Page 97 - Sensors and Control Systems in Manufacturing

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Cha p te r

Key Point T w o Consideration
Range How far is the object to be detected?
Environment How dirty or dark is the environment?
Accessibility What accessibility is there to both sides of the object
to be detected?
Wiring Is wiring possible to one or both sides of the object?
Size What size is the object?
Consistency Is object consistent in size, shape, and reflectivity?
Requirements What are the mechanical and electrical requirements?
Output signal What kind of output is needed?
Logic functions Are logic functions needed at the sensing point?
Integration Is the system required to be integrated?

TABLE 2.3 Key Characteristics of Sensors

can be used will establish a strong foundation. This understanding
also will allow the user to obtain a descriptive picture of the condition
of each manufacturing process in the production environment.
Table 2.3 highlights key questions the user must consider.

2.4 Detection Methods
The three modes of detection used by photoelectric sensors are:

• Through-beam detection
• Reflex detection
• Proximity detection
2.4.1 The Through-Beam Detection Method
The through-beam method requires that the source and detector are posi-
tioned opposite each other and that the light beam is sent directly from
source to detector (Fig. 2.29). When an object passes between the source
and detector, the beam is broken, signaling detection of the object.
Through-beam detection generally provides the longest range of
the three operating modes and provides high power at shorter range
to penetrate steam, dirt, or other contaminants between the source
and detector. Alignment of the source and detector must be accurate.

2.4.2 The Reflex Detection Method
The reflex method requires that the source and detector be installed
on the same side of the object to be detected (Fig. 2.30). The light
beam is transmitted from the source to a retroreflector that returns