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The salinity indicator panel is designed to function
60-Hz power. The cable is secured to the cell by means
in a system having five salinity cells, external alarm
of a gland nut.
bells, and two solenoid trip valves. The panel contains
The electrode assembly comprises the inner
a power unit, a meter unit, five salinity cells, a valve
electrode, adapter, automatic temperature com-
position and meter test unit, and a relay unit, The units
pensator, and the outer electrode. The inner electrode
are of the plug-in type to facilitate removal for
is a hollow platinum-coated brass cylinder closed at
inspection and repairs.
the forward end. It is held in the adapter by means of
POWER UNIT.-- The ship's 115-volt, 60-Hz
a spring-loaded nut on the end of the inner electrode
power is applied to the salinity indicator panel through
holder. A solder lug under this nut connects the white
the power unit (fig. 10-42). The power unit is not a
conductor of the incoming cable.
plug-in type, but is wired directly onto the panel. It is
The outer electrode is a hollow brass cylinder, the
provided with a white power-on indicator lamp, two
inside of which is coated with a thin layer of platinum.
fuse holders, and two blown-fuse indicators. The two
This electrode screws onto the adapter, which in turn
fuses protect only the salinity cell and the alarm circuit
screws onto the cell tube. It is pierced with holes to
wiring. The power circuits to the solenoid-operated
vent the gases trapped in the space between the
control valves are not fused.
electrodes and to allow for free circulation of the
METER UNIT.-- The meter unit (fig. 10-42)
water. The connection for the outer electrode is made
measures the specific electrical conductivity of the
by soldering the green conductor of the incoming
water. The conductivity values are then converted by
cable into the hole provided in the cell tube.
meter scale calibration into equivalent concentrations
The cell body (fig. 10-40, view A) has two
of seawater. The meter is connected to the cell circuits
platinum electrodes with a constant voltage applied to
by individual switches on each salinity cell. The
them. When they are exposed to air, no current flows.
specific electrical conductivity is measured by means
When they are immersed in water, the impurities in
of a bridge circuit that employs a special power-factor
the water determine the amount of current flow. If the
type of meter. The meter measures the ratio of currents
impurities in the water increase, the resistance of the
in the two separate arms of the bridge. One arm of the
water decreases, and this causes a corresponding
bridge is the dilute solution of seawater to be
increase in the current flow. If the current exceeds the
measured. The other arm of the bridge is an automatic
alarm set point, an alarm (visual and/or audible) warns
temperature compensating resistor that has the same
the ship's personnel of the condition.
resistance-temperature characteristics as dilute
solutions of seawater.
A thermistor (fig. 10-40, view B) is located within
the cell which automatically corrects for all
The power-factor type of meter (fig. 10-42)
temperature changes between 40F and 250F. The
employs a fixed coil and a movable coil. The movable
thermistor has a negative temperature coefficient of
coil consists of two windings, A and B, at right angles
resistance, which means that as the temperature
to each other. It is free to rotate within the fixed coil.
increases the resistance decreases. Therefore, the
The movable coil is energized from the secondary of
salinity circuit current is affected only by the
the power transformer, T1. Hence, the currents in
impurities in the water and is unaffected by
windings A and B are in phase with each other and the
temperature changes.
circuits are resistive because of the series limiting
resistor, R6. The fixed coil is energized from the ship's
Salinity Indicator Panel
115-volt, 60-Hz power supply in series with the
voltage dropping resistor, R12. The movable coil turns
The salinity indicator panel (fig. 10-41) indicates
until its resultant field lines up with the field of the
to the operator by meter indication the salinity level
fixed coil. Therefore, the meter indication is directly
of the water at various points in the distillation
dependent on the resultant field of the two movable
process. The salinity indicator panel has switches and
windings, which, in turn, is dependent on the ratio of
alarm indicating lamps for each salinity cell in its
the currents in the two windings. The meter indication
system, as well as an alarm lamp to indicate that the
is independent of minor voltage and frequency
changes of the power supply because there is no iron
dump valve solenoid has "tripped" and water is being
diverted from the potable water tanks. The meter
on the meter magnetic circuits and because the coil
circuits are essentially resistive.
indicating unit is calibrated in epm.
10-27

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