Active Electrical Ionization

         By using AC or DC high voltage, ionized air is produced for neutralising surface electrical charging. 

    AC Eliminators

        AC Eliminators work at source frequency. You can make main voltage increase from 110 or 240 V to 4.5 or 7 kV by using transformer. High voltage is given to the points of the bar while the bar is earthed.(Figure 1)

        If you examine the positive part, you can see the electrode point has a higher voltage than the earth point. So, between these two points, there will be a strong electric field.The molecules are sprayed from the electrode point,according to their charges.

        If you examine the negative part, negative ions occurs on the electrode point.

        Thus, as shown in figure 1, there will be a stack around the ionised pin that has negative and positive ions.Without external effects, positive and negative ions affect each other and then neutralise or go through the earth. Furthermore, if there is an electrical charge, ions are effected opposite direction.Then, electrons on the surface move and make the surface neutral.

        Ionization is free of surface, so ions are produced whether charges on the surface is near or far. The result is the neutralization of all surface.This is an advantage for passive eliminators.

    Pulse DC Eliminators 

        Like AC eliminators, they are used for producing ionized air by using high voltage. AC eliminators work at source frequency, pulse DC eliminators work at lower frequencies.977v2 model has an output of 6-14 kV and pins connected to negative and positive outputs serially.(Figure 2)

        When you analyse the positive part of the output wave of the power source, you can see that the control unit get the high voltage connected to positive transmitter. Thus, an electric field is created between earthed object and transmitting point. This field is very strong at the sharp point of the transmitter. They produce positive ions and make them move away.

Figure 2. Pulsed DC Ionization

        At the negative part, power supply gives high negative voltage to the transmitting part. Like AC eliminator, transmitting part produces negative ions. An object charged static repulses or attracts ions. When ions reach the charged surface, then the neutralization starts. 

        Pulsed DC eliminators provide wide range ionization at low frequencies. The distance between negative and positive ions on the bar decreases the probability of the connection or joining again.

        At further distances from the bar, less ions are sent to the static charged surface. So, in dynamic applications and using pulsed DC eliminators, distance between bar and surface is less important.

        Another specification of Pulsed DC systems is to be able to change the output wave form and increase or decrease the time of the positive or negative parts. For example, if it is known that the object is positive, the time of the negative part of the output is increased or decreased. This time will make the quantity of the negative ions increase and positive ions decrease. This provides that the neutralization is more effective than before.

Passive Ionization

     If a charged object is approached to an conductor, it will give its charges. Radioactive sources like polonium cause the neutralization of the air that is around surface static charges. A disadvantage of the radioactive eliminators is to last just for one year. So they have to be regenerate each year.

Methods of Neutralizing Static Electric

       The basic principle for neutralizing static charges is same for all kinds of techniques. To balance the charging on an object that has a positive surface electrical charge, the electrons have to be distributed towards the surface. When the surface charging is negative, extra electrons have to be got from the surface for neutralizing. To do this, there are three methods:

    1. Electrons are spinned around the object,

    2. Electrons are spinned around the object contacting surface,

    3. Electrons moves with the ionization of the air around the object,

The Factors Affecting Static Electric

    Object Type

        Some objects are more ready for charging. Because of the place of the materials in the triboelectrification series, charging is changing from one material to another one and decided whether they are negative or positive.

    Humidity

        Generally, dry air is suitable for high charging, but if there is high humidity around environment, it causes low static charging. Water is a better conductor than plastic. Atmospheric humidity creates liquids on the surfaces and for this reason electrical charges want to go to the earth by using these liquids.

    Repetition

        Repetitive functions such as friction or isolation will redound the charging level of the object. For example, a plastic moving on the teflon cylinder, surface charges increase while it is touring.

    Battery Effect

        Connection kinds of the charged materials causes magnificant electrical charging. For example, plastic sheets having lower charge density can generate high voltages while forming a stack.

    Heat Changing

        An object which becomes cold wants to generate electric.In fact, all of the object loads a net electrical charge. If the object is a good insulator, it can protect the internal static charge for a long time. Furthermore this static charge flows until becoming a surface static charge. Injection molding is another example that is neutral while it is hot but when it is cold, it has alarge surface charge

Electrostatic Discharging

        This problem is relating to the production tapes in electronic, setting up these tapes and some electronic components.

