Grounding And Shielding Techniques In Instrumentation Pdf

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When asked to quantify what such a ground is, they generally talk about a ground not connected to that dirty, nasty power ground.

Grounding and Shielding - .Grounding and Shielding ... President of INSTRUM and the author of...

If you don't have a login, click here to register Forgot your password? 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.

All this may provoke alterations with the resulting overload, sub-voltage, peaks, voltage transients etc. 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. The biggest problem caused by EMI is the occasional situations that slowly degrade the equipment and its components.

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 topology and the distribution of the wiring, types of cables, proctection techniques are factors that must be considered to minimize the EMI effects. 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. Keep the connections in good conditions.

Innactive connectors may develop resistance or become RF detectors. 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. 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.

Or, still, the transistor polarization currents may be altered and cause their saturation or cut, or burn its components by the joule effect, depending on the intensity. Quite often the reliability of a control system is jeopardized by its poor installations. Commonly, users tolerate them but a close look reveals problems involving cables, their courses and packing, shielding and grounding.

It is extremely important that every person involved is aware and conscious and moreover committed with the plant operational reliability and personal safety. This article provides information and tips on grounding but in case of doubt the local regulations always prevail. 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. Most probably this commuting noise may produce intermittence in nearby equipment.

While most manufacturers take due precaution on their projects to minimize this effect, the complete immunity is not attainable. So, some layout, wiring, grounding and shielding techniques offer a significant contribution to this optimization. The EMI reduction will minimize initial and future operation costs and problems on any system. One of the main goals of a project is to keep all common signal return points on the same potential. As high frequency inverters up to MHz 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.

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. Another important objective is to minimize the magnetic coupling between circuits.

This is normally achieved by minimal separation the segregated routing of cables. Radio frequency coupling is reduced by adequate grounding and shielding techniques.

The transient surges are minimized by proper line filters and energy suppressors on coils and other inductive loads. 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. To summarize, here is a list of their basic functions:. The neutral conductor is normally insulated and the power source system must be the TN-S T: directly grounded point; N: masses directly connected to the grounded power source point; S: different conductor for neutral and protection.

The protection conductor basically bonds the mass currents to earth. All the housings must be connected to the protection conductor. Figure 1 — TN-S System. Regardless of its protective or functional aim, grounding must be a single one on each installation spot. There are situations where earthing wires may be separated, however with precautions. 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.

See figures 2 and 3. The functional equipotentialization equalizes the grounding and guarantees that the signal circuits and the electromagnetic compatibility work well. Figure 2 - Equipotentialization. Figure 3 — Grounding Line and Equipotential. Figure 4 — Equipotential Material.

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. Depending on how the signals are accommodated there might be up to 2. As the conditions for shielding, grounding and equalization improve, we reach the ideal measuring conditions.

Figure 5 — Example of how important are grounding and equipotentialization and their influence on the signal. 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 implications of poor or even inadequate grounding are not limited to safety aspects. 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.

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. This would be the ideal condition, one that, however, is not necessarily true in practice.

This type of grounding is not a zero-resistance type and its potential may vary. However, the loops are mostly connected to the ground to prevent shock risks. 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. Furthermore, the impedance on each wire may be too high and the ground lines may become a source of noise in the system.

This situation may be minimized by choosing the right type of conductor AWG 14 type. Cables with thicker gauge help reduce the ground resistance, while the flexible wire reduces the earth impedance.

For high frequencies, the multipoint system is the most adequate and simplifies the installation, as shown on figure 7. Figure 7 a — Multipoint grounding. 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 8 — Inadequate multipoint grounding. Figure 9 shows adequate grounding whose individual currents are conducted to a single grounding point. Serial grounding connection is very common because it is simple and economical.

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.

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. 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. Figure 11 — Grounding at equipment level in practice. The capacitive coupling is represented by the interaction of electric fields between conductors. A conductor passes near a noise source the disturber , captures this noise and sends it to another part of the circuit the victim. This capacitance effect between two bodies with electric loads separated by a dielectric is called mutual capacitance effect.

The electric field effect is proportional to the frequency and inversely proportional to the distance. Figure 12 b — Example of capacitive coupling effect.

Figure 13 shows the coupling and its voltage and current sources in common and differential modes. Figure 13 — Differential mode and common mode — Capacitive coupling. Always wrap the conductor or equipment with metal material Faraday shield. Figure 14 shows the interference between cables whose capacitive coupling induces voltage transients, such as electrostatic pickups. In this situation the interference current is drained by the shield to the ground, without affecting the signal levels.

Figure 14 — Interference between cables: the capacitive coupling between cables induces voltage transients electrostatic pickups.

Figure 16 shows the capacitance on the coupling between two conductors separated by a D distance. Figure 16 — Capacitive coupling between conductors at a D distance. The inductive coupling increases with:. Figure 17 a — Inductive coupling between conductors. Figure 18 — Inductive coupling between cable and field. Figure 21 — Mutual inductance between two conductors. To minimize the induction effect use the twisted pair cable that reduces the S area and the Vb inducted voltage in function of the B field, thereby balancing the effects average of the effects according to distances :.

Tips on shielding and grounding in Industrial Automation

Skip to search form Skip to main content You are currently offline. Some features of the site may not work correctly. Safety, system protection and performance are the three main reasons to earth a system. Not all electronic equipment needs to be connected to earth to work, satellites are an example. Sometimes wrong grounding configurations, oriented to satisfy the special power and performance requirements of electronic loading equipment, can compromise safety rules generating dangerous situations for personnel and equipment. Save to Library.

Tips on shielding and grounding in Industrial Automation

We use Cookies to give you best experience on our website. By using our website and services, you expressly agree to the placement of our performance, functionality and advertising cookies. Please see our Privacy Policy for more information. Abstract: walkie-talkie rg58 coaxial cable electronic series and parallel circuits flowing c Text: time constants of nanoseconds. Further Reading: Ralph Morrison , op , time constants of nanoseconds.

Tips on shielding and grounding in Industrial Automation

If you don't have a login, click here to register Forgot your password? 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.

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Our website is packed full of both free and paid-for content, including:. Our aim is to help people learn how to more quickly and cost-effectively design and manufacture electronic equipment products, systems, installations, etc. Such equipment should benefit from reduced warranty costs and financial risks, whilst improving uptime, competitiveness and profitability. Find your EMC Standards quickly and easily What EMC issue do you want to learn about today?

Skip to Main Content. A not-for-profit organization, IEEE is the world's largest technical professional organization dedicated to advancing technology for the benefit of humanity. Use of this web site signifies your agreement to the terms and conditions. The single-point grounding methods presented should be recognized as an ideal approach that often has practical limitations in implementation. Article :. Date of Publication: Sep

Good grounding practices - Part 2

Transfer of the immediate discharge of the electrical energy directly to the earth by means of the low resistance path is known as the earthing. Main objective of the earthing system in plant is described as below:. Items or equipment which require earthing, are but not limited to below,.

Objectives Upon completion of this module, the trainee will be able to: 1. Identify the minimum Identify the minimum Properly terminate an Properly terminate an requirements for grounding in an installation. Prerequisites Successful completion of the following Task Module s is required before beginning study of this Task Module: Instrumentation Level 3, Task Modules and Required Trainee Materials 1.

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