Brooks Instrument 5866M User Manual
Installation and Operation Manual
X-PR-5866E-5866M-eng
PN 541-C-005-AAA
April, 2008
Brooks® Compact Pressure Controller
Model 5866
Model 5866
Section 1
Introduction
Section 2
Installation
Contents
Contents
Page
Purpose.......................................................................................1-1
Description..................................................................................1-1
Principle of Operation..................................................................1-1
Specifications..............................................................................1-6
Controller Specifications..............................................................1-7
Receipt of Equipment..................................................................2-1
Recommended Storage Practice................................................2-1
General........................................................................................2-1
Gas Connections.........................................................................2-1
Installation...................................................................................2-2
In-Line Filter................................................................................2-3
Electrical Interface.......................................................................2-3
Remote Setpoint (Command) Input............................................2-3
Valve Override.............................................................................2-5
Precision 5V Reference...............................................................2-5
Remote Transducer Input............................................................2-5
Valve Test Point...........................................................................2-5
Optional Valve Return..................................................................2-6
C
O
N
T
E
N
T
S
Section 3
Operation
Section 4
Maintenance
Section 5
Troubleshooting
Operation.....................................................................................3-1
Proportional Band and Integration Time Constant Adjustment...3-1
General........................................................................................4-1
General........................................................................................5-1
Troubleshooting...........................................................................5-1
Disassembly................................................................................5-2
Assembly.....................................................................................5-5
Adjusting the Control Valve..........................................................5-6
Orifice Sizing..............................................................................5-12
i
Brooks Instrument Model 5866 Mass Flow Controller
Section 6
Calibration
Calibration Procedure..................................................................6-1
Gas Conversion Factors..............................................................6-2
Section 7
Parts List
General........................................................................................7-1
Appendix A
CE Certification
CE Certification for Mass Flow Equipment................................A-1
Figures
1-1 Model 5866 Pressure Transducer.................................1-2
1-2 Model 5866 Silicon Chip Configuration.........................1-2
1-3 Model 5866 System Block Diagram..............................1-2
1-4 Model 5866 Dimensions...............................................1-3
1-5 Model 5866 Upstream Controller..................................1-4
1-6 Model 5866 Downstream Controller.............................1-4
1-7 Typical Application of Downstream Controller...............1-5
1-8 Typical Application of Upstream Controller...................1-6
2-1 Customer Connections and Settings............................2-4
3-1 Error Signal Step Response.........................................3-1
3-2 Proportional Control......................................................3-3
3-3 Integral Control.............................................................3-3
3-4 P.I. Control.....................................................................3-4
5-1 Torque Sequence for the Valve Retainer Plate.............5-6
5-2 Adjustment Test Setup..................................................5-7
5-3 Valve Adjusting Spacer Locations.................................5-9
5-4 Valve Adjusting Spacer Locations, Normally Open
(N.O.) Valve..................................................................5-11
5-5 Application Configuration.............................................5-12
5-6 Example Application of Orifice Sizing Procedure........5-14
7-1 Model 5866E Parts Drawing.........................................7-2
7-2 Model 5866M Parts Drawing.........................................7-4
Page
Tables
ii
2-1 D-Connector Pin Arrangement......................................2-5
5-1 Bench Troubleshooting..................................................5-3
5-2 Sensor Troubleshooting.................................................5-3
5-3 Minimum Flow Values..................................................5-10
5-4 Model 5866 Orifice Selection.......................................5-14
6-1 Conversion Factors.......................................................6-4
7-1 Model 5866E Parts List.................................................7-3
7-2 Troubleshooting Aids and Spare Parts Kit for
Model 5866...................................................................7-3
7-3 Model 5866M Parts List................................................7-5
Introduction
1-1 Purpose
1-2 Description
Introduction
Section
1
This instruction manual is intended to provide the user with all the
information necessary to install, operate and maintain the Brooks® Model
5866 Pressure Controller. This manual is organiz ed into seven sections:
Section 1 - Introduction
Section 2 - Installation
Section 3 - Operation
Section 4 - Maintenance
Section 5 - Troubleshooting and Repair
Section 6 - Calibration
Section 7 - Spare Parts
It is recommended that this manual be read in its entirety before attempting
to operate or repair the Model 5866.
