# Smart Energy Meters for Smart Grids, an Internet of Things Perspective
## 2 Sensing Techniques
### Electricity Meters
#### 2.3.2 Grid Sensing
\begin{table}
\begin{tabular}{p{71.1 pt} p{142.3 pt} p{142.3 pt}} \hline \hline
**Meter Type** & **Working Principle** & **Advantages/Disadvantages** \\ \hline \multirow{3}{*}{Shunt resistor} & Voltage drop parallel to the measured nodes & **Advantages:** inexpensive, good dynamic range, reasonably accurate **Disadvantages:** power loss, overcurrent can permanently damage, no isolation for high voltages \\ \hline \multirow{3}{*}{Current transformer} & Current through conductor generates magnetic field which induces back emf across the transformer terminals & **Advantages:** High-voltage measurements, lower power consumption, stable measurements, isolation **Disadvantages:** large size, relatively expensive, nonlinear, can measure AC only \\ \hline \multirow{3}{*}{Rogowski coil} & Same as current transformer but is air-wound instead of core-wound & **Advantages:** reasonably accurate, low-cost, lower power consumption, uniform scale **Disadvantages:** poor sensitivity, greater output isolation is required, an integrator is required \\ \hline \multirow{3}{*}{Hall effect} & Voltage difference transverse to current in magnetic field perpendicular to that current & **Advantages:** large dynamic range, small size, can be integrated on PCB, measures AC/DC, isolated **Disadvantages:** large thermal drift, overcurrent induces magnetic offset, overheating for large frequency signals \\ \hline \multirow{3}{*}{Fluxgate} & Rate of change in flux linkage generated by opposing magnetic fields picked up by sensing coils & **Advantages:** high accuracy, low thermal drift **Disadvantages:** complicated design, noise, small dynamic range \\ \hline \multirow{3}{*}{AMR (anisotropic magneto-resistance)} & Resistance to flow of current in the conductor placed in magnetic field due to relative direction of current to magnetic field & **Advantages:** large dynamic range, small size, can be integrated on PCB, measures AC/DC, isolated **Disadvantages:** large thermal drift, overcurrent induces magnetic offset, overheating for large frequency signals \\ \hline \multirow{3}{*}{Fiber optic} & Change in characteristics of light due to change in magnetic field & **Advantages:** most accurate, very low thermal drift, very high dynamic range **Disadvantages:** most expensive, most complicated, bending stress. \\ \cline{1-1} \cline{3-3}  & & **Advantages:** large dynamic range, small size, can be integrated on PCB, measures AC/DC, isolated **Disadvantages:** large thermal drift, overcurrent induces magnetic offset, overheating for large frequency signals \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Current sensing techniques review. The sensing technologies outlined above constitute a basic system that can monitor and compute various parameters to optimally represent the state of the consumption at various levels, from a single household to complex interconnecting grids. The state of art in energy metering is evolving with new parameters and paradigms, and techniques continue to evolve, requiring computation and communication enhancements, which tend to keep up with this advancement. This constitutes the next component of the sensing node at the physical level, the computing and communication infrastructure. Different grid sensors, their functionality, and usage are summarized in Table 6.