Bridge circuit, development

During the reaction of the hot catalyst surface with a flammable gas the temperature of the device increases. The Platinum coil itself serves at the same time as a resistance thermometer. The resistance increase of the coil then is a direct measure for the amount of combusted gas. Usually the amount of heat that develops during combustion is small and amounts to 800 kj/mol for methane, for example [8], Therefore the sensor is connected in a bridge circuit to a second resistor which shows the same setup as the pellistor but is catalytically inactive. The bridge voltage is then controlled by the temperature difference of the two sensors (see Fig. 5.34). 

The rapid development of solid-state electronic devices in the last two decades has had a profound effect on measurement capabilities in chemistry and other scientific fields. In this chapter we consider some of the physical aspects of the construction and function of electronic components such as resistors, capacitors, inductors, diodes, and transistors. The integration of these into small operational amplifier circuits is discussed, and various measurement applications are described. The use of these circuit elements in analog-to-digital converters and digital multimeters is emphasized in this chapter, but modern integrated circuits (ICs) have also greatly improved the capabilities of oscilloscopes, frequency counters, and other electronic instruments discussed in Chapter XIX. Finally, the use of potentiometers and bridge circuits, employed in a number of experiments in this text, is covered in the present chapter. 

Electric resistivity. The electric resistance measurement is the same as discussed below under volume resistivity, to which this measurement is temporary adapted. For flexible materials, special electrode systems are developed to clamp sample and electric wires. The measuring equipment is based on a Wheatstone bridge circuit. The conductivity of metal powder-containing epoxy was measured in special dies equipped with built-in brass electrodes inserted to the die. The material was cured in the die to assure good contact with electrodes. Special sample holders and clamping devices are used for precise determination of rubber compounds containing carbon black. ... 

Shortly after Poggendorff s publication. Professor Charles Wheatstone, whose contributions to the development of instrumentation for the study of problems associated with telecommunications are classics, developed a bridge circuit. 

An electronic instrument has been developed in which the DC voltage of the potentiometer, or the bridge, is converted to an AC voltage. The AC voltage is then amplified to a higher (usable) voltage that is used to drive a bi-directional motor. The bi-directional motor positions the slider on the slidewire to balance the circuit resistance. 

Figure 2.4.4 (A) Time-dependent electric current generated from the oxidation of HTC coal in an indirect carbon fuel cell. Solutions of Fe 111 and Vv were prepared in 0.5 mol L 1 H2SO4. (B) Development of open-circuit potential Eoc (up) and current I (down) due to Fe2+ formation in the anodic half-cell via oxidation of HTC coal, indicating the reducing potential of bare hydrothermal carbon (HC) dispersions. Charge equalization between the two half-cells was assured by a salt bridge containing a saturated KC1 solution. Carbon felt was used as electrodes. (C) Comparison of hydrothermal and fossil carbon sources in the same setup.

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