The Brooks Model 5866 Pressure Controller accurately measures and
controls upstream or downstream pressures. The heart of the system is a
solid state pressure transducer which produces an electrical output
proportional to pressure. The electronics use this signal to operate the
control valve and to pro vide an output signal.
1-3 Principle of Operation
The pressure to be measured acts on a stainless steel diaphragm. Via
silicone oil, this pressure is transmitted to the actual sensing element, a
silicon chip (refer to Figure 1-1). The chip consists of an anisotropically
etched diaphragm with four piezo resistiv e resistors , configured in a
Wheatstone bridge, etched into its surface (refer to Figure 1-2). The
mechanical deformation of this diaphragm results in an imbalance of the
resistors which is proportional to pressure. An amplifier provides output to
the control circuit as well as the electrical output signal.
In addition to the pressure transducer the Model 5866 has an integral
control valve and control circuitry. A difference between the pressure and
setpoint signals will cause the electronics to modulate the control valve to
maintain the desired pressure. A system block diagram is shown in Figure
1-3.
The integration of pressure transducer , control electronics and control
valve into one unit results in a compact siz e . The mounting dimensions are
comparable to a mass flow controller. Refer to Figure 1-4.
The “upstream pressure regulation mode” shown in Figure 1-5 places the
pressure controller at the outlet of the pressure vessel. The pressure in the
process upstream of the controller will be constant independent of
downstream variation. Pressure measurement and control takes place at
the outlet side of the pressure vessel.
1-1
Brooks Instrument Model 5866 Pressure Controller
Figure 1-1. Model 5866 Pressure
Transducer .
Figure 1-2. Model 5866 Silicon Chip
Configuration.
Figure 1-3. Model 5866 System Block Diagram (Downstream version).
REMOTE
TRANSDUCER
INPUT
COMMAND
INPUT
COMMAND
POT
PRESSURE
TRANSDUCER
COMPARISON
AMPLIFIER
VALVE
OVERRIDE
LOGIC
5 VOL T
REFERENCE
VALVE
DRIVE
VALVE
OVERRIDE
®
Model 5866
CONTROL
VALVE
= OPTIONAL
1-2
Introduction
.75
(19.0)
9/16 - 18 UNF
(Both Ends)
Integral
Adjustment
Upstream Inlet
(Downstream Outlet)
"A"
0.50
(12.7)
1.50
(38.0)
5.23
(133.0)
3.00
(76.2)
15 Pin Male
D-Connector
Upstream Outlet
(Downstream Inlet)
Proportional
Adjustment
P
I
Upstream/Downstream
Flow Indicator Label
Valve Height w/
Downstream Adapter
.14
(3.6)
.39
(10.0)
.71
(18.0)
2.58
(65.4)
8 - 32 UNC - 2B x 1/4 Deep
(2 Mounting Holes)
1.50
(38.0)
15 Position Male
D-Connector
.71
(18.0)
"Z"
8-32-UNC x 1/4 Deep,
(2 Mounting Holes)
.39
(9.9)
.28
(7.0)
2.07
(52.6)
NOTE:
1. 1/4 VCR Fitting Shown.
1.48
(37.7)
"X"
5.18
(131.5)
"Y"
(See Note)
Inlet
FLOW
.50
(12.7)
.74
(18.7)
Outlet
(See Note)
1.48
(37.7)
Figure 1-4. Model 5866
Dimensions.
Model 5866E
Connection "A" Dim.
