Characteristics And Attributes Of Control Methods - Honeywell AUTOMATIC CONTROL 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 Simple sequence
below freezing of control
Explosion proof Broad
environmental
Simple, powerful, limits
low cost, and
reliable actuators Complex
for large valves modulating
and dampers actuators,
especially when
Simplest spring-return
modulating
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 ENGINEERING MANUAL OF AUTOMATIC CONTROL
CONTROL FUNDAMENTALS