Salinity Indicator Panel - Cont'd -141200410

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

T2.

temperature so that the thermal change transmitted to

the compensator causes its resistance to change

For thyratron V1 to conduct, the voltage between

accordingly.

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

voltage.

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.

10-30