1/4" (M) VCR 4.88/124.0
1/4" (M) VCO 4.56/115.8
1/8" Compression 4.84/122.9
1/4" Compression 5.02/127.5
3/8" Compression 5.14/130.6
6 mm Compression 5.02/127.5
10 mm Compression 5.16/131.1
3/8" or 1/2" (M) VCR 5.18/131.6
3/8" or 1/2" (M) VCO 5.00/125.0
1/4" (F) NPT 5.36/136.1
Model 5866M
Connection "X" Dim. "Y" Dim. "Z" Dim.
1/4" Tube VCR 4.88/124.8 3.22/81.8 1.11/28.2
1-3
Brooks Instrument Model 5866 Pressure Controller
When the pressure controller is used in the “downstream pressure
regulation” mode as shown in Figure 1-6, the pressure in the process
vessel will be constant independent of upstream variation, provided the
upstream pressure does not fall below the do wnstream setting. Pressure
measurement and control takes place at the inlet side of the pressure
vessel.
The most common application of the pressure controller is in conjunction
with a mass flow controller (refer to Figure 1-7). Mass flow controllers
accurately measure and control the required quantity of process gas flows.
In this figure, the mass flow controllers will supply the desired quantity and
mixture of process gas while the pressure controller will maintain the
desired reactor pressure by varying the gas outflow. This system allows
the process reactants to be varied while maintaining a constant reaction
pressure.
The Model 5866 Pressure Controller has proportional and integral control
action. The reset or integral control is combined with the proportional
control action (normally referred to as P.I. control). Both proportional band
(0.5% to 100%) and integration time (0.05 to 5 seconds) are customer
adjustable. Tuning of the pressure controller to perform as a stable
optimum for each application is perf ormed in-process by adjusting easily
accessible P.I. action potentiometers (refer to Figure 1-4).
Figure 1-5. Model 5866 Upstream
Controller.
Figure 1-6. Model 5866
Downstream Controller .
Note: The Controller Mode and valve type are determined at the time of
order. Mechanical parts must be changed to convert modes or valve types.
Model 5866E
Vessel
Pressure Controller
1-4
Model 5866
Pressure Controller
Vessel
Introduction
Upstream Controller Mode sets the controller to maintain the upstream
process pressure constant, independent of downstream pressure or flow
variations (ref. Fig. 1-5). For jumper positions on the PC board see Figure
2-1.
Downstream Controller Mode sets the controller to maintain the
downstream process pressure constant, independent of upstream
pressure or flow variations. For jumper positions on the PC board, see
Figure 2-1.
Normally Open/Normally Closed Control Valve - Both Normally Open
(N.O.) and Normally Closed (N.C.) configurations are a v ailable. Normally
Closed is the standard valve type . The Normally Open valve may be
specified when Safety, Operation or Process considerations warrant this
type of valve .
Remote Pressure Sensor Input allows the use of the integral control
electronics and the valve to regulate the process pressure in response to
the remote pressure transducer signal (refer to Section 2-11).
Voltage and Current Inputs/Outputs - Jumpers are provided on the PC
board to allow 0-5 V, 0-10 V, 0-20 mA or 4-20 mA input/output. 0-5 V input/
output is the standard configuration. F or maxim um accur acy, the Model
5866 should be calibrated with the input/output configuration it will
ultimately use. Controllers will be configured at the factory if requested at
the time of ordering.
Figure 1-7. Typical Application of Downstream Controller.
®
®
Reactor
®
®
Model 5866E
Mass Flow
Controllers
Vacuum Pump
1-5
Brooks Instrument Model 5866 Pressure Controller
V alve Override permits the user to fully open and close the valve
independent of the command setting (refer to Section 2-9).
Precision +5 Volt Ref erence is pro vided to be used in conjunction with a
user supplied command potentiometer to generate a 0-5 V command
signal.
1-4 Specifications
Do not operate this instrument in excess of the specifications listed
below. Failure to heed this warning can result in serious personal
injury and/or damage to the equipment.
Pressure Ranges
7.25 psia to 1450 psia full scale (Elastomer Seals)
7.25 psia to 72.5 psia full scale (Metal Seals)
WARNING
Figure 1-8. Typical Application of Upstream Controller.
