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Page Title: Salinity Indicator Panel - Cont'd
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The currents in the two windings of the movable
The alarm circuit can be traced from the salinity
cell electrodes and compensator through the dual
coil are proportional to the two loads in the bridge
potentiometer, R1, to the primary of the signal
circuit. As previously stated, the load in one leg of
transformer, T2, the secondary of which is connected
the bridge (movable winding A) is the automatic
to the control grid and cathode of the thyratron, V1.
temperature compensator, C, located in the salinity
The plate and cathode of V1 are connected across the
cell, and in the other leg (movable winding B) is the
115-volt, 60-Hz power supply in series with the
resistance of the water being measured by the
flasher, H2, and the red alarm light, I2.
electrodes, E. The meter reading, which is determined
by the ratio of the currents in the crossed windings, is
There are two circuits from the secondary of the
therefore determined by the ratio of the cell resistance
power transformer, T1, through the salinity cell, dual
and the compensator resistance. At any given salinity
potentiometer, R1, and primary of the signal
and temperature there is only one possible meter
transformer, T2. One circuit is through the electrodes,
reading. If the temperature is either raised or lowered
the lower arm of R1, the primary of T2, the upper arm
from this point, the meter reading will remain
of R1, the primary of T2, the lower arm of R1, and
unchanged because of the action of the compensator
resistor R6. The conductance values of the salinity cell
even though the water resistance may change
electrodes and compensator, which are applied to the
secondary of T1 and to the two arms of the
appreciably. The temperature compensation occurs
potentiometer, R1, determine the grid to cathode
because any thermal change of the water being
voltage of V1. The current flow through the two arms
measured by the cell is immediately transferred to the
is in opposite directions or 180 out of phase, and the
automatic temperature compensator. The resistance of
resultant voltage is impressed across the primary of
the compensator is inversely proportional to its
temperature so that the thermal change transmitted to
the compensator causes its resistance to change
For thyratron V1 to conduct, the voltage between
the control grid and the cathode (from the secondary
of T2) must be in phase with the plate-to-cathode
The resistance-temperature characteristics of the
compensator are the same as those of dilute solutions
of seawater. Therefore, the thermal change in the
When the salinity condition of the cell is higher
compensator, which is exactly the same as the thermal
than the alarm setting, the resistance across the two
change of the seawater, causes sufficient resistive
electrodes is decreased and more current flows
change in the compensator to compensate for the
through the lower arm of R1, the primary of T2, the
resistive change occurring in the cell. Although
upper arm of R 1, and resistor R6. The resultant voltage
the absolute values of current in the windings
is impressed across the grid and the cathode of V1
through transformer T2. This voltage is of the proper
have changed, their ratio has not changed and,
phase to cause V1 to conduct during the half cycles
consequently, the meter reading is unchanged.
when the grid and plate voltages of V1 are positive.
Because the temperature compensation is equally
The circuit is completed from one side of line SB
effective at all salinities, the only change that can vary
through the cathode and plate of V1, silence switch
the meter reading is a change in the current ratio
S2, rectifier CR4, flasher H2, rectifier CR3, red alarm
caused by a change in salinity.
I2, to the other side of line SBB.
SALINITY CELL UNIT.-- A salinity cell
The silencing switch, S2, when placed in the
plug-in unit (salinity module, fig. 10-42) is provided
SILENT (down) position, clears the external alarm
for each salinity cell to continuously monitor the
circuit for other incoming alarms and causes the red
purity of the water of the cell. The unit consists of an
alarm light to light steadily. When the high salinity
alarm circuit that includes a dual potentiometer, R1,
condition is corrected, the red alarm light again flashes
signal transformer, T2, thyratron tube, VI, flasher,
to remind the operator to place the switch, S2, in the
H2, red alarm light, I2, and silence switch, S2. A
NORMAL (up) position to extinguish the red alarm
three-position meter switch, S1, is also provided on
light and clear the unit for future alarm signals.
the unit. The alarm point value is predetermined and
set. A high salinity condition is indicated initially by
The meter switch, S1, is a three-position, spring-
flashing of the red alarm light and sounding of the
loaded switch having a NORMAL (center) position, a
TEST position, and a METER position. The meter
external audible alarms.

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