Measuring current

The Index n = k- ) - M + m is the current variable that indicates the sequence for the beam projections. Exploiting the current measurings y fn) one has to estimate the unknown image parameters a, with undefined conditions about their distribution and the noise FDD function. 

The QAP system detects wheather the currently measured suspension is between the given limits or exeeds them. 

The measurement of the current for a redox process as a fiinction of an applied potential yields a voltaimnogram characteristic of the analyte of interest. The particular features, such as peak potentials, halfwave potentials, relative peak/wave height of a voltaimnogram give qualitative infonnation about the analyte electrochemistry within the sample being studied, whilst quantitative data can also be detennined. There is a wealth of voltaimnetric teclmiques, which are linked to the fonn of potential program and mode of current measurement adopted. Potential-step and potential-sweep... 

A key feature of MFC is that future process behavior is predicted using a dynamic model and available measurements. The controller outputs are calculated so as to minimize the difference between the predicted process response and the desired response. At each sampling instant, the control calculations are repeated and the predictions updated based on current measurements. In typical industrial applications, the set point and target values for the MFC calculations are updated using on-hne optimization based on a steady-state model of the process. Constraints on the controlled and manipulated variables can be routinely included in both the MFC and optimization calculations. The extensive MFC literature includes survey articles (Garcia, Frett, and Morari, Automatica, 25, 335, 1989 Richalet, Automatica, 29, 1251, 1993) and books (Frett and Garcia, Fundamental Process Control, Butterworths, Stoneham, Massachusetts, 1988 Soeterboek, Predictive Control—A Unified Approach, Frentice Hall, Englewood Cliffs, New Jersey, 1991). 

Apparatus and circurtry associated with controlled current measurements. 

While conducting the test the negative sequence voltage should be less than 0.5% of the positive sequence component. In terms of current, the negative sequence current should not exceed 2.5% of the positive sequence component of the system current. Measurement of any one of the components will be adequate. 

These are employed for the measurement of power circuit currents through an ammeter, kW, kWh or KVAr and power factor meter, or similar instruments requiring a current measurement. They must have a specified accuracy class as in lEC 60044-1 and the secondary current substantially proportional to the primary within a working range of about 5-120% of its primary rated current. They... 

IZnO(2 = actual leakage current measured at site. 

I When the system voltage is linear (an ideal condition that would seldom exist) but the load is non-linear The current will be distorted and become non-sinusoidal. The actual current /, (r.m.s.) (equation (23.2)) will become higher than could be measured by an ammeter or any other measuring instrument, at the fundamental frequency. Figure 23.13 illustrates the difference between the apparent current, measured by an instrument, and the actual current, where / = active component of the current... 

U2 = 0.1 V) and are suitable for current measurement. For smaller currents, sensitive instruments with 5 kQ per fiPc (Uj = 5 mV) are used. Small currents are usually measured by the voltage drop across a fixed resistance (calibrated shunt) using an electronic amplifier-voltmeter. This method has the advantage that the circuit does not have to be interrupted to measure the current. 

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... 

Contacts with other pipelines or grounds can be localized to within a few hundred meters by pipe current measurements. Contacts with foreign pipelines or cables can also be found by measuring potential at the fittings of the other line while the protection current of the cathodically protected pipeline is switched on and off. While the potential of unconnected pipelines will assume more positive values when the protection current is switched on, the cathodic current may also enter any line in contact with the cathodically protected pipeline and thus shift its potential to more negative values. Should the contacting line not be located by this method, fault location can be attempted with direct or alternating current. 

Fig, 10-7 Aboveground test points, potential measuring points (2) and (3), pipe current measuring point (1/2). 

With unprotected comparison test pieces, the corrosion rate was 4 mm a , which from cell current measurements indicated that the self-corrosion was 50%. 

Fig. 20-7 Potential and protection current measurements on two 750-liter tanks X (20°C) = 730 IJ.S cm operating temperature 70°C.

The algebraic sum of the three currents measured from all three sections have to be theoretically always zero however, minute differences have been found in the separate tests. 

Only the knowledge of relative useful ion yields and isotopic abundances is required to calculate elemental composition from the relative ion current measurements. The useful ion yield is the number of ions x detected relative to the number of atoms of element xsputtered. The measured relative ion current of two isotopes is... 

PTFE is an outstanding insulator over a wide range of temperature and frequency. The volume resistivity (100s value) exceeds lO Gm and it appears that any current measured is a polarisation current rather than a conduction current. The power factor is negligible in the temperature range -60°C to -i-250°C at frequencies up to lO" Flz. The polymer has a low dielectric constant similarly unaffected by frequency. The only effect of temperature is to alter the density which has been found to influence the dielectric constant according to the relationship... 

Cathodic-protection instruments may be classified as potential-measuring, current-measuring, resistance/conductance-measuring, multicombination, recording and ancillary. 

Current measurements—milliammeters or the measurements of the IR drop across a conductor of known resistance. 

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