®
®
1-6
®
Mass Flow
Controllers
®
Model 5866E
Reactor
Introduction
Flow Rates
0-30,000 sccm* (Nitrogen Equivalent).
*Standard pressure and temperature in accordance with SEMI (Semiconductor
Equipment and Materials Institute) standard: 32°F (0°C) and 101 kPa (760 Torr). Other
reference conditions available upon request.
Accuracy
±1.00% full scale including linearity and hysteresis
Repeatability
±0.1% full scale
Control Range
20:1
Zero Stability
0.001% full scale per 30 days
T emperature Range (ambient and gas)
32°F to 150°F (0°C to 65°C)
T emperature Coefficient
0.1% full scale/° C
Maximum T ransducer Pressure
21.75 psia for 0-14.5 psia range
108.5 psia for 14.5-72.5 psia range
435 psia for 72.5-290 psia range
1,450 psia for 290-1,450 psia range
Maximum Design Pressure
1,450 psig
1-5 Controller Specifications
Input/Output Offset
< 0.2% full scale (voltage), < 1.5% full scale (current)
Proportional Gain
Adjustable, 1 to 200%
Integration Time
Adjustable, 0.05 to 5 seconds
Control Action
Upstream or downstream pressure control
Valve Type
Standard: Normally Closed
Optional: Normally Open
Materials of Construction
Model 5866 Model 5866M
Wetted P arts 316 SS 316L V ar SS
Seals/V alve Seats Viton
®
Options Buna-N
®
Teflon
®
Kalrez
Metal
N/A
1-7
Brooks Instrument Model 5866 Pressure Controller
Power Requirements
N.C. 3.5 watts; +15 Vdc (±5%) @ 35 mA, -15 Vdc (±5%) @ 180 mA
N.O. 10.5 watts, ±15 Vdc (±5%) @ 350 mA
Class III Equipment: The dc Mains input shall be supplied from a SELV
(Separated Extra-Low Voltage) source.
Output Signals
Standard: 0-5 Vdc min load resistance 1 k ohm
Optional: 0-10 Vdc min load resistance 2 k ohm, 0 or 4-20 mA into
maximum 500 ohm
5 Volt Reference Output
5 Volts ±0.2% min Load 1 k ohms.
Pressure Setpoint Signals
Standard: 0-5 Vdc input (impedance 1M ohm)
Optional: 0-10 Vdc input (impedance 1M ohm), 0 or 4-20 mA input
(impedance 250 ohm)
Remote Pressure Sensor Input
Standard: 0-5 Vdc input (impedance 1M ohm)
Optional: 0-10 Vdc input (impedance 1M ohm)
Dimensions
Refer to Figure 1-4
Valve Type
Standard: Normally Closed
Optional: Normally Open
Process Connections
Standard: 1/4" stainless steel compression fittings
Optional: 1/4" VCR
TM
, 1/4" VCOTM, 1/8" compression
Electrical Connection
15 pin D-Connector (DA-15P)
Environmental Conditions
Installation Category: “I”
Pollution Degree: 2
Humidity: 50-80% Relative Humidity
Meter Altitude: 6562 feet (2,000 meters)
For Indoor Use ONLY
Mains supply voltage fluctuations not to exceed ±10% of the nominal voltage
Environmental Effects
EMC Effects Meets the requirement of the EMC directive
(89/336/EEC) EN 61000-4-2 thru 4-8
PED Sound Engineering Practice (SEP)
1-8
Area classifcation and certification
Area Certified for use in hazardous areas in Europe
II 3 G EEx nA II T4
KEMA 03ATEX1532 X
Per EN 60079-15:2003
The modules shall be installed in a suitable enclosure providing a degree of
protection of at least IP54 according to EN 60529, taking into account the
environmental conditions under which the equipment will be used.
Installation
Installation
2-1 Receipt of Equipment
When the equipment is received, the outside packing case should be
checked for damage incurred during shipment. If the packing case is
damaged, the local carrier should be notified at once regarding his liability.
