Service manual

20
Mode 7: External Target Temperature using
System Temperature 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 control modulates the boiler to
maintain the boiler target at the outlet 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.
Table 8 shows the relationship between various
external signals to the boiler target temperature.
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 system 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, then closes the
Stage contact (pins 15 & 16) 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 out
to maintain the programmed boiler target
temperature at the system 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 reset limit is set to 210
o
F and is fixed.
In addition to the auto reset limit, Camus installs
a manual reset limit set to 250
o
F.
Figure 22: Mode 7 Piping & Electrical Layout
Mode 8: External Direct Drive Operation
This mode is designed only for hydronic heating
operation. This mode allows for an external control
to operate the boiler through an analog direct drive
input signal provided by a boiler sequencing
control, such as, the S12 Sequencer. When
operating in this mode the external heat demand
and DHW demand are disabled.
An external boiler sequencer provides a positive
0-10 VDC input signal to the control at +V(in),
and the negative signal is applied to the Com/-
input.
The boiler remains off while the direct drive input
signal range is between 0 to 0.5VDC. Once the
direct drive input signal reaches 0.5VDC the
control turns on the appliance pump and
changes the modulating output to Start
Modulation level until the flame is proved and
then the modulating output is adjusted to track
the direct drive input signal up to the maximum
of 10VDC which is equivalent to maximum input
rate. When the direct drive signal modulates
down to 0.5VDC, the boiler operates at minimum
fire. When the signal drops below 0.5VDC the
burner is shut off and the pump continues to
circulate until the PUMP DELAY timer expires,
whereupon the pump shuts off.
The external boiler sequencer can specify the
boiler inlet temperature. However, the BOIL
MAX setting limits the highest temperature at the
outlet sensor. If the outlet temperature exceeds
210
o
F, the modulating output immediately
changes to 0% and the burner is shut off. The
burner is to remain off until the minimum off
timer is satisfied and the boiler outlet
temperature falls by 2
o
F (1
o
C) below the BOIL
MAX setting.
Figure 23: Mode 8 Piping & Electrical Layout