Page 211 - Photodetection and Measurement - Maximizing Performance in Optical Systems

Contamination and Industrial Systems

204 Chapter Nine

Detector

Specular Collimated
reflection source
Meniscus

Overflow
to waste
Long tube
with low
reflectivity
Regulated flow
water supply
Figure 9.11 A free liquid surface can be gener-
ated within an instrument using a well-
controlled flow and overflow system.

Air pump for
periodic cleaning
Water Surface

Detector
Collimated
source

Meniscus

Figure 9.12 Free surfaces within the bulk of a liquid sample
are possible using an inverted-cup. Occasional pressuriza-
tion with a surface air-pump will clean away accumulated
debris.

surface measurements can also be conveniently performed by forcing an
inverted cup below the sample surface (Fig. 9.12). The hydrostatic pressure
compresses the trapped air volume depending on the depth (1 atmosphere =
5
10 Pa ª 10m water depth). This generates a controlled free surface, which can
be positioned in the bulk of a deep sample. If the meniscus surface becomes con-
taminated, it can even be renewed by forcing air through the cup from a surface

Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com)
Copyright © 2004 The McGraw-Hill Companies. All rights reserved.
Any use is subject to the Terms of Use as given at the website.