Current requirement

Current requirements for vehicles are more pronounced for warm conditions than for cold for many reasons e.g., improved aerodynamics, transversal placement of the motor, generally higher temperatures under the hood, such that the automobile manufacturers prefer a reduction, rather than increase in RVP. 

The maximum desilvering speed is related to the maximum current the power supply will deliver. When the efficiency is high, a current of lA will recover 4g of metallic silver per hour. The daily load determines the maximum current required. A 3A unit will typically be used for up to 15 m of film per day. 

An electrochemical method in which the current required to exhaustively oxidize or reduce the analyte is measured. 

Varietal labeling is an important quaUty factor in the United States, and indirectly elsewhere because only certain specific varieties are planted in each prestigious foreign area. U.S. law currently requires that 75% of the wine must come from the V. vinifera variety named on the label. Concord-type varieties only require 51%, owing to their intense, distinctive flavor. If more than one variety is named, the relative amounts must total 100%. 

A strip lamp is a convenient means for the caUbration of secondary pyrometers (Fig. 9). The notched portion of the tungsten strip is the target. A pyrometer which has been caUbrated against a radiafing blackbody is sighted on the target, and the strip lamp current is adjusted to radiate at the iatensity of the blackbody, as transferred by the primary pyrometer. The secondary pyrometer is then substituted for the primary, and the current required to raise the lamp filament to the brilliance of the target of the strip lamp is noted. 

Mean value (C/4) where C is the current required to discharge the ceU ia one hour. 

The bot-wire anemometer consists essentially of an electrically heated fine wire (generally platinum) exposed to the gas stream whose velocity is being measured. An increase in fluid velocity, other things being equal, increases the rate of heat flow from the wire to the gas, thereby tending to cool the wire and alter its electrical resistance. In a constant-current anemometer, gas velocity is determined by measuring the resulting wire resistance in the constant-resistance type, gas velocity is determined from the current required to maintain the wire temperature, and thus the resistance, constant. The difference in the two types is primarily in the electric circmts and instruments employed. 

Power Supplie.s Iligh-voltage ac and dc power supplies for electrostatic separators are iisiiallv of solid-state construction and feature variable outputs ranging from 0 to 30,()()() for ac wiper transformers to 0 to 60,000 for the dc supply The maximum current requirement is approximately 1,0 to 1,5 rnA/rn of electrode length. Powder supplies for industrial separators are typically oil-insulated, but smaller diw-epoxv-insulated supplies are also available. 

Examples of the sacrificial-anode method include the use of zinc, magnesium, or aluminum as anodes in electrical contact with the metal to be protected. These may be anodes buried in the ground for protection of underground pipe lines or attachments to the surfaces of equipment such as condenser water boxes or on ship hulls. The current required is generated in this method by corrosion of the sacrificial-anode material. In the case of the impressed emf, the direct current is provided by external sources and is passed through the system by use of essentially nonsacrificial anodes such as carbon, noncor-rodible alloys, or platinum buried in the ground or suspended in the electrolyte in the case of aqueous systems. 

To the basic current requirement is applied the derating faetors for various service conditions, as noted in Section 1.5.4.2. The equipment, devices and components may then be cbosen to be as close (nearest higher) to this rating as possible from the available standard ratings. Based on these ratings, the minimum cross-sectional areas of the other current-carrying parts used in the circuit, such as interconnecting links and the cables-are calculated. 

I = relay current setting, i.c. minimum spill current required to operate the relay... 

Minimum excitation current required at the relay operating voltage... 

The terms protection current and protection current densities refer to any values of total cathodic currents that meet the criterion in Eq. (2-40). However, in the field, and for designing cathodic protection stations, another term is of interest, the protection current requirement. This term is concerned with the lowest value of the protection current that fulfills the criteria in Eqs. (2-39) or (2-40). Since with an extended object having a surface S the polarization varies locally, only the current density for the region with the most positive potential has the value J. In other regions 17. 1 > 7. . For this reason, the protection current requirement 4 is given by ... 

The variation in the on and off potentials or the potential difference along the pipeline will usually indicate faults that prevent the attainment of complete cathodic protection. The protection current requirement of the pipeline may be estimated from experience if the age and type of pipeline is known (see Fig. 5-3). Figure 3-20 shows the variation in the on and off potentials of a 9-km pipeline section DN 800 with 10-mm wall thickness. At the end of the pipeline, at 31.84 km, an insulating unit is built in. The cathodic protection station is situated at 22.99 km. Between this and the end of the pipeline there are four pipe current measuring points. The applied protection current densities and coating resistances of individual pipeline sections are calculated from Eqs. (3-40) and (3-41). In the upper diagram the values of... 

Like Criterion 2, this relation has no theoretical foundation and only serves as a comparison and for the design of protection installations. For this reason in Eq. (5-110 is sometimes less correctly termed the conventional protection current requirement. 

Coatings of less noble metals than the substrate metal (e.g., Zn on Fe) are only protective if the corrosion product of the metal coating restricts the corrosion process. At the same time, the formation of aeration cells is hindered by the metal coating. No corrosion occurs at defects. Additional cathodic protection to reduce the corrosion of the metal coating can be advantageous. Favorable polarization properties and low protection current requirements are possible but need to be tested in individual cases. The possibility of damage due to blistering and cathodic corrosion must be heeded. 

Even in good alloys and under favorable conditions, the a value does not lie above about 0.6. In enamelled storage tanks where the current requirement is low, the a value can fall to as low as about 0.1. The cause of the high proportion of selfcorrosion is hydrogen evolution, which occurs as a parallel cathodic reaction according to Eq. (6-5b) or by free corrosion of material separated from the anode on the severely craggy surface [2-4, 19-21]. 

In the application of magnesium anodes for enamelled boilers, the consumption rate of the anodes is determined less by current supply than by self-corrosion. The calculation of life from data on protection current requirement, /, and anode mass, m, is difficult because the a value is so low. 

The current requirement of the protected object basically determines the design of the anode bed. For example, for a pipeline requiring 10 A with horizontal anodes laid in soil with p = 45 H m, according to Fig. 9-14, eight anodes are necessary. The grounding resistance of one anode amounts to Rq = 14 H. From Fig. 9-8, the grounding resistance of the anode bed with an interference factor F= 1.34 for 8 anodes spaced at 5 m comes to R = 2.34 Q.. 

The current output of galvanic anodes depends on the specific soil resistivity in the installation area and can only be used in low-resistivity soils for pipelines with a low protection current requirement because of the low driving voltage. Impressed current anode installations can be used in soils with higher specific soil resistivities and where large protection currents are needed because of their variable output voltage. 

Where there is a high protection current requirement, and for long pipelines, the impressed current method is almost always recommended, since it can provide for the increased protection current requirements resulting from branched pipelines by raising the output voltage. The following factors should be taken into... 

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