# Smart Energy Meters for Smart Grids, an Internet of Things Perspective
## 2 Sensing Techniques
### Gas Meters  
In smart energy domains, gas meters are used to measure the total volume of gaseous fuel delivered by a system that is usually held at constant pressure. Gas measurements are usually difficult as the volumetric readings from the flow measurements are cumbersome and prone to error due to the dependence of the volume on temperature and pressure [70]. Flow metering is a very active research area, and numerous techniques have been developed and reported, but there are very few commercially deployed techniques [71] due to the strict nature of the legal and commercial standards. A brief review of the commonly used gas flow metering techniques is provided in Table 3, which includes dynamic and \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Meter Class** & **Meter Type** & **Principle** & **Advantages/Disadvantages** \\ \hline \multirow{4}{*}{Dynamic Meters} & Turbine & Rotation speed proportional to & **Advantages:** cheap, easy to design \\  & & mass flow & **Disadvantages:** nonlinear behavior, \\  & & & sensitive to impurities, small dynamic range \\ \cline{2-4}  & Impeller & Displacement proportional to & **Advantages:** can measure large flows \\  & & mass flow & **Disadvantages:** wear and tear, \\  & & & startup threshold \\ \hline \multirow{4}{*}{Static Meters} & Magnetic Induction & Voltage proportional to velocity of & **Advantages:** less obstruction, accurate \\  & & flow through the magnetic field & **Disadvantages:** nonlinear behavior, costly \\ \cline{1-1} \cline{2-4}  & Ultrasonic & Difference in time flow of & **Advantages:** can measure large flows \\ \cline{1-1}  & & ultrasonic pulses propagating in & **Disadvantages:** nonlinear behavior, less \\ \cline{1-1}  & & and against the flow direction & accurate, complex \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Review of different types of heat meters. static meters. Dynamic meters include diaphragm-based meters and mechanical rotatory measuring device-based flow meters. Diaphrag-based flow meters are the most common, with the greatest consumer and industrial installation base; they are robust and reasonably accurate, especially for the energy gases. Greater accuracy and range could be achieved using mechanically precision-machined rotatory meters that measure the speed of the gas flow [72] and infer the volumetric flow rate. Dynamic meters are prone to wear, tear, measurement drifts, and limited response speeds. Static meters use measurement processes that do not require the movement of measuring elements for the flow measurement, such as ultrasonic meters and Coanda effect meters; hence, they are more robust with regard to errors, wear, tear, and fatigue, resulting in better performance, longevity, and smaller size [70]. The Coanda effect is the preferential nature of the fluid jet towards the stable solid surface, which is employed in gas meteorology by making a gas jet flow in the chamber with feedback, resulting in induced oscillations whose frequency can be measured by a piezoelectric sensor, for example, which is proportional to the gas flow [73]. These meters are commonly known as fluidic oscillator meters [74] and include feedback oscillator and target fluidic oscillator meters [75]. Other types of fluidic flow meters are vortex shedding [76], which is the oscillation when a fluid flows past a bluff, and vortex whistle meters [77], which measure the frequency of sound generated as the gas passes through the cylinder downstream, in the cylindrical cavity that is tangentially connected to the inlet. Another commonly used static flowmeter is the ultrasonic flow meter, which uses the difference of frequency of the ultrasound waves travelling along and opposite to the flow of the gas [78]. Ultrasound meters are not commonly employed in domestic and industrial fuel gas measurements due to the cost, complexity, and dynamic range, but are finding increasing applications in metrology [79].