Page 91 - Sensors and Control Systems in Manufacturing

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Cha p te r

Source T w o Detector Source Detector
Beam Complete Object Detected
FIGURE 2.9 Components of photoelectric control.

The control unit modulates and demodulates the light sent and
received by the source and detector. This assures that the photoelec-
tric control responds only to its light source. The control unit also
controls the output device in self-contained photoelectric controls. The
control unit and sensor are built into an integral unit.
Controls can be configured to operate as light-actuated devices.
The output is triggered when the detector sees light. They can also
be dark-actuated devices, where the output is triggered when the
detector does not see light.
Output devices may include relays such as double pole, double
throw (DPDT) and single pole, double throw (SPDT). Output devices
may also include a triac or other high-current device and may be
programmable-controller-compatible.
Logic modules are optional devices that allow addition of logic
functions to a photoelectric control. For example, instead of provid-
ing a simple ON/OFF signal, a photoelectric control can (with a logic
module) provide time-delay, one-shot, retriggerable one-shot, motion-
detection, and counting functions.

2.3.2 Manufacturing Applications of Photodetectors
The following applications of photoelectric sensors are based on nor-
mal practices at home, at the workplace, and in various industries.
The effective employment of photoelectric sensors can lead to suc-
cessful integration of data in manufacturing operations to maintain
an error-free environment and assist in obtaining instantaneous infor-
mation for dynamic interaction.
A photoelectric sensor is a semiconductor component that reacts
to light or emits light. The light may be either in the visible range or
the invisible infrared range. These characteristics of photoelectric
components have led to the development of a wide range of photo-
electric sensors.
A photoelectric reflex sensor equipped with a time-delay module
set for delay dark ignores momentary beam breaks. If the beam is
blocked longer than the predetermined delay period, the output ener-
gizes to sound an alarm or stop the conveyer (Fig. 2.10).
A set of photoelectric through-beam sensors can determine the
height of a scissor lift, as illustrated in Fig. 2.11. For example, when