A report should be submitted to the Product Service Department, Brooks
Instrument, 407 West Vine Street, Hatfield, Pennsylv ania 19440.
Remove the en v elope containing the packing list. Carefully remov e the
equipment from the packing case. Make sure spare parts are not
discarded with the packing material. Inspect for damaged or missing parts.
2-2 Recommended Storage Practice
If intermediate or long term storage is required for the equipment, as
supplied be Brooks Instrument, it is recommended that said equipment be
stored in accordance with the following:
a. Within the original shipping container.
b. Store in a sheltered area with the following conditions:
1. Ambient temperature 70°F (21°C) nominal, 90°F (32°C) maximum/
45°F (7°C) minimum
2. Relative humidity 45% nominal, 60% maximum 25% minimum.
Section
2
2-3 General
2-4 Gas Connections
Upon removal from storage , a visual inspection should be conducted to
verify the condition of the equipment is “as receiv ed". If the equipment has
been in storage for an e xcess of ten (10) months or under conditions in
excess of those recommended, all pressure boundary seals should be
replaced and the device subjected to a pneumatic pressure test in
accordance with applicable vessel codes.
A pressure controller system can be built in upstream or downstream
control configurations (refer to Figures 1-7 and 1-8). When the controller is
placed downstream (upstream pressure controller) of the pressure vessel,
the flow is usually determined by MFC(s) in the line upstream of the
vessel.
With the pressure controller upstream of the vessel (downstream pressure
controller), the most likely application is controlling a subatmospheric
pressure in the vessel. The inlet of the pressure controller can be at
atmospheric gas pressure or at vapor pressure of a liquid source. The flow
in this situation is usually determined by the characteristics of a vacuum
pump.
Standard inlet and outlet connections on the Model 5866 and 1/4"
compression fittings. Optional VCOTM and V CRTM connections are availab le
upon request.
2-1
Brooks Instrument Model 5866 Pressure Controller
Prior to installation, insure that all piping is clean and free of obstructions.
Install the piping in such a manner that permits easy removal if the
instrument is to be removed for cleaning or test bench troub leshooting.
2-5 Installation
Do not operate this instrument in excess of specifications. Failure
to heed this warning can result in serious personal injury and/or
damage to the equipment.
When installing the instrument, insure that no f oreign materials enter
the inlet or outlet of the meter. Do not remove the protective end
caps until time of installation.
Any Brooks Instrument mass flo w meter or flow contr oller with a 15
pin D-Connector PC Board bearing the "CE Mark" must use a 100%
shielded cable and metal shell mating connectors. The shield is tied
over 360 degrees to the shell at both ends. This is mandatory to be in
compliance with the EMC Directive (89/336/EEC). Refer to
Appendix A.
WARNING
CAUTION
CAUTION
Recommended Installation Procedures
a. The Model 5866 should be located in a clean, dry atmosphere relatively
free from shock and vibration.
b. Leav e sufficient room f or access to the electrical components.
c. Install in such a manner that permits easy removal if the instrument
requires cleaning.
CAUTION
When used with a reactive (sometimes toxic) gas, contamination
or corrosion may occur as a result of plumbing leaks or impr oper
purging. Plumbing should be checked carefully for leaks and the
controller purged with dry nitrogen before use. See Brooks’
Te chnical Bulletin T-086 for further information.
d. The Model 5866 pressure controller may be installed in an y position.
Note: The control valve in the Model 5866 provides precision control and is
not designed for positive shut-off. If positive shut-off is required, it is
recommended that a separate shut-off valve be installed in-line .
2-2
2-6 In-Line Filter
Installation
CAUTION
Since the Model 5866 Control Valve is not a positive shut-off, a
separate solenoid valve may have been installed f or that purpose.
It should be noted that a small amount of gas may be trapped
between the downstream side of the pressure controller and the
solenoid, resulting in a sur ge upon opening of the solenoid v alve.
