Biomedical Engineering Reference
In-Depth Information
However, to further restrict this definition to the principle of a sensor device,
one definition can be found in Britannia, Merriam-Webster Dictionary on the word
“sensor”;
“a device that responds to a physical stimulus (as heat, light, sound, pressure, magnetism,
or a particular motion) and transmits a resulting impulse (as for measurement or operating
a control)”.
This means that a sensor device can be described as an artificial device with
physical properties. The sensor measures a specific local range of measurement
interest, with indirect or direct operational principle and provides the foremost
task of collecting specific information from that specific part of environment.
However, to be correct in including all types of sensor principles, the refined
version of the above definition may be as follows;
“a device that responds to a physical, biological or chemical stimulus and transforms it to
communicable data ”.
In the following sections, the imperfection, behaviours and limitations of sen-
sors will be discussed, that make further advances of the operational principle
interesting. The processing of sensor data is well-established in order to increase
the performance of a sensor system. Also the benefit of combining sensors with
different and complementary specifications will, in many cases increase the total
information.
But as in all considerations the use of a sensor, or several sensors in a system,
will be of importance, when the output performance decides the inquired level of
conceivable information. As always, a detailed knowledge about performance and
sensor limitations are required and can be found in for example, Wilson (2005) and
Fraden (1993).
4.1
INTRODUCTION
A sensor is a device that transforms a physical, chemical, or biological stimuli into
a corresponding detectable value, normally an electrical signal. The sensor output
can, in principle, respond to anything that reacts in a certain manner on the stim-
uli. Figure 4.1 shows the transformation principal system. From an environment,
a specific measurement volume influences the sensor, i.e., the sensing volume, is
measured. The range of the sensor performance normally corresponds to the object
or measurement parameter(s) to be measured, e.g., a volume or area. The sensor
reacts on the specific environmental parameter(s), the response is detected and fur-
ther processed or communicated, which is illustrated in the principles and figures
below. The sensing unit can be placed directly at the sensing spot or as illustrated
indirectly below from a distance.
An artificial sensor is a device that in most cases measures the stimuli indi-
rectly, which means that the stimuli is often transformed by a physical, chemi-
cal or biological input stimuli into an indirect value corresponding to the input
Search WWH ::




Custom Search