Constant voltage source

Cold-junction compensation can be provided by a network which includes a constant voltage source and a temperature-sensitive bridge to provide an offset voltage which is proportional to the temperature sensitivity of the thermocouple and of opposite sign. 

Use of C is to hold the charge and provide a near constant voltage source to the Inverter... 

Smoothing circuit To obtain a near-constant voltage source for the inverter circuit a smoothing capacitance across the d.c. link is used to smooth the a.c. ripples present in the d.c. link after cotiversion. The capacitor retains the charge and provides a near-constant d.c. voltage output. 

Network with linear circuit parameters and constant voltage sources... 

Alternatively, one may control the electrode potential and monitor the current. This potentiodynamic approach is relatively easy to accomplish by use of a constant-voltage source if the counterelectrode also functions as the reference electrode. As indicated in the previous section, this may lead to various undesirable effects if a sizable ohmic potential drop exists between the electrodes, or if the overpotential of the counterelectrode is strongly dependent on current. The potential of the working electrode can be controlled instead with respect to a separate reference electrode by using a potentiostat. The electrode potential may be varied in small increments or continuously. It is also possible to impose the limiting-current condition instantaneously by applying a potential step. 

For the familiar dropping mercury electrode, the electrical potential 1J1 at the metal surface relative to the bulk region of the electrolyte is controlled by an external potential source - a constant voltage source. In this case, can be set to any value (within reasonable physical limits) as the mercury/electrolyte interface does not allow charge transfer or chemical reactions to occur (at least to a good approximation for the case of NaF). Therefore, we can say that the equation of state of the mercury surface is... 

It has also been demonstrated that the sensing electrode can be maintained at a predetermined voltage of 1.0 V by electrically biasing (constant voltage source) the sensing electrode vs. a stable counter-reference, such as Pt/Hp, H+ or PbOp/PbSO, H+ (1, 2,3). With the former, the sensing electrode is electrically biased 1.0 V above the Pt/Hp,H+ potential (0.0 V) and with the latter 0.7 V below the PbOp/PbSOi, H+ potential (1.7 V). Both of these counter-reference electrodes exhibit good reversibility, but reliability and life are not adequate. 

Note that it would be most improbable for i0 and i0 to be equal.) Now let a constant voltage source be placed across the cell so that the zinc is forced to assume a less negative potential and the copper a less positive potential than their equilibrium values. The altered electric field across the zinc/ solution interface makes it easier for zinc atoms to be oxidized but hinders the reduction of zinc ions. Hence ia increases from its equilibrium value while ic decreases therefore... 

Both NTC and PTC units can be used to indicate changes in ambient conditions since the power they draw from a source depends on the heat that they can dissipate into their surroundings. PTC units have the advantage that they are unlikely to overheat since an increase in temperature cuts down the power that they need to dissipate. Precautions must be taken with NTC units to ensure that runaway conditions cannot arise, because an increase in their temperature increases the power that they can draw from a constant voltage source (see Section 5.2.2). 

The following is another simple example solving a differential equation in a DC circuit, as shown in Figure B. 1. This DC circuit contains a constant voltage source, a capacitor, a resistor, and a switch, connected in series. The question is if the timing starts from the moment of turning on the switch, what will Vc (t) be as a function of time ... 

Assemble a Clark electrode (with a fresh membrane, if necessary), constant temperature bath, constant voltage source, and recorder following the manufacturer s instructions. In the subsequent discussion the Yellow Springs Instrument s Clark electrode and sample chamber are used. 

After the recorder stabilizes to a perfectly horizontal trace, adjust it to a full scale (100%) reading using the variable output voltage divider which is part of the constant voltage source. Full scale on the recorder now corresponds to an oxygen concentration of 237 nmoles/ml. 

For ease of explanation, let us confine our discussions here to constant-current or constant-voltage sources. A schematic of a simple firing circuit is shown in Figure 24.16. 

Now suppose that while the capacitor is connected to a constant voltage source, a dielectric (such as the sample under study) is inserted in the space between the capacitor plates. Additional current will flow into the capacitor owing to polarization of the dielectric material. The polarization itself is time dependent but, at equilibrium, the original charge density er0 will increase to a, where... 

