Sunday, July 11, 2010
Control Loop Hardware and Troubleshooting
Chapter
Control Loop Hardware and Troubleshooting
Overall Course Objectives
•
Develop
the skills necessary to function as an industrial process control engineer.
–
Skills
•
Tuning
loops
•
Control
loop design
•
Control loop troubleshooting
•
Command
of the terminology
–
Fundamental
understanding
•
Process
dynamics
•
Feedback
control
Control Relevant Aspects of Control Loop
Hardware
•
Necessary
for control loop troubleshooting:
–
To
determine if each subsystem (control computer, actuator system, and sensor
system) is functioning properly
–
To
understand the proper design and operation of all the components that make-up
each of the subsystems of a control loop
Control Diagram of a Typical Control Loop
Components and
Signals of a Typical Control Loop
Controllers/Control Computers
•
Pneumatic
controllers
•
Electronic
analog controllers
•
Supervisory
control computers
•
Distributed
Control Systems (DCS)
•
Fieldbus
technology
Pneumatic Controllers - Phase I
•
Introduced
in the 1920’s
•
Installed
in the field next to the valve
•
Use
bellows, baffles, and nozzles with an air supply to implement PID action.
•
Provided
automatic control and replaced manual control for many loops
Pneumatic Controllers - Phase II
•
Transmitter
type pneumatic controllers began to replace field mounted controllers in the
late 1930’s.
•
Controller
located in control room with pneumatic transmission from sensors to control
room and back to the valve.
•
Allowed
operators to address a number of controllers from a centralized control room.
Pneumatic Controller Installation
Electronic Analog Controllers
•
Became
available in the late 1950’s.
•
Replaced
the pneumatic tubing with wires.
•
Used
resistors, capacitors, and transistors based amplifiers to implement PID
action.
•
Out
sold pneumatic controllers by 1970.
•
Allowed
for advanced PID control: ratio, feedforward, etc.
Electronic Controller Installation
Computer Control System
•
Based
upon a mainframe digital computer.
•
Offered
the ability to use data storage and retrieval, alarm functions, and process
optimization.
•
First
installed on a refinery in 1959.
•
Had
reliability limitations.
Supervisory Control Computer
Distributed Control System- DCS
•
Introduced
in the late 1970’s.
•
Based
upon redundant microprocessors for performing control functions for a part of
the plant. SUPERIOR RELIABILITY
•
Less
expensive per loop for large plants.
•
Less
expensive to expand.
•
Facilitates
the use of advanced control.
DCS Architecture
DCS and Troubleshooting
•
The
data storage and trending capability of a DCS greatly facilitate
troubleshooting control problems. That
is, the sources of process upsets can many times be tracked down through the
process by trending a group of process measurements until the source of the
process upset is located.
Control Relevant Aspects of a DCS
•
The
most important control aspect of a DCS is the cycle time for controller
calls. The shortest cycles times are
typically around 0.2 seconds while most
loops can be executed every 0.5 to 1.0 seconds.
These cycle times affect flow control loops and other fast control
loops.
PLCs
•
PLCs
can withstand has industrial enviroments.
•
PLCs
are used for discrete and continuous control.
•
Discrete
control is used for startup and shutdown and batch sequencing operations.
•
Ladder
logic is used to program PLCs.
PLCs vs. DCSs
•
Advantage
of PLCs:
–
Better
to withstand harsh operating enviroments, faster cycle time are possible,
easier to maintain due to modular nature and lower cost for small and medium
sized applications.
•
Advantage
of DCSs:
–
Lower
cost per loop for applications involving a large number of control loops.
PLC Architecture
Fieldbus Technology
•
Based
upon smart valves, smart sensors and controllers installed in the field.
•
Uses
data highway to replace wires from sensor to DCS and to the control valves.
•
Less
expensive installations and better reliability.
•
Can
mix different sources (vendors) of sensors, transmitters, and control valves.
•
Now
commercially available and should begin to replace DCSs.
Fieldbus Architecture
Actuator System
•
Control
Valve
–
Valve
body
–
Valve
actuator
•
I/P
converter
•
Instrument
air system
Typical Globe Control Valve
Cross-section of a Globe Valve
Types of Globe Valves
•
Quick
Opening- used for safety by-pass applications where quick opening is desired
•
Equal
Percentage- used for about 90% of control valve applications since it results
in the most linear installed characteristics
•
Linear-
used when a relatively constant pressure drop is maintained across the valve
Inherent Valve Characteristics
Use of the Valve Flow Equation
Typical Flow System
Pressure Drop vs. Flow Rate
Installed Flow Characteristic
Slope of Installed Characteristic
Effect of Linearity in the Installed Valve
Characteristics
•
Highly
nonlinear installed characteristics can lead to unstable flow control or a
sluggish performance for the flow controller.
