Page 99 - Sensors and Control Systems in Manufacturing

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Cha p te r
T w o

Light Reflected
by Object
Field of View

Source/
Detector

FIGURE 2.31 Proximity detection.

The optimum range for the proximity and reflex sensors is more
significant than the maximum range. The optimum range is the range
at which the sensor has the most power available to detect objects.
The optimum range is best shown by an excess gain chart (Fig. 2.32).
Excess gain is a measure of sensing power available in excess of
that required to detect an object. An excess gain of 1 means there is
just enough power to detect an object under the best conditions with-
out obstacles placed in the light beam. The distance at which the
excess gain equals 1 is the maximum range. An excess gain of 100
means there is 100 times the power required to detect an object. Gen-
erally, the more excess gain available at the required range, the more
consistently the control will operate.
For each distance within the range of the sensor, there is a specific
excess gain. Through-beam controls generally provide the most excess
gain, followed by reflex and then proximity sensors.

RANGE (mm)
0.03 0.3 3.0 30.5
1000

EXCESS GAIN 100

10

1
0.1 1 10 100
RANGE (feet)

FIGURE 2.32 Photoelectric excess gain and range.