Page 113 - Sensors and Control Systems in Manufacturing
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Cha p te r
T w o
Sn
3Sn
(a)
6Sn
(b)
FIGURE 2.60 Adjacent sensors.
• Adjacent sensors. When two similar sensors are located adja-
cent to or opposite each other, the interaction of their fields
can affect operation. Figure 2.60 provides the guidelines for
placing two similar sensors adjacent to each other. Alternate-
frequency heads will allow adjacent mounting of sensors with-
out interaction of their sensing fields.
• Magnetic fields. Electrical wiring in the vicinity of the sensor
face may affect sensor operation. If the magnetic field around
the electrical wiring reaches an intensity that would saturate
the sensor ferrite or coil, the sensor will not function properly.
Use of inductive sensors in the presence of high-frequency
radiation can also unexpectedly affect their operation. Sensors
specially designed for welding applications can be used with
programmable logic control (PLC). The PLC can be pro-
grammed to ignore the signal from the sensor for the period
that the high-frequency welder is operated. A slight OFF-time
delay assures proper operation of the sensor.
• Radio-frequency interference (RFI). Radio transceivers, often
called walkie-talkie devices, can produce a signal that can
cause an inductive proximity sensor to operate falsely. The
radio transceiver produces a radio-frequency signal simi-
lar to the signal produced by the oscillator circuit of the
sensor. The effect that RFI has on an inductive proximity
switch can vary. The factors that determine this variation
are as follows:
