Page 100 - Sensors and Control Systems in Manufacturing

Through-beam
Environment Classification and Types of Sensors 61
Proximity
Reflex
Relatively clean 1.25 per side 1.6 per side
Office clean 1.6 total 2.6 total 2.6 total
Lightly dirty 1.8 per side 3.2 per side
Warehouse, post 3.2 total 10.5 total 3.2 total
office
Dirty 8 per side 64 per side
Steel mill, saw mill 64 total 64 total
Very dirty 25 per side
Steam tunnel, painting 626 total
rubber or grinding,
cutting with coolant,
paper plant
Extremely dirty 100 per side
Coal bins or areas 10,000 total
where thick layers
build quickly

TABLE 2.4 Excess Gain Chart

General guidelines can be provided for the quantity of excess
gain required for the amount of contamination in an environment.
Environments are classified as one of the following: relatively clean,
lightly dirty, dirty, very dirty, and extremely dirty. Table 1.4 illustrates
the excess gain recommended for these types of environments for
each sensing mode.

Example. If in a through-beam setup, the source is in a lightly dirty environment
where excess gain is 1.8, and the detector is in a very dirty environment where
excess gain is 25, the recommended excess gain is 1.8 × 25 = 45, from Table 1.4.

2.5 Proximity Sensors
Proximity sensing is the technique of detecting the presence or
absence of an object with an electronic noncontact sensor.
Mechanical limit switches were the first devices to detect objects
in industrial applications. A mechanical arm touching the target
object moves a plunger or rotates a shaft, which causes an electrical
contact to close or open. Subsequent signals will produce other con-
trol functions through the connecting system. The switch may be acti-
vating a simple control relay, or a sophisticated programmable logic