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The coexistence of equipment of different technologies and the inadequacy of the installations favors the emission of electro-magnetic energy and often causes problems of electro-magnetic compatibility. EMI is the energy that causes undesirable response to any equipment and may be generated by sparking on the motor brushes, tension circuits switching, activation of inductive and resistive loads, activation of switches, circuit breakers, fluorescent bulbs, heaters, automotive ignitions, atmospheric discharges and even the electrostatic discharge between persons and equipment, microwaves devices, mobile communication equipment etc. The biggest problem caused by EMI is the occasional situations that slowly degrade the equipment and its components. The topology and the distribution of the wiring, types of cables, proctection techniques are factors that must be considered to minimize the EMI effects. A typical example of how the EMI may affect the work of an electronic component is a capacitor exposed to a voltage peak higher than its specified nominal voltage.
Do not be neglectful, imprudent, irresponsibly inexpert or incompetent on technical problems.
Whenever possible refer to the physical regulations, as well as the safety practices for each area. Act safely on measurements, avoiding contact between terminals and wiring, as high voltage may cause electric shock.
In order to minimize the risk of potential problems related to safety, comply with the safety standards and those of the local classified areas regulating the equipment installation and operation. The inadequate installation or use of equipment in non-recommended applications may damage the system performance and consequently the process, as well as be a source of danger and accidents. It is extremely important that every person involved is aware and conscious and moreover committed with the plant operational reliability and personal safety. The control of noises in automation systems is vital, as it may become a serious problem even with the best devices and hardware to collect data and work.
Any industrial environment has electric noises in sources, including AC power lines, radio signals, machines and stations etc. Fortunately, simple devices and techniques as the use of adequate grounding methods, shielding, twisted wires, the average signal method, filters and differential amplifiers may control noise on most measurements. Frequency inverters have commuting systems that may generate electromagnetic interference (EMI). One of the main goals of a project is to keep all common signal return points on the same potential. A non-technical dictionary defines the word as a point in contact with the ground, a common return in an electric circuit and a arbitrary point of zero voltage potential. To ground or to connect some part of an electric circuit guarantees personal safety and generally improves the circuit work. Unfortunately, a safe and robust environment in terms of grounding quite often does not occur simultaneously. Grounding systems must execute multiple simultaneous functions: provide personal safety and protect the equipment. Regardless of its protective or functional aim, grounding must be a single one on each installation spot. Each building must have a principal equipotentialization and the installation masses located in the same edification must be connected to the main one, thereby creating the same and only grounding electrode. The functional equipotentialization equalizes the grounding and guarantees that the signal circuits and the electromagnetic compatibility work well. Figure 5 shows a generating source for high voltage and high frequency noises, besides a system for temperature measuring 23 m distant from the control room. In distributed systems like industrial process control, with distant physical areas and power supplied by different power sous, it is recommended grounding on each location and to apply EMI control techniques on each signal routing, as shown on figure 2.
The result is that equipment with metal housing is subject to noise on the power source and lightning grounding loops. In order to meet the safety standards and protection against lightning and EMI the grounding system should be a zero impedance plan, whose mixture of different current levels would turn these systems free from interference.
The grounding system at a single point can be seen on figure 6, whose striking feature is a single grounding point evenly distributed to the entire installation. This configuration is best suitable for low-frequency spectrum and satisfies perfectly high frequency electronic systems installed in reduced areas. Moreover, this system must be insulated not to work as a return path for signal currents circulating through signal conductors with balanced pair, for example.
This type of parallel grounding eliminates the common impedance problem, although detrimental to the use of a pile of wiring. For high frequencies, the multipoint system is the most adequate and simplifies the installation, as shown on figure 7. Many low impedance connections between the PE conductors and the grounding electrodes combined with multiple-impedance paths between the electrodes and the impedance on conductors create a complex grounding system with an impedance network (see figure 7 b), and the currents that flow through it cause different grounding potentials on the the network interconnections. The multipoint grounding systems that use balanced circuits normally do not have noise problems due to filtering, where the noise field is limited between the cable and the grounding plan. Figure 9 shows adequate grounding whose individual currents are conducted to a single grounding point. A grounding loop occurs when there is more than a grounding path, which generates undesirable currents between these points. These paths form the equivalent to an antenna loop that captures the interference currents with high efficience.
