Download Measurement and Control Design Standards I. Background and Overview

Measurement and Control
Design Standards
I.
Background and Overview
A.
The City’s Program Standards and Procedures (PSP) are intended to be used in
conjunction with the data contained in related standards and procedures. They are not
intended to be used as stand alone documents. It is the responsibility of the Designer
to become familiar with all the PSP documents and comply with the criteria set forth
as a whole.
B.
Designer shall adhere to the design standards without exception unless permission is
granted by the City’s Project Manager to deviate from these standards. The City
Project Manager shall be notified in writing of the need to deviate from any standard
and approval issued by the Owner in writing before the design deviation is made.
Approval will be authorized by the City Project Manager in writing before the design
deviation is made. Should a design be made that deviates from these standards
without approval from the City Project Manager, the Designer shall bear the cost of
modifying the design to conform. This standard is divided into the following sections:
II.
III.
IV.
V.
VI.
VII.
VIII.
IX
X.
XI.
XII.
XIII.
XIV.
XV.
XVI..
XVII.
XVIII.
XIX.
General Requirements
Nameplates and Labels for Control Enclosures
Boxes, Control Panels, and Control Centers
Low Voltage Motor Controls
Uninterruptible Power Supply for Control Equipment
Noise and Electrical Magnetic Interference (EMI) Suppression
Control I/O Database
Distributed Control System
Fire Alarm and Life Safety Systems
I/O Fusing
Control Circuit Sourcing in General
Motor Control Circuit Configuration
General Control Circuit Configuration
Analog Circuits
Emergency Stop Circuits
Data Collection
Alarms
Alarm Indication
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II.
General Requirements
A.
Apply the more restrictive requirements of the applicable codes and these design
standards. Reference the Life Safety and Maintenance Access Design Standard for
additional requirements.
B.
Provide National Electrical Code (NEC) working clearance requirements as a
minimum to provide access to accommodate assembly, disassembly, and routine
maintenance of equipment.
C.
Design shall ensure compliance with Seismic Zone 4.
D.
Floor mounted electrical equipment shall be installed on a concrete housekeeping pad
3.5 inches high. The concrete pad shall extend two inches in all directions beyond the
foot print of all equipment. Refer to Drawing Requirements for example.
E.
Electrical equipment shall be placed to allow maintenance activities to be performed
in areas protected from rain and wind.
F.
All electrical equipment and materials including, but not limited to, panels,
instruments, transformers, conduits, and etc. shall be labeled as required by the State
of Oregon Building Codes Division.
G.
Control circuits shall be shown in the de-energized (power off) position.
H.
Equipment shall be designed to not allow starting in the power off condition.
I.
Scaled plan views shall be provided for all electrical and measurement and control
equipment and components.
J.
Scaled elevation drawings shall be provided for all areas containing electrical and
measurement and control equipment or components, except for general purpose light
switches and receptacles.
K.
All products referenced in this design standard (e.g., UPS, MCC, VFD, relays,
selector switches, instrument transmitters, etc.) shall be those as specified in the
Willow Lake Master Guide Specifications and the design documents shall be based
on these products. The Designer must be familiar with the products specified so that
all unique characteristics of each product are accurately reflected and reproduced in
the design.
L.
The Drawing Library contains samples of the standard control circuits configuration
to be used at the Willow Lake Water Pollution Control Facility (WLWPCF).
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III. Nameplates and Labels for Control Enclosures
All nameplates and labels for control enclosures shall be pursuant to Section VI of the
Process Identification, Finishes and Labeling Design Standards.
IV. Boxes, Control Panels, and Control Centers
Control Panel Design:
A.
Enclosures located in dedicated electrical or control rooms shall be rated NEMA 12.
All other locations shall be stainless steel enclosures rated NEMA 4X. Reference
Master Guide Specification, Section 13430 - Boxes, Control Panels, and Control
Centers, for specific product data.
B.
No devices, component, or instrument shall be mounted higher than 72 inches or
lower than 24 inches above the finished floor.
C.
The design shall provide adequate space above components requiring natural
convection for heat removal. This area shall be that as recommended by the
manufacturer of the control component. If the manufacturer does not have a
recommendation, the minimum distance shall be three inches.
D.
Terminal strips shall be mounted on back-panels. Relays and other like control
devices are to be mounted around the center and top portions of the enclosure backpanel.
E.
Electrical enclosures supplied with 480-volt and above shall be provided with a main
disconnect.
F.
Enclosures with power supplied from more than one source shall have a warning
label affixed to the cover stating equipment is fed from more than one source.
G.
Scaled elevation drawings shall be provided for all exterior control panels and backpanel layouts with all the control devices mounted on the door and back-panel shown.
