Redundant control system (RCS)
Name:
Thierry Bakker
Project Pursuit manager
What is Redundancy?
Definitions:
Common definition:
Surplus to requirements; unnecessary or superfluous
Engineering definitions
“A device that will provide its intended function upon loss of power.” (2007 NFPA-80)
An operation which ensures that a failure of equipment, process, or system does not
propagate beyond the immediate environs of the failing entity.
Redundant Control System
Safety Instrumented Systems
Process Reliability
Process Valve Diagnostics
Redundancy with solenoid valves
++ Safety
- - Reliability (production)
1
2
3
1
1oo2
One out of two
2
3
1
2
2oo2
3
Two out of two
1
2
3
++ Reliability (production)
- - Safety
Redundancy with solenoid valves
2oo2D
1
2
3
1
2
3
Safety
++ Reliability (production)
Reasons for RCS design

Redundant SOV commonly used in continuous run
processes to prevent spurious trip (Nuisance trip) due
to coil failure.

Typical Redundant SOV installations:– Do not provide indication of SOV safe failure.
– Do not provide online maintenance facilities.
– Do not provide the ability to automatically test for “stuck”
SOVs or plugged vents.
– Do not provide ability to automatically partial stroke test the
process valve
– Have difficulty meeting SIL requirements.
RCS Product Evolution
Typical 2oo2 SOV Installation
3 way – Normally closed - Energized
SOV1
S
Air Supply
2oo2 installation
SOV2
S
vent
Issue: Cannot easily detect failure or its location
Block Valve
RCS Product Evolution
Addition of pressure Switches – Status Indication
SOV1
PS1
S
Air Supply
SOV2
PS2
S
vent
Block Valve
Issue: How do you repair the problem without shutting down the process ?
RCS Product Evolution
Addition of maintenance bypass
Isolation Valves
SOV1
PS1
S
Air Supply
SOV2
PS2
S
vent
By-Pass valve
Issue: 1) How do you know when you are in by-pass ?
2) How do you know when repair is complete ?
Block Valve
RCS Product Evolution
Addition of maintenance bypass PS indication
SOV1
PS1
S
Air Supply
SOV2 PS2
S
vent
PS3
Block Valve
RCS Product Evolution
The ASCO RCS Product
SOV1
PS1
S
Air Supply
SOV2 PS2
S
vent
PS3
Block Valve
RCS Concept
ASCO’S RCS package consolidates many of the
components using known technology to create a more
complete package with unique features to meet today's
needs…
RCS Product Features
Ground
Din Mounted Terminal
• Accommodates up to 14 AWG wiring
Keyed Maintenance Bypass
• Permits user to service unit without
disturbing the process
ISO-3 Low Power Solenoids (2)
• 4 bolts permit quick replacement
• 1.4 watts (24vdc)
• Class 1, Div 2 solenoids (non incendive)
Pressure Switches (3)
• Monitors solenoid valve position
(diagnostics)
• Class 1, Div 2
• Stainless Steel
Air-operated Bypass Valve(1)
• Maintains process while main solenoid
valves are serviced during bypass
Enclosure
• 304 or 316 Stainless Steel or Fiberglass
• UL Type 4, 4X
Breather vent
• Limits condensation build-up
Pneumatic connections
RCS 1oo1HS
RCS 2oo2D
Normally Closed Version
•Normally Closed RCS operates like a 3 way Normally Closed valve
•In the de-energized state the unit is venting the process valve actuator
•As long as one solenoid valve is energized air is supplied to the process valve.
•When both solenoid valves are de-energized the process is vented.
•Typical application: “ESD systems” (Emergency Shut-down valve) – Fail Safe
Bypass (B/P) valve shown in
the normal state
SOV1 and SOV2
de-energized
SOV1
out
SOV2
e
out
in
ps
B/P 3
out
SOV1
in
e
ps
SOV2
in
e
ps
Inlet
e
Outlet
Exhaust
PS1
PS2
PS3
Contact
Closed
Contact
Closed
Contact
Closed
Status:SOV1 & SOV2 de-energized
Valve
Closed
Normally Open Version
•Normally open RCS operate like a 3 –way normally open.
•In the De-energized state, air is supplied to the process valve
•As long as one solenoid valves is energized the process valve will be open to
exhaust and remain in the normal position.
•Typical application: “vent valves”
Bypass (B/P) valve shown
in the normal state
SOV1 and
SOV2 de-energized
Outlet
SOV1
out
SOV2
in
out
SOV1
e
e
ps
ps
in
B/P
plug
in
ps
e
in
out
e
Valve
Open
Exhaust
Air Supply
PS1
Contact
Open
PS2
Contact
Open
PS3
Contact
Closed
Status: SOV1 & SOV2 de-energized
Double Acting Version
• Similar to having one 3 way normally closed valve & 3 way normally open
• When both solenoid valves are de-energized one side of the actuator is venting while
the opposite side is being pressurized
• Customer must define desired position “Fail close / fail open”
• If the event of single SOV failure
actuator becomes balanced – actuator
maintains last position
Bypass (B/P) valve shown
in the normal state
SOV1 and SOV2
de-energized
SOV1
• Available only in 2oo2 operation
ps
out
SOV2
e
in
out
e
ps
For use with valves that
have a safe state of open
the connections to the
valve actuator from the
RCS, C1 and C2, would
be reversed
B/P
e
in
out
e
ps
SOV2
in
Air Supply
e
C2
Exhaust
C1
PS1
PS2
PS3
Contact
Closed
Contact
Closed
Contact
Closed
Valve in closed position
Valve Safe State Closed
RCS Versions
Series 5R – No on-board diagnostic processor (AC or DC)
Series 5L – with on-board diagnostic processor (DC only)
• Main Components
• 2 - Solenoid Valves = 2 Digital Output D/O
• 1- Maintenance By-Pass
• 3- Pressure switches = 3 Digital inputs D/I
• Key function Monitor status of SOV’s & bypass
•Functional testing capabilities
• Automated through PLC or DCS
• Manually initiated test
• Optional panel mount push button and lights
• Initiates program test
RCS Versions
Series 5L – with on-board diagnostic processor (DC only)
Siemens PLC - main Function
• reduce programming and total I/O count
• Controls outputs to SOV’s
• Receives diagnostic input from pressure switches
• Provides testing and diagnostic information
• Power is supplied to Siemens PLC via the users controller
• Testing and diagnostic reporting to any human machine interface (HMI)
can be facilitated via MODBUS 485
IMPORTANT:
Onboard PLC provides testing and diagnostic information only.
