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156
JOHNSON CONTROLS
FORM 100.50-NOM6 (1207)
Service
Furnace Status Input
The Unit Controller monitors the operation of the
Staged and Modulating Gas Heat sections and displays
the status through the STATUS screen of the User
Interface. The operation of each of the gas heat sections
is monitored by a multiplexer installed in the gas heat
section. When a gas heat section is energized, it sends a
24-volt signal to the multiplexer. The multiplexer takes
the fi ve “ON”/”OFF” inputs and converts them into a
0 to 5 volt DC signal that is sent to the Unit Controller.
The Unit Controller then decodes this analog input and
displays the furnace section status. Tables 8-9 and 8-10
show the relationship between the DC voltage and the
furnace operation status.
PPM CO2 OUTPUT
VOLTAGE
VDC
PPM CO2 OUTPUT
VOLTAGE
VDC
80 0.20 1120 2.80
160 0.40 1200 3.00
240 0.60 1280 3.20
320 0.80 1360 3.40
400 1.00 1440 3.60
480 1.20 1520 3.80
560 1.40 1600 4.00
640 1.60 1680 4.20
720 1.80 1760 4.40
800 2.00 1840 4.60
880 2.20 1920 4.80
960 2.40 2000 5.00
1040 2.60
TABLE 8-7 – CO2 SENSOR OUTPUT
CO
2
Sensor
Two CO
2
sensors are used in conjunction with the
“DEMAND VENTILATION” option. In “DEMAND
VENTILATION” the Unit Control monitors the CO
2
level
of the outdoor air and the CO
2
level in the conditioned
space and varies the amount of ventilation air based on
the relationship between these two values. Table 8-7
gives the volts DC output for a given CO
2
level.