Page 127 - Sensors and Control Systems in Manufacturing

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T w o
Cha p te r

LED is usually furnished with this type of device to indicate the
shorted condition.
2.9.5.3 Reverse-Polarity Protection
Reverse-polarity protection is special circuitry that prevents damage
in a three-wire DC sourcing (PNP) or sinking (NPN) device when it is
connected to control circuitry incorrectly. Although reverse polarity
is relatively common, not all switches are equipped with this option.

2.9.5.4 Wire Termination
Wire terminals are common on limit-switch enclosure-type sensors.
The terminal designations are numbered and correspond to the
device wiring diagram (Fig. 2.78). Cable/wire stub terminations are
most common on tubular sensors. Color-coded conductors are essen-
tial for correct wiring. Most sensor wires are color-coded to comply
with industry wire color-code standards.

2.9.5.5 Pin Connectors
Pin-connector-terminal sensors feature a male pin connector recep-
tacle on the switch or at the end of the wire/cable stub. The female
receptacle is at the end of the matching cable cord. Most industry-
standard pin connectors are either the mini type—approximately
18 mm in diameter—or the micro type—approximately 12 mm in
diameter (Fig. 2.79).

2.9.6 Inductive and Capacitive Switching Logic
The outputs of two or more inductive or capacitive proximity sensors
can be wired together in series or parallel to perform logic functions.
The ON, or activated, switch function can be either a normally open
or a normally closed output function, depending on the desired con-
trol logic.
Although sensors are the most effective means for the data acqui-
sition role in manufacturing, care must be exercised when sensors are

FIGURE 2.78 Wire terminal.