Honeywell R7426B Product Data page 8

R7426A,B,C TEMPERATURE CONTROLLER
Controller Functions
Outside Air Temperature Compensation
Outside air temperature compensation is performed when I03
is connected. The parameter W
winter compensation changeover point. Parameters Wi and
Su define the degree of summer and winter compensation.
• Winter compensation is performed if
• Summer compensation is performed if
CTRP1
W1+XOFFS+CPA
M17451
Fig. 11. OAT compensation.
SMOOTHING FILTER FOR OUTSIDE AIR TEMPERATURE INPUT
A smoothing filter for OAT input I03 is incorporated to
eliminate sudden temperature variations. This provides more
stable control system operation.
Summer/Winter Changeover Function (R7426A only)
The occupancy input can alternatively be used for summer/
winter changeover. Activate the summer/winter changeover
function by setting the control parameter O1CTRF to 2.
A potential free contact can be used between terminals 1 and
4 to switch the controller mode to heating (contact open) or
cooling (contact closed).
Freeze Protection
See Table 5 for actions executed when the contact connected
to the freeze protection input is opened. A closed contact
performs frost recovery (see Table 6).
NOTE: Freeze protection operation takes priority over all
other control operations.
Table 5. Freeze Protection Actions.
Parameter
Model O1CTRF
R7426A 0 (Cooling)
1 (Heating)
2 (Summer)
2 (Winter)
R7426B —
R7426C —
63-2564—1
defines the summer and
comp
<
.
I03 W
COMP
>
I03 W
COMP
Wi
Su
W comp
IO3
Freeze Protection Action
Outputs (in percent) On/Off
O1 O2 O3 Output
0 — — Off
100 — —
0 — —
100 — —
0 0 100
0 0 100
Conditions of Outdoor
Temperature (I03)
Greater than 43°F (6°C)
or I03 not connected.
Less than 43°F (6°C).
.
Optimum Start Program
The optimum start program objective is to minimize total
energy consumption. It calculates heating or cooling mode
start time in room control applications to bring space
temperature to the comfort zone boundary at occupancy start
time. The optimum start program uses historical data for self-
adaptive adjustment.
Night-cycle Program
The night-cycle program offers the ability to assign
unoccupied night low or high limits with 2°F (1K) hysteresis
during OFF mode. This is for protection of a space and its
contents against temperature extremes. It automatically cycles
between user-selected upper and lower limits and turns on full
heating or cooling whenever a limit is reached.
Output Functions
The controller provides a choice of output signals suitable for
operating a range of final control devices. Suitability is based
on the parameter setting of OMode and OxMode (where x is
1, 2 or 3) parameters.
R7426A and R7426B
The R7426A,B have unconfigured outputs. This is done to
avoid damaging installed devices by sending improper output
signals when power is applied to the controller.
FLOATING VALVE OR DAMPER ACTUATORS (FLOATING MODE)
Parameter setting for Heating/Cooling Control Outputs:
OMode is 0, 1, 2, 3 or 4 (R7426B only); OxMode (where x is 1,
2 or 3) is 0.
The controller converts the deviation signal to a proportional
output pulse which drives the actuators depending on the
Runtimex (where x is O1, O2 or O3) parameter value.
An automatic synchronization function ensures correct
actuator positioning. This is performed by periodically running
all actuators to the closed position. Synchronization run time
is derived by control parameter Runtimex (where x is O1, O2
or O3) multiplied by 1.25.
Synchronization by the controller is initiated:
• After power up reset (initial start).
• After 250 control steps as soon as control output is below
5 percent.
ELECTRIC HEAT CURRENT VALVE (PWM OUTPUT)
PWM output is suitable for driving European electric heat
current valves. It is controlled from the heating signal. The
interval or total cycle time is set by the parameter Runtimex
(where x is O1 or O3).
8
Table 6. Frost Recovery.
Frost Recovery
Main temperature control.
Setpoint W1 raised by Xp1 and
linearly decreased to normal value
over an adjustable delay time.