Equipment Frequency response analyzer

The two codes, written in basic language for an Apple He computer, use the galvano-static mode and drive, respectively, the Solartron mod. 1286 electrochemical interface and the EG G mod. 173 potentiostat, which is equipped with a mod. 276 interface. In both cases use is made of a Solartron mod. 1250 frequency response analyzer. 

Special equipment for transient and impedance measurements consists of a digital storage oscilloscope and a frequency response analyzo. A suitable oscilloscop>e should have at least two channels with 1 kB (1024 measurement points) storage capacity. A frequency response analyzer is usually a complete unit which can produce the excitation signal, make naeasurements, process and analyze the measurement data. 

In addition to performance evaluations, many photoelectrochemical experiments are aimed to identify performance-Umiting steps or to determine certain materials properties. Examples of the latter are donor or acceptor densities and the flatband potential of a material, which can be determined by electrochemical impedance measurements. The challenge with these measurements is that they always yield data, but that it can be difficult - and sometimes even impossible - to translate the measured data to the desired materials parameters. Carefully performed control experiments and a good basic understanding of the measurement equipment -in particular, the potentiostat and the frequency response analyzer (FRA) - are essential for obtaining meaningful results. 

In general, direct methods can be used to acquire impedance data significantly more rapidly than bridge methods. This is particularly true for digitally demodulated, phase-sensitive detectors, for which only a single cycle is required. Nevertheless, in unstable systems, such as rapidly corroding specimens, acquisition rate is an important consideration, and a major criticism of PSD methods is that these must be performed frequency by frequency. Fortunately, this often is not a serious hindrance when such equipment is automated. In the past decade, a number of experimenters have used automated frequency response analyzers as digitally demodulated, stepped-frequency impedance meters. Typical of this class are the Solartron 1170 and 1250 series frequency response analyzers (FRAs). 

For measurements in the frequency domain, capacitance bridges, impedance analyzers, frequency response analyzers, radio-frequency reflectometers and network analyzers are typically employed. Figure 1 shows schematically the frequency range of dielectric measurements covered by different techniques and equipments [17]. The principle of these measurements is as follows. The sample... 

Figure 1. Techniques and equipment for dielectric measurements. FRA means frequency response analyzer, TDS is time domain spectroscopy...

Analysis of Lissajous figures on oscilloscope screens was the accepted method of impedance measurement prior to the availability of lock-in amplifiers and frequency response analyzers. Modern equipment allows automation in applying the voltage input with variable frequencies and collecting the output impedance (and current) responses as the frequency is scanned from very high (MHz-GHz) values where timescale of the signal is in micro- and nanoseconds to very low frequencies (pHz) with timescales of the order of hours. 

Single-sine equipment—lock-in amplifier and frequency-response analyzer... 

Frequency-response analysis [1] is the most widely used technique for impedance testing. Similar to the lock-in technique, it can extract a small signal from a very high background of noise, automatically rejecting DC and harmonic responses. The difference is that a frequency-response analyzer (FRA) correlates the input signal with the reference sine waves. To achieve faster measurements, FRAs are usually equipped with separate analyzers for each input chaimel. 

The equipment required to analyze the frequency response in impedance spectroscopy is sophisticated, and is thus too expensive to be practical for an operating sensor. In some systems it may be possible to identify a critical frequency (or a limited number of frequencies) that provides the desired response, so that simpler circuitry can be used. However, because of the complicated electronics, impedancemetric sensors are less common than potentiometric sensors. 

The equipment required to measure in-phase and quadrature linear dichroic spectra consists of two components, the transducer necessary to provide the small amplitude oscillatory strain and a suitably modified infrared spectrometer. So far as the former is concerned, it is desirable that the transducer system is capable of operating over a range of frequencies, in order to provide the flexibility that may be required in probing a change of re-orientational responses. The transducer may either form part of a dynamic mechanical analyzer, as described by Noda et al. [17] or may be a simple unit used solely as part of an infrared spectrometer system. 

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