Flow System with Relatively Constant Valve
Pressure Drop
Pressure Drop vs. Flow Rate
Installed Valve Characteristics
Analysis of These Examples
•
Note
the linear installed valve characteristics over a wide range of stem positions.
•
If
the ratio of pressure drop across the control valve for the lowest flow rate to
the value for the highest flow rate is greater than 5, an equal percentage
control valve is recommended.
Control Valve Design Procedure
•
Evaluate Cv
at the maximum and minimum flow rate using the flow equation for a valve (Eq
2.3.3).
•
Determine which valves
can effectively provide the max and min flow rate remembering that, in general,
the valve position should be greater than about 15% open for the minimum flow
rate and less than 85% open for the maximum flow rate.
•
Choose the smallest
valve that meets the above criterion for the minimum capital investment or
choose the largest valve to allow for future throughput expansion.
Additional Information Required to Size a
Control Valve
•
CV
versus % open for different valve sizes.
•
Available
pressure drop across the valve versus flow rate for each valve. Note that the effect of flow on the upstream
and downstream pressure must be known.
Valve Sizing Example
•
Size
a control valve for max 150 GPM of water and min of 50 GPM.
Determine CV at Max and Min FV
•
Use the valve
flow equation (Equation 2.3.3) to calculate Cv
•
For DP, use pressure drop versus flow rate (e.g., Table on page 82)
Valve Position for Max and Min Flows for
Different Sized Valves
Analysis of Results
•
2-inch
valve appears to be best overall choice:
least expensive capital and it can provide up to a 50% increase in
throughput.
•
3-inch
and 4-inch valve will work, but not recommended because they will cost more to
purchase. The 2-inch valve will provide
more than enough extra capacity (i.e., something else will limit capacity for
it)
Valve Deadband
•
It is
the maximum change in instrument air pressure to a valve that does not cause a
change in the flow rate through the valve.
•
Deadband
determines the degree of precision that a control valve or flow controller can
provide.
•
Deadband
is primarily affected by the friction between the valve stem and the packing.
For Large Diameter Lines (>6”), Use a
Butterfly Valve
Valve Actuator Selection
•
Choose
an air-to-open for applications for which it is desired to have the valve fail
closed.
•
Choose
an air-to-close for applications for which it is desired to have the valve fail
open.
Cross-section of a Globe Valve
Optional Equipment
•
Valve
positioner- a controller that adjusts the instrument air in order to maintain
the stem position at the specified position.
Greatly reduces the deadband of the valve. Positioners are almost always used on valves
serviced by a DCS.
•
Booster
relay- provides high capacity air flow to the actuator of a valve. Can significantly increase the speed of large
valves.
Photo of a Valve Positioner
Adjustable Speed Pumps
•
Used
extensively in the bio-processing industries (better to maintain sterile
conditions and relatively low flow rates).
•
Fast
and precise.
•
Do
require an instrument air system (i.e., 4-20 mA signal goes directly to pump).
•
Much
higher capital costs than control valves for large flow rate applications.
Control Relevant Aspects of Actuator
Systems
•
The
key factors are the deadband of the actuator and the dynamic response as
indicated by the time constant of the valve.
•
Control
valve by itself- deadband 10-25% and a time constant of 3-15 seconds.
•
Control
valve with a valve positioner or in a flow control loop- deadband 0.1-0.5% and
a time constant of 0.5-2 seconds.
Chapter
Control Loop Hardware and Troubleshooting
Overall Course Objectives
•
Develop
the skills necessary to function as an industrial process control engineer.
–
Skills
•
Tuning
loops
•
Control
loop design
•
Control loop troubleshooting
•
Command
of the terminology
–
Fundamental
understanding
•
Process
dynamics
•
Feedback
control
Control Relevant Aspects of Control Loop
Hardware
•
Necessary
for control loop troubleshooting:
–
To
determine if each subsystem (control computer, actuator system, and sensor
system) is functioning properly
–
To
understand the proper design and operation of all the components that make-up
each of the subsystems of a control loop
Control Diagram of a Typical Control Loop
Components and
Signals of a Typical Control Loop
Controllers/Control Computers
•
Pneumatic
controllers
•
Electronic
analog controllers
•
Supervisory
control computers
•
Distributed
Control Systems (DCS)
•
Fieldbus
technology
Pneumatic Controllers - Phase I
•
Introduced
in the 1920’s
•
Installed
in the field next to the valve
•
Use
bellows, baffles, and nozzles with an air supply to implement PID action.
