Electricity, quantity measurement

We shall use mainly the cgs Gaussian system of units. This is a mixed system with electrical quantities measured in cgs electrostatic units (esu) and magnetic quantities measured in cgs electromagnetic units (emu). 

Both electronic and microcomputer-based controls require information about the state of the controlled system. Sensors convert different physical variables into an electric signal that is conditioned and typically converted to a digital signal to be used in microcontrollers. The trend in the construction techniques of modern sensors is the use of silicon microstrnctures because of the good performance and the low cost of this type of device. In the energy control scope the main quantities to be measured are the temperature, pressure, flow, light intensity, humidity (RH), and the electric quantities of voltage and current. 

As a first step, you need information about measurements in electricity. You know that the flow of electrons through an external circuit is called the electric current. It is measured in a unit called the ampere (symbol A), named after the French physicist Andre Ampere (1775-1836). The quantity of electricity, also known as the electric charge, is the product of the current flowing through a circuit and the time for which it flows. The quantity of electricity is measured in a unit called the coulomb (symbol C). This unit is named after another French physicist, Charles Coulomb (1736-1806). The ampere and the coulomb are related, in that one coulomb is the quantity of electricity that flows through a circuit in one second if the current is one ampere. This relationship can be written mathematically. 

Mass spectrometry is a sensitive analytical technique which is able to quantify known analytes and to identify unknown molecules at the picomoles or femto-moles level. A fundamental requirement is that atoms or molecules are ionized and analyzed as gas phase ions which are characterized by their mass (m) and charge (z). A mass spectrometer is an instrument which measures precisely the abundance of molecules which have been converted to ions. In a mass spectrum m/z is used as the dimensionless quantity that is an independent variable. There is still some ambiguity how the x-axis of the mass spectrum should be defined. Mass to charge ratio should not lo longer be used because the quantity measured is not the quotient of the ion s mass to its electric charge. Also, the use of the Thomson unit (Th) is considered obsolete [15, 16]. Typically, a mass spectrometer is formed by the following components (i) a sample introduction device (direct probe inlet, liquid interface), (ii) a source to produce ions, (iii) one or several mass analyzers, (iv) a detector to measure the abundance of ions, (v) a computerized system for data treatment (Fig. 1.1). 

Recently flow coulometry, which uses a column electrode for rapid electrolysis, has become popular [21]. In this method, as shown in Fig. 5.34, the cell has a columnar working electrode that is filled with a carbon fiber or carbon powder and the solution of the supporting electrolyte flows through it. If an analyte is injected from the sample inlet, it enters the column and is quantitatively electrolyzed during its stay in the column. From the peak that appears in the current-time curve, the quantity of electricity is measured to determine the analyte. Because the electrolysis in the column electrode is complete in less than 1 s, this method is convenient for repeated measurements and is often used in coulometric detection in liquid chromatography and flow injection analyses. Besides its use in flow coulometry, the column electrode is very versatile. This versatility can be expanded even more by connecting two (or more) of the column electrodes in series or in parallel. The column electrodes are used in a variety of ways in non-aqueous solutions, as described in Chapter 9. 

Primary quantity measured local interactions (magnetic, electric field gradient) atomic, molecular potentials... 

Line and multiplet strengths are useful theoretical characteristics of electronic transitions, because they are symmetric, additive and do not depend on the energy parameters. However, they are far from the experimentally measured quantities. In this respect it is much more convenient to utilize the concepts of oscillator strengths and transition probabilities, already directly connected with the quantities measured experimentally (e.g. line intensities). Oscillator strength fk of electric or magnetic electronic transition aJ — a J of multipolarity k is defined as follows ... 

One application of Eq. 2 is the determination of a reaction free energy—a thermodynamic quantity—from a cell potential, an electrical quantity. Consider the chemical equation for the reaction in the Daniel cell (reaction A) again. For this reaction, n = 2 because 2 mol of electrons migrate from Zn to Cu and we measure E = 1.1 V. It follows that... 

To determine in a simple way the connection of the electric energy with the calorific energy caused by it, an electric circuit can be closed by a metallic wire placed in a calorimeter, and the current measured calorifically by the heat effects produced by the different electromotive forces and intensities. The result of such measurements is the equivalence of the heat occurring in the conductor with the electric energy, hence with the product of electromotive force into the electric quantity... 

These empirical laws of electrolysis are critical to corrosion as they allow electrical quantities (charge and current, its time derivative) to be related to mass changes and material loss rates. These laws form the basis for the calculations referenced above concerning the power of electrochemical corrosion measurements to predict corrosion rates. The original experiments of Faraday used only elements, but his ideas have been extended to electrochemical reactions involving compounds and ions. 

It has been proved by infrared spectroscopy (Section 2.2.5 and 3.4.1.2) and data of electrical conductivity measurements [328,329,333,334] that there is water in the NBF. It is more probable that the adsorption layers contain certain quantity of water but are not separated by an aqueous core. This has been confirmed by the electrical conductivity of black foam... 

Resistors whose values can be varied are termed potentiometers. They are made of the same materials as fixed resistors but have a movable wiper to contact a coil of resistance wire or a strip of resistive film at any point along the resistor. Potentiometers used only occasionally to adjust a circuit are called trimmers, while those employed for high-wattage applications such as control of heating mantles and ovens are called rheostats. Precision potentiometers have played an important role in the measurement of electrical quantities and are considered in detail in a later section. 

The uncertainty of optical radiation metrology is high compared to electrical measurements, which are accurate to many decimal places. But with electrical quantities, there is no distribution of signal, except perhaps for time. Because either voltage... 

The examples of transfer functions presented here involve exclusively electrical quantities, but are distinct from the usual impedance measurements described in other parts of this book. 

An atom or molecule distorts under the action of an external field, the measure of distortion being expressed through a second-order electrical quantity called the (dipole) polarizability a, which we define in terms of a transition moment /q from state i//0 to t/q and an excitation energy s, as ... 

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