Current converters

This enables to locate both small surface cracks from 0.1 mm deep and undersurface defects with one and the same eddy-current converter. This also allows to reveal corrosion between sheets while suppressing the influence of variation of clearance between them. 

Maximum gap between the eddy-current converter and the expected surface- 10mm Inspected surface electrical conductivity- 0.5-r60MS/m. 

Foxboro s Model 823 transmitter uses a taut wire stretched between a measuring diaphragm and a restraining element. The differential process pressure across the measuring diaphragm increases the tension on the wire, thus changing the wire s natural frequency when it is excited by an electromagnet. This vibration (1800—3000 H2) is picked up inductively in an oscillator circuit which feeds a frequency-to-current converter to get a 4—20 m A d-c output. 

More sophisticated instruments use special circuitry to obtain the rms values of non-sinusoidal signals. The current converter usually consists of low-value resistors in the input, and one of these is chosen as a shunt resistor... 

Amorphous carbon is wet by KF-2HF, but the passage of anodic current converts the surface to CFX, which is not wet by KF-2HF. Figure 2 shows the results from an experiment4,14 in which a fresh piece of carbon was made anodic in KF-2HF. The initial voltage at a constant 15 mA cm"2... 

Ethylene is currently converted to ethylene oxide with a selectivity of more than 80% under commercial conditions. Typical operating conditions are temperatures in the range 470 to 600 K with total pressures of 1 to 3 Mpa. In order to attain high selectivity to ethylene oxide (>80%), alkali promoters (e.g Rb or Cs) are added to the silver catalyst and ppm levels of chlorinated hydrocarbons (moderators) are added to the gas phase. Recently the addition of Re to the metal and of ppm levels of NOx to the gas phase has been found to further enhance the selectivity to ethylene oxide. 

Uranium is extracted by a series of reactions that lead to uranium hexafluoride the isotopes are then separated by a variety of procedures. Some radioactive waste is currently converted into glass or ceramic materials for storage underground. 

ISBN 978-0-7506-8421-7 (hardcover alk. paper) 1. Electric current converters. 

The logarithmic converter is implemented with a voltage-to-current converter (OPAM, Ml, and Rs) and a pair of diode-connected, vertical pnp transistors (Qi and Q2). The relation between the differential output voltage (AVeb) and the sample resistance (Rs) is given by the equation ... 

The control voltage drives the voltage-to-current converter. The polysilicon reference resistor (Pref) used in the converter is located on the microhotplate in order to be at the same temperature as Pheat- This configuration eliminates the temperature dependence of the proportionality coefficient between I control and the power dissipated by Pheat (Pheat) as shown in Eq. (5.4) ... 

Generally, a continuous recording of electrically available data - for example, current, cell voltage, electrode potentials, temperatures - is beneficial to supervise the proper procedure of each experiment. Especially in case of a failure this will be a valuable help to find the reason. Today, the best way is to use a data acquisition system in a computer that offers the results directly for further calculations, for example, integration of the consumed current (converted charge). For continuously operated experiments the addition of scales, which acquire the weight of input and output reservoirs, will be advantageous in order to supervise the mass balances continuously. 

NFPA 850. 2000. Recommended Practice for Fire Protection for Electric Generating Plants and Fligh Voltage Direct Current Converter Stations. National Fire Protection Association, Quincy, MA. 

The electronic components for the measurements consisted of EG Q Model 173 Potentiostat equipped with slow sweep option (0.1 mv/sec) and EG G Model 376 Logarithmic Current Converter. An EG G Model 175 Universal Programmer supplied the waveform for running the polarization experiment. The output from the electrometer of the 173 and the log output of the 376 were connected to a Hewlett-Packard Model 7036B X-Y Recorder and the potential plotted versus log current. 

Low- and intermediate-level waste is currently converted to cement and bitumen waste forms, but the existing trend is toward an increase in the radiation safety levels and reliability of immobilization. From this point of view, LILW should also be incorporated in vitreous and crystalline matrices. Current Russian and US experience on vitrification of such waste demonstrates the potential of the melting/vitriflcation process. Major advantages of vitrification over bituminization and cementation are a greater waste volume reduction, higher productivity, and higher durability of the final product. 

For small low-current applications (laptop computers, cell phones, etc.), solid-state voltage-to-current converters using operational amplifiers will transform 110 to 250 V 50 or 60 HZ AC into a desired 9,12, or 15 V and maybe 20-mA DC supplies. 

