Instrumentation amplifier excitation

Figure 8.34 Impedance measurement using current excitation and a tetrapolar interface. The V/l-converter supplies the current, whereas the high impedance instrumentation amplifier yields the voltage difference across the inner electrodes.

All experiments were performed in a 1.9-T horizontal bore magnet (Oxford Instruments, Oxford, UK) with a dear bore diameter of 31 cm. Magnetic field gradients were produced by a 12-cm id water-cooled gradient set (Resonance Research, Billerica, MA, USA), capable of a maximum output of 300 mT m-1, and were driven by Techron 7700 amplifiers (Techron Inc., Elkhart, IN, USA). Rf excitation was accomplished using either a quadrature driven birdcage coil (Morris Instruments, Ottawa, ON, Canada), or an 8-tum laboratory-built solenoid coil, driven by an ENI LPI-10 1000 W amplifier or a Matec Model 525 class-C amplifier. 

The instrumentation for voltammetry is relatively simple. With the advent of analog operational amplifiers, personal computers, and inexpensive data acquisition-control system, many computer-controlled electrochemical systems are commercially available or custom made. Programming complex excitation waveforms and fast data acquisition have become a matter of software writing. 

The fluorescence quenching of Pe and derivatives has been investigated by fluorescence upconversion. Excitation was performed with the frequency-doubled output of a Ti Sapphire amplifier. The instrument response time was around 240 fs with 0.4 mm thick samples. The data were analysed by iterative reconvolution of the instrument response function with trial functions. For most samples, measurements were carried out at three different wavelengths (438, 475, and 490 nm). Global fits were done with all the available data. 

A conventional <111> oriented Pb(Zro.45Tio.55)03 (pzt) ferroelectric film, deposited on Pt/Ti02/Si02/Si substrate by sol-gel spin casting and Pt-sputter top electrodes, was used in this study [24], The pzt film thickness was 175 nm. The experimental set-up used for the afm assisted piezoresponse imaging study of the pzt film consisted of a Park Scientific Instrument Autoprobe cp afm combined with a lock-in amplifier to excite and collect the piezoelectric vibration response amplitude and phase. 

The basic operation of the instrument (3) consists of the Ionization of the sample in the cell by a timed electron beam which Is followed, after a short Interval, by an RF pulse applied to the plates of the cell. This pulse coherently excites all ions In the cell into cyclotron motion. The motion continues after cessation of the pulse, and the resonance is detected by the plates of the cell, amplified and the data stored In the computer. The excltatlon/detection cycle is repeated numerous times and the collected data summed. The data Is then subjected to fourler transformation and the frequency spectrum resulting converted into a mass spectrum. The spectrum Is normalized to the major peak. For quantitative work, the calibration can be based either on peak height or peak area. Here, major considerations will Include the resolution chosen and the relative concentrations of the constituents under Investigation. 

The various instruments used for the measurement of atomic fluorescence have been similar to each other in principle and optical design. In most studies, the source of excitation, of whatever type, has been focused on the flame the fluorescence, usually at a right angle, has been focused on the entrance slit of the monochromator. The detector in all studies has been a photomultiplier tube, the output of which has been amplified and recorded. Figure 1 is a block diagram of the apparatus used successfully in our laboratory (5) it is quite similar to one described by Winefordner... 

Laser Fluorescence Detector. A helium-cadmium laser (Model 4240B, Llconlx, Sunnyvale, CA) was (diosen as the excitation source because of Its stability and convenient wavelengths (325 and 442 nm). The UV laser radiation (325 nm, 5-10 mH cw) was Isolated with a dielectric mirror and was focused on the miniaturized flowcell with a quartz lens. Sample fluorescence, collected perpendicular to and coplanar with the excitation beam, was spectrally Isolated by appropriate Interference filters and then focused on a photomultiplier tube (Centronlc Model Q 4249 B, Bailey Instruments Co., Inc., Saddle Brook, NJ). The resulting photocurrent was amplified with a plcoammeter (Model 480, Kelthley Instruments,... 

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