Service manual

19
Mode 6: External Target Temperature using
Boiler Inlet Sensor
The external input signal can be provided from a
BMS, EMS or a tekmar tN4 System Control. The
external input signal creates an internal demand
and changes the boiler target according to a
linear scale. The BTC 1 modulates the boiler to
maintain the boiler target at the inlet sensor.
An internal heat demand is generated when an
analog positive 2-10VDC signal is applied to the
+V input and a negative DC signal is applied to
the Com/- input.
The following table shows the various signals
required to generate various Target
temperatures.
Table 8: External Signal Cross Reference
Chart
4
-
20
mA
Boiler
Target
0
-
10V
(dc)*
Boiler
Target
0 - - - (OFF) 0 - - - (OFF)
2 - - - (OFF) 1 50
o
F (10
o
C)
4 50
o
F (10
o
C) 2 68
o
F (20
o
C)
6 70
o
F (21
o
C) 3 86
o
F (30
o
C)
8 90
o
F (32
o
C) 4 103
o
F (39
o
C)
10 110
o
F (43
o
C) 5 121
o
F (49
o
C)
12 130
o
F (54
o
C) 6 139
o
F (59
o
C)
14 150
o
F (66
o
C) 7 157
o
F (69
o
C)
16 170
o
F (77
o
C) 8 174
o
F (79
o
C)
18 190
o
F (88
o
C) 9 192
o
F (89
o
C)
20 210
o
F (99
o
C) 10 210
o
F (99
o
C)
* requires 500Ω resistor
A 4-20mA signal can be converted to a 2-
10VDC signal by installing a 500Ω resistor on
the external input signal device’s terminal.
If the inlet sensor is ½ (half) of the differential
below the Boiler Target, the BTC 1 then
changes the proportional modulation output to
the START modulation setting, the Stage
contact (pins 15 & 16) closes to proceed to trial
for ignition. The burner remains at minimum
modulation until the flame is proved and then the
modulating output changes the boiler burner
output to maintain the programmed boiler target
temperature at the inlet sensor. If the inlet
sensor reaches ½ (half) of the differential above
Boiler Target, the burner shuts off. Once the
external heat demand is removed, the BTC 1
turns off the appliance and operates the boiler
pump based on the PUMP DELAY setting.
The auto re-set limit is set to 210°F and is fixed.
In addition to the auto reset limit the factory
installs a manual re-set limit set to 250°F.
Figure 21: Mode 6 Piping Schematic