H.
The Designer shall ensure that all control enclosures are large enough to
accommodate the required components and meet all design criteria including the
spare space requirements stated in these standards.
I.
Control enclosures shall be designed with an additional 20 percent usable spare space
available on the back-panel for future additions. This additional space does not need
to be in one specific area, but can occupy up to three different areas that total the 20
percent requirement. The area shall be measured by using X and Y coordinates in a
two-dimensional layout.
J.
Control enclosures, excluding MCC sections, shall contain primarily voltages equal
to or less than 120 VAC and DC.
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K.
All back-panel layouts shall be designed to NEC Class 1 and Class 2 wiring
requirements. The two classes shall be separated from each other by a distance of six
inches:
1.
When Class 1 and Class 2 circuits must cross, they shall do so at right angles or
as close to right angles as possible.
2.
Class 1 and Class 2 may be ran parallel when connecting to the same control
device. This shall occur only for the minimum distance required to make the
connection to the device.
3.
Control enclosure design layouts shall clearly show and label Class 1 and Class
2 areas, terminal strips and wireways.
4.
The Designer shall design control enclosures that will accommodate the
construction of control systems using the above listed Class 1 and 2 standards.
L.
Back-panel layout design showing wire ducts running parallel with terminal strips,
shall show a minimum of three inches distance between the wire duct and terminal
strip. Terminal strips shown next to the edge of the back-panel without an adjacent
wire way shall be shown to have a minimum of three inches distance between the
terminal strip and the edge of the back-panel.
M.
All control panels larger than 36 inches high and 24 inches wide shall have a panel
light fixture mounted on the ceiling of the control panel, near the front, with a door
activated switch.
N.
During the design process, all control equipment enclosures shall have internal
temperature analysis performed. This analysis shall be performed by charts, formulas
or software provided by the enclosure manufacturer. The data from this analysis shall
be provided to the City Project Manager at design reviews. This data shall be utilized
by the Designer to ensure adequate temperature control is designed into the system to
meet the requirements of all components located within the enclosure.
O.
Panels located in outdoor areas and unheated areas shall have heaters and ventilation
fans or air conditioning installed. Indoor enclosures in climate controlled areas shall
be only be required to have supplemental ventilation fans. All fans and intake
ventilation louvers shall have filters that can be removed and cleaned. Heaters,
ventilation fans, or air-conditioning units shall be operated from a thermostat
mounted within the enclosure unless the temperature control is integral to the heater,
fan, or air conditioner. Internal enclosure temperatures shall not exceed the
temperature rating of any control components installed within the enclosure.
P.
Enclosures shall not be used as pull boxes.
Q.
Push button switches shall have button construction pursuant to Section 13430 Boxes, Control Panels, and Control Centers.
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R.
V.
The standard selector switch operator shall be without level, cylinder locks, etc. and
maintained in all positions. Should a clear advantage exist to deviate from this
standard, approval shall be obtained from the City Project Manager.
Low Voltage Motor Control Circuits
Control Circuit Sourcing for Motor Control Circuits (MCC).
A.
Typical motor control circuits for 480 volt, three-phase motors shall be derived from
individual Control Potential Transformers (CPT). These CPTs shall be connected to
the load side of the motor branch circuit protection device for the motor. Both legs of
the high voltage winding shall be fused. The ungrounded leg of the low voltage
winding shall be fused with the other low voltage leg grounded at the point of
installation for the CPT. All fuses shall have blown fuse indication.
B.
Typical motor control circuits for 240 and 208 single phase motors shall be derived
either from CPTs that are connected to the load side of the motor branch circuit
protection device for the motor or preferably by connecting to one leg of the 240 or
208 conductor and grounded neutral for the system. The CPTs shall be fused on the
ungrounded leg of the low voltage winding with the other low voltage leg grounded
at the point of installation for the CPT. If no CPT is used, the ungrounded conductor
shall be separately fused.
C.
For packaged, Original Equipment Manufacturer (OEM) provided equipment, all
motor starters that are not located in a MCC and are an integral component of the
OEM provided system shall be permitted to operate from one single 120 VAC
(nominal) control power source provided by the manufacturer.
VI. Uninterruptible Power Supply for Control Equipment
Control Circuit Power Sources:
A.
The 120 VAC control power for DCS I/O shall be from an Uninterruptible Power
Supply (UPS). The 120 VAC supplying power to the UPS from a lighting panel or
dedicated CPT shall be used as an alternate source of power by the use of a threeposition selector switch with Line/Off/UPS positions.
B.