Conduction through common impedance (grounding): It occurs when the current on two different areas pass by the same impedance. The capacitive coupling is represented by the interaction of electric fields between conductors. The electric field effect is proportional to the frequency and inversely proportional to the distance. The distance between the disturber and the victim cables and the length of the cable that runs alongside them. The impedance of the victim circuit input (circuits of high input impedance are more vulnerable). The victim cable insulation (cable insulation εr), mainly for strongly coupled cable pairs.
Figure 13 shows the coupling and its voltage and current sources in common and differential modes. Use of conduits and grounded metal boxesFigure 16 shows the capacitance on the coupling between two conductors separated by a D distance. In high frequencies ground the shield on two points (caution!) and in low frequencies on a single point. The use of twisted pair cables is very efficient as long as the induction in each tortion area is approximately equal to the adjacent induction. This is the effect of metal plates and screens on the incidence of electromagnetic waves; they generate their own fields that minimize or even nullify the field through them, therefore working as true shields against electromagnetic waves. Although the cables are shielded, the shielding against magnetic field is not as efficient as against electrical cables.
Most makers of field equipment as pressure, temperature transmitters, positioners, converters etc, recommend the local grounding of theirs products.
When installing the equipment, normally the housing is in contact with the structural part or piping and consequently is grounded.
Some factories recommend their equipment to float insulated from the structure and not grounded, to avoid current loops.
For microprocessers and digital communication equipment, some industries incorporate or make surges of transient protectors.available.
Use RFI filter and always connect it the closest possible to the noise source (between the RFI filter and the drive). All motors activated by inverters must be powered preferably by shielded cables grounded on both ends. To meet EMI protection requirements all external cables must be shielded, except power source cables. On control cables install a small (100 nF a 220 nF) capacitor between the shield and the ground to avoid the return of AC circuit to the ground wire. Use isolated and shielded cables (4 paths) between the inverter and the motor and between the inverter power supply along the inverter. Inverters generate escape currents and in this case a line reactor can be introduced on the inverter output. Line reactors are a simple and inexpensive way to increase the impedance of an isolated load source (as a variable frequency command, in the case of inverters). The reactors are connected in series to the load that generates harmonics and, by increasing the source impedance, the magnitude of the harmonic distortion may be reduced to the load where the reactor is added.
The main function of the RFI input filter is to reduce the emissions conducted by readiofrequency to the principal lines of distribution and the ground. Reflected waves: if the cable impedance does not match that of the motor, there will be reflections.
Special cables: another important detail to help minimize the effects of the electromagnetic noises generated in installations with inverters and AC motors is the use of special cables to avoid the corona effect of discharges that may deteriorate the dielectric rigidity of the insulation and allow the presence of stationary waves and noises on the ground loops.
In terms of digital networks, move them away from the inverter whose signals will go the motors and install repeaters isolating the areas.


Ground connectors must be classified according to the maximum capacity of the inverter current. For applications of AC variable frequency inverters that must comply with EMC standards use the same type as the shielded cable specified for the AC motors to be used between the inverter and the transformer. Keep the motor cable length within the limits established by the inverter user manual to prevent several problems, including the cable load current and the effort of the reflected wave tension.
When having TE and PE terminals, ground them separately at the closest panel point using a twisted loop.
Motor and input cable shields must be connected on both ends to provide a continuous way to the common-mode noise current. The cable shielding between two cabinets must be connected to the cabinet containing the signal source. The cable shielding between a cabinet and an external device must be connected to the end of the cabinet unless specified otherwise by the external device maker. Never connect a shielding on the common side of a logic circuit, as this will cause noise on the circuit. Make the termination of the inverter power source, motor and terminal block control connections. In low DC frequencies up to 1 MHz, the cable shielding may be grounded on a single end of the cable and provide good response concerning the electromagnetic interference.
