**1. Introduction**

Today, no one doubts that the production and the use of large amounts of electrical equipment and electronics have brought an important requirement: electromagnetic compatibility (EMC). It turns out that the requirements for an electrical product to comply with EMC have two aspects. The first aspect follows naturally to ensure that the product complies with EMC regulations. The second aspect, still influenced by environmental experts whose efforts are to monitor the long-term effects of electromagnetic fields generated by technical devices in the environment on living organisms. It is likely that with the growing awareness of the population, in the future, more attention will pay to the effects of electromagnetic fields acting simultaneously from multiple electrical devices on the environment.

According to the International Electrotechnical Vocabulary (IEV) IEV 161-01- 07, EMC is the ability of an equipment or system to function satisfactorily in its electromagnetic environment without introducing intolerable electromagnetic disturbances to anything in that environment [1]. Electrical equipment and electrical systems are always exposed to internal and external electromagnetic disturbances. However, it should be noted that each electrical device is at the same time more or less a source of electromagnetic interference (EMI) [2–6].

#### **Figure 1.**

*Optimal financial costs for EMC provision: Point O; 1 – Operating costs, 2 – Costs of ensuring EMC compliance, 3 – Total costs; pre-compliance measurements shift the point O to lower values.*

If the EMI level of the equipment under test1 (EUT) is below the permitted EMC level of the standard, the EMC compatibility goal of the product is achieved. Otherwise, further measures are needed to reduce the EMI level from the EUT. The role of the engineers is to adjust the internal layout of the functional blocks in the EUT and connect (or disconnect) some components to the EUT to eliminate EMI, especially according to their professional experience. Subsequently, the results of the modifications are verified by re-sending the EUT to the EMC test facility. The process of making changes to reduce EMI and then repeat testing in the EMC test room can be time-consuming and costly until the EUT passes the EMC test. Every manufacturer of electrical equipment wants to gain a foothold in the market and sell the product. The necessary condition for selling products on the marketplace is to obtain an EMC certificate of conformity. The manufacturer must therefore take into account the costs to ensure the EMC conformity of the product.

In recent years much effort has been made to reduce the cost of EMC compliance and speed up the EMC compliance process. The EMC pre-compliance methodology in the test room or at the open site of the product manufacturer is proposed in the early 1990s. In the initial phase, EMC preliminary conformity measurements were performed in a product manufacturer's test facility with standard EMC test equipment and standard test methods. Later, more flexible EMC compliance measurements were developed and introduced an alternative test apparatus or test methodology to reduce compliance costs [7].

The selection of specific permissible levels and the related reserves for the devices are not prescribed. It is within the competence of the device manufacturer. If the manufacturer chooses too large EMC reserves, then unnecessarily high financial costs for interference are incurred. Conversely, if the EMC reserve is too small, there is a greater risk that the equipment will not pass EMC certification. Subsequent measures must take to achieve EMC.

<sup>1</sup> In some professional and scientific sources such as journals, standards, and books, DUT (Device Under Test) is used instead of EUT.

The graph in **Figure 1** represents a typical course of financial costs for the production and operation of technical equipment depending on the probability of failures. It is clear from the graph that as the number of failures increases, additional operating costs increase. Conversely, the failure probability by failing to comply with EMC principles is inversely proportional to the amount of investment in providing EMC equipment.

Therefore, the total operating costs of the equipment are the sum of the two mentioned components, which have the minimum marked as point P in **Figure 1**. The part of the EMC compliance investment of the equipment must choose (point O) so that the total costs are equal to the minimum.

The optimal costs of providing EMC should be about 2–10% of the development and production costs. Under certain conditions, the total cost of providing EMC is less than 1%, which can be considered a success [8]. The area marked with the letter "A" corresponds to too high a cost of providing EMC at the planning stage. The area marked with the letter "B" corresponds to the conditions under which the costs of ensuring EMC are neglect at the planning stage of the equipment production, which results in a high rate of failures.

Pre-certification EMC pre-compliance measurements significantly reduce the cost of developing new electrical equipment and shorten the time to market. Thus, point O in the graph in **Figure 1** defining the optimal cost for EMC provision shifts towards lower values.
