Frequency response analyser

AC impedance measurements were also made in bulk paints. A Model 1174 Solartron Frequency Response Analyser (FRA) with a Thompson potentiostat developed ac impedance data between 10 KHz and 0.1 Hz at the controlled corrosion potential The circuit has been described in the literature( ). 

Fig. 8.7. Experimental arrangement for intensity modulated photocurrent spectroscopy (IMPS). FRA frequency response analyser. LED light emitting diode.

In passive methods, the quartz crystal is perturbed with a sinusoidal high frequency ac voltage in a few kHz frequency range around resonance. The most commonly used instrument is the Frequency Response Analyser (FRA) at I-lOMHz. Several commercial instruments can measure automatically a range of frequencies and evaluate the BVD circuit parameters. 

Another passive method is the transference function method (TFM) introduced by Muramatsu [6]. The method consists of an oscillator that drives a crystal through a known measuring impedance and a radiofrequency voltmeter which measures the transference modulus of the system. Muramatsu [6] neglected the effect of the parasitic capacitance and his expression for the quartz impedance resulted in a nonlinear relationship between the measured resistance R with the ac voltage divider and the value of R measured by an impedance analyser. Calvo and Etchenique [74] improved the method and introduced an analytical expression to fit the entire transfer function around resonance in order to obtain the same values of R, L and C as measured by a frequency response analyser. 

The entry into the measurement scene of efficient, commercial frequency response analysers, combined with digital signal processing capability,... 

Fig 5.13 Block diagram, showing frequency response analyser method of measurement. 

Fig 5.14 Circuit for connecting sample to a frequency response analyser. 

Impedance spectra are usually measured with automated frequency-response analysers using single sine wave applied fields. Measured data are resolved into real (in-phase) and imaginary (out of phase) or quadrature constituents. The frequency is usually swept over a certain range, either linearly or logarithmically. The measurements can also be done with sols between the electrodes, to study the dielectric response of colloids. We will return to that in sec. 4.5d. For general information on such techniques and their interpretation, see ref. 

There are two main sources of error in this type of measurement. The first arises from the failure of the approximation Y jcoCsd if the sample has a poor ohmic contact or the frequency is too high. If this is the case, the out-of-phase component is no longer a linear function of Csd. The error, which usually manifests itself as an unexpected frequency dependence of Csd, can be avoided by making frequency-dependent impedance measurements with a frequency response analyser (as discussed in Section 12.2.2). The other source of errors arises from the frequency response of... 

Figure 12.33 illustrates the set-up for LMMRS. The frequency response analyser replaces the single frequency lock-in amplifier used in the potential and light modulated microwave measurements described in Section 12.3. LMMRS detects the frequency-dependent modulation of the microwave reflectivity AR associated with the photogenerated minority carriers. This concentration decays by interfacial charge fransfer k d and recombination kKc)- The LMMRS response is therefore a semicircle with a characteristic frequency otam = + rec)- The low-frequency intercept of the... 

Fig. 3. Sketch of the hardware and software system used in the author s laboratory to investigate the electrode kinetics of electrochemical reactions. D.A.C are digital-to-analogue convertors, F.R.A. is a frequency response analyser, A.D.C. are analogue-to-digital convertors (used to switch devices), D.P.M is a panel meter, and NTWK is the university network serial connection to an Amdahl computer. The units I are the appropriate interfaces.

AC impedance measurements were carried out on 300 0.m thick polymer electrolyte samples, with n=16 and an exposed area of 0.20 cm, using a Pt/PEGi6Mg(CI04)2/Pt cell configuration results for the other molar ratios will be reported later. Regarding the experimental set-up, major equipment included a Schlumberger 1255 HF Frequency Response Analyser, electrochemically interfaced to a Western Systems 486 PC via a PAR 273A... 

Fig.II.5.1 Block diagram of a potentiostatic frequency response analyser...

The 1170 and 1250 families of frequency response analyser, Schlumberger-Solartron Electronic Group Ltd. 

Figure 11.17 The common experimental arrangement for electrochemical impedance experiments relies on the use of a frequency response analyser to derive the Cartesian or polar coordinates of the impedance and admittance.

As mentioned previously, the raw transfer function given by the frequency response analyser, A Ff/A V( >), must be corrected to obtain the final mass/potential transfer function, Am/AE co). 

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