Grounding and shielding are mandatory requirements to guarantee the integrity of a plant data. Noise effects can be minimized with adequate techniques of projects, installation, cable distribution, grounding and shielding. The shield must be connected to the signal reference potential of what is being protected (see figure 25). When there are multiple segments keep them connected, ensuring the same reference potential, according to figure 26. In this case the current will not circulate through the loop and will not cancel the magnetic fields. A distribution of currents occurs here, in function of the frequencies, since the current tends to follow the course of lower impedance. Up to a few kHz: the inductive reactance is neglectable and the current will circulate by the way of less resistance. Above kHz: the inductive reactance predominates and this will make the current circulate by the way of less inductance. The way of less impedance is that whose course of return is close to the course of departure for presenting distributed capacitance and lower distributed inductance. The length of the conductor extending outside the conductor should be minimized and guarantee good connection between the the shield and the ground. Significant damages may be caused to active equipment when the ground potential difference between both ends goes beyond 1 V (rms).
The grounding electrical resistance should be the lowest possible on both segment ends to minimize the ground loops, mainly in low frequencies.
The cable grounding is used to eliminate interferences by capacitive coupling due to electrical fields. The grounding loop must be connected to the ground reference potential that is bening shielded. Figure 29 – The length of the ground-reference connection should be minimized as it works as a coil. Electric fields are much easier to shield than magnetic fields and the use of shielding on one or more points work against electric fields.
To prevent radiator from a conductor, a grounded shield on both sides is generally used above the cut frequency, but some precautions must be taken.
Always check the NBR 5418 standard or local regulation for shielding and connection with intrinsically safe equipotential systems. An intrinsically safe circuit must float or be connected to the equipotantial system associated with the classified area on only one point. Shielding must be connected to the ground or the structure compliant to ABNT NBR IEC 60079-14 standard.
Never install a device that has been previously used without an intrinsically safe barrier on an intrinsically safe system, as the protection zener may be burned and will not work in instrinsically safe areas. According to IEC 61158-2, to ground means to be permanently connected to the ground by a sufficiently low impedance and with enough conductive capacity to prevent any voltage from causing damages to equipment or persons. Preferably, the shield must be grounded on two points, a the beginning and the end of the bus, provided there is no difference potential between these points and allows the existence and paths to loop currents.
The shield must cover entirely the electric circuits through the connectors, couplings, splices and junction and distribution boxes. In classified areas, if the equalization potential between the safe and the hazardous areas is not possible, the shield must be connected directly to ground (Equipotential Bonding System) only at the hazardous area side. Another additional manner is to ground the equipment junction boxes and housings on a ground equipotential line on the non-safe side. Multiple grounding is also usual and provides more effective protection on situations of high frequency and electromagnetic noises. The shield (the loop and the aluminum blade) must be connected to the system functional ground on all stations through the connector and DP cable) to provide a large connection area with the grounded conductive surface. Maximum protection is provided with all points grounded through a low impedance path to the high frequency signals.
In cases with voltage diferential between the grounding points, pass close to the wiring an equalization potential line (the metal duct or an AWG 10-12 cable can be used). When referring to shield and grounding, in practice there are other ways of handling this subject, one with much controversy, as for example, the shield grounding can be made in each station with the sub D 9-pin connector (figure 34), where the connector housing  makes contact with the shield and is grounded when connecting with the station.
In hazardous areas always use the recommendations from the certifying bodies and the installation techniques demanded by the area classification.
For grounding, group circuits and equipment with similar noise characteristics in serial distribution and connect these points on a parallel reference and also ground ducts and boxes. CEIA EMVS is a complete system, aimed at the detection of metallic UXOs and ERWs, conceived in order to offer a deterministic result to the operator through its visual and audio signals.
The results of calculations of the efficiency of the shielding of a photoelectronic spectrometer by amorphous alloys, designed to protect the instrument from the Earth’s magnetic field, are presented. JavaScript is currently disabled, this site works much better if you enable JavaScript in your browser. APPLIED PRODUCTS RF Discharge Type Excimer Lamp Conventional cylindrical excimer lamps have the problem of poor irradiation uniformity because they can only be used to irradiate close objects directly under the center of the lamp. This electromagnetic induction-type sensor detects the change in magnetic flux caused by the revolution of a rotor mounted on the vehicle shaft. Abnormal radiator water temperature and 4WD transmission system temperature can be detected by thermal reed switches, which are a combination of a normal reed switch in a heat-sensitive ferrite casing. Reed switches combined with coils are able to detect damaged lamps, including burnt-out headlights and rear lights. These reed switches detect the limit of the longitudinal movement of electrical power seats and the reclining angle.
