Correlation chopper

Figure B2.3.3. Crossed-molecular beam apparatus employed for the study of the F + D2 -> DF + D reaction. Indicated in the figure are (1) the effusive F atom source (2) slotted-disk velocity selector (3) liquid-nitrogen-cooled trap (4) D2 beam source (7) skimmer (8) chopper (9) cross-correlation chopper for product velocity analysis and (11) rotatable, ultrahigh-vacuum, triply differentially pumped, mass spectrometer detector chamber. Reprinted with permission from Lee [29]. Copyright 1987 American Association for the Advancement of Scienee. 

All of these processes have been observed in atomic-beam surface-scattering experiments, during which a beam of atoms of well-defined kinetic energy impinges on a single-crystal surface. The kinetic energy distribution of the back-scattered atoms can be detected by using a correlation chopper velocity selector [18]. 

G. Comsa, R. David, and B.J. Schumacher. Magnetically Suspended Cross-Correlation Chopper in Molecular Beam Experiments. Rev. Sci. Instrum. 52 789 (1981). 

Figure 9.12. A correlation radiometer where the chopper is replaced by a hybrid circuit. Separate amplifier chains amplify the sum and difference signals which are then multiplied.

FIGURE 8 Correlation between intragranular porosity and the percentage of binder solution added in a high shear granulator (impeller speed 4[Pg.288]

X = 363 nm modulated at a frequency of 200 Hz with an optical blade chopper. The PA spectrum is dominated by a sharp transition at 1.43 eV which has been identified as excited-state absorption of triplet excitons.10 The PA spectrum of a doped PFO film containing 8 wt% PtOEP is shown in Fig. 10.41b. The PFO triplet peak at 1.43 eV is the strongest feature in the PA spectrum of the blend, although there is an additional PA band between 1.5 and 1.7 eV. This additional PA band is correlated with PtOEP, having the same relative weight to the in-phase and quadrature components as the phosphorescence. 

Two different schemes are used for modulation chopper stabilization, which works similarly to an AM radio, and correlated double sampling (CDS), which performs two measurements of the noise only and the noise plus signal [19]. Fig. 6.1.11 shows conceptual diagrams of the two techniques. Although the additional circuitry looks complex, actual implementations are surprisingly simple [20, 21]. 

Fig. 6.1.11 Modulation techniques a) chopper stabilization, b) correlated double sampling...

Many other integrated solutions are documented in the literature. These include single-ended and differential solutions employing chopper stabilization [1, 20, 24, 31], circuits using correlated double sampling [2, 3, 32] and applications for capacitive readout circuits and corresponding implementations [15]. 

The emf of the bulk liquid thermocouple was measured with a 10,000 juv L N White double potentiometer, using a dc chopper amplifier and strip chart recorder to record the potentiometer unbalance continuously on a chart annotated so that it could be correlated with the chart recording the test-piece resistance. 

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