# Smart Energy Meters for Smart Grids, an Internet of Things Perspective
## 2 Sensing Techniques
### Gas Meters
Another type of static meter is the Coriolis meter, which uses oscillating tubes, whose oscillations vary with the variation of the mass flow, thus directly measuring mass flow instead of using volumetric flow [80]; this makes the Coriolis meter arguably the most accurate meter in flow measurement, with a long life [81] and wide industrial usage in the food, beverage, and chemical sectors [82], and it is now finding increasing usage in domestic metrology [83]. Finally, several international organizations have drafted gas metrology standards for domestic and commercial installations, \begin{table}
\begin{tabular}{c c c} \hline \hline
**Meter Type** & **Working Principle** & **Advantages/Disadvantages** \\ \hline Diaphrag/bellows & Displacement of the diaphragm/bellow & **Advantages:** cheap, easy to design, widely adopted, tested for legal meteorology \\  & Displacement of the diaphragm/bellow & **Disadvantages:** for small flows, sensitive to impurities, small dynamic range \\ \hline Rotary & Rotation speed & **Advantages:** accurate, can measure large flows, can withstand high pressures \\  & & **Disadvantages:** maintenance, wear and tear, expensive \\ \hline Turbine & Rotation speed & **Advantages:** accurate, can measure large flows, can withstand high pressures \\  & & **Disadvantages:** maintenance, wear and tear, expensive \\ \hline Orifice & Pressure differential across the orifice & **Advantages:** no moving parts, easy to service \\  & & **Disadvantages:** small flows only, complex measurement \\ \hline Ultrasonic & Difference in time of flight of ultrasonic signal along and against the flow & **Advantages:** accurate, works best for dry gases, wide dynamic range \\  & the flow & **Disadvantages:** complex measurement, low value output \\ \hline Coriolis & Oscillations of tubes measure the mass flow or density & **Advantages:** most accurate, can measure large flows, wide dynamic range \\  & & **Disadvantages:** needs additional elements \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Different types of gas meters. such as the OIML reference document R-137 part 1 and 2, which specifies the requirements and technical guidelines for domestic gas metrology. Based on the designs, several implementations have been reported in the literature. Two types of domestic gas meters using a mechanical sensor fitted with an electronic index and an ultrasonic mechanism with temperature compensation are reported in [84], where both of these meters are fitted with an electronic communication mechanism for smart metering. A radio module for automatic reading is reported in [85]; it interfaces with the pulse interface of the gas meter to transmit the volume consumed. One of the earliest ultrasound meters is designed in [86] for domestic application. A high-resolution retrofit module for a mechanical meter is designed in [87]; it uses an encoder with 90 pulses per revolution for measuring the gas usage at finer scales. An ultrasonic domestic meter is developed and tested in [88] for industrial scale productions. An application note describing the design of a simple fluid flow meter is given in [89]; it can be built at lower cost and, hence, can be used frequently for increasing the sampling of the domain in the smart solution. In [90], a bi-directional communicating gas meter for IoT-enabled operation is developed and tested for smart gas management, reporting a reduction of 37% in consumption. An automated meter reading framework for the smart metering domain is implemented for utility gas in [91]; it can integrate automated billing using consumption slab data. A novel polysilicon-based thermal flow sensor is developed and tested for domestic gas metering in [92]. An integrated CMOS-based gas mass flow meter for multiple applications in measuring mass flow is developed in [93]. Another method to read the mechanical meter via an electronic technique is given in [94]; it uses need switches and Hall effect sensors interfaced to an MCU for the electronic readout.