A reed switch type proximity sensor detects whether the door is open or closed and can be linked to an alarm system or internal lighting for security and convenience.
This reed switch type shock sensor tighten and locks the seat belt instantaneously (20 - 30ms) when an impact of above 2 G is experience. A combination of multiple reed switches and magnets sense uneven loading of the vehicle and trigger the suspension levelling system for safer driving. All this may provoke alterations with the resulting overload, sub-voltage, peaks, voltage transients etc., which may cause high impact on a communication network. Keep in mind that in high frequencies the cables work as a transmission system with crossed and confused lines, reflect and scatter energy from one circuit to another. This may deteriorate the dielectric, whose width is limited by the capacitor operation voltage, which may produce a gradient of potential inferior to the dielectric rigidity of the material, causing malfunctioning and even the capacitor burning. Therefore, only use trained and qualified professionals on installation, operation and maintenance jobs. Commonly, users tolerate them but a close look reveals problems involving cables, their courses and packing, shielding and grounding. This article provides information and tips on grounding but in case of doubt the local regulations always prevail. As high frequency inverters (up to 300MHz) generate harmonics through the commuting amplifiers on these frequency levels, the grounding system resembles more a series of inductors and capacitors rather than a low resistance channel.
Depending on how the signals are accommodated there might be up to 2.3KV at the measuring terminals. The main effects of inadequate grounding are electric shocks to users through contact, low or intermittent response from the protection systems, such as fuses, circuit breakers etc.). Furthermore, the impedance on each wire may be too high and the ground lines may become a source of noise in the system. A conductor passes near a noise source (the disturber), captures this noise and sends it to another part of the circuit (the victim).


The ideal is to cover 100% of the protected part and to ground this shield so that the parasite capacitance between the conductor and the shield does not function as a repowering or crosstalk element. The one-pair wire is wound in spiral and through the cancellation effect reduce  the noise and keep the medium electric properties constant through its whole length. Its use is efficient in differential mode, balanced circuits and has low efficiency in low frequencies on unbalanced circuits.
In addition, this discontinuity may help ease the difference of potential between each duct segment, and, in the event of current surge generated by an atmosphere discharge or a short circuit, the lack of continuity will not allow the current to circulate along the aluminum duct and consequently will not protect the Profibus cable. In low frequencies, the twisted pair absorbs most parts of the effect from electromagnetic interference. In cases where the housing is insulated from any structure point, the manufacturers recommend local grounding with the shortest possible connection with an AWG 12 wire.
Inside the panel create distinct zones and even use separating plates that served as shield.
The RFI input filter is connected between the input power source AC line and the inverter input terminals. Remember that the cable between the inverter and the motor presents impedance to the inverter output pulse (called surge impedance). The cable shield is recommended to help reduce the twisted coupling noise on the power source cables. In these cases, it is very important that the differences in ground potential in both connection points are the minimum possible. In practice, it is very common to watch intermittent work and gross errors in measurements due to the bad installations.
Inadequate grounding may be the source of undesirable and dangerous potentials that may endanger the effective operation of an equipment or the work system itself.
The length of the conductor extending outside the shield should be minimized and guarantee good connection between the ground and the shield. More than one ground connection is allowed on the circuit, provided the circuit is divided in galvanically insulated subcircuits, and each one is grounded at only a single point. Voltage lines with 0 Volts must be connected to ground and galvanically insulated from the fieldbus bus. Always verify the shield continuity until the last PA segment in the segment, with due analysis of the connection and finishing, as it should not be grounded on the equipment housing. In this case, though, annalyze and verify punctually the ground graduation potential and, if necessary, equalize it. The distribution of the magnetic induction inside the shield for different positions of the instrument is measured. RF (radio frequency) discharge type excimer lamps, however, have uniform emission over a wider area since they use a long, flat rectangular bulb. The signal pulse is transmitted to the control unit and used to control the ABS and active suspension.
This is very common in industries and factories, where EMI is fairly frequent in function of the larger use of machines such as welding instruments, motors (MCCs) and in digital networks and computers in the vicinity of these areas.
It is very common the occurrence of noises in power source lines due to bad grounding and shielding or even error in the project. The user is responsible to determine which rules to follow in his applications and guarantee that each device is installed in compliance with them. The use of loops and twists instead of wires (short wires are better for high frequencies) interconnecting the grounding points is more efficient in this case (see figure 4). As the conditions for shielding, grounding and equalization improve, we reach the ideal measuring conditions.
