Electrical circuits power sources

Internal sources of noise arise from any power-dissipating device. Of course, every laboratory apparatus is a potential source of contamination. For example, Johnson noise arises because the electrons that carry an electric current always have a thermal motion, causing small fluctuating voltages across any resistor in the electrical circuit. One source of environmental noise is the "pick-up" of a 50-Hz signal due to the main supply in the laboratory. 

The various welding processes result in systems of varying complexity. They include at least the electrode and a device for holding or feeding it, the work piece, the power source, and heavy-duty cabling to provide a complete electrical circuit. Provisions for supply and control of gas and control of wire feed and movement of the electrode assembly are required, depending on process type and degree of automation. 

The system for shielded-metal arc welding, shown in Figure 2a, is the simplest system. It consists of the power source, electrode and holder, the base metal, and the electrical cables or leads. When the arc is stmck, a complete electrical circuit is provided. With d-c welding, the electrode maybe either negative (straight polarity) or positive (reverse polarity). Shielded metal arc welding is only used manually. 

It is important first to distinguish between a closed cyclic power plant (or heat engine) and an open circuit power plant. In the former, fluid passes continuously round a closed circuit, through a thermodynamic cycle in which heat ((2b) is received from a source at a high temperature, heat (Qa) >s rejected to a sink at low temperature and work output (IT) is delivered, usually to drive an electric generator. 

From a basic physics standpoint, a circuit is a complete loop. Electric current can flow only if it returns to its source, i.e., completes the circuit. The path tlirough which tlie current returns to its source is called the "retum or ground. The reason for the tenn "ground is tliat the ctirlh is literally used to provide the return patli no matter what distance separates tlie equipment from the power source. Ground comiections can be made to a cold water system as its components provide a reliable, low-resistance patli for contact witli tlie earth. 

Two directions of current flow in galvanic cells are possible a spontaneous direction and an imposed direction. When the cell circuit is closed with the aid of electronic conductors, current will flow from the cell s positive electrode to its negative electrode in the external part of the circuit, and from the negative to the positive electrode within the cell (Fig. 2.2a). In this case the current arises from the cell s own voltage, and the cell acts as a chemical source of electric current or battery. But when a power source of higher voltage, connected so as to oppose the cell, is present in the external circuit, it will cause current to flow in the opposite direction (Fig. 2.2b), and the cell works as an electrolyzer. 

The source range uses a proportional counter. The intermediate range uses a compensated ion chamber. The power range uses an uncompensated ion chamber. Terms used to describe the electrical circuits are summarized below. 

A well-known fact of fundamental solution science is that the presence of ions in any solution gives the solution a low electrical resistance and the ability to conduct an electrical current. The absence of ions means that the solution would not be conductive. Thus, solutions of ionic compounds and acids, especially strong acids, have a low electrical resistance and are conductive. This means that if a pair of conductive surfaces are immersed into the solution and connected to an electrical power source, such as a simple battery, a current can be detected flowing in the circuit. Alternatively, if the resistance of the solution between the electrodes were measured (with an ohmmeter), it would be low. Conductivity cells based on this simple design are in common use in nonchromatography applications to determine the quality of deionized water, for example. Deionized water should have no ions dissolved in it and thus should have a very low conductivity. The conductivity detector is based on this simple apparatus. 

Electrochemical cells produce electrical energy from a spontaneous chemical reaction. In electrolysis, the process is reversed so that electrical energy is used to carry out a nonspontaneous chemical change. A cell arranged to do this is called an electrolytic cell. An electrolytic cell is similar to an electrochemical cell except that an electrolytic cell s circuit includes a power source, for example, a battery. The same electrochemical cell terminology applies to electrolytic cells. Reduction occurs at the cathode and oxidation at the anode. 

Consider now a situation where, instead of a measuring instrument, one inserts (Fig. 6.31) into the circuit a source of potential (e.g., an electronically regulated power supply). Here, the total potential difference across the cell must equal (in magnitude) that put out by the source.18 This is, in fact, the law of conservation of energy applied to an electrical circuit, or Kirchhoff s second law The algebraic sum of all potential differences around a closed circuit must be equal to zero. For the simple hypothetical system shown in Fig.6.32, one has... 

There are two big advantages of electroless plating. The first is that one needs no power source or external electric circuit What one has to pay for, the oxidizable organic material, may well be cheaper than the electricity one would have to use... 

Miniature batteries based on aqueous, non-aqueous and solid electrolytes are manufactured as power sources for microelectronics and other miniaturized equipment. In Fig. 1.2, the sizes and shapes of some representative button cells are shown. A typical application for such cells is in the electric watch, where the oscillator circuit draws a continuous current of 0.2-0.6 pA and depending on the type of frequency divider and display, the complete unit may require a total of up to 0.5-2.0 pA for operation. Hence the total amount of electrical energy consumed in driving the watch for a year is in the range 15-60 mWh. At present, batteries are manufactured which last for 5-10 years. Watch batteries must have exceptionally low self-discharge rates and very reliable seals to prevent leakage. Further, they... 

The electrons pumped into the corrodible metal have come, in the above method, from the dissolution of a scarificial auxiliary metal. Instead, they can come from an external current source (i.e., an electrical power supply). The electrical circuit, however, has to be completed, and toward this end, an auxiliary inert electrode can be immersed in the corrosive electrolyte to provide a return path for the electron current (Fig. 12.38). The external source can then be adjusted so that the potential difference between the corrodible metal and its environment becomes negative with respect to its equilibrium potential. Under these circumstances, the whole of the metal to be protected against corrosion will function as an electron source for the electronation reaction, and the second electrode will serve as an electron sink for some deelectronation reaction (Hoar). 

The simple series RLC electrical circuit of Fig. 9.2 consists of a direct-current (DC) power source (here a 3-V battery), a relay, and three loads in series a resistor of resistance R, a capacitor of capacitance C, and an inductor of inductance L. Assume first a DC potential E = E0, in series with R, C, and L the capacitance stores charge, the inductance stores current, and the resistance dissipates some of the current into Joule13 heating. The arrow shows the direction of the current (which, thanks to Franklin s unfortunate assignment, is the direction of motion of positive holes—that is, the opposite of the flow of negative electrons) the relay across L avoids conceptual difficulties about an initial current through the inductor. The current is usually denoted by I (from the French word "intensite"). These three components (R, C, and L) will be explored in sequence. 

Short-circuit current — It is the current supplied by an electrical -> power source device if the two terminals of the device are connected, without associated dissipation -> resistance, i.e., load resistance equal to zero. The short-circuit current is determined by the power source characteristics, given by the quotient between electromotive force and internal resistance. See also -> fill factor. 

The wire(s) connecting the electrical power source with the electric blasting cap circuit. 

A very generalized principle of an intrinsically safe electric circuit is shown in Fig. 6.169. Power source, voltage and current limitation are located in a safe area or shall be explosion protected (e.g. in a flameproof enclosure) if located in a hazardous environment. The electric circuit entering the hazardous area as an intrinsically safe circuit is not capable of producing ignitable sparks at make or break. 

---