9
operation
Operation
The LLC+u water level control system consists of an ultrasonic sensor placed
to measure the water level in the cold water basin. The senor is typically located
inside the cooling tower or on some cooling towers in an external chamber. A
PLC with HMI touch screen is used to program water level heights and offers
a visual indication of the water level. Internal relays with form "C" contacts are
used as switches, one for each water setpoint.
Programming is accomplished in the field based on recommended cooling
tower water level heights. Contact your Marley sales representative for recom-
mended setpoint levels. The sensor is programmed with a height from sensor
to bottom of the basin floor. Individual setpoint levels are programmed for high
cutoff, high alarm, makeup, low alarm and low cut off.
Alarm set point may be used to complete a remote BMS alarm circuit. Cut off
set point may be used to shut of a circulating pump.
A 4-20mA output is provided for BMS remote monitoring of water level
Water Makeup Function
The circuitry for water makeup in the LLC+u control panel provides an inde-
pendent circuit breaker for direct connection to a 110-120VAC water solenoid
valve. This added feature allows customer installation without having to provide
an additional power circuit to energize the solenoid. The solenoid is connected
to terminals 2A and 4A as represented on the control’s specific wiring diagram.
Purpose and Function of the HAND-OFF-AUTO Switch
Located on the right side of the control’s enclosure is a
HAND-OFF-AUTO switch. This switch is used primarily
at cooling tower startup and in maintenance procedures
where the tower basin is empty or has been drained. When
the tower’s basin needs to be manually filled, the switch is
placed in the HAND position. This selection bypasses the
probe assembly’s feedback and directly energizes the solenoid
valve connected to the water supply. Once the cooling tower basin is filled,
the switch is placed in the AUTO position to allow the adjusted ultrasonic
sensor to monitor and sustain the proper operating level. Placing the switch
in the OFF position completely interrupts any monitoring or fill action normally
provided by the LLC+u control panel. Normal tower operation depends upon
the HAND-OFF-AUTO switch being positioned in the AUTO mode at all times.