However, since this corrosion reaction is short-circuited on the corroding surface, no current will flow in any external measuring circuit. Consequently, a direct electrochemical measurement of the corrosion current (convertible to corrosion rate by the application of Faraday s law) cannot be made. Despite this limitation, electrochemical techniques can be used to decouple the two half-reactions, thereby enabling each to be separately and quantitatively studied. This involves the determination of the current-potential relationships for each half-reaction. Subsequently, the behavior under electrochemically unperturbed (open-circuit or natural corrosion) conditions can be reconstructed by extrapolation of these relationships to Ecorr-... 

Most of the current converters consist of a flow-through ceramic monolith with its channel walls covered with a high-surface-area 7-AI2O3 layer (the washcoat) which contains the active catalyst particles. The monolith is composed of cordicrite, a mineral with the composition 2MgO 2AI2O3 5Si02. The chemical composition of a modern TWC is quite complex. In addition to alumina, the washcoat contains up to 30 wt% base metal oxide additives, added for many purposes. The most common additives are ceria and lanthana in many formulations BaO and Zr02 are used, and in some converters NiO is present. The major active constituents of the washcoat are the noble metis Pt, Pd, and Rh (typically 1-3 g). Most of the TWC systems in use today are still based on Pt and Rh in a ratio of about 10 1. 

Preservation and improvement of the environment is a contemporary necessity that involves all the humanity. Terms like sustainable development or green chemistry have become something more than a literary topic and are currently converted into widely claimed social demands. Destruction of environmental pollutants is one of the aspects dealing with environmental management, a term where concepts such as environmental preservation, environmental remediation, etc., are included. Here, the attention will be focused in the electrodegradation of pollutants. 

Most electronic equipment shares the television set s need for a number of differing voltages for the operation of individual components. This alone may be sufficient justification for the inclusion of a direct current to alternating current converter in fuel cell power systems. In addition, alternating current electric motors are more suitable in most applications. They tend to operate at a rotational speed controlled by the frequency of the current. If completely unloaded they speed up to this fixed velocity and accelerate no further. Many types of direct current motors, if operated unloaded, will continue to accelerate until they fail. A belt driven fan operated by an alternating current motor is undamaged by the failure of the belt. A direct current motor will require a special safety circuit to shut it down in case of belt failure. If the belt and the safety circuit both fail, the motor will speed up until it destroys itself. 

In power conversion, we may have noticed that we always talk rather instinctively of voltage rails. That is why we also have dc-dc voltage converters forming the subject of this book. But why not current rails, or current converters for example ... 

Industrially, iodoform is prepared by electrolysis, at 60- 5 C, of a solution of 60 kg of KI, 20 kg of Na COs, and 80 liters of ethanol per 400 liters of solution. The iodine set free by the current converts the ethanol and the sodium carbonate into iodoform and sodium iodide. In practice, part of the iodine reacts with the caustic alkali formed at the cathode and forms an iodate. Prevention of this reaction by surrounding the cathode with a porous cup brings the yield of iodoform up to about 90 per cent of the theoretical. 

Alternating current motors can be designed to be highly efficient and can be controlled with modern power circuitry. Because of the development and wide spread dissemination of switching direct current converters, it is quite feasible to use alternating current motors with a battery supply. To date, alternating current motors have only been used in research on power wheelchairs. The output of the motor is controlled by varying the phase or the frequency. 

Figure 8.27 On-chip current mode lock-in amplifier. VCC voltage to current converter, CCC = current to current converter, ADC = analog to digital converter...

A differential current-to-current converter produces the output current which is filtered and converted into output voltage Vq by the LPF. 

Basic electronic circuits are similar for both frequency domain and time domain modes [1]. For example, it may be a voltage-to-current converter feeding a current into the MUT while the voltage across is monitored (Fig. 32). 

The signal from a resonant transducer resembles an AM radio signal. It has a carrier wave, at the resonance frequency of the transducer, which is amplitude modulated by the process. The information about the process is in the modulation envelope. An RMS-to-DC (root mean square-to-direct current) converter is used to demodulate the signal. The output of this device is the amplitude of the envelope. 

Voltage-to-current converter with grounded load... 

CFBs can be used to reaHze inverting and noninverting amplifiers, current-to-voltage and voltage-to-current converters, and summing and differencing amplifiers. Thus, they can be utilized in a variety of active filters such as Sallen-Key active filters. However, careful stability analysis must be performed for circuits in which CFBs have reactive components in their feedback networks. For example, the usual Miller... 

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