• Siemens PLC is benign to the safety action
• Power is supplied to the on-board PLC by users controller
• User’s controller is always responsible for the safety action
• Safety action is executed by de-energizing the output power to Siemens PLC
RCS Versions
Series 5L – with on-board diagnostic processor (DC only)
In the event of a PLC failure
Watch Dog Relays
•Watchdog relays are provided to prevent de-energizing the SOV’s due to a failure
Of the on-board PLC outputs.
• Each SOV receives power through a separate normally closed relay contact on
separate watchdog relays .
• Watchdog relays are energized by a output from on-board PLC
• This keeps normally closed contact in the open position
• If on-board PLC fails the watchdog relay close and SOV 1 & SOV 2 are connected to
controller allowing the controller to have supervisory control over SOV 1 & SOV2
• Power to SOVs is maintained avoiding accidental shutdown
• Loss of PLC will be detected and annunciated
RCS Product – 1oo1 HS
1. In the 1oo1HS operational mode one SOV is selected as primary and is
normally energized.
2. The Hot Standby SOV is normally de-energized and its associated PS verifies
the vented state. With only one SOV energized position the safety availability
SOV1
is increased.0
Primary
S
PS1
Air Supply
SOV2
Hot Standby
S
PS2
ZSO
vent
PS3
Block Valve
Normally Closed - De - Energized - to - trip
SOV' Status
Pressure Switch Indication
Solenoid Valves
P.S. 1
P.S.2.
P.S.3
Both SOV's Energized
O
O
CL
Both SOV's De-Energized
CL
CL
CL
SOV 1 De-Energized only
CL
O
CL
SOV 2 De-Energized Only
O
CL
CL
Bypass mode
O
O
O
= Closed contact
= Open contact
RCS Product – 1oo1 HS
1. If the primary SOV shifts to the vented state (coil failure) its associated PS
identifies the failure and the Hot Standby SOV is energized.
2. The Hot Standby prevents the closure of the process valve
3 The reliability of the 1oo1HS is the same as 2oo2 operation.
SOV1
Primary
S
PS1
Air Supply
SOV2
Hot Standby
S
PS2
ZSO
vent
PS3
Block Valve
SOV' Status
Solenoid Valves
Both SOV's Energized
Both SOV's De-Energized
SOV 1 De-Energized only
SOV 2 De-Energized Only
Bypass mode
CL = P.S. contact is closed
O = P.S. contact is open
Pressure Switch Indication
P.S. 1
P.S.2.
P.S.3
O
O
CL
CL
CL
CL
CL
O
CL
O
CL
CL
O
O
O
= Closed contact
= Open contact
RCS ATEX Certification
RCS SIL Certification
Certified SIL 3 Capable by Exida for 1oo1HS, 2oo2D
•
•
•
•
Available as an optional feature on configurator
SIL certified units will have a different catalog number than non-SIL units
If required, must be identified at the time of part number configuration
Currently SIL certification is only available on units without onboard PLC
Supporting documentation for certified units:
•
•
•
•
Exida Certificate
FMEDA
IEC61508 Assessment
Safety Manual
RCS in the field
The RCS solution combines the benefits of safety and reliability in a single package.
“it’s the only pilot valve system that has no single point of failure that can result in an unwanted closure of
the process valve. With the RCS, customers will benefit from higher asset availability, less risk of spurious
trips, and safe shut downs of mission critical systems, time after time.”
The RCS achieves higher levels of safety by incorporating a redundant, fault-tolerant architecture,
high diagnostic coverage, and automated testing. Its self-diagnostic capabilities test both the safety
system and process valve to ensure continuous proper operating performance.
The ASCO RCS was designed to meet the expanding national and international hazardous
location requirements for safety systems, high reliability, and critical control applications. It allows the
end-user to specify a normally closed, normally open or double acting configuration in redundant
control “2oo2” (two-out-of-two) or single solenoid with back-up “1oo1” (one-out-of-one)
operation.
All types of RCS are available with “automatic on-line testing” of the solenoid valves and “partial
stroke testing” of the process valve. The RCS also provides users with a maintenance/ by-pass mode,
which permits service to the device without taking the process valve off line. This allows the plant to
maintain production without jeopardizing its safety.
RCS Information
RCS Brochure
Contains:
• Product specifications
• Technical details on
RCS operation
• Optional features
• Introduction to the
RCS Configurator
Available online @
www.ascovalve.com
RCS Configurator
“LIVE” demonstration
Redundant Control System
Safety Instrumented Systems
Process Reliability
Process Valve Diagnostics