•
Provided
automatic control and replaced manual control for many loops
Pneumatic Controllers - Phase II
•
Transmitter
type pneumatic controllers began to replace field mounted controllers in the
late 1930’s.
•
Controller
located in control room with pneumatic transmission from sensors to control
room and back to the valve.
•
Allowed
operators to address a number of controllers from a centralized control room.
Pneumatic Controller Installation
Electronic Analog Controllers
•
Became
available in the late 1950’s.
•
Replaced
the pneumatic tubing with wires.
•
Used
resistors, capacitors, and transistors based amplifiers to implement PID
action.
•
Out
sold pneumatic controllers by 1970.
•
Allowed
for advanced PID control: ratio, feedforward, etc.
Electronic Controller Installation
Computer Control System
•
Based
upon a mainframe digital computer.
•
Offered
the ability to use data storage and retrieval, alarm functions, and process
optimization.
•
First
installed on a refinery in 1959.
•
Had
reliability limitations.
Supervisory Control Computer
Distributed Control System- DCS
•
Introduced
in the late 1970’s.
•
Based
upon redundant microprocessors for performing control functions for a part of
the plant. SUPERIOR RELIABILITY
•
Less
expensive per loop for large plants.
•
Less
expensive to expand.
•
Facilitates
the use of advanced control.
DCS Architecture
DCS and Troubleshooting
•
The
data storage and trending capability of a DCS greatly facilitate
troubleshooting control problems. That
is, the sources of process upsets can many times be tracked down through the
process by trending a group of process measurements until the source of the
process upset is located.
Control Relevant Aspects of a DCS
•
The
most important control aspect of a DCS is the cycle time for controller
calls. The shortest cycles times are
typically around 0.2 seconds while most
loops can be executed every 0.5 to 1.0 seconds.
These cycle times affect flow control loops and other fast control
loops.
PLCs
•
PLCs
can withstand has industrial enviroments.
•
PLCs
are used for discrete and continuous control.
•
Discrete
control is used for startup and shutdown and batch sequencing operations.
•
Ladder
logic is used to program PLCs.
PLCs vs. DCSs
•
Advantage
of PLCs:
–
Better
to withstand harsh operating enviroments, faster cycle time are possible,
easier to maintain due to modular nature and lower cost for small and medium
sized applications.
•
Advantage
of DCSs:
–
Lower
cost per loop for applications involving a large number of control loops.
PLC Architecture
Fieldbus Technology
•
Based
upon smart valves, smart sensors and controllers installed in the field.
•
Uses
data highway to replace wires from sensor to DCS and to the control valves.
•
Less
expensive installations and better reliability.
•
Can
mix different sources (vendors) of sensors, transmitters, and control valves.
•
Now
commercially available and should begin to replace DCSs.
Fieldbus Architecture
Actuator System
•
Control
Valve
–
Valve
body
–
Valve
actuator
•
I/P
converter
•
Instrument
air system
Typical Globe Control Valve
Cross-section of a Globe Valve
Types of Globe Valves
•
Quick
Opening- used for safety by-pass applications where quick opening is desired
•
Equal
Percentage- used for about 90% of control valve applications since it results
in the most linear installed characteristics
•
Linear-
used when a relatively constant pressure drop is maintained across the valve
Inherent Valve Characteristics
Use of the Valve Flow Equation
Typical Flow System
Pressure Drop vs. Flow Rate
Installed Flow Characteristic
Slope of Installed Characteristic
Effect of Linearity in the Installed Valve
Characteristics
•
Highly
nonlinear installed characteristics can lead to unstable flow control or a
sluggish performance for the flow controller.
Flow System with Relatively Constant Valve
Pressure Drop
Pressure Drop vs. Flow Rate
Installed Valve Characteristics
Analysis of These Examples
•
Note
the linear installed valve characteristics over a wide range of stem positions.
•
If
the ratio of pressure drop across the control valve for the lowest flow rate to
the value for the highest flow rate is greater than 5, an equal percentage
control valve is recommended.
Control Valve Design Procedure
•
Evaluate Cv
at the maximum and minimum flow rate using the flow equation for a valve (Eq
2.3.3).
•
Determine which valves
can effectively provide the max and min flow rate remembering that, in general,
the valve position should be greater than about 15% open for the minimum flow
rate and less than 85% open for the maximum flow rate.
•
Choose the smallest
valve that meets the above criterion for the minimum capital investment or
choose the largest valve to allow for future throughput expansion.
Additional Information Required to Size a
Control Valve
•
CV
versus % open for different valve sizes.
•
Available
pressure drop across the valve versus flow rate for each valve. Note that the effect of flow on the upstream
and downstream pressure must be known.
