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ENVIRONMENTAL INTERFACES
The APS-3C determines when to start heater operation
by monitoring the signals produced by up to six ETI
sensors, paralleled together using a 3-wire bus.All
sensors are Class 2low voltage for safety reasons.
Available sensors include:
•SIT–6E Pavement Mounted Snow and Ice Sensor
•SNOW OWL Aerial Snow and Ice Sensor
•GIT–1 Gutter Snow and Ice Sensor
When used either alone or in combination, these sensors
accurately determine whether snow and ice melting is
required.If snow and/or ice is present, these sensors will
provide the signal required to control your snowmelt
system.
Sensors measure ambient temperature and detect
moisture in any form.Snow, sleet, freezing rain, etc., is
assumed if moisture is present at temperatures below 38°F
(3.33°C).Beginning heater operation at temperatures
slightly above freezing is essential to meeting customer
expectations.It takes along time for snow to melt at 34°F.
Using severalsensors improvessnow melting effectiveness
by compensating for environmental variations.Consider a
typical pavement snow and ice melting system.Vehicular
and pedestrian traffic in commercial environments often
expose the pavement to tracked slush and blowing or
drifting snow.Because refreezing could create a
hazardous situation, these hazards must be cleared.The
solution is to combine several SIT–6E Pavement Mounted
Snow and Ice Sensors in expected pedestrian and
vehicular pathways ,along with aSNOW OWL Aerial
Snow and Ice Sensor placed high in an open ,
unobstructed location, exposed to falling snow.One or
more additional SIT –6E sensors might be needed in
areas subject to drifting and blowing snow and/or melt
water run-off and refreezing.
The first sensor detecting freezing precipitation calls for
snow melting.The last sensor detecting frozen
precipitation signals the APS Control Panel that
precipitation has stopped.
Sensors employ aheated interdigitated grid for moisture
detection.Heat melts frozen precipitation to form water
which is abetter conductor of electricity.Circuits detect
water as achange in resistance between the fingers of
the interdigitated grid.The temperature of the moisture
sensor is regulated electronically.
Each sensor has its own microcontroller for signal
processing, logic and control.This enables the use of a
simple 3-wire bus to connect sensors with the Control
Panel.Extension wire function and colors follow:
•Supply (Red)
•Signal (White)
•Ground (Black)
Sensors are wired together in parallel in a“wired OR”
configuration.That is, red to red, white to white, and black
to black.When several sensors are connected in parallel,
any sensor asserting aground on the signal conductor
enables snow melting heater operation.No ground on
the signal line indicates the absence of snow.
The APS-3C Controller includesatemperature sensor for
measuring pavement slab or ambient air temperature.Its
signal is used to provide an adjustable high limit
thermostat function.This sensor, or abypass resistor, is
required for proper system operation.This feature is
essential when using apotentially high temperature
heater such as MI cable.
HIGH LIMIT THERMOSTAT
The calibrated 40°F to 90°F (4°C to 32°C) high limit
thermostat prevents excessive temperatures when using
constant wattage and MI heaters.It also permits safe
testing at outdoor temperatures too high for continuous
heater operation.The temperature sensor is included and
must be connected to the system for proper operation.
There are two DIP switch configurable operation modes
for the high limit thermostat.See figure 6 . The factory
default operation mode uses the high limit thermostat as
aslab temperature regulator, preventing heater
operation at temperatures
SNOW/ICE CONTROLS INSTALLATION MANUAL | PART NO. 25680 REV 0.0