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Input / Output Devices
Capacitive Sensors & Current Sensors
Since magnetic sensors can detect ferrous discontinuities through nonferrous metals, they can be hermetically sealed within nonferrous housings to withstand 100% humidity or complete immersion in water and oil. Magnetic sensors enclosed in stainless steel can operate in salt spray or sand and dust environments, and under differential pressures up to 20,000 PSI.
Capacitive Sensors & Current Sensors:
Eddy current sensors detect ferrous and nonferrous metals. A high-frequency magnetic field induces eddy currents in metal targets. The eddy currents generally changes the oscillation amplitude for many current sensors and capacitive sensors. This is sensed by a coil to create an output signal. For measuring speed, current sensors and capacitive sensors register metallic discontinuities in a moving target at a rate of about 5 kHz, but some models respond up to about 20 kHz.
Maximum response speed is determined by the method used to sense oscillator amplitude. Devices that sense amplitude changes with conventional demodulator/integrator circuits are slower than those that convert oscillator amplitude into a string of pulses whose widths vary with frequency.
Eddy current sensors and capacitive sensors also produce pulses with high positional accuracy. Because both eddy current sensors and capacitive sensors do not depend on a time rate of change to register motion, their response does not diminish near zero speed like that of magnetic pickups.
Eddy current sensors and capacitive sensors are seldom contaminated by dirt or metal particles, but sensing distance is typically limited to the diameter of the sensor (usually 0.06 to 3 in.). Both current sensors and capacitive sensors must be enclosed in nonmetallic packages because they cannot sense through metals.
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