Johnson Controls P352PN-2, P352PN-4, P352PN-3 Product Manual
System 350 Product Guide 930
Basic Controls Section
Product/Technical Bulletin P352P
Issue Date 0300
System 350TM P352PN Electronic Proportional Plus Integral
Pressure Controls for PSI Applications
The P352PN Series controls are electronic
proportional plus integral or proportional-only pressure
controls that generate a 0 to 10 VDC and a 0 to 20 mA
analog output signal based on sensed pressure.
Three models are available with setpoint ranges of
0-100 psi, 90-250 psi, and 240-600 psi.
The P352PN Series controls have a wide adjustable
throttling range (proportional band), as well as three
selectable integration constants.
The P352PN Series controls are housed in a NEMA 1
high-impact thermoplastic enclosure. The modular
design provides easy, plug-together connections for
quick installation and integration with specified power,
stage, and display modules.
Features and Benefits
Modular Design
❑
Plug-together Connectors
❑
and 35 mm DIN Rail
Mounting
❑ Three Models Cover Wide
Setpoint Ranges: 0-100 psi,
90-250 psi, and 240-600 psi
❑ Adjustable Minimum Signal
Output
Wide Adjustable Throttling
❑
Ranges: 5 to 50 psi and
10 to 100 psi
Reverse or Direct Acting
❑
Modes
Figure 1: P352PN Electronic Proportional Plus
Integral Pressure Control for PSI Applications
Provides the flexibility to add a D352 Pressure
Display Module, S352 Stage Modules, and a
Y350R Power Module
Eliminates wiring between modules and
reduces installation costs
Reduces inventory while providing control for
most positive-pressure refrigeration and
HVAC applications, in three overlapping
pressure ranges
Allows the user to adjust the minimum output
between 0 and 60% of the output signal range
Enables user to match the range of pressure
control to specific application requirements
Works in a variety of pressure applications
Three Selectable
❑
Integration Constants
© 2000 Johnson Controls, Inc.
Part No. 24-7664-1911, Rev. — www.johnsoncontrols.com
Code No. LIT-930044
Allows the user to adjust system recovery rate
to setpoint pressure at slow, medium, or fast
to meet application requirements
1
pplication
A
A P352PN Series pressure control may be set as a
proportional-only control or as a proportional plus
integral control, to generate two standard analog
output signals (0 to 10 VDC and 4 to 20 mA).
The P352PN controls can be used as stand-alone
devices or in conjunction with plug-together power,
stage, and display modules.
A typical System 350 pressure control application
includes the following:
•
P352PN Pressure Control
•
Y350R Power Module (or 24 VAC transformer)
•
S352AA-2 Stage Module
•
D352AA-2 Digital Pressure Display Module
•
P399 Pressure Transducer
Typical P352PN pressure control applications include:
•
Condenser fan speed control
•
Damper positioning
•
Flow valve positioning
peration Overview
O
IMPORTANT: The P352PN controls are intended to
control equipment under normal
operating conditions. Where failure or
malfunction of the P352PN control
could lead to an abnormal operating
condition that could cause personal
injury or damage to the equipment or
other property, other devices (limit or
safety controls) or systems (alarm or
supervisory systems) intended to warn
of, or protect against, failure or
malfunction of the P352PN control
must be incorporated into and
maintained as part of the control
system.
The P352PN control operates on 24 VAC and provides
two analog output signals: 0 to 10 VDC and 0 to
20 mA. A 10-segment front panel LED bar graph
indicates percentage of output. Adjustable features
include:
•
Setpoint
•
Minimum output
•
Throttling range (proportional band)
•
Integration constant
•
Reverse acting or direct acting mode of operation
Setpoint Potentiometer
Minimum Output
Potentiometer
Throttling Range
Potentiometer
Integration
DIP Switch
43
21
O
N
0 to 10 VDC Output
0 to 20 mA Output
Common for Analog
Outputs
Module Connector
J1 Jumper
Positions
LED Indicator
24 VAC Transformer
(If a Y350R Power Module
Red wire to VDC
Reverse Acting
Direct Acting
is not used)
120/240 VAC
Black wire to C
White wire to SN
THROT
RANGE
OUTPUT
I
V
MIN
PSI
SN
VDC
24V
C
(Percent of Output)
24 VAC
Connect Cable
Shield to C
Figure 2: Interior View and Typical Wiring of P352PN Control
P399
Transducer
WHA-P 399
Wiring Harness
2
Basic Controls—P352PN Electronic Proportional Plus Integral Pressure Controls for PSI Applications
Proportional-Only Controls
Proportional Plus Integral Controls
Proportional-only controls work by continuously
adjusting the magnitude of the control’s output signal in
proportion to the difference (input-error) between the
control’s setpoint value and the actual value sensed in
the controlled system. As load on a system increases,
the input-error to the control increases. The control
reacts by increasing the magnitude of the output
signal, driving the controlled device to respond to the
increased load. (See Figure 3.)
The advantages of proportional-only controls are that
they are easy to set up and adjust, and they provide
good stability and rapid response to changing load
conditions.
A disadvantage of proportional-only controls is they
can not maintain a system process at the exact control
setpoint. A proportional offset (or droop) is always
present when there is a steady load on the controlled
system. (See Figure 3.)
