strong>D-A93L One type of proximity switch is an enclosed reed switch that is activated by a permanent magnet mounted to the piston. As the piston approaches, the magnetic field closes the switch, completing an electric circuit and producing an electric signal. Others prefer to use Hall-effect (Solid-State) sensors in combination with a piston-mounted magnet. The main difference between these two devices is that a reed switch is a mechanical device, while a Hall-effect (Solid-State) switch is electronic, with no moving parts to wear out. Reed switches have the advantage of operating on AC or DC current; Hall-effect (Solid-State) switches are limited to DC only. Also, reed switches are about half the price of their electronic counterpart, although the price differential is decreasing. On the other hand, Hall-effect (Solid-State) devices react much faster than reed switches, on the order of 100,000 versus 500 Hz. It is a waste of money to install microprocessor-based logic, and then be hampered by a slow switch.
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