1.4.11
Microprocessor
A microprocessor refers to the central processing unit (CPU) that contains
all registers and logic circuitry that allow digital controllers to
function.
1.4.12
Output Signal Conversion
Output signal conversion refers to changing one
kind of control output into
a proportionally related signal appropriate for
direct actuation of the
controlled device. An example is converting a 4
to 20 mA or 0 to 10 VDC
signal to a proportional 3 to 15 psig signal to
operate a pneumatic
actuator.
1.4.13
Optimum Start
Optimum start is a method of starting HVAC equipment prior to scheduled
occupancy in order to have the building at setpoint when occupied. Optimum
start is based on the zone temperatures, zone setpoints, and outdoor
temperature.
1.4.14
Peer-to-Peer
Peer-to-peer refers to controllers connected on a communications LAN that
act independently, as equals, and communicate with each other to pass
information.
1.4.15
PID
PID refers to proportional, integral, and derivative control; the three
types of action that are used in controlling modulating equipment.
1.4.16
Resolution
Refers to the number of possible states an input value or output value can
take and is a function of the digital controller I/O circuitry; the A/D
converter for input and the D/A converter for output. Ten bit resolution
has 1024 possible states.
1.4.17
Stand-Alone Control
Refers to the digital controller performing required climate control, and
energy management functions without connection to another digital
controller or computer. Requirements for stand-alone control are a time
clock, a microprocessor, resident control programs, PID control, and I/O.
All stand-alone controllers have a communication port and firmware for
direct connection and interrogation with a laptop computer or similar
hand-held device. This interrogation includes parameter changes and
program downloads.
1.4.18
Terminal Control Unit (TCU)
An off-the-shelf, stand-alone digital controller equipped for communication
on a lower level LAN. TCUs may deviate from stand-alone only in receiving
energy management and time information from a stand alone digital
controller. A TCU is commonly application specific and is used for
distributed control of specific HVAC subsystems. A TCU communicates with
other digital controllers. Typically, a TCU communicates on a lower level
LAN. Examples where TCUs are used include small air handling units (AHUs),
SECTION 15910N
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