All UPS shall be pursuant to Master Guide Specification, Section 13455 Uninterruptible Power Supplies for Control Equipment.
C.
A UPS under 700 VA shall be installed within a dedicated enclosure. A UPS over
700 VA shall be installed on a shelf for visibility and ease of access and properly
secured for the Seismic Zone 4.
D.
The UPS shall be monitored for failure alarms by the Foxboro DCS. The UPS shall
generate a discrete 120 VAC input to the DCS that indicates a general UPS failure or
fault alarm. If this contact is not rated for 120 VAC, an alternate power supply and
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slave relay shall be installed to accommodate the required alarm input to the DCS.
Reference Drawing Library for typical installation detail.
E.
The UPS shall be configured to prevent shutdown from external devices.
VII. Noise and Electrical Magnetic Interference
Suppression
A.
For systems that are supplied power from UPS units, protection for electrical noise
transmission from power sources shall be provided through the UPS unit itself. No
additional noise suppression shall be necessary.
B.
For non-UPS power, noise suppression for electrical noise transmission from power
sources shall be provided by a dedicated Transient Voltage Surge Suppression
(TVSS) device.
C.
The TVSS shall be inserted in the control circuit to protect the loads sensitive to
electrical noise transmissions such as controller processors and instrument power
supplies. Equipment such as panel lights, enclosure temperature control equipment,
relay control circuits, etc. are not required to be protected by TVSS devices.
D.
Electrical noise from non-power sources are primarily large inductive devices such as
size three and greater motor starters, solenoid valves drawing 300 mA and greater,
and small, fractional horsepower motors (1/8 Hp and less). If these devices are
powered directly from the controller outputs, individual noise suppression devices
shall be installed and connected to the coil of each device. These devices shall be
Metal Oxide Varistors (MOV).
E.
Protection from other sources, such as Variable Frequency Drives (VFD), shall be
considered provided by the design requirements for electrical construction.
Components such as conductors installed in rigid conduit, control enclosures
constructed of metal, and instrument cable shields/ drain wires are to be properly
grounded. This does not rule out the possibility that additional measures may be
required. The Designer shall determine the need of additional noise suppression and
recommend such measures to the City Project Manager during the design process. An
example may be the use of EMI resistant control enclosures in areas containing
VFDs.
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VIII. Control I/O Database
A.
A Control I/O Database will be developed for all projects at WLWPCF. The database
will be created during the Schematic Design Phase of a project by the Design Team
and continue to be expanded through all phases of the project. The database shall be
managed by one-individual selected by the City Project Manager. Any and all
modifications to the project database shall be submitted to the Database Manager.
The database shall be utilized for control development, construction, startup, and
commissioning activities.
B.
At the completion of the Schematic Design Phase of a project the database shall be
provided as a deliverable to the Owner.
C.
During each phase of the project various members of the Project Team will be
providing information that will be added to the database. Specific database
information required to be provided by team members is detailed below. The required
information listed is the minimum database information requirements. Any additional
information that Project Team members identify as information that will contribute to
the success of the project should be submitted to the Owner for approval to be
included in the database. The Owner may request additional information be provided.
D.
The Control I/O Database shall be developed utilizing Microsoft Access.
E.
Following lists the minimum database information that will be provided by Project
Team members:
1.
The Design Team shall provide (at minimum) the information detailed in Table
1 for every I/O point developed. Each item listed in Table 1 represents a
separate field for each database record.
Table 1 Design Team—Database Requirements
Database Field
Description of database field
REF_NO (Reference Number)
The Reference Number is the principal method of
uniquely identifying records in a database.
EQUIP_TAG (Equipment Tag)
Lists the Equipment Tag assigned to the I/O point.
DESCRP (Description)
A description of the I/O point
Facility Code
The plant facility code that the I/O point is associated
with.
Process
The plant process that the I/O point is associated with.
P&ID_DWG
Number(s))
(P&ID
Drawing
Measurement and Control Design Standards
Lists the P&ID drawings that the I/O point is detailed on.
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ELEC_DWG (Electrical Drawing Lists the Electrical drawings that the I/O point is detailed
Number(s))
on.
SIG_TYPE (Signal Type)
Defines the type of signal used by each I/O point. This
field normally contains one of five values:
AI - analog input
AO - analog output
DI - discrete input
DO - discrete output
PI - pulse input
SIG_RANGE (Signal Range)
Defines the type and level of field signal used by each
I/O point. (e.g. 4-20 ma for analog, 24VDC for discrete)
PSOURCE (Power Source)
Defines source power for instrumentation (Internal or
External).
