Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

DRIFT combination with frequency response

Accessories necessary for DRIFT measurements are described in the literature and in part are commercially available [174-176]). However, reflectance equipment maybe also conveniently made in the laboratory using commercial lenses and mirrors [177]. An interesting new combination of DRIFT spectroscopy with the frequency response technique was recently developed and tested by Harkness et al. [178]. This enables one to measure simultaneously the dynamic responses of both the gas and adsorbate, which should be of great potential for the study of heterogeneous catalysis. A cell for fast response DRIFT spectroscopy is described in Ref. [178]. [Pg.43]

The most common way to deal with the problem of stochastic drift is to modulate the exposure of the analyte to the sensor and to synchronously detect the sensor response. When the analyte is off (i.e., the sensor is zeroed ), the sensor signal can be recorded as the baseline value. Drift-corrected signals can be obtained by subtracting the baseline signal from that recorded when the analyte is on. If the frequency of the on/off modulation is much higher than the frequency of the baseline drift, then this scheme results in dramatically improved stability in the measured data. An implicit requirement in this measurement strategy is that the response kinetics of the sensitive film/analyte combination be sufficiently fast to allow on/off modulation at the desired frequency. [Pg.385]

In the 3200 Particle Mass Monitor system the collection surface is a piezoelectric crystal coated with metal on two sides connected into an oscillator circuit. A piezoelectric crystal alters its shape when it is subjected to an electrical field. Thus, if an alternating electrical field is applied to such a crystal, the crystal expands and contracts in response to this electric field that is, it acts as an oscillator. The frequency at which a piezoelectric crystal oscillates is related to the mass of crystal. If the effective mass of the crystal changes, as a result of the deposition of fineparticles onto its surface, while it is oscillating, the frequency at which it oscillates shifts. This frequency shift can be related to the mass of fineparticles deposited on the crystal. The aerosol being studied is deposited onto the crystal by a combination of electrostatic forces and impaction forces. The change in oscillation fi equency is proportional to the mass of deposited aerosol fineparticles. In this instrument a reference crystal is used to allow for any drift... [Pg.149]

Even with combination electrodes, it is helpful to diagnose whether the main problem is with the measurement or reference electrode so the design can be improved. For example, it might be best to change the reference rather than the glass type or shape. If the pH indication has high frequency noise, a slow response, or a shortened span, there is most likely a measurement electrode problem. If the pH indication drifts or develops an offset, it is probably a reference electrode problem. If the offset is very large, the reference electrode is probably contaminated. If you have multiple electrodes, you can swap wires to try different pairs of measurement and reference electrodes to find out which electrodes are the culprits and which combination most closely matches the process sample or buffer pH. [Pg.136]


See other pages where DRIFT combination with frequency response is mentioned: [Pg.561]    [Pg.349]    [Pg.18]    [Pg.363]   


SEARCH



Drift

Drifting

Frequency responses

© 2024 chempedia.info