readily available from known suppliers. Analog computing and logic modules
shall be designed for plug-in rack mounting in the system cabinets. Module
pins and mating connectors shall be gold plated on nickel to withstand
chemical attack by ambient atmospheric chemicals. Modules of the same type
shall be interchangeable to facilitate maintenance and trouble-shooting by
substitution. Pretest and age each module before installing in the module
racks. Factory assemble, wire, and test the system using the operating
stations and actual plug-in cables for the system. Provide input and
output test jacks on each module for tests. Controllers and analog
computing circuits shall perform as follows unless specifically noted
otherwise for a particular system or control loop: Provide calibrated,
front-mounted controls on appropriate modules, to adjust proportional,
integral and derivative action. Adjustments shall be possible while
operating in automatic without causing undesirable upsets such as a
proportional step. Prevent reset windup action and design to develop
response to demand without the system first performing internal controller
balancing. Provide means to automatically balance each loop that has a
manual-automatic operating station so that bumpless transfer may be made
from manual to automatic and from automatic to manual without any
intermediate manual balancing. Where both master stations and individual
final control element stations are employed in a loop, the master, as well
as individual stations shall transfer bumplessly and without balancing, and
be tied together, as appropriate. Bumpless transfer is effected if the
output signal to the final control element does not vary more than 2
percent of the full-scale output signal range when transferring from
automatic to manual and from manual to automatic. Provide for all
interlocks and contact inputs and outputs and all digital logic functions
necessary to control or interface the analog circuits throughout the
system. Provide signal monitor modules to track analog signals where
required to produce contact outputs for alarm or interlock with other logic
when the signal exceeds a predetermined level. Signal monitor units shall
be equipped with independently adjustable high and low set points. Provide
suitable isolating devices such as relays or optical couplers to protect
the control system from external outputs or inputs. Provide indicating
lights on the modules to show the status of all logic, transfer relays, and
signal monitors. Lights shall be visible without removing or withdrawing
the modules from the racks.
2.12.2.2
Input and Output Signals
Input signals from field transmitters shall be 4-20 mA dc "two-wire."
Provide output signals to panel recorders and indicators. Provide square
root extraction for flow signals outputs to devices furnished. Output
signals shall be 4-20 mA dc. Transmitters required to provide multiple
outputs to recorders, and indicators as well as providing an input to the
control system shall be buffered so that disconnecting, shorting or
grounding of the input at the recorder or indicator shall not cause an
upset or failure in the control system. Output control signals to final
control elements shall be 4-20 mA dc. The final control elements shall be
provided with the proper signal converter.
2.12.2.3
System Electrical Power and Power Supplies
The following power sources will be provided by the Government: Source "A"
120-V ac from station inverter. Source "B" 120-V ac from station service.
The Contractor shall furnish fuses or circuit breakers for each source to
protect against faults or overloads at the system modules. System
computing and logic power, transmitter power, or other power used for
control or indication, used either remotely or internally, shall originate
SECTION 15864N
Page 86
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