Honeywell T7200D Product Data page 21

T7200D,E, T7300D,E,F AND Q7300 SERIES 2000 PROGRAMMABLE COMMERCIAL THERMOSTATS AND SUBBASES
offset. This makes temperature control more accurate than
the conventional electromechanical or electronic thermostats.
The temperature control algorithm is called proportional plus
integral (P+I) control.
The thermostat sensor, located on the thermostat or remote,
senses the current space temperature. The proportional error
is calculated by comparing the sensed temperature to the
programmed setpoint. The deviation from the setpoint is the
proportional error.
The thermostat also determines integral error, which is a
deviation based on the length of error time. The sum of the
two errors is the (P+I) error. The cycle rate used to reach and
maintain the setpoint temperature is computed using the P+I.
The addition of the integral error is what differentiates the
thermostat from many other electronic and electromechanical
thermostats. See Fig. 17.
PROPORTIONAL COOL
CONTROL POINT
P+I CONTROL
POINT
PROPORTIONAL HEAT
CONTROL POINT
THERMOSTAT
HEAT SETPOINT
HEATING
100 50
PERCENT LOAD
Fig 17. Proportional temperature control
versus P+I temperature control.
Equipment Protection
As part of the operational sequence, the T7200/T7300
microprocessor also incorporates minimum on and off times
for all heating and cooling stages. Minimum on time is set in
THERMOSTAT
COOL SETPOINT
P+I CONTROL POINT
COOLING
0 50 100
M4414
the installer setup number 32. Using the minimum on and off
times assures that rapid cycling of equipment does not occur,
which extends equipment life. Minimum on and off times are
set in the Installer Setup.
T7200/T7300 Thermostat Operation
Startup
When power to the thermostat is turned on, a startup and
initialization program begins. The startup occurs only on initial
powerup. After total loss of power for an extended period, the
current time and day may need to be set, but the user
program is held. The initial default values are heating 68°F
(20°C) and cooling 78°F (26°C) for the Occupied periods.
Unoccupied default values are heating 55°F (13°C) and
cooling 90°F (32°C).
NOTE: The thermostat controls to the Unoccupied default
setpoints of 55°F (13°C) for heat and 90°F (32°C) for
cool when no program is set.
Occupied Operation
When the thermostat is operating in the Occupied period, the
temperature is controlled to the occupied heat or cool
setpoint. The normally open (A1 ) auxiliary relay contacts are
closed and the normally closed (A3) auxiliary relay contacts
are opened during the Occupied periods (if the subbase
being used has this option). The fan operates as follows: fan
selection can be set to On (always energized) or Auto (cycles
with Y1 or W1).
Unoccupied Operation
When the thermostat is operating in the Unoccupied period,
the temperature is controlled to the Unoccupied heat or cool
setpoint. The normally open (A1) relay contact is open and
the normally closed (A3) relay contact is closed. The fan
operates as follows: fan is always intermittent (cycles with Y1
or W1).
21 63-4355—1