Valve Sizing Example
•
Size
a control valve for max 150 GPM of water and min of 50 GPM.
Determine CV at Max and Min FV
•
Use the valve
flow equation (Equation 2.3.3) to calculate Cv
•
For DP, use pressure drop versus flow rate (e.g., Table on page 82)
Valve Position for Max and Min Flows for
Different Sized Valves
Analysis of Results
•
2-inch
valve appears to be best overall choice:
least expensive capital and it can provide up to a 50% increase in
throughput.
•
3-inch
and 4-inch valve will work, but not recommended because they will cost more to
purchase. The 2-inch valve will provide
more than enough extra capacity (i.e., something else will limit capacity for
it)
Valve Deadband
•
It is
the maximum change in instrument air pressure to a valve that does not cause a
change in the flow rate through the valve.
•
Deadband
determines the degree of precision that a control valve or flow controller can
provide.
•
Deadband
is primarily affected by the friction between the valve stem and the packing.
For Large Diameter Lines (>6”), Use a
Butterfly Valve
Valve Actuator Selection
•
Choose
an air-to-open for applications for which it is desired to have the valve fail
closed.
•
Choose
an air-to-close for applications for which it is desired to have the valve fail
open.
Cross-section of a Globe Valve
Optional Equipment
•
Valve
positioner- a controller that adjusts the instrument air in order to maintain
the stem position at the specified position.
Greatly reduces the deadband of the valve. Positioners are almost always used on valves
serviced by a DCS.
•
Booster
relay- provides high capacity air flow to the actuator of a valve. Can significantly increase the speed of large
valves.
Photo of a Valve Positioner
Adjustable Speed Pumps
•
Used
extensively in the bio-processing industries (better to maintain sterile
conditions and relatively low flow rates).
•
Fast
and precise.
•
Do
require an instrument air system (i.e., 4-20 mA signal goes directly to pump).
•
Much
higher capital costs than control valves for large flow rate applications.
Control Relevant Aspects of Actuator
Systems
•
The
key factors are the deadband of the actuator and the dynamic response as
indicated by the time constant of the valve.
•
Control
valve by itself- deadband 10-25% and a time constant of 3-15 seconds.
•
Control
valve with a valve positioner or in a flow control loop- deadband 0.1-0.5% and
a time constant of 0.5-2 seconds.
Thursday, July 8, 2010
Wednesday, July 7, 2010
EPLAN_Electric_P8_1.9.5
Electrical computer-aided design as the vanguard of the times, since 1984, EPLAN has been planning for the electrical, engineering and project management in the field to provide intelligent software solutions and professional services to global enterprises mark. EPLA N Cabinet, EPLAN product family is not only the leadership of the global market, has now become the industry standard electrical design of the world’s family of CAE software, but also to the electrical control cabinet for 3D design EPLA N Cabinet, for fluid EPLAN Fluid Engineering and Process industries such as EPLAN PPE Products.
source by:http://www.eplan.in/en/solutions/electrical-engineering/eplan-electric-p8/
book series plc
Mitsubishi FX Programmable Logic Controllers, 2 Ed: Applications and Programming
source by:http://www.mitsubishielectric.asia/india/products/automation/
Tuesday, July 6, 2010
FactoryTalk RSView Machine Edition 5.0 CPR 8
source by:http://www.rockwellautomation.com/rockwellsoftware/support/software-downloads.page?
RSLinx
---------------------------
Serial port Emulator, Serial port Monitor, Virtual Serial Port
----------------------------------------------------
source by: http://www.eltima.com/products/
- Serial port Monitoring http://www.eltima.com/download/serial_port_monitor.exe
- Serial port Emulator
- Virtual serial port http://www.eltima.com/download/vspd.exe
- Serial port splitter http://www.eltima.com/download/serial_splitter.exe
- Serial port terminal http://www.eltima.com/download/serial_port_terminal.exe
- Serial port over ethernet http://www.eltima.com/download/serial_ethernet_connector.exe
- Serial RS232 data logger http://www.eltima.com/download/rs232_data_logger.exe
-------------------------------------
source by: http://www.eltima.com/products/
- Serial port Monitoring http://www.eltima.com/download/serial_port_monitor.exe
- Serial port Emulator
- Virtual serial port http://www.eltima.com/download/vspd.exe
- Serial port splitter http://www.eltima.com/download/serial_splitter.exe
- Serial port terminal http://www.eltima.com/download/serial_port_terminal.exe
- Serial port over ethernet http://www.eltima.com/download/serial_ethernet_connector.exe
- Serial RS232 data logger http://www.eltima.com/download/rs232_data_logger.exe
-------------------------------------
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