Biomedical Engineering Reference
In-Depth Information
Sensors in the Laboratory
The previous section focussed on the internal measurement effects that may in-
terfere with the sensor performance. However, the external interference with the
measurements normally creates an effect which has to be taken into considera-
tion. The measurement procedure is always restricted to minimise the ambient
effects that influence the sensor measurements. In a specific measurement labora-
tory, the atmosphere is considered to be clean. Ambient characteristics provide
relative elimination of external disturbances. The air is controlled and relatively
free from contaminants, the temperature is kept in a stable range, the area is free
from vibration, and the personnel are specially trained in the handling of measure-
ment principles and the equipment they use. The industrial measure is often made
under reverse conditions. When testing a sensor system, there is a possibility to
substitute the sensor unit with a corresponding test-generating unit, i.e., a calibrat-
ing unit. The signal produced must be capable of using the ordinary system from
transmission to the collecting and processing equipment included, which may be
a considerable distance away. The substitution of the sensor device intends to
compare the performance of the sensor devices by then using the same remaining
system. The tests will have the aim to verify the performance from the view of the
sensor and secure the elimination of the system errors.
4.4
BASIC SENSOR PRINCIPLES
The sensor principles are of most importance when investigating the achieved
performance that is required, in order to deliver the proper capability to an elec-
tronic system. There is, in many aspects, a question of chosen sensor operational
principles to appropriate applications and their demands for specificity. The sys-
tem characteristics required will in most cases regulate the selection of sensing
unit. The system specification including the strength to process measured infor-
mation conditions, will decide the requirement level of confidence and success.
The absolute minimum requirement is then to know the measurement conditions.
The system requirements are dependent on several conditions, where a few of the
more important sensor systems characteristics are presented below. Essential dis-
crimination that can be related to system performance is, as given, the concepts
of identification of human involvements, gathering of sensor information, indi-
rect/direct operational principles and single/multi-sensor systems. Therefore due
to its complexity, a structure of application related sensor principle toward the di-
rection of this topic, intelligent human sensors are needed.
4.4.1 Relation to Human Abilities
The classification presented here is maybe comprehensive in a multi-dimensional
perspective, and challenges the traditional measurement approach. However, the
proposed classification suggests a related aspect of measurement and is directed
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