CAL_REL (Calibration Relationship)
This field is used for analog inputs. It should be left
blank unless the input signal should be square-rooted., in
which case the field should contain the value “SQRT”, or
another appropriate indication that the calibration is other
than linear.
INST_TYPE (Instrument Type)
Defines type of Instrument (e.g. Pressure Transmitter).
EO1 (Engineering Units)
Defines the Engineering Units that the analog input,
analog output, or pulse input point is measuring.
HSCO1 (High Scale)
This field is used for analog-input, analog-output, and
pulse-input points. It defines the maximum permissible
value of the point, in engineering units. For 4-20mA
analog inputs and outputs, this is typically the
engineering unit value at 20 milliamps.
LSC01 (Low Scale)
This field is used for analog-input, analog-output, and
pulse-input points. It defines the minimum permissible
value of the point, in engineering units. If not supplied,
the default value is 0. For 4-20mA analog inputs and
outputs, this is typically the engineering unit value at 4
milliamps.
Failsafe
If applicable defines the Failsafe state (Energized, Deenergized).
ALM (Alarm)
This field should contain a “Yes” or “No” indicating
whether or not the I/O point will generate alarms.
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ALM_STATE (Alarm State)
This field is used for discrete inputs. It normally contains
“TRUE” or “FALSE,” indicating whether the point
generates an alarm in the closed state (closed field
contact) or the open state (open field contact). This
information is extremely important to define the action or
polarity of Discrete inputs used for logic functions. If this
information is not supplied, the default value is alarm on
closed state (“TRUE”).
HALIM (High Alarm Limit)
This field is used for analog inputs. It defines the value,
in engineering units, at which point the I/O point will go
into a high alarm condition. If not provided by the
Design Team this information will be provided by the
owner.
HHALIM (High High Alarm Limit)
This field is used for analog inputs. It defines the value,
in engineering units, at which point the I/O point will go
into a high high alarm condition. If not provided by the
Design Team this information will be provided by the
owner.
LAL (Low Alarm Limit)
This field is used for analog inputs. It defines the value,
in engineering units, at which point the I/O point will go
into a low alarm condition. If not provided by the Design
Team this information will be provided by the owner.
LLALIM (Low Low Alarm Limit)
This field is used for analog inputs. It defines the value,
in engineering units, at which point the I/O point will go
into a low low alarm condition. If not provided by the
Design Team this information will be provided by the
owner.
Design Comments
Utilized for any Design Team comments relating to the
control point.
2.
The Owner shall provide (at minimum) the DCS information detailed in Table 2 for
every DCS I/O point developed. Each item listed in Table 2 represents a separate
field for each database record.
Table 2 Owners—Database Requirements
Database Field
Description of database field
Block Name
Contains the control block name
Compound
Contains the name of the control compound that the
control block resides in
IOM_ID
Contains the 6-character letterbug address of the FBM
that the I/O point is connected to.
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PNT_NO (Point Number)
Contains the 2-digit point address within the FBM that
the I/O point is connected to.
Block Type
Contains the type of control block utilized to connect
the I/O point in the DCS (e.g. AIN, AOUT, CIN,
COUT.
Card Type
Contains the type of FBM that the I/O point is
connected to.
ENCL_NAME (Enclosure Name)
Contains the name of the enclosure in which the I/O
point’s module resides.
ALM (Alarm)
This field should contain a “Yes” or “No” indicating
whether or not the I/O point will generate alarms. This
field is generated by the Design Team but should be
reviewed by the Owner and changed if required.
ALM_STATE (Alarm State)
This field is used for discrete inputs. It normally
contains “TRUE” or “FALSE,” indicating whether the
point generates an alarm in the closed state (closed
field contact) or the open state (open field contact).
This information is extremely important to define the
action or polarity of Discrete inputs used for logic
functions. If this information is not supplied, the
default value is alarm on closed state (“TRUE”). This
field is generated by the Design Team but should be
reviewed by the Owner and changed if required.
HAL (High Alarm Limit)
This field is used for analog inputs. It defines the
value, in engineering units, at which point the I/O point
will go into a high alarm condition. If not provided by
the Design Team this information will be provided by
the owner. If this information is not provided by the
Design Team it shall be provided by the Owner.
HHALIM (High High Alarm Limit)
This field is used for analog inputs. It defines the
value, in engineering units, at which point the I/O point
will go into a high high alarm condition. If not
provided by the Design Team this information will be
provided by the owner.
LAL (Low Alarm Limit)
This field is used for analog inputs. It defines the
value, in engineering units, at which point the I/O point
will go into a low alarm condition. If not provided by
the Design Team this information will be provided by
the owner.
