Lennox LGM092U - Sensors and Control Inputs; Temperature, Room, and CO2 Sensor Details; Pressure, Humidity, and Economizer Sensor Details

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Temperature Sensors
The return air (RT16) and discharge air (RT6) duct probes
and the outdoor air (RT17) are all two wire thermistors. The
resistance vs. temperature table is shown below:
Table 1
Resistance vs. Temperature
Temp. °F (°C) Resistance +/-2%
Temperature °F
(°C)
Resistance +/-2% Temp. °F (°C) Resistance +/-2%
-40 (-40) 335,671 40 (4.4) 26,106 90 (32.2) 7,332
-20 (-28.9) 164,959 50 (10) 19,904 100 (37.8) 5,826
0 (-17.8) 85,323 60 (15.6) 15,313 120 (48.9) 3,756
20 (-6.7) 46,218 70 (21.1) 11,884 130 (54.4) 3,047
30 (-1.1) 34,566 80 (26.7) 9,298
Room Sensors
Room sensor (A2) is a two-wire thermistor with 1k series resistor.
Table 2
Two-Wire Thermistor
Temp. °F (°C) Resistance +/-2%
Temperature °F
(°C)
Resistance +/-2% Temp. °F (°C) Resistance +/-2%
40 (4.4) 27,102 60 (15.6) 16,313 80 (26.7) 10,299
45 (7.2) 23,764 65 (18.3) 14,474 85 (29.4) 9,249
50 (10) 20,898 70 (21.1) 12,882 90 (32.2) 8,529
55 (12.8) 18,433 75 (23.9) 11,498
Carbon Dioxide Sensor
The indoor carbon dioxide sensor (A63) is an analog sensor with a 0-10VDC output over a carbon dioxide range of 0-2000
ppm as shown in the following table. The sensor is powered with 24VAC.
Table 3
Carbon Dioxide Range
Carbon Dioxide
PPM
DC
V
Carbon Dioxide
PPM
DC Voltage
Carbon Dioxide
PPM
DC Voltage
Carbon Dioxide
PPM
DC
V
0 0 600 3 1200 6 1800 9
200 1 800 4 1400 7 2000 10
400 2 1000 5 1600 8
VAV Supply Static Sensor
The supply duct differential static pressure sensor (A30) is an analog sensor with a 0-10VDC output over a range of 0-5"w.c
as shown in the following table. The sensor is powered with 24VAC.
Table 4
Static Pressure
Pressure "w.c. DC Voltage Pressure "w.c. DC Voltage Pressure "w.c. DC Voltage Pressure "w.c. DC Voltage
0 0 1.5 3 3 6 4.5 9
0.5 1 2 4 3.5 7 5 10
1 2 2.5 5 4 8
Relative Humidity Sensor - Optional
The indoor relative humidity sensor (A91) is an analog sen
sor with a 0-10VDC output over a relative humidity range of
0-100% relative humidity. The sensor is powered with
24VAC.
Enthalpy Sensor - Optional
The optional enthalpy sensors (A7 and A63) used with the
economizer have an output of 4-20mA. The sensor is pow
ered with 18VAC provided by M3 unit control.
Economizer Differential Pressure Sensor - Optional
Rooftop units installed with Smart Airflow™ will have a
Pressure Transducer (PT5) present in the economizer.
PT5 requires 5VDC power supply (P266-5 and {P266-6)
and gives 0.25 VDC to 4 VDC output (P266-4) correspond
ing to 0” water column and 2” water column respectively.
For all practical purposes the output should be less than
1.2” water column if not an error code is stored and service
alarm output is turned on.