Voltage coefficient of temperature

The temperature voltage coefficient has several names temperature coefficient, voltage coefficient or temperature coefficient of voltage. Table 7.3 contains a few values of (d (emf)/dT). 

In some cases they were able to quench deton completely by an applied magnetic field, and in one experiment they determined the temperature coefficient of voltage required to quench detonation in 20 mol % acetylene and 80% air to be positive. Malinovskii Lavrov stated that negative charges actively propagate the deton wave in 25/75 mol % acetylene... 

Effect of temperature and temperature coefficient of voltage AEtAT on heat content change of cell reaction 1/28... 

Ta ble 1.6 Electromotive force and temperature coefficient of voltage for various concentrations of sulphuric acid electrolyte in the lead-acid battery... 

Table 1.6 and Figure 1.9 illustrate the effect of cell temperature on thermodynamic cell e.m.f. at various sulphuric acid concentrations. Three temperatures likely to be encountered in battery operation are included IS C, 25°C and 40°C. Also calculated arc the average temperature coefficients of voltage... 

Ideally a standard cell is constmcted simply and is characterized by a high constancy of emf, a low temperature coefficient of emf, and an emf close to one volt. The Weston cell, which uses a standard cadmium sulfate electrolyte and electrodes of cadmium amalgam and a paste of mercury and mercurous sulfate, essentially meets these conditions. The voltage of the cell is 1.0183 V at 20°C. The a-c Josephson effect, which relates the frequency of a superconducting oscillator to the potential difference between two superconducting components, is used by NIST to maintain the unit of emf. The definition of the volt, however, remains as the Q/A derivation described. 

These relationships can be used to obtain thermodynamic data otherwise difficult to get. Vice versa they can be used to calculate the temperature coefficient of a cell voltage respectively an electrode potential based on known thermodynamic data. 

KMP010-NT-A7G-XXX Pressure rango Sensitivity Temperature coefficient of output span (TCS) Temperature coefficient of olfeel voltage (TCO) 12 -0.19 -0.05 1.000 20 -0.17 26 -Q.14 +0.05 kPa MV/VkPa W %VK... 

KMP100-NT-AJG-XXX Pressure range Sensitivity Temperature coefficient of output spen (TC ) Temperelure coefficient of offset voltage fTCO) 4 -0.19 -0.05 10 000 5 -017 6 -0.15 +0 05 kPa pV/VkPa %/K %/K... 

Average values of heat-transfer coefficients to liquid-solids systems 97-99 have been measured using small electrically heated surfaces immersed in the bed. The temperature of the element is obtained from its electrical resistance, provided that the temperature coefficient of resistance is known. The heat supplied is obtained from the measured applied voltage and resistance and is equal to V2/R, where V is the voltage applied across the element, and R is its resistance. 

A katharometer is employed to determine the concentration of H2 in a H2/CH4 mixture. The proportion of H2 can vary from 0 to 60 mole per cent. The katharometer is constructed as shown in Fig. 6.54 from four identical tungsten hot-wire sensors for which the temperature coefficient of resistance ft, is 0.005 K. The gas mixture is passed over sensors R, and R whilst the reference gas (pure CH4) is passed over sensors R2 and R,. The total current supplied to the bridge is 220 mA and it is known that the resistance at 25°C and surface area of each sensor are 8 Q and 10 mm2 respectively. Assuming the heat transfer coefficient h between gas and sensor filaments to be a function of gas thermal conductivity k only under the conditions existing in the katharometer and that in this case h = k x 10 (h in W/m2K and k in W/mK), draw a graph of the output voltage V0 of the bridge network as a function of mole per cent H2. 

Eq. (4.4) indicates that the voltage permanently applied to a YDR must be carefully limited. For instance with a = 25 a 10% increase in voltage would increase the power dissipation by a factor of about 2.5. Since YDRs usually have negative temperature coefficients of resistivity, it can be seen that a runaway condition can easily be precipitated. ... 

Calculate the free energy change (heat change) of the cell reaction (AH) in calories for two battery systems (a) A lead-acid cell with an open-circuit voltage of 2.01 V at 15 °C and a temperature coefficient of resistance (dE/dT) of 0.0037 V/K. (b) A Zn-Hg cell (Clark cell) with an open-circuit potential of 1.4324 V at 15 °C and a temperature coefficient of 0.00019 V/K. (Bhardwaj)... 

Because of the high resistance of the glass membrane (10 to 100 MO), it is not practical to measure the emf directly. Instead, pH meters either use a direct-reading electronic voltmeter or electronically amplify the small current that flows through the cell and detect the voltage drop across a standard resistor potentiometrically. Both battery-operated and ac line-operated pH meters are available connnercially from such firms as Beckman Coulter, Thermo Orion, and Coming. Such pH meters are calibrated to read directly in pH units, have internal compensation for the temperature coefficient of emf, and have provision for scale adjustments. 

Suppose a current I flows through a sample of resistance Rq. Rq is defined as the resistance of the sample at zero current. Because of the Joule effect, the resistance will increase by AR = Rof3AT, where (3 is the temperature coefficient of the resistance. As above, one can write AT rsj RqP, and this approximation therefore gives AR Rol)", The voltage V across the sample is therefore given by... 

The simplest and most inexpensive temperature monitors are thermocouples, such as copper-constantin (type T). Although the temperature coefficient of the thermoelectric effect is low (39 /nV/K at room temperature for type T), there exist excellent tables for common thermocouples which make them extremely reproducible (see, e.g., the helpful handbook on temperature measurements from Omega Engineering, Stamford, CT). Unfortunately, below about 30 K the thermoelectric coefficient decreases by at least a factor of 10 and thermocouples become not useful (unless one uses exotic and expensive couples like gold/iron). Further, because the voltages measured are so low, artifacts such as ground loops and stray return currents from the typical 1-5 A current being applied to the heater can lead to serious errors. 

Temperature coefficient of the cell voltage of the lead—acid battery as a function of acid concentration Pb + 2H2SO4 + Pb02 = 2PbS04 + 2H2O [13]. 

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