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LLALIM (Low Low Alarm Limit)
This field is used for analog inputs. It defines the
value, in engineering units, at which point the I/O point
will go into a low low alarm condition. If not provided
by the Design Team this information will be provided
by the Owner.
HAT (High Alarm Text)
The HAT (High Alarm Text) field is used for analog
inputs. It contains the text that the DCS will display in
the alarm summary when the block goes into high
alarm.
HHATXT (High High Alarm Text)
The HHAXT (High High Alarm Text) field is used for
analog inputs. It contains the text that the DCS will
display in the alarm summary when the block goes into
high high alarm.
LAT (Low Alarm Text)
The LAT (Low Alarm Text) field is used for analog
inputs. It contains the text that the DCS will display in
the alarm summary when the block goes into low
alarm.
LLATXT (Low Low Alarm Text)
The LLATXT (Low Low Alarm Text) field is used for
analog inputs. It contains the text that the DCS will
display in the alarm summary when the block goes into
low low alarm.
HLPR (High/Low Alarm Priority
This field is used for analog inputs. It sets the alarm
priority if the I/O point goes into alarm.
NM0 (Name for Zero State)
The NM0 field is used for Discrete-input fields. It
contains the text that I/A will display when the point
changes to the 0 state (open contact). Typical values
are ON, OFF, RUN, STOP, E-STOP, etc.
NM1 (Name for One State)
The NM1 field is used for Discrete-input fields. It
contains the text that I/A will display when the point
changes to the 1 state (closed contact). Typical values
are ON, OFF, RUN, STOP, E-STOP, etc.
SAT (State Alarm Text)
The SAT field is used for discrete inputs. It contains
the text that the DCS will display in the alarm
summary when the block goes into a state alarm.
SAP (State Alarm Priority)
This field is used for discrete inputs. It sets the alarm
priority if the I/O point goes into a state alarm.
Verified
This field is used for commissioning. It will remain
blank until the I/O point (and all I/O point info.) has
been verified. When The I/O point has been verified
this field will contain the verification date.
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Verified By
This field is used for commissioning. When the I/O
point has been verified this field shall contain the
initials of the person who verified the I/O point.
Rev_Date (Revision Date)
Shall contain the date on which the Database Manager
last revised the I/O point.
Owner Comments
Utilized for any Owner comments relating to the
control point.
IX. Control Drawings
A.
B.
The Designer shall provide the following detailed drawings for all new and modified
processes:
1.
Piping and Instrumentation Drawings (P&IDs).
2.
Control system discrete input diagrams
3.
Control system discrete output diagrams.
4.
Control system analog input loop diagrams.
5.
Control system analog output loop diagrams.
6.
Control system architecture drawings.
All drawings shall be pursuant to the Willow Lake WPCF Drawing Requirements
Standard..
X. Process Control Narratives/Control Strategies
A.
The designer shall provide a process control narrative/strategy for all new or
modified processes and equipment control. Process control narrative/strategy shall be
submitted in the following format:
1.
Introduction
The introduction shall provide an overview of the process and equipment that is
to be controlled. This section will include an overview of the process and the
associated equipment that will be utilized to control the process.
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2.
Control Description
Shall be a detailed step by step narrative of the control strategy required to
control the process or equipment. Control for every piece of equipment in the
process shall be detailed in this section.
3.
Common Monitoring
Shall detail all locations that equipment is being monitored and controlled from.
Each individual control variable being monitored from the common locations
shall be listed in this section.
4.
Field/Local Control
Shall detail the control functionality that will be available locally at the
equipment that is to be controlled.
5.
DCS Manual Control
Shall detail the manual control functionality that will be available from the DCS.
6.
DCS Automatic Control
Shall detail the automatic control and functionality that will be provided by the
DCS.
7.
Monitoring and Alarms
Shall detail indications and alarms that will be available at the DCS in addition
to the common monitoring.
XI. Distributed Control System
Distributed Control System Design General Requirements:
A.
Refer to the Distributed Control System (DCS) Design Standards for detailed data.
B.
The DCS for the WLWPCF is Foxboro I/A. The existing facility operates with the
Foxboro I/A Series control processors and compatible I/O modules. The new facility
shall use Foxboro I/A Series control processors and I/O modules to control and
monitor new process equipment. The Designer shall note that certain areas of the
existing facility will be upgraded during the design process. Equipment removed from
operation shall be salvaged and given to the Owner.
C.
It is imperative to have one control system that is common to all unit processes. There
should be one common method of operator interface, information sharing, reporting,
data collection, database maintenance, trending and alarming. All control design shall
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be performed with these criteria in mind. The control system of choice for the
WLWPCF is the Foxboro I/A system.
D.
