Lennox LGM Series Manual page 15

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:
Temp. °F (°C) Resistance +/-2%
-40 (-40) 335,671
-20 (-28.9) 164,959
0 (-17.8)
20 (-6.7)
30 (-1.1)
Room Sensors
Room sensor (A2) is a two-wire thermistor with 1k series resistor.
Temp. °F (°C) Resistance +/-2%
40 (4.4)
45 (7.2)
50 (10)
55 (12.8)
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.
Carbon Dioxide DC
PPM V
0 0
200 1
400 2
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.
Pressure "w.c. DC Voltage
0 0
0.5 1
1 2
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.
Resistance vs. Temperature
Temperature °F
(°C)
40 (4.4)
50 (10)
85,323 60 (15.6)
46,218 70 (21.1)
34,566 80 (26.7)
Two-Wire Thermistor
Temperature °F
(°C)
27,102 60 (15.6)
23,764 65 (18.3)
20,898 70 (21.1)
18,433 75 (23.9)
Carbon Dioxide Range
Carbon Dioxide
DC Voltage
PPM
600 3
800 4
1000 5
Pressure "w.c. DC Voltage
1.5
2
2.5
Table 1
Resistance +/-2%
26,106
19,904
15,313
11,884
9,298
Table 2
Resistance +/-2%
16,313
14,474
12,882
11,498
Table 3
Carbon Dioxide
PPM
1200
1400
1600
Table 4
Static Pressure
Pressure "w.c.
3 3
4 3.5
5 4
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.
Page 15
Temp. °F (°C) Resistance +/-2%
90 (32.2)
100 (37.8)
120 (48.9)
130 (54.4)
Temp. °F (°C) Resistance +/-2%
80 (26.7)
85 (29.4)
90 (32.2)
Carbon Dioxide
DC Voltage
6
7
8
DC Voltage Pressure "w.c.
6 4.5
7 5
8
7,332
5,826
3,756
3,047
10,299
9,249
8,529
DC
PPM V
1800 9
2000 10
DC Voltage
9
10