18
CNT-SVX05A-EN
Analog inputs
Discharge air temperature
The Tracer
™
AH.540 controller cannot operate if the controller does not sense a
valid discharge air temperature input. If the sensor returns to a valid input, the
controller automatically allows the unit to resume operation.
The Tracer AH.540 controller uses analog input 4 (IN 4) as the discharge air
temperature input with a 10k
Ω
thermistor only. This sensor is hardwired and
located downstream from all unit heating/cooling capacity at the unit discharge
area. The discharge air temperature is used as a control input to the controller
which is used for all control modes of operation: constant volume space
temperature control, constant volume discharge air temperature control, and
variable air volume control.
Any time the discharge air temperature signal is not present, the controller
generates a
Discharge Temperature Failure
diagnostic and performs a unit
shutdown. If the sensor returns to a valid input, the controller automatically
clears the diagnostic and allows the unit to resume operation.
Outdoor air temperature
Analog input IN 5 is used for outdoor air temperature (10k
Ω
thermistor only).
When a valid outdoor air temperature (either hardwired or communicated) and
an economizer outdoor air damper exist, the controller uses this value to
determine if economizing (free cooling) is feasible and (only if economizing is
enabled) if the controller should enter freeze avoidance when the supply
fan is off.
If the outdoor air temperature is below the economizer enable point (default
60
°
F, adjustable), then economizing is allowed. When the outdoor air
temperature is not present, then economizing is not allowed. If both the
hardwired and communicated outdoor air temperatures are present, the
controller uses the communicated value for control decisions.
When an outdoor air temperature is established (either hardwired or
communicated), the controller generates an
Outdoor Air Temp Failure
diagnostic if the signal is no longer valid, and the unit disallows economizing. If
the sensor returns to a valid input, the controller automatically clears the
diagnostic and allows economizer operation.
Mixed air temperature
The Tracer AH.540 controller uses analog input IN 6 as the mixed air temperature
input with an averaging, 1000
Ω
(at 0
°
C, 32
°
F) RTD sensor only. The controller’s
mixed air temperature input is used for mixed air tempering and outdoor air
economizing operations.
The Tracer AH.540 controller disallows economizing if the controller does not
sense a valid mixed air temperature input. If the sensor returns to a valid input,
the controller automatically checks to see if economizer operation is possible.
If a valid mixed air temperature signal has been established by the RTD sensor,
but then the value is no longer present, the controller generates a
Mixed Air
Temperature Failure
diagnostic and disallows economizer operation. When the
sensor returns to a valid input, the controller automatically clears the diagnostic
and checks to see if economizer operation is possible.
Duct static pressure
The duct static pressure input (terminal J43) interfaces with a specialized
pressure transducer only. When a valid duct static pressure value (either
hardwired or communicated) exists and a variable air volume supply fan is
present, the controller uses this value for duct static pressure control.
