16
CNT-SVX07D-EN
Input/output functions and wiring for typical applications
the default configuration. If a valid hard-wired or communicated fan mode value is established and
then is no longer present, the controller generates a Fan Mode Failure diagnostic.
AI1: Entering water temperature
The AI1 analog input functions as the local (hard-wired) entering water temperature input. An
entering water temperature communicated via the LonTalk communications link can also be used
for controllers operating on a BAS. If both hard-wired and communicated entering water
temperature values are present, the controller uses the communicated value. If a valid hard-wired
or communicated entering water temperature value is established and then is no longer present,
the controller generates an Entering Water Temp Failure diagnostic.
For units configured as 2-pipe or 4-pipe changeover units, the entering water temperature is used
to make heating/cooling operation decisions. If neither a hard-wired nor a communicated entering
water temperature value is present on changeover units, the controller will always operate in
heating mode.
For units not configured as changeover units, the entering water temperature value is used for
information and troubleshooting only and does not affect the operation of the controller.
Note:
AI1 is not polarity sensitive; you can connect either terminal to either sensor lead.
AI2: Discharge air temperature
The AI2 analog input functions as the local discharge air temperature input.
Important:
The Tracer ZN521 cannot operate without a valid discharge air temperature value.
The controller receives the temperature as a resistance signal from a 10 k
Ω
thermistor wired to
analog input AI2. The thermistor is typically located downstream from all unit heating and cooling
coils at the unit discharge area.
If a discharge air temperature value is invalid or is not present, the controller generates a Discharge
Air Temp Failure diagnostic and shuts down the equipment. When the thermistor returns to a valid
temperature, the controller automatically allows the equipment to resume normal operation.
Note:
AI2 is not polarity sensitive; you can connect either terminal to either sensor lead.
AI3: Outdoor air temperature or generic temperature
The AI3 analog input can function as either:
•
An outdoor air temperature input
•
A generic temperature input
If AI3 is configured as the local (hard-wired) outdoor air temperature input, the controller receives
the temperature as a resistance signal from a 10 k
Ω
thermistor wired to analog input AI3. An
outdoor air temperature value communicated by means of a LonTalk link can also be used for
controllers operating on a BAS. If both hard-wired and communicated outdoor air temperature
values are present, the controller uses the communicated value. If a valid hard-wired or
communicated outdoor air temperature value is established and then is no longer present, the
controller generates an Outdoor Air Temp Failure diagnostic.
Economizing (
free cooling
) is a function whereby outdoor air is used as a source of cooling before
hydronic or DX cooling is used. The Tracer ZN521 uses the outdoor air temperature value to
determine whether economizing is feasible. Economizing is not possible without a valid outdoor
air temperature. (For more information, see
“Economizing (free cooling),” p. 38
.)
The outdoor air temperature value is also used for the freeze avoidance function. This function is
used for low-coil-temperature protection when the fan is off. The controller enters the freeze
avoidance mode when the outdoor air temperature is below the freeze avoidance setpoint
(configurable using the Rover service tool). (For more information, see
If AI3 is configured as a generic temperature input, it can be monitored by a BAS. The controller
receives the temperature as a resistance signal from a 10 k
Ω
thermistor wired to analog input AI3.
Содержание Tracer ZN521
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