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PRINCIPLE OF OPERATION
The sensor is a magnetostrictive device consisting of a
diaphragm, nickel tube, magnet, drive coil and pickup coil.
When 40kHz energy is applied to the drive coil, it causes
the diaphragm to vibrate at a frequency determined by the
mechanical resonant system of the sensor. Electrical energy
is transferred to the pickup coil when the diaphragm is free to
move in gas. When the diaphragm motion is loaded by a
process liquid, less energy is transferred to the pickup coil.
The pickup coil of the sensor is connected to the input of an
amplifier and the output of the amplifier to the drive coil to form
a feedback loop circuit. Any energy appearing in the output of
the sensor will be fed to the amplifier, amplified and returned
to the input of the sensor. This causes oscillations at 40kHz
to occur in the diaphragm. When the gain of the amplifier is
adjusted so as to exceed the losses within the sensor,
continuous oscillations are produced.
If the diaphragm of the sensor is exposed to a process liquid
which offers mechanical resistance to the motion of the
diaphragm, the transfer of energy to the pickup coil decreases.
This results in a decrease in the signal feedback into the
amplifier and a corresponding decrease in the signal available
from the output of the amplifier. The decreased signal triggers
a voltage sensitive network that controls the 4-20mA step
change output current.
A change of state condition (sensor covered by liquid) will cause
a step change in current in the output circuit. This can be used
to operate a remote relay or develop a voltage that will indicate
a change in level to a computer or data logging system. Multiple
sensors can be operated from a single power supply.
The Delavan Sonac® 1100 may be powered by the users 12 or
24 volt power supply or a Delavan 920-2F power supply with two
control relays. The 920-2F provides a relay output with 1 Form C
SPDT contacts, the power supply operates with a supply voltage
of 115 or 230 Volts AC, 50-60Hz.
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