Detectors impedance

Equation (16) holds only if again wTr 1. the detector impedance is much smaller than that of the load, and wr, I, where t, C /I is the electrical time constant of the whole RC circuit, c is the dielectric constant and F is the irradiated detector area. To obtain a maximum signal noise/ratio with the satiK conditions as given above, a u.se(ul figure of merit is the reciprocal of the minimum detectable power (IPJ [163] ... 

Detector impedance strongly influences the optimum ROIC design, and it is eonvenient to treat deteetors as one of two classes high-impedance deteetors such... 

Figure 7.21 Application space of various ROIC unit ceU types is driven by detector impedance and flux range.

Spectral band Detector Impedance Dark Current Back-Bias Range Range of In-Band Irradiance... 

Signal processing in mechanical impedance analysis (MIA) pulse flaw detectors by means of cross correlation function (CCF) is described. Calculations are carried out for two types of signals, used in operation with single contact and twin contact probes. It is shown that thi.s processing can increase the sensitivity and signal to noise ratio. 

The new instrument introduced for inspection of multi-layer structures from polymeric and composite metals and materials in air-space industry and this is acoustic flaw detector AD-64M. The principle of its operation based on impedance and free vibration methods with further spectral processing of the obtained signal. 

There are important figures of merit (5) that describe the performance of a photodetector. These are responsivity, noise, noise equivalent power, detectivity, and response time (2,6). However, there are several related parameters of measurement, eg, temperature of operation, bias power, spectral response, background photon flux, noise spectra, impedance, and linearity. Operational concerns include detector-element size, uniformity of response, array density, reflabiUty, cooling time, radiation tolerance, vibration and shock resistance, shelf life, availabiUty of arrays, and cost. 

The noise is expressed as noise density in units of V/(Hz), or integrated over a frequency range and given as volts rms. Typically, photoconductors are characterized by a g-r noise plateau from 10 to 10 Hz. Photovoltaic detectors exhibit similar behavior, but the 1/f knee may be less than 100 Hz and the high frequency noise roU off is deterrnined by the p—n junction impedance—capacitance product or the amplifier (AMP) circuit when operated in a transimpedance mode. Bolometers exhibit an additional noise, associated with thermal conductance. 

The impedance can be measured in two ways. Figure 5.23 shows an impedance bridge adapted for measuring the electrode impedance in a potentiostatic circuit. This device yields results that can be evaluated up to a frequency of 30 kHz. It is also useful for measuring the differential capacity of the electrode (Section 4.4). A phase-sensitive detector provides better results and yields (mostly automatically) the current amplitude and the phase angle directly without compensation. 

Even if we forget, for a moment, the overlap problem and assume that we obtained a pure sensitized emission image, interpretation of this image is still ambiguous. That is because first, the intensity of S varies linearly with the excitation intensity and with the detector sensitivity. The exact same preparation will, when measured on a different microscope, yield different s.e. intensities. In fact, as much as renewing the arc lamp would impede comparison of results obtained on the same microscope. Second, the interpretation... 

A wide range of NTD materials is available to tailor the impedance of the device to the desired range (see ref. [14] and Section 15.2.1.1). With a typical bolometer impedance of a few Mft, low-noise J-FETs preamplifiers (see section 10.6) are used with these detectors. The use of an AC bias at 100 Hz allows the signal information to be extracted without degradation by preamplifier Ilf noise [72],... 

CUORICINO crystals are grouped in elementary modules of four elements (see Fig. 15.7) held between two copper frames joined by copper columns. PIPE pieces are inserted between the copper and TeOz, as a heat impedance and to clamp the crystals. There is a 6 mm gap between crystals with no material in between. The four detectors are mechanically coupled some of the PTFE blocks and springs act simultaneously on two crystals. 

Ionization and condensation nuclei detectors alarm at the presence of invisible combustion products. Most industrial ionization smoke detectors are of the dual chamber type. One chamber is a sample chamber the other is a reference chamber. Combustion products enter an outer chamber of an ionization detector and disturb the balance between the ionization chambers and trigger a highly sensitive cold cathode tube that causes the alarm. The ionization of the air in the chambers is caused by a radioactive source. Smoke particles impede the ionization process and trigger the alarm. Condensation nuclei detectors operate on the cloud chamber principle, which allows invisible particles to be detected by optical techniques. They are most effective on Class A fires (ordinary combustibles) and Class C fires (electrical). 

For kilohertz measnrement frequencies and above, the contribution of Qi can generally be neglected. McWhorter and Soper employed a simple two-electrode contact conductivity detector with reverse-phase ion pair chromatography, and achieved a detection limit of 3.46pg in a lOOnL volume (464nM) for KCl [54]. Four-electrode setups, in which two leads are nsed to measure current and the other pair to measure voltage, can also be nsed in order to eliminate the effect of the impedance of the electrical leads on the measnrement. 

Electrical conductivity detector is commonly use. The sensor of the electrical conductivity detector is the simplest of all the detector sensors and consists of only two electrodes situated in a suitable flow cell. The sensor consists of two electrodes sealed into a glass flow cell. In the electric circuit, the two electrodes are arranged to be the impedance component in one arm of a Wheatstone bridge. When ions move into the sensor cell, the electrical impedance between the electrodes changes and the out of balance signal from the bridge is fed to a suitable electronic circuit. The out of balance signal is not inherently linearly related to the ion... 

It is easily argued that, if the voltage measured by the detector D equals zero, the impedance of the cell must be equal to the impedance of the series combination, i.e. Z = Rs and Z" = (coCs) 1. Usually, the values of Rs and Cs needed to balance the bridge vary with the applied frequency as a consequence of the fact that the cell impedance has a frequency dependence different from that of a simple RC series combination. 

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