Original Equipment Manufacturer (OEM) may routinely provide a process purchased
as a packaged unit that is provided with a control system. These processes are
frequently controlled by Programmable Logic Controllers (PLCs). Regardless of the
method of control selected, the process will be integrated into the Foxboro I/A DCS.
E.
The OEM system controller shall be hardwired to provide necessary I/O to the DCS
for basic control and alarm status.
F.
Heat, Ventilation, and Air Conditioning (HVAC) systems typically have their own
control systems requiring little or no intervention by the plant operator. The DCS will
monitor the HVAC system and alarm status through the use of hardwired inputs to the
DCS.
G.
Communication busses and data highways for all control systems shall be redundant.
H.
Control of primary process, control equipment (pumps, blowers, etc.) within a process
area shall be distributed between separate I/) modules. This is to ensure that loss of
single I/O module will not result in complete failure of a critical process or result in
plant upset.
XII. Fire Alarm and Life Safety Systems
A.
Fire Alarm and Life Safety systems shall have their own control and monitoring
systems. Supervisory, trouble and alarm conditions shall be interfaced with the DCS.
B.
The Designer shall provide designs using standard industrial control enclosures based
on control panel design as given in this guideline to house the DCS I/A systems
components unless otherwise specified by the City Project Manager.
C.
The Designer shall provide for program backup of non-DCS controller processor
programs. The preferred method is to use Electrically Erasable Programmable ReadOnly Memory (EEPROMS) if available. If not, the design shall specify other available
means such as battery backup.
D.
Control program software and hard copies of the program shall be provided to the City
Project Manager for controllers of non-DCS systems.
E.
The designer shall recommend control redundancy for Fire Alarm and Life Safety
Systems.
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XIII. AC and DC conductors
A.
AC and DC conductors shall be routed in separate conduits
B.
All conductor terminations shall be pursuant to Section 13420-2.06.AA Hollow Shaft
Terminations.
XIV. I/O Fusing
Fuse discrete inputs to the Foxboro DCS system when power originates from the DCS.
XV. Control Circuit Sourcing in General
Typical control voltage for all discrete control circuits shall be 120-VAC powered from a
source with a grounded neutral:
A.
Lower voltage exceptions must be approved by City Project Manager.
B.
Devices installed in areas classified as hazardous by the NEC shall use intrinsically
safe devices as required by code. Intrinsically safe devices installed in areas containing
substantial moisture or other conducting mediums that could provide and electrical
shock hazard shall be powered by 24 volts DC or 24 volts AC.
XVI. Motor Control Circuit Configuration
A.
Motor control circuits using hand only control functions shall use “Start” and “Stop”
pushbuttons in a three-wire control configuration such that after the motor starter is
energized by the Start pushbutton, the motor starter will remain energized until either
the Stop pushbutton is pushed, an overload contact opens, electrical power is lost, or a
safety interlock turns the motor starter off. Once off, the motor starter will remain deenergized until the Start pushbutton is once again pressed.
B.
Motor control circuits using a combination of hand and auto control functions shall be
designed with a three-position, Hand-Off-Auto (HOA) switch to provide hand (local)
control through the Start/Stop pushbuttons and auto control (or remote) mode of
operation. The selector switch shall electrically disable all operation of the controlled
motor when placed in the “Off” position.
C.
All motor control circuits shall provide indication of motor status through the use of
indicating lights.
D.
Motor running status shall be provided by a “red”, push-to-test, Light-Emitting Diode
(LED) indicating light. The light shall be labeled as directed in the Process
Identification, Finishes and Labeling Design Standards.
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E.
Motor stopped status shall be provided by a “green,” push-to-test, LED indicating
light that is connected directly to the “hot” side of the motor control through a
normally closed motor starter auxiliary contact. This light shall be labeled as directed
in the Process Identification, Finishes and Labeling Design Standards.
F.
For pump motors with check valves installed on the pump discharge, the preferred
method of validation that the connected pump is pumping shall be through the use of
limit switches mounted on the check valve arm. This switch shall detect if the valve is
open by sensing the position of the check valve arm when in the open position. For
this application, the preferred limit switch shall be a magnetic proximity switch.
G.
For pump motors controlled by the Foxboro DCS, the limit switch shall provide an
input directly to the DCS. The DCS shall generate a “Pump Failed” alarm if the check
valve does not open within a short time delay after the motor is energized or if the
valve is not closed when the motor is de-energized.
H.
All motor circuit designs shall require hand resettable overload contacts.
I.
All motor overload devices shall provide a minimum of two contact closures, the
required normally closed contact to de-energize the hardwired motor controls on
motor overload conditions and a second contact to provide a discrete input to the
Foxboro DCS should a motor overload condition exist.
