GENERAL
DESCRIPTION
The RP920 Modular Pneumatic Controller, in
conjunction with remote sensors, provides Proportional (P)
or Proportional Plus Integral (p + I) control of temperature,
humidity, pressure, or dewpoint in WAC systems.
APPLICATION
In the mixed air control application (Fig. l), the primary
sensor modulates the outdoor and return air dampers
LIMIT
CONTROLLER
MIXED AIR CONTROL SYSTEM
through the primary controller (RP920C) maintaining a
constant mixed air temperature. The limit controller
(RP920A) and limit sensor sets outdoor air intake to
a
minimum.
In the hot water converter control application (Fig. l), the
primary sensor modulates the steam valve on the converter
to maintain the hot water temperature. On CPA models the
hot water temperature can be adjusted remotely using a
gradual switch.
PRIMARY
M
CPA
1
2 4
r
CPA
, MODELS ONLY
PRIMARY
SENSOR
IN HWS
4 8 9
OR C
2 3 1
DA
r - l
LINE
STEAM
TO CONVERTER
SUPPLY
HOT WATER CONVERTER
CONTROL SYSTEM
Fig. 1 Typical Single-Input Controller Applications.
In a dual-input control application (Fig. 2), the RP920B
or D provides reset capability. Often, control of a building
is more efficient if the setpoint of the controller is reset to a
different value as a function of some parameter other than
COMPENSATION
SENSOR (OUTDOOR AIR)
VALV
N.O.
Fig, 2. Typical Dual-Input Control System.
the controlled variable, in this system, outdoor air
temperature. To use compensation, a reset schedule must be
set up (Fig. 3).
F U L L
F U L L
COMPENSATION
COMPENSATION
START
COMPENSATION SENSOR
WHERE:
LOWEST VALUE OF CONTROLLED VARIABLE.
HIGHEST VALUE OF CONTROLLED VARIABLE.
VALUE OF COMPENSATION VARIABLE WHEN
CONTROLLED VARIABLE IS AT ITS LOWEST VALUE.
VALUE OF COMPENSATION VARIABLE WHEN
CONTROLLED VARIABLE IS AT ITS
VALUE.
2 1 3 6 5 - l
Fig. 3. Compensation Reset Schedule.
3
85-O 142
