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Analog inputs
CNT-SVX07C-EN 19
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 economiz-
ing is feasible. Economizing is not possible without a valid outdoor air
temperature. (For more information, see “Economizing (free cooling)” on
page 45.)
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 (config-
urable using the Rover service tool). (For more information, see “Freeze
avoidance” on page 50.)
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 kΩ thermistor wired to analog input AI3. The generic tempera-
ture input can be used with any Trane 10 kΩ thermistor. The thermistor
can be placed in any location and has no effect on the operation of the con-
troller. The controller will generate a Generic Temperature Failure diag-
nostic if the input becomes invalid or goes out of range.
AI4: Universal 4–20 mA
The AI4 analog input can be configured in one of the three ways shown in
Table 5.
If this input is not needed for an application, configure it as Not Used.
This will disable the generation of diagnostics.
For the generic input configuration, a 4–20 mA sensor must be hard-
wired to the AI4 terminal. (Wiring is dependent on the specific applica-
tion.) The sensor communicates a value of 0–100% to the BAS. This con-
figuration has no direct effect on Tracer ZN521 operation. If a valid value
Note:
AI3 is not polarity sensitive; you can connect either terminal to
either sensor lead.
Table 5. AI4 configuration options and associated measurement ranges
Configuration Measurement range
Generic 4–20 mA input 0–100%
(4 mA=0%; 20 mA=100%)
CO
2
measurement 0–2000 ppm
(4 mA=0 ppm; 20 mA=2000 ppm)
Relative humidity (RH) measurement 0–100%
(4 mA=0% RH; 20 mA=100% RH)
Note:
AI4 is polarity sensitive.