control valves in industrial plants
Control Valves are valves used mainly within industrial plants to control
operating conditions such as flow, pressure, temperature, and liquid level by
fully or partially opening or closing in response to signals received from
controllers that compare a "setpoint" to a "process variable" whose value is
provided by sensors that monitor changes in such conditions.
The opening
or closing of control valves is done by means of electrical, hydraulic or
pneumatic systems. Positoners are used to control the opening or closing of the
actuator based on Electric, or Pnuematic Signals. These control signals,
traditionaly based on 3-15psi (0.2-1.0bar), more common now are 4-20mA signals
for industry, 0-10V for HVAC systems, & the introduction of "Smart" systems,
HART, Fieldbus Foundation, & Profibus being the more common protocols.
2012-07-20
