Biomedical Engineering Reference
In-Depth Information
exhibits certain specific disadvantages and advantages. However, there is a gen-
eral consensus that the system specification, with the known properties, makes the
measurement procedure more or less standardised in the way that we can contin-
uously make reliable measurements. Even if the biological sensor (e.g. the bird in
a cage) has to be replaced when the measurement of contaminated gases reaches a
certain level - Fig. 4.6(b).
4.4.2.2
DIRECT SENSOR PRINCIPLE
The measurement process using a direct operational sensing element is usually
the most effective process when parameters such as simplicity and direct conver-
sion are highly required. Direct sensing techniques, used as operational principles
are seldom seen in traditional measurement tools, mainly due to the advanced
electronic technology, which provides the manufacturers with electronic solutions
when choosing highly effective conversion processes in the sensing elements.
Traditionally independent techniques used as direct processing sensors can, for ex-
ample, be experienced in the affecting properties that correspond to the influence
on an environment, which an object perceives when placed in a flow. The same
properties occur when applying a weather vane outside the house on a windy day.
The vane will then provide the wind properties and we can measure the behaviour
or just observe the sensor device, i.e., vane. The direct principle can be commonly
used as a floating device that expresses the level of fluid in a tank or the surface
properties of a lake. The connection to the device moves in a direct connection to
the level as illustrated in Fig. 4.7.
Figure 4.7.
Illustrating of the direct measurement principle by a floating device in a fluid
tank and level of sea surface.
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