Scully ST-15C Series, Technical Manual

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1.0 GENERAL
The ST-15C is a single point overfill prevention (or liquid level detection) Control Unit. Single point means
that it can monitor only one Scully liquid level sensor and provides a relay output and a visual indication of
the sensor status, dry or wet.
This control unit is used at loading terminals for overfill prevention on single compartment vehicles (tank
trucks or rail cars). In most of these applications, volume to be loaded into a compartment is pre-set via a
pre-set meter. Under normal loading operations the pre-set meter shuts down the loading after the pre-set
volume is loaded. The liquid does not reach the overfill sensor as it is set at a level higher than the rated
capacity of the tank. However, if the liquid level goes above the rated capacity and reaches the overfill
sensor, ST-15C Overfill Prevention System detects the overfill condition and signals for shutdown of loading.
Thus, it acts as a secondary (emergency) shutdown system, primary shutdown control being provided by
the pre-set meter.
It is typically used for overfill prevention on bottom loading or top loading vehicles. It is mounted at the
loading rack/gantry and connects to a vehicle via a Scully plug and cable assembly.
The system incorporates Scully’s unique and exclusive Dynacheck® concept. To ensure that it will always
detect an overfill condition, the controller uses pulsed signals which continuously check the entire system
operation including the controller, wiring connections and sensors. If the sensor comes in contact with
liquid, or in the unlikely event of a system fault, the pulsed signals cease and the controller automatically
signals for immediate shutdown of the loading operation.
The ST-15C uses intrinsically safe voltage and current to connect to Scully liquid level sensors and provides
control for external electrical devices by opening and closing relay contacts.
Scully loading rack overfill protection monitors have been carefully engineered to provide reliable and safe
performance when installed in conjunction with related Scully equipment according to the instructions in this
manual. Adaptations of, and additions to this equipment such as the use of multiple cables and plugs,
loading arm position indicating switches, enclosure heaters and similar peripheral devices may void
warranties unless authorized in writing by Scully Signal Company. Please contact Scully prior to performing
any installation or maintenance not specifically described in this manual.
1.1 Description
The ST-15C Control Unit interfaces with one of the following Scully liquid level sensors:
SP-BLUK Thermistor Sensor (for light or dark liquids)
SP-BLHK Heated Product Thermistor Sensor (for liquids loaded at high temperature)
SP-TO, SP-IO and SP-IR Series 2-Wire Optic Sensors (for light and clear liquids)
If a sensor detects liquid, the ST-15C will respond to this “wet” condition; output relay contact opens and red
light turns on. Although its typical application is monitoring sensor mounted on a vehicle it can also be
used for liquid level detection in storage tanks (tank farms).
The ST-15C Control Unit is also used with Scully’s portable (cane) sensors that employ one of the sensors
listed above.
ST-15C is also used with vehicles equipped with Scully’s IntelliCheck® series or ONBOARD Overfill
Prevention Monitors. It interfaces with thermistor or 2-wire optic socket on these vehicles.
The Control Unit has an explosion proof enclosure for mounting in locations that are classified as hazardous.