The result is that a proportional-only control maintains
a system process at a control-point instead of the
desired setpoint. Control-point is setpoint plus the
proportional offset. The greater the load on the system,
the greater the proportional offset and the further the
control-point is from the system setpoint. A
proportional-only control can not adjust the output
signal to drive a system process from the control-point
to the desired setpoint. (See Figure 3.)
Systems with proportional-only controls and large
loads or highly variable load conditions may operate at
control-points that vary significantly from the desired
setpoint.
The P352PN proportional plus integral (PI) pressure
control incorporates integral (or reset) control action
along with proportional-only control action. The
advantage to this is that the PI design effectively
eliminates proportional offset, and the PI control can
adjust the output signal to not only match a steady load
on the system, but also drive the system process
towards setpoint. On a properly sized system with
steady load conditions, a PI control can maintain the
system process very close to the system setpoint. (See
Figure 3.)
The speed at which the PI control drives the system
process to setpoint (recovery rate) is determined by
the system’s capacity, the size of the load, and the
integration constant set on the PI control.
The integration constant establishes the rate at which
the control re-adjusts to the load as it drives the
process towards setpoint. The faster the integration
constant, the faster the control re-adjusts the
magnitude of the output signal, and the faster the
recovery rate of a properly sized and setup system.
On traditional PI controls, the rate of re-adjustment can
become too large if the process load exceeds the
capacity of the equipment. When the controlled
equipment is at full capacity and the setpoint still
cannot be reached, traditional PI controls continue to
readjust the magnitude of the output signal. The result
is called
The P352PN Series proportional plus integral controls
avoid
dynamic ceiling on the integrator, which allows the
process to recover from an out-of-range condition
without experiencing a long period of overshoot.
integral windup
integral windup
.
with a patented circuit that puts a
Basic Controls—P352PN Electronic Proportional Plus Integral Pressure Controls for PSI Applications
It should be noted that PI controls might not be suitable
for all applications. Improperly applied PI controls may
be unstable and overshoot setpoint.
Also, PI controls require two separate adjustments that
are dependent on each other. The system must be
properly sized to handle the maximum process load,
and close observation is necessary when the PI
controls are initially set up and checked out. But on the
proper applications PI controls provide superior
accuracy and continuous setpoint control.
3
Temperature
Proportional Only Control
Proportional
Offset
Proportional
Offset = 0
Load Change
Setpoi nt
Temperature
Load Change
Setpoi nt
Error
Time
Proportional Plus Integral Control
Error
Time
Figure 3: Operation of Proportional Only vs. Proportional Plus Integral Control
Minimum Output Adjustment and LED Bar
Graph Output Indicator
The minimum output adjustment sets the minimum
signal output (in VDC or mA) that the P352PN control
provides to the controlled device. The minimum output
can be set between 0 and 60% of the output range
(up to 6 VDC or 12 mA).
Example: For a controlled device that responds to a
4 to 20 mA output signal, the minimum output must be
4 mA or 20% of the 0 to 20 mA range. (See Figure 4.)
Adjust the MIN OUTPUT potentiometer located in the
center of the circuit board. The LED bar graph will
advance one LED segment for each 10% increase in
output range. The first segment lights at 10%, the
second segment at 20% and so on, until the tenth
segment lights at 100%.
Output
20
Range
(in mAs)
Minimum
Output
Setting (20%)
Minimum Output Set to 20% (4 mA) and
Throttling Range Set to 50 psi for P352PN-2
or 100 psi for P352PN-3 and P352PN-4.
10
4
0
Setpoi nt
Pressure
25
50
Throttling Range (psi)
50
100
(Range for
P352PN-2)
(Range for
P352PN-3 or
P352PN-4)
System Load
Throttling
Control Point
Follows the Load
System Load
Integration adjusts the
proportional output to
bring the process to
setpoint regardless of load.
Range
Throttling Range (Proportional Band)
On controls set for proportional only, the throttling
range or proportional band setting establishes how far
the system pressure must deviate from the P352PN
control setpoint to generate a 100% output signal from
the control.
Thus, on a proportional only control with a throttling
range setting of 25 psi, the output signal (VDC or mA)
is 0% when the system pressure equals the setpoint
pressure. The output signal increases to 100%
(10 VDC or 20 mA) when the system pressure rises
25 psi above the setpoint in DA mode, or drops 25 psi
below the setpoint in RA mode.
When setting up controls for proportional plus integral
operation, start with the integration constant OFF (in
the proportional only mode), and set the throttling
range (or proportional band) to a wide setting (60% or
more of the total range) to assure a stable control loop.
Then set the integration constant as slow as possible.
(Refer to
Adjust the throttling range by turning the THROT
RANGE potentiometer located under the control cover
on the center of the circuit board.
The throttling range can be adjusted from 5-50 psi on
the P352PN-2 model and 10-100 psi on the P352PN-3
and P352PN-4 models. (See Figures 4 and 5.)
Integration Constant DIP Switch Settings.
)
Figure 4: Minimum Output and Throttling Ranges for
the P352PN Controls
4
Basic Controls—P352PN Electronic Proportional Plus Integral Pressure Controls for PSI Applications
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