CleaverBrooks CFC-500 Operation, Service And Parts Manual page 150

CB FALCON
Parameter
Modulation sensor
CH Demand source
4 mA water temperature
20 mA water temperature
CH time-of-day setpoint
CH off hysteresis
CH on hysteresis
CH hysteresis step time
CH P-gain
CH I-gain
CH D-gain
CH setpoint source
Modulation rate source
CH ODR low water temperature
CH ODR maximum outdoor
temperature
Outdoor Reset and Boost
The outdoor reset function is symmetrical for each of the
control loops that use it, although they each have their own
parameters.
If the outdoor reset feature is enabled and the sensor is
functioning, the current outdoor temperature is used to
determine the setpoint by interpolation. The lookup function
uses two X, Y points to determine a line on the graph, as
shown in Fig. 9. The Y coordinate of the top-right point
depends on the time-of-day input; if TOD is off, then CH
750-265
Table 8. Central Heating Hydronic Parameters. (Continued)
Inlet (S1), Outlet (S3, S4), S5
The selected input provides the temperature for modulation control.
As a startup check, if the CH Loop is enabled for a hydronic system, then if the select sensor
is not a temperature input (i.e. S1 is a 4-20 ma input for Steam), then this causes an alert and
causes the CH loop to suspend.
Local, Modbus, 4-20 mA
Degrees
Establishes temperature for 4 mA input
Degrees
Establishes temperature for 20 mA input
Degrees or None
This setpoint is used when the time-of-day input (J10-2) is on.
If the ODR function is inactive then the setpoint is used as-is.
If the ODR function is active then this setpoint provides one coordinate for the shifted
(because TOD is on) outdoor reset curve, as described in "Outdoor Reset and Boost" on
page 26.
Degrees or None
The off hysteresis is added to the setpoint temperature to determine the temperature at which
the demand turns off.
Similarly, the on hysteresis is subtracted from the setpoint to determine the temperature at
which demand turns on.
These may be set to None to indicate that no hysteresis has been defined.
The On and Off hysteresis are adjusted at the time the burner changes from off to on, and
from on to off, as shown in Fig. 12. This gives the PID algorithm some room to be more
aggressive in tracking the load, which can result in overshoot (or undershoot). (see the
Setpoint and Hysteresis section, page 31)
seconds
Time of each step. A step time of zero - disables this feature. (see the Setpoint and
Hysteresis section, page 31)
0-400
These parameters are the gains applied to the proportional, integral, and differential terms of
the PID equation for the CH loop.
Local, S2 4-20mA
If the setpoint source is Local, then the control's local setpoint system is used. This setting
enables the normal use of the CH setpoint, CH TOD setpoint, and the CH outdoor reset
parameters and functions.
If the setpoint source is S2 4-20mA, then the setpoint is determined by the 4-20mA setpoint
routine. If this sensor is invalid then the control behaves as if Local were selected.
Local, S2 4-20mA
• If the modulation rate source is Local, then the control's PID algorithm determines the
modulation rate.
If the modulation rate source is S2 4-20mA, then the modulation rate is determined by the S2
4-20mA modulation routine that exists in prior controls. If this sensor is invalid then the
control behaves as if Local were selected.
Degrees or None
These two parameters determine the lower-right point on the graph.
Comment
setpoint is used. If TOD is on, the CH TOD setpoint provides
the Y coordinate and the and the lower-left point is recalculated
to shift the graph in a parallel way.
• For outdoor temperatures lower than the minimum, the
water temperature provided by the appropriate setpoint is
used.
• For outdoor temperatures higher than the maximum, the
minimum water temperature is used.
• For outdoor temperatures between the minimum and the
maximum, a linear interpolation is used to find the setpoint.
26