Controls And Functions; Definitions - Carrier 48FP Controls Operation And Troubleshooting

Fig. 5 — Space Humidity Sensor (P/N HL39ZZ001)
Fig. 6 — Air Quality (CO
(Wall-Mount Version Shown)
AIRFLOW
SENSOR
LEG (4 TOTAL)
END VIEW
Fig. 7 — Outdoor Air Control Velocity Probe
HUMIDIFIER DEVICES — The unit control is capable of
controlling two different types of humidifier devices, a 1-step
discrete step humidifier control (via a contact closure) or a pro-
portional control humidifier control valve (with a 4 to 20 mA
signal and an impedance not to exceed 600 ohms). Humidifier
devices must be field-supplied and -installed, for location in
ductwork outside the unit cabinet.
NOTE: Sizes 034-074 also require the installation of the
control options module (PSIO2), available as a factory-
installed option or field-installed accessory.
HYDRONIC COIL AND CONTROL VALVE — The unit
control can provide a 4 to 20 mA proportional signal to a hy-
dronic coil control valve. All hydronic coils and control valves
must be field-supplied and -installed.
) Sensor
2
SIDE VIEW
8
NOTE: Sizes 034-074 also require the installation of the
control options module (PSIO2), available as a factory-
installed option or field-installed accessory.

CONTROLS AND FUNCTIONS

The internal logic circuits of the PIC controls consist essen-
tially of seven sets of control loops that provide direction and
control for the major unit systems. These seven major unit sys-
tems are:
• Cooling Stages
• Staged Heating
• Economizer Position
• Building Pressure
• Supply Fan Volume
• Heating Coil (position)
• Humidifier (staged or position)
Each of these unit systems is controlled by a set of logic
loops. Each set consists of a "Master Loop" and a correspond-
ing "Submaster Loop." Each Master Loop surveys configura-
tion inputs, time schedules, set points, and current operating
conditions (via all available sensor inputs). From this informa-
tion, each Master Loop will decide which functions are avail-
able within its own system group and which functions should
be in operation. Each loop then calculates the required leaving
condition from the unit that will be necessary to satisfy the set
points consistent with current occupancy requirements. These
required leaving condition values are called "Submaster Refer-
ence Values" (or SR). Typically the SR values are updated
every two minutes by each Master Loop.
The Submaster Loops in the control system provide specific
operating instructions to their specific unit functions. Each of
these Submaster Loops receives a unique SR from its Master
Loop. Each Submaster Loop then surveys its own control out-
puts for current status or position, and then generates appropri-
ate changes in its own outputs that will produce the desired op-
eration as determined by its Master Loop. Submaster Loops re-
compute their required outputs much more rapidly than do
their Master Loops (typically every two seconds).
The following sections provide descriptions of the available
functions of the unit control system that the users can select and
configure for their own requirements. For each function, there
is a brief description of what the feature is intended to do for
the user, what additional hardware is required to use the fea-
ture, an expanded sequence of operation, instructions on con-
figuring the function, and any formulae used by the Master
Loop for determining the appropriate Submaster Reference
Values for this algorithm.

Definitions

ALGORITHM — A series of instructions that translate an in-
put value into a specific set of output commands that will mod-
ify the operation of the system, until the modified system oper-
ation satisfies the required input command value.
DEMAND TERM — Difference between desired position or
value and current position or value. (Control designers also re-
fer to this as an "error term.")
PID (Proportional Integrated Derivative) — A
process that considers the difference between desired condition
(set point) and current condition (actual value), plus the direc-
tion of change (increasing or decreasing) and the rate of change
(is the difference between set point and actual condition chang-
ing at increasing rate or slowing rate). A PID process will at-
tempt to reverse a change quickly when needed or "soft-land" a
change that is already approaching its set point without over-
shooting the set point.
FORCED VALUE — A submaster reference value that over-
writes a calculated value from a function master loop or a real
value direct from a sensor. Forced values may be generated by
calculation