The extraction TOF method can be done using either pulsed or constant voltage sources to the acceleration and repeller grids of a Wiley-McClaren TOF-MS. The first extraction TOF experiments were Mons and Dimicoli [56] on N02 photodissociation using constant voltage sources. Later, Black and Powis [88] used a similar extraction TOF technique, also with constant voltage sources, in order to study CH,I photolysis reactions. Most subsequent experimentalists have used pulsed voltage sources. 

In precision measurements, for SPRTs in particular, the simple potentiometric circuit shown in Fig. 16.11 is not sufficient. With this potentiometric method, a problem arises from the difficulty in maintaining a constant voltage source and measuring it to an acceptable accu-... 

FIGURE 16.11 Resistance thermometer circuit where Rc and Rt are the resistance of leads C and T, respec-with constant voltage source. tively, and RDI is the value of RD required for zero current in... 

For most applications, an alternative is employed. Recall that, in measuring the resistance of a thermistor, a fixed resistor is normally connected in series with the sensor. If a constant-voltage source ( s) is used, the circuit current is inversely proportional to the total resistance. Then the relationship between the measured voltage drop across the fixed resistor and the thermistor temperature can be almost linear over a range of temperature. The linear part of this curve can be shifted along the temperature scale by changing the value of the fixed resistor. 

Fig. 3.4. Kinetics of temperature variations in pyrolytic ceQs of different types. (A),(B) = in filament-type cells directly heated by electric current (A) 1,300°C 2,500 C 3,800°C pyrolysis time 10 sec from ref. 48 (B) 1, with constant-voltage source, heating time (HT) = 10 sec 2, with constant-voltage source and additional source of special powerful discharge for rapid heating, HT = 15 msec diameter of heated platinum wire 0.25 mm pyrolysis temperature 800°C reprinted with permission from ref. 57. (C) In Curie-point cell for certain ferromagnetic materials with wire diameter of 0.5-0.6 mm. 1 =CoNi (60 40) 2 = Fe(Zn) 3 = Fe 4 =CoNi (33 67) 5 = NiFe (60 40) 6 = NiCrFe (51 1 48) 7 = NiFe (45 55) 8 = Ni oscillator frequency 0.45. MHz from ref. 65. (D) In Curie-point cell for wire (1) 0.05 mm and (2) 0.5 mm in diameter pyrolysis time 1 sec HT = 0.02 and 0.1 sec from ref. 65. (E) In Curie-point cell for wire (filament) 0.5 mm in diameter. 1, 30-W Philips oscillator, HT = 1.3 sec 2, 2.5 kW oscillator, HT = 120msec reprinted with permission from ref. 57.

This equation should not be used for a constant voltage source measurement since in this case the charge on the surface will vary when the meter (and its ground plate) are inserted. 

For a constant voltage source, the charge on the test surface will be altered by the capacitance of the meter however, the voltage of the test surface can be correctly read from the meter (reading in V/m multiplied by the separation distance in m). For closely spaced parallel plates, the original charge density on the test surface is calculated by the relation... 

When charging Pb cells from a constant voltage source the charging current starts high and slowly decreases to a constant value when the cells become fully charged. The constancy of the current is an approximate indication that the cells are fully charged. 

As an example, the circuit with one switch in Fig. 4.1, is considered. To keep the illustration of the procedure short and simple it is assumed that only one parameter is uncertain. Accordingly, the incremental bond graph is obtained by replacing the element by its incremental model and by replacing the constant voltage source Se Vi by an effort source of value zero and by replacing detectors by dual virtual detectors for the variations of ARR residuals. 

The manganin pressure gauge is supplied by a constant voltage source that gives a rectangular voltage pulse. The pulse has an amplituduration time of 100 ps, and a current of 3-30 A. 

FIGURE 2.1 Circuit schematic symbol and corresponding value notation for (a) resistor, (b) capacitor, (c) inductor, (d) voltage source, and (e) current source. Note that a constant voltage source, or battery, is distinguished from a voltage source the value of which varies with time. 

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