        Unimportantly small voltages (5 V) damaging electronic components, can cause serious and expensive problems. This is not limited to the electronics industry - it occurs where sensors, weighers, printers and similar controls are close to statically charged materials.

Safety - Electrical Shocks

     According to the companies, safety preventations are so important that electrical shocks can be dangerous for operators.The effect of the shock is short-time and overcomed easily. But it causes hazardous conditions like fire or explosion.Namely, Static discharges which give shocks to personnel are not usually dangerous, but are certainly unpleasant and can cause secondary reactions. A real danger exists from static discharges in the coating industry and similar areas where combustible solvents are used.

Misbehaviour of the Product

        Electrostatic attraction (or repulsion) causes materials to stick to machinery, or to each other, resulting in slow machine speeds, reduced productivity and lower quality.

        During the production of printing sheets and fibreglass, materials cling to each other or their machines. These machines don?t accept and repulse them. Then the material follow wrong war on the conveyor. Espcially you can meet this problem in automatic system.

Attraction of Dust and Contaminants

        Charged particules are attracted either a charged or a neutral surface. You can meet this problem in kinds of industry such as painting, food, medical products and pharmacy.

        In printing industry, dust attraction damages printing sheets and products. Low quality infilm industry is another problem. Microscopic products used semiconductor technology can affect from static.

        Consequently, the electrostatic field can attract airborne dust and other contaminants to the product. This causes high reject rates and low productivity.

Electrostatical Charging

        The electric field on the conductor defines the effect of static.

    Examples

        The electric field from A insulator makes the electrons of B conductor move towards the surface of A looking at B. These electrons make up the bound induced charge.Unless B isn?t in the electric field from A, the movement of charges doesn?t occur. The free induced charge (positive) creates an electric field outside of B, with the field lines eventually terminating on some grounded object. If this field is integrated from B to a ground point, we will get a positive figure, which, by definition, is the voltage of B. Thus we have an uncharged conductor with a positive voltage.

Figure 1. Insulated conductor in the field from a charged insulator

        The condition in Figure 2?de is same as im Figure 1 .But the conductor is grounded.Thus, the voltage of B is zero.But, B has negative charge at the bound. If the ground connection is broken, and B is moved away from the neighborhood of A (in an insulated way), B will still have its negative charge, giving B a negative voltage.Consequently, B is charged by induction.

Figure 2. Grounded conductor in the field from a charged insulator

       In figure 3 an operator holding a positively charged insulative material is standing on an insulating floor. The charge from the material will bind a negative charge on the operator by induction. A positive charge of the same numerical magnitude as the negative charge will cause the operator to have a positive voltage. The field lines from the operator's positive charge will run through the floor covering to the grounded underlayer.

Figure 3. Insulated operator handling a charged piece of insulative material

       In figure 4 there is a hazardous induction event. Operatör is pouring powder from a plastic bag into a tank containing explosive vapors. At the beginnig the operator who is not grounded ,has no charge.But the plastic bag gives him some charge and generate a positive voltage. If operator accidentally touches the tank, a spark discharge occurs, resulting in an explosion that hurts the operator badly.

Figure 4. Ungrounded operator handling insulative materials in an unsafe environment

Charging of Gases

      The kinetic energy that might be imparted to a gas molecule in an airflow even at high velocities is much lower than the thermal kinetic energies at normal temperatures. It is also much lower than the level required to knock an electron off either the gas molecule itself or the container walls

Charging of Powders

      Dust and powders can get charged by contact or friction between the particles, especially if the individual particles have different properties, such as varying sizes or differing materials. Such charging could result in the particles sticking together. More common, however, are processes in which a powder is being transported through a system of tubes, and the powder as a whole is being charged by friction with the walls of the tube system. This kind of charging might take place if either the powder, the tubes, or both are insulative.

Flow and Spraying

        If the surface of a liquid is changed, the electric double layer has to be formed or destroyed. These processes are supposed to have a certain inertia, which implies that it is possible to separate the charges of the double layer by mechanical action on the liquid. 