This surge can be reduced in magnitude by locating the controller
and solenoid valve close together or by mo ving the solenoid v alve
upstream of the controller.
It is recommended that an in-line filter, such as the Brooks Model 5848, be
installed upstream from the controller to prev ent the possibility of any
foreign material entering the meter. The filter porosity should be
approximately ten times smaller than the orifice used in the installation,
however, it is recommended that the minimum porosity that does not
restrict the flow rate being used. The filtering element should be
periodically replaced or cleaned.
2-7 Electrical Interface
To insure proper operation, the Model 5866 must be connected per Figure
2-1. As a minim um, the following connections must be made for new
installations.
Pin Number Description
1 Command Common
2 or 4 Signal Output
5 +15 Vdc Supply
6 -15 Vdc Supply
8 Command Input
9 Supply V oltage Common
10 V oltage Signal Common
13 +15 Vdc Supply (Current I/O)
Note: The Command Return is internally connected to Signal Return and Supply
Voltage Common.
2-8 Remote Setpoint (Command) Input
If the pressure controller will be commanded by an external voltage or
current signal, the command potentiometer is not used.
The command hookup is as follows:
a. Voltage Signal: Connect the external command signal to Terminal 8 and
the external command return to Terminal 1. Refer to Figure 2-1 and
Table 2-1.
b. Current Signal: Connect the command signal to Terminal 8 and the
command return to Terminal 1. Jumper J4 should be ON. Refer to
Figure 2-1 and Table 2-1.
Note: The command return is internally connected to signal return and
power supply common. Current supplied by the device providing the set
point will not be returned on the current loop.
2-3
Brooks Instrument Model 5866 Pressure Controller
Figure 2-1. Customer Connections and Settings.
2-4
Table 2-1. D-Connector Pin Arrangement.
Installation
PIN NO. FUNCTION COLOR CODE
1 Command Common (Command Pot "CCW") Black
2 Voltage Signal Output White
3 Remote Valve Return Red
4 Current Output Green
5 +15 Vdc Supply Orange
6 -15 Vdc Supply Blue
7 Valve Voltage Out/External Valve Control Wht/Blk
8 Command Input (Command Pot "S") Red/Blk
9 Supply Voltage Common Grn/Blk
10 Voltage Signal Common Org/Blk
11 +5 Volt Reference (Command Pot "CW") Blu/Blk
12 Valve Override Blk/Wht
13 +15 Vdc Supply (1) Red/Wht
14 Chassis Ground (2) Grn/Wht
15 External Sensor Input Blu/Wht
2-9 V alve Override
The valve o v erride function allows full opening and closing of the v alv e
independent of the command setting.
The valve o v erride f or the pressure controller is as follows:
a. To open the valve, apply +15 Vdc to the valve override terminal.
b. To close the valve, apply -15 Vdc to the valve override terminal.
1
9
NOTES:
1. Pin 13 does not have to be
connected if current I/O is
not used.
2. Cable shield tied to chassis
ground in meter connector.
8
15
The valve o v erride function is accessed from Terminal 12 (refer to Figure
2-1 and Table 2-1).
Note: F or normal operation, Terminal 12 may be left open (floating) or
grounded.
2-10 Precision 5V Reference
The Model 5866 is equipped with a precision 5 Vdc reference. The
reference is used internally for precise zero adjustment and is also
availab le as a buffered output for use in conjunction with a 1 to 10 k ohm
potentiometer to provide 0-5 Vdc set-point. The 5 Vdc reference is
availab le at Terminal 11 (refer to Figure 2-1 and Table 2-1).
2-11 Remote Transducer Input
To allow the Model 5866 control circuitry and valve to be used with an
external transducer signal such as a capacitance manometer , J umper J2
“C” or “D” must be moved to the Position B. Jumper J2, "A" can be in either
P osition a or b depending on v alve/controller type. The external sensor
signal (0-5 or 0-10 Vdc) must be connected to Terminals 15 and 10 (refer
to Figure 2-1 and Table 2-1).
