Bridge Circuit Construction

A new vapor pressure osmometry (VPO) apparatus having a very high sensitivity has been constructed by Kamide et al. 50). In order to match a pair of thermistors, a conventional Wheatstone bridge circuit was modified by introducing a matching resistor, which permits to detect a temperature difference of ca. 6x 10-6 °C. 

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. 

The formation of electrical contacts between metal structures and devices is an integral aspect of circuit construction at all scales of commercial importance. Currently photolithographic, screen printing and microsoldering techniques are the methods of choice to establish connections. However, these approaches require masks, templates or intimate physical contact with the components. Spatially Coupled Bipolar Electrochemistry (SCBE) is a novel technique which makes use of electric fields to create electrical connections between components, which not only avoids physical contact but is also applicable in principle to the formation of three dimensional circuitry. The SCBE technique has been developed to a point where the construction of functional robust circuits has been achieved. Preliminary data demonstrating the application of this approach to the formation of polypyrrole bridges between isolated gold structures is also presented. 

The Corona model 117 is based on the principle established by Kamide et al. [14], who constructed a modified version of the sol vent-vapour chamber and thermistor assembly of Dohner et al. [15], and installed them in a Hitachi model 115 to obtain a new prototype VPO apparatus with increased sensitivity. With the conventional Wheatstone bridge circuit modified by introducing a matching circuit that has two precision variable resistors, the measurements can be made at any desired temperature without changing the thermistors. This enables a temperature difference of about 6x 10" °C to be detected. 

Employing a specially constructed electrical circuit to avoid use of a salt bridge and its associated IR drop, and a two compartment cell, Weise and Weil [80] also confirmed that, in the absence of H2CO, the deposition rate of Cu was significantly lower than would be obtained in a full electroless solution. They employed solutions somewhat similar to Feldman and Melroy [79], but carried out their experiments at room temperature. 

We can employ the following technique. A clean silver electrode is immersed in a solution of chloride ion of known concentration, while a calomel electrode (SCE) is immersed in a second solution of saturated KNO3. The two containers are connected via a salt bridge (to minimize junction potentials, Ej), thus constructing the circuit shown in Figure 4.6. 

Apparatus. All electrical resistances were measured with an electrolytic conductivity bridge (Leeds and Northrup model 4666) which was constructed according to specifications set forth by Jones (28) and described by Dike (29). The audio-frequency source was a General Radio Co. type 1311-A audio oscillator used with the frequency regulated at 1000 Hz and the output at about 5 V. The detector circuit consisted of a high-gain low-noise tuned amplifier and null detector (General Radio Co. type 1232-A) and an oscilloscope (Heathkit model O-ll) ... 

If we have a solution in which both iron(II) and iron(III) ions are present, we can construct a half-cell by immersing a platinum foil as an electrode into it, and connecting the platinum electrode to the electrical circuit. The platinum should not be coated with platinum black in this case as we do not want any adsorption to take place on the surface, a so-called bright platinum electrode must therefore be used. With a suitable salt bridge we can connect this solution to another half-cell (e.g. a standard hydrogen or calomel electrode) and the e.m.f. of this cell can be measured. The potential of the half-cell corresponds to the half-cell equilibrium ... 

The way to get around this problem is to construct a circuit out of lumped components which takes the place of a quarter wave cable. There are many such circuits in the literature and, in fact, many of the single coil duplexers which are not bridges and which do not use quarter wave cables probably utilize such a circuit, intentionally or otherwise. See, for example, the articles by Clark and McNeil (1973) and McLachlan (1980) as well as the widely quoted older works by Gray, et al. (1966) and McKay and Woessner (1966). As far as we know, however, there has been only... 

As a first example of CNLS fitting, the circuit shown in Figure 3.3.5 was constructed with lumped elements whose values were measured on an impedance bridge (top figures) (Macdonald, Schoomnan, and Lehnen [1982]). This circuit leads to very little structure in either the Z or T 3-D plots shown in Figures 3.3.6 and 3.3.7. The... 

Another distinguishing feature of ferroelectric behavior is the polarization versus electric field P—B) hysteresis loop. The hysteresis loop results from the domain reorientation which occurs as the electric field direction is varied. The size and shape of the loop is determined by the magnitude of the dipole moment of the unit cell and the domain-switching characteristics of the material. Hysteresis loop behavior is measured using either a Sawyer—Tower circuit or a Diamant—Pepinsky bridge. Details of the construction and operation of a Sawyer—Tower circuit are given in Reference 24. Thin film properties have also been measmed with these two devices, and in addition, a commercially available measurement system has been widely used. ... 

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