tekmar 667 Snow Detector & Melting Control Installation - Manual (Page 11)

11 of 32 © 2009 D 667 - 03/09
15 16
Melt / Idle
Demand
24 to 230 V (ac)
L
N
Idle Demand
Melt Demand
External Idle Demand (DIP switch set to Idle Demand)
The snow melting system is disabled when a voltage between 24 and 240 V (ac) is
applied across the Melt / Idle Demand terminals (15 and 16). An external idle demand must
be present for at least 4 seconds in order to stop the snow melting system.
Note: This operation only occurs if the Idle Demand / Melt Demand DIP switch is set to
the Idle Demand position.
If the snow melting system is placed into Idling mode by an external idle demand, then
a manual melting enable signal is applied, the idle demand is overridden until either the
running time has expired, a stop signal is given, or the external idle demand is removed
and reapplied.
Section E: Melting Operation
Section E1
General Melting
Operation
Section E1: General Melting Operation
In order for the snow melting system to be started, one of the methods described in section D1 must be used. Once a melting enable
signal is applied and the system is not in WWSD or CWCO, the Melting mode begins. When the control is in the Melting mode, the
Melting pointer is visible in the VIEW menu. The Melt setting in the ADJUST menu sets the slab surface temperature. When the system
is melting and the slab temperature is warming up to the slab target temperature, STRT is displayed in the Status item while in the
VIEW menu. The system finishes melting when the slab temperature has been at least the slab target temperature for a period of time.
This period of time is based on whether an automatic or manual melting enable signal starts the snow melting system.
If an automatic melting enable signal starts the snow melting system and the slab temperature reaches the slab target temperature,
DET is displayed in the Status item while in the VIEW menu. The system continues to melt until the 090 becomes dry and any
additional running time has expired. Once the Melting mode is complete, the system operates in the Idling mode.
If a manual melting enable signal starts the snow melting system, the running time is displayed in the Status item while in the VIEW
menu and begins counting down once the slab temperature reaches the slab target temperature. The system continues to melt until
the running time counts down to 0:00 and there is no external melt demand. Once the Melting mode is complete, the system operates
in the Idling mode. The table on page 12 describes how the control responds to enable and disable signals.
SLAB TEMPERATURE CONTROL
The 667 uses a snow / ice sensor or slab sensor to provide slab temperature control.
Surface temperature = 35°F
Decreasing Air Temperature
Increasing Slab Core T
e
mperature
Slab Surface Temperature is Constant
Slab Outdoor Reset Slab Outdoor Reset
Core (sensor)
is warmer
AUTOMATIC MELTING DISABLE (Snow / Ice Sensor 090)
Once the 090 is dry, the Water pointer turns off in the LCD. The system slab temperature has to be at least the slab target temperature
for a minimum of thirty minutes in order for the system to turn off. If a manual melting disable signal is applied the snow melting
system turns off immediately.
Slab Sensor
If a Slab Sensor is used, the control assumes that the sensor is
approximately 1 inch below the surface of the snow melting slab. Since
this point is closer to the source of the heat, this point is warmer than
the surface of the slab. Therefore, the sensor must be maintained at
a higher temperature in order to ensure that the surface of the slab
is maintained at the correct temperature. The amount of temperature
difference between the surface of the slab and the slab sensor changes
with the outdoor temperature. Therefore, the slab core temperature
is increased as the outdoor air temperature drops. The temperature
displayed as SLAB is the temperature of the slab sensor.