2-12 V alve T est Point
The valve voltage may be monitored on Terminal 7 of the D-Connector.
2-5
Brooks Instrument Model 5866 Pressure Controller
2-13 Optional Valve Return
Units manufactured after J anuary, 1992 with a Normally Closed valve can
be configured so the valve current can be returned to the power supply on
a separate line. This is recommended if the power supply lines are longer
than 10 feet. The feature is enab led b y connecting Pin 3 of the D-Connector
to power supply common with a separate lead and moving J umper J3 to
the Position a.
2-6
Operation
Operation
Section
3-1 Operation
a. Purge the system with dry nitrogen for at least thirty minutes prior to
start-up to prevent the formation of deposits if reactive gas is to be
used.
b. In unpressurized piping, apply power to the controller and allow
approximately fifteen minutes f or it to w arm up and stabilize its
temperature.
c. Slowly apply gas pressure to the system.
d. Set the command for the desired pressure to assume normal operation.
3-2 Proportional Band and Integration Time Constant Adjustment
The Model 5866 Pressure Controller has proportional and integral control
action. The reset, or integral, control is combined with the proportional
control actions, commonly referred to as P.I. control. Both proportional
band and integration time are user adjustable. Refer to Figure 1-4 for P
and I adjustment potentiometer locations. The dynamic behavior of the
control system is influenced by flow range , pressure range , fluid type,
orifice size and system volume. Therefore, Model 5866 may have to be
adjusted in the field to achiev e the best dynamic response.
3
Figure 3-1. Error Signal Step
Response.
The factory settings are typically: proportional band minimum, 0.5%,
potentiometer fully counterclockwise (c.c.w .) and integ ration time
minimum, 0.05 seconds, potentiometer fully clockwise (c.w.). This
combination of adjustments usually results in stable control. For most
systems the dynamic response is adequate with the factory settings.
Improved response can be had b y final tuning the P and I potentiometers
in the system by the user. The tuning of the P and I constants does not
affect the calibration of the instrument.
Definitions
Both proportional and integral control actions are defined with respect to a
step response error signal. Refer to Figure 3-1.
3-1
Brooks Instrument Model 5866 Pressure Controller
Proportional Control
Proportional control is a basic continuous control mode in which the
controller output is proportional to the error input signal to the controller.
Refer to Figure 3-2. It provides very rapid response and is relatively stable.
Used alone, proportional control has one major disadvantage: at steady
state it exhibits an offset. That is there is a difference betw een the desired
value, or setpoint and the actual v alue of the controlled variable. An
integral action added to the proportional mode eliminates offset.
Integral Control
Integral or reset action is an integration of the input error signal ov er time.
Refer to Figure 3-3. This means that with integral action the v alue of the
manipulated variable changes at a rate proportional to the error . With
integral action present there can be no offset at steady state since the
manipulated variable will continue to change as long as an error is present.
Characteristics of P.I. Control
By using both proportional and integral control actions, rapid control can
be achiev ed with out a steady state offset. Refer to Figure 3-4. Typically
there is a slight decrease in system stability due to the presence of the
integral mode. The dynamic response of the system is better than the
response would be with integral alone. Because the two controller modes
are interactive the P.I. controller is somewhat more difficult to tune.
Tuning the P.I. control
Turning the P potentiometer clockwise (c.w .) will increase the proportional
band thus increasing the offset and system response time. If the
proportional band is too low, the system ma y o v ershoot the command, or
oscillate. Turning the I potentiometer counterclockwise (c.c.w.) will increase
the integration time, making the system respond slower, but more stable.
Adjust the P and I potentiometers until the optimum response is achiev ed.
Check the adjustment in the system ov er the expected range of pressures
and flows.
Fastest controller response to set point changes are obtained with the P
potentiometer fully counterclockwise and the I potentiometer fully
clockwise.
3-2
Figure 3-2. Proportional Control.
Operation
Figure 3-3. Integral Control.
3-3
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