# Remote Low-Cost Differential Isolated Probe for Voltage Measurements
## 4 Discussion  
Following the tests carried out and the obtained results, the following issues can be analysed. The measurements show a mismatch produced by the gain error of the isolation amplifier itself and by the deviations existing in the rest of the amplifier stages constituting the measurement circuit. This error is easily correctable, either by performing a previous hardware calibration though a potentiometer, or by making a compensation via software in the microcontroller, or by developing a protocol and a self-calibration system, leaving the latter case as a future improvement of the system. On the other hand, the use of batteries for a device that relies on Wi-Fi as a communication system may be questionable due to the high-power consumption of this protocol, which shortens battery life. It should be noted that the use of batteries is intended for one-off measurements or for short periods of time. For continuous measurements or longer periods of time, the mains connection is available. In the case of needing to measure over long periods of time with a battery-powered system, it would be necessary to resort to another communication technology such as LoRa, which presents a much lower power consumption than a Wi-Fi network. On the other hand, it will be necessary to deploy the LoRa network if it does not exist, as this communication protocol is less common, while the use of Wi-Fi networks is more common and can result in savings in terms of communication network deployment. Therefore, this issue should be carefully analysed before making a decision. The main characteristics of the commercial probes and the proposed probe are listed in Table 3. The commercial probes have wider input voltage ranges as well as wider bandwidths. The input range, in our case, could be adjusted by modifying the values of the attenuation stage used. However, the selected values allow us to properly deal with the values of a three-phase distribution system, both in line and phase voltage. Regarding bandwidth, the EN 50160 standard requires measuring up to the 25 th harmonic of the mains voltage, with a frequency of 1250 Hz for a 50 Hz network. Therefore, the proposed probe has a sufficient bandwidth to meet the requirements. The advantage of the proposed development is that it is cheaper than commercial probes and includes isolation. The isolation limits the bandwidth and increases the price, as the ISO122 is an expensive device (between EUR 15 and 20). Despite this, the price is much lower than the other options, which is important for a device that can be part of an IoT network where different devices are simultaneously measuring at different points in the installation. Moreover, isolation is important to safeguard the integrity of the measurement and the communication microcontroller. In the field of intelligent energy management within intelligent buildings, there are several proposals for the measurement of energy consumption, such as those in [28; 29; 30]. In [28], the researchers use an Arduino Pro Micro as microcontroller with an IEEE 802.15.4 communication protocol using an XBee Pro as transceiver, which requires the use of a custom IoT gateway. In [29], the authors use an Arduino One for data acquisition, but do not detail which communication protocol is established for the IoT device, while in [30], they use an Arduino MKR WAN with LoRa integrated and already specifically designed for IoT applications, also following the philosophy proposed in the present work. In the case of needing a LoRa communication to increase the monitoring time by feeding the proposed IoT probe with batteries, it could be interesting to replace the Arduino Nano 33 IoT with the Arduino MKR WAN, as both devices are based on the SAMD21 microcontroller, so the programming should require few modifications. Table 4 gives a summary of these features. The probe proposed in this work can be used for this same purpose without adding a current sensor.