        If a liquid is flowing through a tube, there is a tendency for the outer charge of the double layer to be given off to the tube and the inner charge to be carried along with the flow. The effect of the charging increases with the resistivity of the fluid (and depends on several other parameters). Consequently, only highly insulative liquids (r > ca. 107 W•m) will show charging by flow. Water, therefore, will not charge by flow.

Electrification by fluid of liquid

        Although charging of liquids by flow can only occur with highly insulative liquids, charging by spraying can happen with almost any liquid.

Electrification by spraying of liquid

Charging of Solids - Triboelectrification

The most important type of charge separation involves the contact and friction between solids known as triboelectrification. When two solid materials, A and B (see Figure 3.1), contact and possibly rub against each other, electrons could move across the interface.

Metals

        Triboelectrification also happens when the two contacting materials are metals. When two metals contact, a voltage difference is established across the interface, with a magnitude from a couple of tenths to a few volts. 

        If the metals are "well-defined" metals, the contact potential difference can be calculated from the work functions., the energy it takes to remove a loosely bound electron from the metal. It should be stressed, however, that this charge exchange between metals only gives rise to what we normally understand as static electricity when the two metals are separated extremely quickly, such as when a metal powder is blown against a metal.

Insulators

        It is conceivable that only electrons located close to the surface can participate in the charging of highly insulative materials. Similar to metals, for some of these materials it is possible to measure the work function for loosely bound electrons. charging experiments with insulators can only yield quantitatively predictable results if the surfaces are carefully prepared and the experiments are performed in vacuum. And such experiments might disclose very little about what one could expect to find under more-practical conditions.

Contact Electrification:Triboelectric Series

        One of the material parameters influencing the course of a charging process between two solid materials is the permittivity. Scientifically speaking, permittivity is defined as the ratio between corresponding values of the dielectric displacement and the electric field strength. The stronger the forces, the higher the permittivity of the material.

        This is the background for Coehn's law, which states that when two materials are in contact with each other, the one with the highest permittivity becomes positive. This law was originally based on a comparison of known values of permittivity and published triboelectric series

        Table I shows an example of a triboelectric series. Such a series should be used with caution because the order of the materials could vary from series to series.

Most Positive (+)
Air	+++ +
Human Hands, Skin
Asbestos
Rabbit Fur
Glass
Human Hair
Mica
Nylon
Wool
Lead
Cat Fur
Silk
Aluminum
Paper
Cotton
Steel	-  - - -
Wood
Lucite
Sealing Wax
Amber
Rubber Balloon
Hard Rubber
Mylar
Nickel
Copper
Silver
uv Resist
Brass
Synthetic Rubber
Gold, Platinum
Sulfur
Acetate, Rayon
Polyester
Celluloid
Polystyrene
Orlon, Acrylic
Cellophane Tape
Polyvinylidene chloride (Saran)
Polyurethane
Polyethylene
Polypropylene
Polyvinylchloride (Vinyl)
Kel-F (PCTFE)
Silicon
Teflon
Silicone Rubber
Most Negative (-)

Generation Of Static Electric

 An electric effect can be seen only when electrons are removed from some of the atoms in one material and transferred to atoms in another (or maybe even the same) material. Theelectric effect is caused by the attraction between opposite charges and the repulsion between like charges.

         The number of electrons transferred in any charging process is enormous. Here are some examples. If a powder, such as sugar or flour, slides down a tube and sticks to the wall, the charge on each tiny particle could be 10?14 to 10?13 C, i.e., 100,000 to 1 million electrons have been transferred per particle. A person who has walked across a carpeted floor receives a shock when touching a doorknob that typically has a charge of about 10?7 C. Powder sliding down a tube often has a specific charge of about 10?7 C•kg?1. A plastic folder rubbed with a piece of cloth or fur typically produces a charge of 10?7 C per sheet.

Static Background

      The effects of friction have been known for 2700years.Especially,when you wear a sweater that has more nylon, creation of sparks is an example of the movement of the electrical charges.It is an another example that while it is raining, flashes between cloud and earth or cloud and cloud occur. Then, due to the observations and friction, it was found that there were two kinds of electrical charges. If a glass bar rubbed with silk is positioned near another one, they repulse each other. But If you position a plastic bar rubbed with fur near a glass bar, they attract each other. Benjamin Franklin(1706?1790), entitled electrical charges occured on the plastic bar as (-) negative and on the glass bar as (+) positive. Ben Franklin's lightning rod was an important electrical invention.

