, cost-effective, and yet configurable solution for measurements of AC power signals.
  • With the GPS component on the RMC, measurement units can be placed at dispersed locations while still providing adequate synchronization of acquired waveforms for localizing and understanding disturbances in power transmission and distribution, irrespective of any specific application.

 

Author Information:
Jim Campbell
Viewpoint Systems
800 West Metro Park
Rochester, NY

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