XVII.
General Control Circuit Configuration
A.
The HOA designation shall be used when Auto refers to control by the Foxboro DCS.
The Hand-Off-Remote (HOR) designation shall be used when remote refers to hand
only or a combination of hand and auto control provided at a control station located
remotely from the HOR switch.
B.
Standard design will be that the Auto position will refer to DCS control. If Auto does
not refer to DCS, the phenolic nameplate mounted above the switch will reference the
name of the auto device (source of control other than DCS).
C.
For HOA selector switches used in control circuits that provide two modes, or sources,
of Auto control, one HOA selector switch will select the mode, the second selector
switch shall select the sources of Auto control.
XVIII.
Analog Circuits
A.
Loop powered instruments connected to Foxboro Field Bus Modules (FBM) will be
connected to the 24 VDC loop power provided by the FBM.
B.
Loop powered instruments connected to analog input modules other than Foxboro
shall be connected to a common 24 VDC, DIN rail mounted power supply within the
same enclosure. Typically, power supplies providing instrument loop power shall
consist of a single power supply per each application. For critical systems, the use of
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two redundant, parallel connected power supplies is to be considered. The Designer
shall determine if parallel power supplies are warranted and present the need for City
Project Manager approval. Reference the Drawing Library for examples of the
preferred single and redundant power supply configurations.
C.
Each instrument loop connected to a common power supply and each loop connected
to a Foxboro analog input module shall be fused at the point of supply with a 50 mA
fuse located in a fusible terminal block provided with a blown fuse indicator.
D.
All field located analog instruments shall generate a 4-20 mA signal.
E.
All installed devices operating from the converted 4-20 mA loop shall be designed to
operate from 1-5 VDC. If connection is made to a single device that accepts 1-5 VDC
only and the field cable is providing 4-20 mA, the added 250Ω resistor shall be
connected, along with the enclosure instrument cable, at the device termination, not
the field terminal strip where the field cable is connected.
F.
Each analog device connection within an enclosure shall be the same instrument cable
as that used for field connections, except cable that does not leave the enclosure shall
be #20 AWG with 600-volt insulation. The wire shall be sized to limit voltage drop to
less than two volts.
G.
The design shall be configured so the panel builder is not required to use only one
conductor of a Twisted Shielded Pair (TSP) instrument cable or be required to strip
more than four inches of cable insulation to install the circuit as designed.
H.
Conductor colors for instrument cables shall be “red” for positive and “black” for
negative.
I.
Each instrument control enclosure shall have a low resistance, copper ground bus bar
installed. The ground bus bar shall be connected through a ground wire to the ground
connection located at the source of power for the panel. Each ground bus bar shall also
be grounded to the enclosure back-panel through the use of “star” washers on threaded
screws.
K.
The shield (or drain wire) for instrument cables for analog circuits shall be grounded
at one-point throughout the entire circuit. The point of grounding shall be as required
by the instrument manufacturer for the device specified.
L.
The ground bus shall be used to ground all enclosure located instruments and control
components that are required to be grounded by the manufacturer.
XIX. Emergency Stop Circuits
A.
Typical design for an emergency stop circuit shall be a red mushroom head,
maintained, push/pull, non illuminated, pushbutton switch connected in series with the
device to be de-energized such as a motor starter, solenoid, and control valve, etc.
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B.
This requirement is not intended to exclude other emergency stop devices from being
included in the design whenever appropriate for the use. The Designer shall always
consider the most appropriate device providing the greatest degree of protection. Other
commonly available and used devices are as follows:
1.
Light curtains.
2.
Limit switches (mechanical, magnetic proximity and photoelectric).
3.
Safety mats.
4.
Pull chains and ropes.
C.
The emergency stop circuit should be designed such that a common voltage to all
devices is turned off when the emergency stop function is activated. The use of relays
to turn off multiple devices is to be avoided. To achieve this design for systems with
multiple voltage sources, add contacts to the emergency stop switch as required.
D.
When pull chains and ropes are used as emergency stop switches, the chains/ropes are
to be tied to a pull switch specifically designed for the purpose. These switches are of
heavy duty construction and have contacts that once opened, must be manually reset at
the switch itself.
E.
The emergency stop device must be designed to be hardwired connected directly to the
device to be de-energized in an emergency stop condition. The DCS shall not be
utilized to perform emergency stop functions. The DCS shall only monitor the status
of the emergency stop device.
XX. Field Start Stop Switches
A.
Field Start/Stop switches shall be located adjacent to the equipment that the switches
operate.
B.
Field Start/Stop switches shall only be active when the associated equipment LOR
switch is in the Remote position.