Lightening Rod

         The simple construction of this device has changed little over the last 250 years, and it is still in use worldwide. The construction, however, may have certain nationally conditioned variations. For instance, until the 1970s in France, all lightning rods on public buildings, such as post offices and police stations, had tips covered with radium (226Ra). The idea was that the increased ionization around the tip would increase the neutralizing current to the base of a thundercloud. Although this was correct?at least in theory the rods also produced a little extra radon (222Rn). Because the half-life of radium is about 1600 years, we must hope they had (and still have) a good system for disposing of old lightning rods.

         But, with the notable exception of the lightning rod, it wasn't until the beginning of the twentieth century that we found the first industrial application of electrostatics. In 1906, Frederick Cottrell invented the electrofilter or electrostatic precipitator (see Figure 2). The industrial revolution had started to put its black fingerprints on the environment, and the greatest polluters were the smelters and cement mills. The electrofilter was a genuine breakthrough because it trapped ash from coal-burning power plants. It is difficult to imagine what our pollution levels would be like today without this, in principle, very simple but ingenious electrostatic invention.,

Electrofilter

          The precipitator was only the beginning. Soon after, methods were discovered for separating mixtures of widely different types of particles, followed shortly by methods for electrostatic spray painting and for producing dry coatings for the manufacture of grit cloth and sandpaper. All of these inventions were, in principle, very simple. That was not the case, however, with the work of Chester Carlson. With a degree in law and physics, Carlson worked in a patent office and, therefore, understood the need for copies of patent papers. So, he decided to invent a better copier. After years of honing the experiments, however, the end result was the Xerox process, which has had a great impact on society. Still, all of these processes were known as electrostatics. 

          In the 1930s, explosions in grain silos were reported at a rate of approximately one per week in the midwestern United States. With this and with increasing explosions in hospital operating rooms and in chemical and pharmaceutical laboratories, people called the cause of these explosions static electricity.

Ignition of explusive vapors

          It was quite natural to suspect that an electrostatic discharge was the igniting source in such explosions. But in the 1950s and 1960s, a "new" type of explosion started to appear. Several serious accidents happened when oil tanks were being cleaned with a high-pressure water jet. Although an explosive vapor-air mixture might have originated from the hydrocarbon residue, the ignition source was still unknown. But the cause seemed to be awater slug moving in an inhomogeneous field.

          Already in the 1930s, static electricity was a nuisance in the printing industry as well as in the textile industry. Lengths of paper would stick together, and fibers would filter and be hard to control during spinning and weaving. Static electricity made the car radio crackle or caused a minor shock when you handed your nickel to the toll collector. It was these two problems more or less that led to the development in the 1930s of carbon-black-loaded conductive rubber.

          With the development in the 1940s and 1950s of all kinds of polymeric materials?such as nylon, orlon, and Teflon?static electricity became a household word. People identified static electricity as the source for why clothing stuck to your body or the reason you got a nasty shock when you touched a water tap. And it was static electricity that made TV screens and monitors dirty. And, according to folklore, static electricity was blamed for headaches and for ruining the "balance between the good negative and the evil positive ions" in the atmosphere.

          In the 1960s, static electricity spread into a whole new area: the world of electronics. Some people consider the appearance of the metal oxide semiconductor field-effect transistors (MOSFETs) as the start of this period. That is probably an oversimplification. Static electricityhad definitely made itself felt in electronics before the MOSFET, but it was little known. Electrostatics, not to mention static electricity, was not really something that fit into the sophisticated electronics world.

 Human-Body-Model event

          However, when the output of sensitive components showed a high percentage of failures and, even worse, when complicated circuits had latent breakdowns, some electronic physicists considered relations between charges in the nC-range and field strengths high enough to cause breakdown, such as that illustrated in the diagram for a human-body-model event

          For many people in the electronics industry, however, the field of static electricity was completely new. "They Think They Invented It," and since they considered it a new field, they needed a new name, and thus electrostatic discharge (ESD) was coined.