When the circuits share the same ground wire, the circuit currents that flow through the finite impedance of the common base line may cause ground potential variations on the other circuits. This capacitance effect between two bodies with electric loads separated by a dielectric is called mutual capacitance effect. Figure 14 shows the interference between cables whose capacitive coupling induces voltage transients, such as electrostatic pickups. In high frequency circuits with grounded multipoints, the efficiency is high, since the return current tends to flow through the adjacent return. In this case, watch the difference of potential between the grounded point and the panel where the controller (PLC) is located. Also note that commutation frequencies vary from 1k to 34KHz, usually 30khz, and may have great influence on the Foundation Fieldbus and the Profibus-PA networks . The minimum and maximum gauges depend on the nominal inverter current and the physical limitation of the terminal blocks.
Individual standard conductors that meet the general type specifications concerning temperature, gauge and applicable codes are acceptable, provided they are distant from high voltage cables to minimize the coupling noise.
However, high peak load currents in cables may cause inverter overcurrents or ground failures.
If possible, avoid passing large lengths of power source cables and motor conductor by the same duct. Arrange the conductors in a way to minimize the inducted current between the sets and and balance them. The voltage difference between both ends should be a maximum of 1 V (rms) to minimize the ground loop effects. Make sure the continuity of the shielded cable is longer than 90% of the cable total length. In this method, the shield is grounded on the ground point of the power source or the safe side of the intrinsic safety barrier, besides the ground on the equipment junction boxes and housings, and is also grounded on the non-safe side. Grigor’ev, “Electromagnetic contamination of the environment as a factor affecting humans and the bioecosystem,” Electromagnetic Safety. RF (radio frequency) discharge also gives a highly uniform and stable output with minimum of flicker that is often a problem in conventional dielectric barrier discharge.
While most manufacturers take due precaution on their projects to minimize this effect, the complete immunity is not attainable.
The transient surges are minimized by proper line filters and energy suppressors on coils and other inductive loads.
Cables with thicker gauge help reduce the ground resistance, while the flexible wire reduces the earth impedance. If the currents are large enough, the potential variations may cause serious disturbances on the operation of all the circuits connected to the common signal ground.
This is critical in inverters with nominal power of 200 HP (150 KW) and keep the power source cables and the control cables separated.
It is also important to be aware that in high frequencies there is parasite coupling capacitance that tends to complete the loop when the shielding is grounded on a single cable extreme. In this instance, the shield is insulated on all grounds, with exception to the negative ground point of the power source or the intrinsic safety barrier on the safe side. An additional an complementary situation is one whose grounds would be grounded in a set on an equipotential ground line, connecting the non-safe side to the safe side. On classified areas, avoid grounding intrinsically safe components, unless it is necessary for functional reasons, when employing galvanic insulation. Common high frequency conductors have the disadvantage of having high impedance and current loops should be avoided. Kuznetsov, The Construction of Effective Electromagnetic Protection Systems Based on Soft Magnetic Amorphous Nanocrystalline Alloys of Co and Fe: Auth. So, some layout, wiring, grounding and shielding techniques offer a significant contribution to this optimization.
When arranging the boxes with cables for large inverters, check if the box or duct containing the signal wiring stay at 30cm or more from the one containing the motor or the power wiring.
The standards establish the minimum insulation of 500V resistance between the ground terminal, while the system ground must be lower than 1Ω.
The grounding system should be seen as a circuit that favors the flow of current under the minimum possible inductance. In Brazil, the installation on potentially explosive atmospheres is regulated by the NBR-5418. This method has the disadvantage that it does not protect totally the high frequency signals and, depending on the topology and cable length, may generate occasional communication intermittence. Petzold, “Advantages of soft magnetic nanocrystalline materials for modern electronic applications,” J.
Merkulov, “The problem of image jitter of video monitors at the working places of personal computer users,” ibid., pp. Glezer, “Amorphous and nanocrystalline structures: similarities, differences, and mutual transitions,” Ross. Grebenshchikov, et al., “A shielding chamber for reducing the Earth’s magnetic field based on rolled magnetic materials,” Izmer.



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