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106308-05 - 3/23
APEX Installation, Operating, & Service Instructions
TEMPERATURE SENSORS
Modbus
Register
Protocol
Name
Description
Read (R) /
Write (W)
410007 Supply sensor -40 F (-40°C) to 266 F (130°C) R
410011 Return sensor -40 F (-40°C) to 266 F (130°C) R
410013 Header sensor -40 F (-40°C) to 266 F (130°C) R
410014 Stack sensor -40 F (-40°C) to 266 F (130°C) R
410170 Outdoor sensor -40 F (-40°C) to 266 F (130°C) R
400015 4 - 20 mA sensor
mA value for S2 (J8-6) parameter selectable as
(remote set point) & (remote modulation)
R
410817
Modbus Outdoor
Temp
Building Automation may send the controller the outdoor air temperature. Use
this register to change the outdoor temperature. When this register is not written
every “Modbus Command Time Out” parameter seconds (default 30 seconds),
temperature is set to bad data quality and outdoor air reset is set back to local
setpoint.
valid range -40°F to 302°F
W
BURNER
400581 CH Modbus Rate
Use this register to drive individual boiler firing rates. This register is used when
firing rate control is performed by an external building automation system.
Firing rate reverts to local control when register is not written every “Modbus
Command Time Out” parameter seconds (default 30 seconds),
Range is 0 to 200 % provides 0-100% firing rate.
W
400008
Fan Speed
Measured
Speed of the combustion air blower in rpm R
400009
Fan Speed
Commanded
Speed of the combustion air blower in rpm R
400010 Flame signal 0.01V or 0.01μA precision (0.00-50.00V) R
400033 Burner control state
0 Initiate
1 Standby Delay
2 Standby
3 Safe Startup
4 Prepurge - Drive to Purge Rate
5 Prepurge – Measured Purge Time
6 Prepurge – Drive to Lightoff Rate
7 Preignition Test
8 Preignition Time
9 Pilot Flame Establishing Period
10 Main Flame Establishing Period
11 Direct Burner Ignition
12 Run
13 Postpurge
14 Lockout
R
Table 10-26: Modbus Register List (continued)
10 Operation (continued)
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