Constant current generator

Constant-current generators are sometimes called galvanostats. 

The above example was given to show the versatihty of the coulometric titration method. A more typical example would be one where the constant current generates electrolyticaUy, with 100 percent, a substance which reacts immediately with the analyte species in solution. A typical example is the generation of iodine between two platinum electrodes immersed in an oxygen-free solution of potassium iodide. The generating reaction at the anode is ... 

In coulometric titrations, a constant current generates the litrant eleclrolytically. In some analyses, Ihe active electrode process involves only generation of the reagent." An example is the titration of halides by silver ions produced at a silver anode. In other titrations, the analyte may also be directly involved at the generator electrode. An example of this type of titration is the coulometric oxidation of iron(ll)-in part by elec-trolytic.illy generated cerium(l V) and in part by direct electrode reaction (Section 24B-2). Under any circumstance. the net process must approach 100% current efficiency with respect to a single chemical change in the analyte. 

An interesting variation of this circuit is the cascode amplifier shown in Fig. 9.13. Here, the drain load is exchanged for a constant-current generator. Theoretically this gives infinitely high impedance thus yielding a very high level of amplification. 

Fig. 9.13. (Left) the circuit outline of a one-transistor amplifier, for which the amplification is dictated by the ratio of R and RO. (Right) the same principal circuit but R has been replaced by a constant-current generator...

The dart electrodes have a length of 9—14 mm. The shock is given by a constant current generator with a voltage limitation of 50 kV. This is sufficient to form an arc if the dart tip does not reach the skin. The output is pulsed with pulse duration about 0.1 ms, delivered pulse charge 0.1 mC, current 1 A, and repetition frequency 19 Hz for duration 5 s. 

In Fig. 2.12, middle, we show a large finite array of dipoles backed by a finite groundplane as large as the array. When fed from constant current generators, we obtain the currents under transmitting condition, and the transmit pattern Paf is obtained in the traditional way based on these currents and their approximate images in the finite groundplane. 

Scenario (d) is possible only by feeding the elements from constant current generators... 

In the electrode switching studies, the VCCS was developed with a modified Howland constant-current generator (Figure 30.4) and it was fed by the VCO. The VCCS had two operational amplifier AD811 ICs (Analog Devices Inc., United States) [51]. The AD811 is a high-speed wideband current feedback operational amplifier which is suitably used in modified Howland current source with a feedback resistor [50]. 

Now, if the network is excited by applying a constant current generator (at the fixed frequenej, r) to one of the junctions, the 11 will be zero at all other junctions, and as resonance is approached, the E s will become very large so that the righ1>hand side of (19) can be neglected in comparison with the left-hand side. In other word.s, the condition for resonance is... 

The constant-current generation of bromine is carried out in a medium of dichloroacetic acid, hexafluoroisopropanol, water, potassium bromide and mercury(II)chloride. To this medium an amount of the polymer, previously dissolved in hexafluoroisopropanol and diluted with anhydrous dichloroacetic acid, is added and bromine generated. The end of the reaction is detected biamperometrically. The suitability of this method was tested against methyl vinyl terephthalate. 

Figure 38 shows the schematics of the method forpreparing roughened electrodes. In a typical preparation, commercially available silver electrodes are placed in deionized water 10 mm apart. A constant current of 60 pA was supplied across the two electrodes for 10 minutes by a constant current generator. Figure 39 shows the time dependent... 

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