Characteristics And Attributes Of Control Methods - Honeywell AUTOMATIC CONTROL SI Edition Engineering Manual

CHARACTERISTICS AND ATTRIBUTES OF CONTROL METHODS

Review the columns of Table 4 to determine the characteristics and attributes of pneumatic, electric, electronic, and microprocessor
control methods.
Pneumatic
Naturally Most common for
proportional simple on-off
control
Requires clean dry
air Integral sensor/
controller
Air lines may cause
trouble below Simple sequence of
freezing control
Explosion proof Broad
environmental limits
Simple, powerful,
low cost, and Complex
reliable actuators modulating
for large valves and actuators,
dampers especially when
spring-return
Simplest
modulating control
ENGINEERING MANUAL OF AUTOMATIC CONTROL
Table 4. Characteristics and Attributes of Control Methods.
Electric Electronic
Precise control
Solid state
repeatability and
reliability
Sensor may be up
to 300 feet from
controller
Simple, remote,
rotary knob
setpoint
High per-loop cost
Complex actuators
and controllers
Microprocessor
Precise control
Inherent energy management
Inherent high order (proportional plus integral) control,
no undesirable offset
Compatible with building management system. Inherent
database for remote monitoring, adjusting, and alarming.
Easily performs a complex sequence of control
Global (inter-loop), hierarchial control via
communications bus (e.g., optimize chillers based upon
demand of connected systems)
Simple remote setpoint and display (absolute number,
e.g., 74.4)
Can use pneumatic actuators
35
CONTROL FUNDAMENTALS