Methodology for assessing the energy consumption of three-dimensional electrical impedance tomography technical means

. The paper deals with the issues of energy consumption of complexes of three-dimensional electrical impedance tomography. The designs of stationary complexes and wearable devices are considered. Their block diagrams are developed and considered. The main elements of the considered versions are described, their contribution to the total energy consumption of EIT devices is estimated. Consumers of electrical energy critical for one or another performance are indicated.


Introduction
The need to assess the energy consumption of technical means of EIT [1,2] is dictated not only by the mandatory certification procedures that establish the energy efficiency class of medical equipment [3].Such information becomes relevant and necessary when designing the power systems of medical institutions: not only systems for distributing electrical energy, but also systems that ensure its uninterrupted supply, which is especially important in intensive care units, operating rooms, etc.
In addition, the task of establishing the energy consumption class of a medical de-vice becomes relevant when implementing a wearable design that provides for long-term wearing.Considering that the EIT device can be implemented as a wearable electronic de-vice, the establishment of quantitative indicators of energy consumption will contribute to the correct choice of an autonomous power source.

Materials and research methods
The total power consumption of the device P is: where i = 1 .. N, the number of consumers , N is their maximum number.
The block diagram of a stationary hardware-software complex of a three-dimensional EIT (see Fig. 1).A stationary electrical impedance tomography device [1,2] (EIT) generally consists of a personal computer with a monitor, an EIT module control unit, an injected current source, a switching circuit, and a measurement circuit.All components of the device are powered by a multi-channel power supply.
From the block diagram of the three-dimensional EIT stationary device shown in Figure 1, the following Pi can be distinguished :  PPC -power consumption of a personal computer;  PMON -power consumption of the monitor;  PICS -power consumption of the injected current source;  PCU -power consumption of the EIT device control unit;  PSU -power consumption of the switching unit;  PMU -power consumption of the measuring unit;  PPU -own power consumption of the power supply (conversion losses).
Obviously, in this case P 3D EIT devices must meet the requirements.The block diagram of a wearable device of a three-dimensional EIT is shown in Fig. 2. As can be seen from the block diagram shown in Fig. 2, in terms of power consumption, a three-dimensional EIT device is divided into a wearable module with an autonomous power source (battery) and a stationary computing module, communication with which can be implemented in the form of wireless data transfer protocols.The total energy consumption P will consist of two components: PWM wearable module, and PCM computing module.Accordingly, for a wearable module, the following Pi can be distinguished, included in PWM:  PICS -power consumption of the injected current source;  PCU -power consumption of the EIT device control unit;  PSU -power consumption of the switching unit;  PMU -power consumption of the measuring unit;  PPU -own power consumption of the power supply (conversion losses);  PRF -power consumption of the wireless data transmission unit. For the computing module, the following Pi can be distinguished, included in PCM:  PPC -power consumption of a personal computer;  PMON -power consumption of the monitor;  PPU -own power consumption of the power supply (conversion losses).
For a wearable module, the calculation of PWM is also important because of the direct relationship of this parameter with the battery life of the wearable module from the built-in battery.The battery capacity, in turn, determines the weight and overall dimensions of the 3D EIT wearable module.

Results and discussion
As shown in the block diagram of the EIT module, the power supply is connected to the blocks of the wearable module EI.For the functioning of the units of the wearable EIT module, a set of the following supply voltages is required: U1 = 5 V, U2 = ± 12 V.
The source of each U with an output current IU must ensure the current consumption of all consumers connected to it IP: Current consumption IUn is calculated based on the reference values of the current consumption of the microcircuits that make up each of the blocks.
The results of calculations of the energy consumption of the units of the wearable EIT module are shown in Table 1.Thus, PWM of the power supply must be at least 2235.5 mW, or 2.2 W, and the battery capacity to provide 10 hours of battery life of the wearable module must be at least 22 W‧h.As can be seen from the data presented in Table 1, a significant part of the power consumption of the entire EIT module falls on the switching unit due to the large number of analog multiplexers.

Conclusion
The paper considers the issues of assessing the energy consumption of devices for threedimensional electrical impedance tomography.The importance of assessing energy consumption for both stationary and portable devices is shown, for which the weight and size indicators are determined by the electric capacity of the batteries.Typical block diagrams of stationary and portable devices for three-dimensional electrical impedance tomography have been developed.Based on the constructed block diagrams, the main consumers of electrical energy are identified.An example of calculating the power consumption of a wearable device for three-dimensional electrical impedance tomography is presented, on the basis of which it is possible to select a battery, the electrical capacity of which will ensure autonomous operation of the device for a given time.

Fig. 1 .
Fig. 1.Structural diagram of a stationary hardware-software complex of three-dimensional EIT.

Fig. 2 .
Fig. 2. Structural diagram of a wearable device of a three-dimensional EIT.

Table 1 .
Reference values for the energy consumption of the main components of the blocks of the EIT module.