Current transducer

This work presents the theoretieal results and their experimental verifications concerning two possible methods for predicting the material discontinuities shape and severity. The methods are developed for the case of the eddy current transducer with orthogonal coils, for two situations for long crack-tjfpe discontinuities, a metod based on the geometrical diffraction has been used, while in the ease of short discontinuities the holographic method is prefered. 

The methods have been developed for an eddy current transducer with orthogonal coils... 

The first method, based on the geometric theory of diffiaction, can be used in the case of cracks, while the second - the holographic one, can be used for small discontinuities. The both methods have been developed for the case of an eddy current transducer with orthogonal coils. 

Calculating power developed by the expander before breaker opening, is described in Step 1. The generator power, can be measured by using a kilowatt transducer. The kilowatt transducer (or current transducer) is typically available in the motor/generator control panel. If not, it can be added to the machine at a low cost. Knowing both J(,gf and Jg, can be calculated. 

The torque can be measured e.g. electrically with a torsion shaft with strain gauges or eddy current transducers or mechanically with the swiveling motor. The stirrer speed is indicated by mechanical, electrical (photocell) or optical (stroboscope) instruments. 

Figure 3-5. (A) Assembly of reconstituted glucose oxidase on a PQQ-FAD monolayer linked to an Au-electrode. (H i Faradaic impedance spectra of the modified electrode at time intervals of reconstitution, (a) 0.1 h, (b) 0.25 h. (c) 0.5 h. (d) 1 h. (e) 2 h, (f) 4 h. Inset Interfacial electron transfer resistance of the modified electrode at time-intervals of reconstitution. (C) Cyclic voltammograms corresponding to the bioelectrocatalyzed oxidation of glucose, 80 mM, by the enzyme-functionalized electrode at time-intervals of reconstitution (a) 0 h, (b) 0.1 h, (c) 0.25 h, (d) 0.5 h, (e) 1 h, (f) 2 h, (g) 4 h. Inset Electrocatalytic currents transduced by the enzyme-modified electrode at time-intervals of reconstitution. Reproduced with permission from ref. 32. Copyright 2002 American Chemical Society.

The ability of the current transducer to amplify low-current signals must be considered when choosing a potentiostat for SECM experiments. As a tip is miniaturized to nanometer dimensions, the accurate and stable measurement of SECM probe current becomes challenging. A 10 /xm diameter disk electrode produces about 2 nA of steady-state limiting current in a 1 mM solution of mediator, but a 10 nm disk electrode would produce only 2 pA. In the... 

Figure 15.7.1 A low-current transducer for insertion between the working electrode and the current follower (CF) of a potentiostat. Depending on which feedback resistor is chosen in the first stage, the ampUfication factor in this system is 10, 10, or 10. The capacitors in the feedback loops provide some filtering (time constant, 100 fjLs). An inductor-capacitor network was inserted in each power supply connection to minimize noise coupling. [Reprinted with permission from H.-J. Huang, P. He, and L. R. Faulkner, Anal. Chem., 58, 2889 (1986). Copyright 1986, American Chemical Society.]...

The current-follower OA configuration (Fig. 6d) is often used as a current transducer in potentiostat circuits (Fig. 13). The output voltage is proportional to the feedback resistor, R, making amplification of the current signal straightforward. In this... 

An alternate method for construction of multipotentiostats is to use a grounded rrf-erence configuration (Eig. 15). Here the RE is maintained at virtual ground and the potential of the working electrode is changed at the noninverting input of the current transducer. Since the output of the current transducer floats above circuit common by... 

E n, the output is referenced to common by a differential amplifier. Additional working electrodes are added by replicating the current-transducer/differential ampK-fier combination. All working electrodes share the auxiliary and reference electrodes in this configuration. 

Currently, transducer arrays are formed by ceramic polymer composite elements. A variety of technical solutions have been applied to improve their mechanical characteristics. In particular, piano-concave elements can be used to provide a uniform elevation plane radiation pattern both in the near and in the far field (Jedrzejewicz 1999). Similar results have been obtained producing multi-layered piezoelectric elements (Whittingham 1999b) or shaping the elements in other suitable ways. These refinements led to the use of very short pulses, increased bandwidth and better intrinsic collimation of the ultrasound beam (Fig. 1.1). 

The pool of transducers can be classified in different ways. Following the quantity appearing at the transducer output, we encounter types like current transducer . Voltage transducer etc. In the international literature, there exists no systematic concept for classification. In what follows, an attempt is made to find a classification scheme which refiects the inner function of the transducers using only a few transducer principles. It is based on a scheme developed by electronics engineers but has not been applied to sensors till now (Malmstadt et al. 1981). Among the examples given are those that develop their sensor function only in combination with an additional receptor layer. In other types, receptor operation is an inherent function of the transducer. 

Further examples for limiting-current transducers are the vacuum phototube and the flame ionization detector. 

Figures 12.14 and 12.15 show data obtained in tension using cast films oscillated with the help of an electromagnetic reed vibrator operating at resonance. Commercial instruments available today use forced vibrations without resonance. These are desirable because they allow the user to vary temperature and frequency over wide intervals. For example, in the dynamic mechanical thermal analyzer (DMTA), an instrument made by the Rheometrics Company, a bar sample is clamped rigidly at both ends and its central point is vibrated sinusoidally by the drive clamp. The stress experienced by the sample is proportional to the current supplied to the vibrator. The strain in the sample is proportional to the sample displacement and is monitored by a nonloading eddy current transducer and a metal target on the drive shaft. In this instrument, the...

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