C.
Field Start/Stop switches shall connect to DCS I/O discrete inputs. The Start position
shall be connected to one input and the Stop position shall be connected to a separate
input.
D.
When the Start button is depressed the DCS will place the associated equipment
control into the Remote-Manual mode and issue a start command. The command shall
remain latched until a stop command is issued.
E.
When the Stop button is depressed the DCS shall issue a Stop command. Once the
associated equipment has been identified as stopped the DCS shall place the associated
equipment control into the Remote-Automatic mode.
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XXI.
Actuators
A.
Process Control Valve Actuators shall be pneumatic. All other Valve actuators shall
be electric.
B.
All Gate Actuators shall be electric.
C.
All Valve and Gate Actuators shall have a manual override (hand wheel).
D.
All Electric Actuators shall be provided with local open/close/stop and HOR
switches.
XXII.
Data Collection
Electrical power monitoring devices shall be connected to the DCS using 4 - 20 mA analog
loops or discrete inputs.
XXIII.
A.
B.
Alarms
Alarms are defined as all conditions, either event (discrete) or value (analog) driven,
that require timely operator notification for the purpose of initiating operator response.
The intended response can be either the recording of information or the modification
of the process monitored.
The design requirement for establishing an alarm condition is normally intuitive.
Examples include high levels in a reservoir, wet well or other similar high liquid level
condition, high levels of life threatening chemicals such as chlorine should be alarmed.
A complete list of proposed alarm conditions shall be provided by the designer to the
City Project Manager at completion of Schematic Design for approval.
C.
Typically alarms shall be value based derived from analog signals generated by field
instruments such as flow and level transmitters monitored by the DCS with alarms
generated as determined by the software program resident in the DCS. The use of this
type of alarm generation results in maximum flexibility as alarm set-points can be
adjusted easily and alarms configured without modification of hard wired devices.
D.
Crucial alarms should be primarily value (analog) based but may also require a
hardwired, event-based alarm used for backup should the primary analog device fail.
The City Project Manager should help identify these cases by the completion of the
Schematic Design Phase.
E.
Analog circuits shall alarm at two percent above or below scale and out of range.
F.
The preference for discrete alarm design is to require the energizing of the alarm
circuit though the action of closing a normally open set of contacts controlled by the
alarm monitoring control component.
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G.
For critical systems where the failure of the alarm circuit to energize due to broken
wires, loose connections, etc., would result in equipment damage and/or would create
a safety hazard to on-site personnel, the alarm circuit shall be designed fail safe. This
means that under normal, safe conditions, the alarm circuit is energized. To alarm, the
circuit must be de-energized. The Owner must approve the use of fail safe alarm
circuits during initial design reviews before the use of these circuits can be included in
the final design.
H.
Critical alarms shall be local latching with field reset only. This requirement is meant
to establish the necessity for field observation to ensure that the condition has actually
cleared before the alarm can be reset.
I.
A class of specialized alarms shall be “Help Me” switches. The intent of this switch is
to provide emergency notification for injured personnel to signal for assistance.
J.
The “Help Me” switch shall be a single, blue mushroom head, maintained, push-pull,
non-illuminated, pushbutton switch mounted in a small control enclosure and placed at
strategic areas throughout the facility. These pushbutton switches shall in turn be
connected to the DCS system for monitoring.
K.
A unique nameplate shall be mounted immediately above each “Help Me” switch. The
nameplate shall be as described in the Process Identification, Finishes and Labeling
Design Standards.
L.
Eyewash stations shall include a flow switch alarm to be connected to the DCS
system.
XXIV.
Alarm Indication
A.
Except for localized alarming, all other alarm logic functions shall be provided by the
Foxboro DCS.
B.
The strobe light color for the “Priority 1 Life Safety Alarm” shall be red. The “High
Alarm” would be activated at a pre-defined value based on the level of danger and
activate the strobe light. If the level of danger increases, the “High-High Alarm”
would activated at a higher pre-defined value and activate the horn. Alarms are
latching. The acknowledge button will silence the horn. The strobe light will shut off
only after the level of danger has dropped below the pre-defined “High Alarm.”
C.
When horns and strobe lights are used as alarms, the devices shall have warning
nameplates mounted within one-foot of the horn/strobe. This nameplate shall be red
with white letters and be capable of being read at a minimum distance of 20 feet and
shall identify the type of alarm and provide instructions as to the appropriate response
the alarm demands, such as “Evacuate.”
D.
Horns for critical alarms shall not be located outside of buildings typically. This
requirement is intended to keep outdoor noise levels to a minimum.
—End of Section—
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