CEMP-E
TI 811-12
18 August 1998
and controls. Digital inputs include contact closures of limit switches, flow switches, temperature
switches, and pressure switches. Digital outputs include on/off commands to relays, motor starters, or
solenoid valves. Analog outputs include commands such as valve or damper positioning or remote reset
of analog controllers. Analog inputs include measurements from temperature, humidity, pressure, flow
and other specialized sensors.
a. Analog input (AI) functions. The AI function is the interface between analog (continuously
variable) field measurements and the field equipment panel. Instruments monitoring physical properties
such as temperature, flow, and pressure, require circuitry to convert the analog measurement to digital
data. The AI function is designed to accept analog signals when measuring parameters such as
temperature, flow, and pressure, and to convert each to a digital quantity usable by the system.
b. Analog output (AO) functions. The AO function is the interface between commands generated
by the field equipment panel and controlled equipment. The field equipment panel commands are
converted to an analog value which is compatible with individual controllers or local loop controls.
c. Digital input (DI) functions. The DI function provides interfacing between field equipment on/off
or two-state indicators and the field equipment panel. DIs monitor both momentary and maintained
contacts and serial digital pulses from electrical power meters, gas flow meters, water meters and other
utility meters.
d. Digital output (DO) functions. The DO function interfaces output signals between the field
equipment panel and field controls that require digital commands. DOs are capable of performing
momentary or maintained switching. This allows incremental control of setpoints, and momentary contact
closures for devices such as motor starters, or maintained contact closures for devices such as electric
heaters, solenoid valves , and lighting.
e. Pulse accumulator functions. The pulse accumulator (PA) function interfaces pulse initiator
signals from electric or natural gas meters to the field equipment panel. The PA function is provided
through Dis with buffer memory to totalize pulses. The field equipment panel microprocessor periodically
interrogates the buffer and resets the pulse count.
f. Binary coded decimal function. The binary corded decimal (BCD) function interfaces specialized
instruments, utilizing BCD format singals, to the field equipment panel. The BCD format utilizes four-bit
groups to represent the units, tens, hundreds and higher decimal positions of an analog value (for
example, the analog value 6,144 is represented in BCD format as 0110 0001 0100 0100). The binary
signals representing individual bits are interfaced to the field equipment panel as DIs.
7. CHILLER CONTROL PANEL. Existing electronic, pneumatic, or relay logic chiller control panels
may be replaced with microprocessor chiller control panels providing the same safety and operating
fnctions as the original panels. These chiller control panels have communication ports which allows them
to be interfaced to a smart field panel, similar to the way a unitary controller is interfaced. This
communiation interface provides two-way data transfer, allowing the UMCS to access real-time chiller
status and operational data and to command the operation of the chiller. Chiller control panels will be
considered in UMCS design when existing chiller controls are in poor condition or replacement is
economically feasible. Chiller control panels will also be considered when the specific installation
requires many UMCS input/output interfaces with the chiller. In this situation, the use of a chiller control
pnael may be more cost-effective than installing the required chiller instrumentation of interface to the
UMCS.
8. BOILER CONTROL PANEL. Existing electronic, pneumatic, or relay logic boiler control panels may
be replaced with microprocessor boiler control panels providing the same safety and operatingfunctions
as the original panels. These boiler control panels have communication ports which allows them to be
interfaced to a smart field panel, similar to the way a unitary controller is interfaced. This communication
interface provides two-way data transfer, allowing the UMCS to access real-time boiler status and
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