# A Cyber-Physical Approach for Residential Energy Management: Current State and Future Directions
## 4 Data Acquisition
### Metering Devices
Smart meters have built-in current and voltage sensors to sense current and voltage quantities, providing the single point of sensing needed for NILM. However, the access to smart meter data is still limited in many countries due to regulations and privacy concerns, hindering its use for load monitoring [43]. Current and voltage sensors are one of the most popular electrical sensors for load control. Current transformers (CTs) are generally used for power measurement, thus both sensors may not be enough for monitoring and forecasting requirements. The main cause is that direct current (DC) and high frequency current signatures cannot be captured. To achieve device-level measurement, a considerable amount of current sensors are required, making it impossible to reach each individual device [43]. To overcome this constraint, the electromagnetic field sensor was proposed by the authors of [52] to indirectly obtain gross apparatus level operating states. Figure 6: Schematic diagram of a metering device for HEMS according to IEC TS 63297:2021 standard. In [92], the authors developed their own metering system using an off-the-shelf power strip using a voltage-sensing circuit, current sensors, and a single-board PC as a data aggregator. The six-port monitoring unit can achieve up to 50 kHz for all signals simultaneously. Two types of sensors (current and voltage sensors) were integrated to fully capture the energy consumption data of appliances. In the case of [93], the authors designed a smart socket composed of a common socket, a sampling module, and a processor. Among them, the sampling module adopts the alternating current (AC) power transmitter SUI-101A, which can measure parameters such as voltage, current, active power, power factor, frequency, and cumulative power consumption in real-time. In [94], the authors introduced a measurement system to capture the unique characteristics of the devices. Current and voltage signals were captured with current sensors and voltage probes for all three phases. These signals were input into a Siemens SENTRON PAC4200 network analyzer and an NI USB-6259 acquisition module. The energy used by household appliances can be highly dependent on environmental conditions, such as temperature, humidity, light, and others. Therefore, ambient sensors have also been introduced in HEMS. As an example, in the BLUED residential charging dataset [95], light level, sound intensity, vibration, humidity, barometric pressure, and PIR motion were measured. In the case of the PECAN Street Dataport (see [[https://dataport.pecanstreet.org/](https://dataport.pecanstreet.org/)]([https://dataport.pecanstreet.org/](https://dataport.pecanstreet.org/)) (accessed on 10 May 2021)), the water data was also taken into account. Figure 7: Schematic diagram of the four groups in terms of deployment granularity in HEMS. For some authors [43], the information on the occupation of a house is also important to save residential energy because it involves the control of the heating, ventilation and air conditioning (HVAC) system, water heater, lighting, as well as residential energy storage such as batteries and electric vehicles (EV), in case there is any. A variety of sensors can be used to detect the presence, including acoustics, lighting, camera, motion, CO\({}_{2}\), temperature, laser beam, Radio Frequency Identification (RFID), and humidity [51; 34]. As an economical solution, information from existing WiFi connections or HVAC sensors has also been used for presence detection. Recent studies, such as [43], argue that efforts to develop high-frequency smart plugs to capture load signatures are not available for widespread deployment. However, in [96], the authors perceive smart plug's technology success addresses all aspects for effective load monitoring, such as prosumers (original fusion of the words producer and consumer) being able to make energy consumption and/or production changes, ensuring the security and privacy of metering data, and enabling to manage and store vast quantities of the collected data.