22-02-2013, 04:40 PM
Wireless Energy Meter
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Abstract
This paper describes the ongoing development of an
Energy Meter (EM) with an interface to a wireless sensor
network based on IEEE 802.15.4 technology.
INTRODUCTION
In the age of ecological awareness, and the conclusion that
energy should not be wasted, it is necessary to investigate the
places where electrical energy is consumed. The effective
energy usage of a device can often be determined by
monitoring the according electrical devices over a long space
of time. The measuring can easily be done by simple Energy
Meters from the local do-it-yourself store. But sometimes the
limited functionality of these meters also limits their area of
application. If, for example, a refrigerator shall be measured,
the power cord may not be easily accessible. And most of the
“standard” Wireless Energy Meters show their calculations on
a small display directly on the meter. A solution is a Wireless
Energy Meter which is able to transmit its measured data
wirelessly to a computer. There the data can be interpreted and
maybe even compared to data from other wirelessly connected
devices.
RELATED WORK
In [1] an AC Meter (ACME) development for IP based
Wireless AC Energy Monitors is presented. The developed
platform consists of four main sections: power supply, signal
filtering, Wireless Energy Metering and microcontroller. All
embedded Software developments are done with TinyOS. In
[2] an electronic system is described to measure the active,
apparent and reactive energies delivered to a load of an AC
voltage line. The proposed system is directly connected to a PC
running visualization software of the power consumption. In
[3] a case study of an inexpensive student designed power
monitoring instrument for campus submetering is described.
This system is build up with an Energy Metering IC connected
to a PIC controller. Over a serial interface measured values can
be accessed.
HARDWARE OVERVIEW
The Wireless Energy Meter (see also Figure 1) consists of
two major elements to measure the different kinds of the power
consumption. These two elements are the IEEE 802.15.4 [4]
ICradio Module 2.4G [5] and the Energy Measurement IC
ADE7753 [6] which will be introduced below.
ADE7753
The ADE7753 allows the control and the read out of
several energy registers over a serial interface which is
compatible to SPI. Through this registers it is possible to read
out the accumulated values of active and apparent energy, the
rms values of current and voltage and for example get
information about the line period. In addition, it is possible to
write to the ADE7753 registers to configure for example gains
or compensate offsets among all the operations.
Wireless Energy Meter Hardware Design
The needed voltages for the two main hardware
components, the ADE7753 and the ICradio Module 2.4G, are
provided by a power supply which uses direct rectification. For
the current sensing a shunt resistor is used, over which a
comparatively low voltage drops when a current flows. The
voltage sensing is done by a simple voltage divider, which
scales the line voltage from 230Vrms to about ±0.5V.
SPI Communication
The entire communication process to the ADE7753 takes
exactly 225us (see also Figure 3). During this time frame the
transceiver has no SPI connection to the microcontroller
because only one device at time can transfer data to the
microcontroller via SPI. Thus, the EM node is temporary not
part of the wireless network. In multi-hop networks the routing
protocol has to take this into account. In this current setup the
communication is done by a pull mechanism of the node itself
to a sink node in a peer-to-peer star network.
CONCLUSION AND FUTURE WORIK
In this paper a wireless energy metering device is described
which allows the visualization of power consumption of
electrical devices like a TV or washing machine in real time.
The current system enables residents to have an immediate
overview about the actual and short term history power
consumption. Future work will include developments towards
automatic and remote control of devices. A further approach
could be that once a day accumulated data is sent from the
household to the energy provider.