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CEMP-E TI 811-12 18 August 1998 11-1 CHAPTER 11 EQUIPMENT MODIFICATIONS 1. CEMP-E
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CHAPTER 11
EQUIPMENT MODIFICATIONS
1.
MODIFICATION GUIDELINES. UMCS implementation requires modifications to mechanical and
electrical systems and their associated instrumentation and controls. Interface to mechanical and
electrical systems will require coordination with manufacturer's operating recommendations and site
associated equipment/systems operating constraints.
2.
INSTRUMENTATION AND CONTROLS. Existing local controls will be removed and replaced with
the application of DDC. For supervisory control applications existing local control system equipment will
be shown to include modifications required for interfacing with the UMCS. Except for existing time clocks,
the existing local loop control system must remain and perform as originally designed for UMCS
supervisory control applications. It will be necessary to indicate replacement of controllers to provide
capability for remote control point adjustment. The local loop controls will be interfaced so they will
operate in a predetermined manner upon UMCS failure. New sensors dedicated for UMCS use must be
shown as new rather than reusing existing sensors. When interfacing the field equipment, all existing
indicating devices such as gauges and thermometers will be shown as remaining in service for direct
digital control applications. The local controller will be replaced but the existing final control element
(valve/damper) will operate as originally designed.
3.
LOCAL CONTROLLERS UNDER SUPERVISORY CONTROL.
a. Existing local control systems using sensor, controller, and actuator require a controller with CPA
port for remote control point adjustment. This will necessitate the replacement of the existing controller
without CPA by a new controller with CPA. The CPA will be reset from an analog output.
b. Single input CPA controller. Single input CPA controllers permit remote changing of control
points by varying the CPA port value. CPA port value variation must be plus or minus 10 percent of
primary sensor span. The controller must include an adjustable setpoint, adjustable gain (proportional
band) with field selectable direct or reverse acting action. The controller inputs and outputs must have
internal or external gauges for calibration of input and output signals.
c. Two input controllers. Two input controllers permit remote changing of control points by varying
the second port input value. Effect of the secondary sensor on the setpoint is adjustable as a percentage
of the secondary sensor span, usually 33 to 100 percent of primary sensor span. The controller must
include an adjustable set point, adjustable gain (proportional band) with field selectable direct or reverse
acting action. The controller inputs and outputs must have internal and external gauges for calibration of
input and output signals.
4.
CONTROLLER INTERFACES.
a. Typical controller interfaces are shown in Appendix B .
b. A two-position pneumatic override incorporates a three-way solenoid to switch the signal to a
predetermined UMCS signal. The UMCS control signal value depends on the operation required and the
equipment being controlled. The existing control signal will operate the device being controlled during
field equipment panel failure. The UMCS control diagrams (Chapters 8 and 9) will define the failure
mode. The electrical equivalent to the two position pneumatic override is accomplished with a relay with
Form C contacts.
c. A three mode pneumatic override control incorporates two 3-way EP valves controlled from the
field equipment panel electrical output. The operation of the solenoids allows either for the dampers to be CEMP-E
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under local control of the mixed air controller or for override to allow for 100 percent outside air supply or
minimum outside air supply.
d. Transducers are used for changing pneumatic signals to electric signals and vice versa or for
changing a current signal to a voltage signal. Transducers are used in conjunction with sensors and
controllers. Electric to pneumatic transducers can be used to convert field equipment panel electrical
output signals to pneumatic signal inputs to a local pneumatic control loop or to a pneumatic actuator.
Pneumatic to electric transducers can be used to convert local loop pneumatic signals to electric signals
inputs to the field equipment panel.
e. A local loop pneumatic controller must be retrofitted with a CPA port for supervisory control. The
operation of a local loop 3 to 13 psi air signal on a CPA changes the setpoint plus or minus 10 percent
(the percentage will vary depending on the manufacturer of the controller). The UMCS will drive a
transducer to change the setpoint from the high to the low (or low to high) setting.
f. The designer will determine the failure mode of operation for each CPA point. In order to fail to
high, low, or local loop control, main air is fed through a pressure reducing station to produce fixed
pressure input to the three-way EP valve. A similar arrangement will use a Form C relay in lieu of a 3-
way solenoid. If the required failure mode is to remain in the last command state, the 3-way EP valve or
Form C relay is eliminated and the transducer (on UMCS failure) remains at the last command position.
g. The local electric controllers will have the same functions as the pneumatic controllers described
above.
5.
TIME CLOCKS. The implementation of UMCS time dependent control programs requires
elimination of existing time clocks. The existing time clock start/stop contacts are replaced with start/stop
contacts operated from the field equipment panel.
6.
SINGLE LOOP DIGITAL CONTROLLERS. Existing single loop digital controllers may have to be
replaced with controllers having an EIA 485 serial interface with adjustable data transmission rates up to
19.2 Kbps in order to interface with the UMCS. The controller will provide the UMCS with process values,
setpoints, alarms and controller status (local-off-auto) and will allow the UMCS to perform remote
controller setpoint adjustment.
7.
INSTRUMENT AIR SUPPLY.
a. Existing instrument air supplies must be checked for water and oil contamination. If
contamination is present the affected pneumatic lines must be replaced and tested prior to UMCS
operation. All other devices in the local control loop that have been contaminated must be replaced.
b. The instrumentation air compressor must be oil free. Duplex air compressors are recommended.
c. The instrumentation air supply must have an air drier. Filtration must be provided before and
after the air dryer.
d. Air filters must be installed with bypass and isolation valves to permit filter
replacement without instrument air supply disruption.
e. Pressure switches must be installed for all major supply air branches to detect loss of air supply.
f. Air drying and filtration at buildings must be provided when instrument air enters a building from
an outdoor distribution system.
g. The designer must evaluate the cost effectiveness of replacing a damaged instrumentation air
system versus replacement of pneumatic control devices with electric devices (e.g. actuators, controllers). CEMP-E
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8.
ELECTRICAL EQUIPMENT.
a. Existing equipment being connected to the UMCS will require the installation of disconnect
switches or locking starters within sight of the controlled equipment as required by NFPA 70.
b. Spare electrical circuits may be locally available to supply power to UMCS equipment. If these
circuits do not exist, or are inadequate for the intended service, new panels or circuit breakers will be
required.
9.
SUBSTATIONS. Selection and installation of current and voltage transducers for UMCS must be
coordinated with the facility and with the equipment manufacturer. Placement of transformer winding
temperature sensors must also be coordinated with the manufacturer.
10. SWITCHGEAR. UMCS can monitor the status of electrical distribution switchgear equipment such
as:
a. Circuit breakers.
b. Breaker over current trip relays.
c. Tie breaker.
If there are no spare contacts in the switchgear monitoring relays, interposing relays must be provided.
Interposing relay kits must be obtained from the original breaker manufacturer. The UMCS will not
perform switchgear control functions. These functions may be provided by a Supervisory Control and
Data Acquisition (SCADA) system.
11. EMERGENCY GENERATOR. The remote start/stop of emergency generators must be coordinated
and reviewed with the installation electrical engineer and with the generator manufacturer. The UMCS
will monitor generator status and common alarms either from available contacts at the generator control
panel or by means of interposing relays