Honeywell AUTOMATIC CONTROL SI Edition, Engineering Manual

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ENGINEERING MANUAL OF AUTOMATIC CONTROL
ELECTRIC CONTROL FUNDAMENTALS
106
LINE
VOLTAGE
ACTUATOR
W R B
W R B
T2
T1
DAMPER
TRANSFORMER
FLOATING STATIC PRESSURE
CONTROLLER
REFERENCE
STATIC
C2519
SERIES 60 FLOATING CONTROL CIRCUITS
APPLICATION
A Series 60 floating control circuit is a line- or low-voltage
control circuit comprising a spdt controller with a center-off
(floating) position and a reversible actuator. On a change in
the controlled variable, the controller drives the actuator to
an intermediate position and then opens the circuit to the
actuator. The actuator remains in this position until a further
change at the controller. The actuator is said to float between
the limits of the controller to satisfy various load requirements.
In many systems, Series 60 floating control provides adequate
modulating control.
To provide stable Series 60 floating control, careful
consideration must be given to the speed of response of the
controller and the timing of the actuator. For a given change in
the system, the actuator timing and the subsequent change in
the controlled variable must be slower than the response time
of the controller. To accomplish this, Series 60 actuators are
available with various drive speeds.
Series 60 floating control circuits can be used for:
1. Control of two-way or three-way valves.
2. Control of dampers.
3. Control of inlet vane or other static pressure regulating
equipment.
The basic Series 60 floating control circuit consists of a
Series 60 actuator and a Series 60 floating controller. Various
limit controllers can be added where required.
EQUIPMENT
CONTROLLERS
1. Floating temperature controllers.
2. Floating pressure controllers.
3. Simulated Series 60 floating control using two Series 40
or 80 controllers.
Series 60 floating controllers are three-wire, line- or low-voltage
devices with a spdt switching action and a center off position.
ACTUATORS
The actuators discussed in SERIES 60 TWO-POSITION
CONTROL are also used for floating control. In addition,
actuator assemblies are available with two, single direction
motors driving a common shaft. One motor drives the shaft
in one direction, and the other motor drives the shaft in the
other direction.
OPERATION
Operation of the Series 60 floating control circuit is similar
to that discussed in SERIES 60 TWO-POSITION CONTROL
with one major difference: the controller has a center off
position allowing the actuator to stop at positions between
the open limit and the close limit.
CONTROL COMBINATIONS
Series 60 floating control can be used to regulate static or
differential pressures in applications where the pressure pickup
can sense changes and position a damper actuator at
intermediate locations between open and closed. Figure 18
illustrates a static pressure controller connected to a Series 60
damper actuator. A drop in static pressure to the controller
setpoint closes R to B at the controller and causes the actuator
to drive toward open. As soon as the static pressure increases
above the setpoint, R to B opens and the actuator stops. The
moveable contact R of the controller remains at the center or
neutral position until a further drop causes the actuator to open
the damper further. On a rise in static pressure to the setpoint
plus a differential, or dead band, R to W closes driving the
actuator toward closed. When the controller is satisfied, R to
W opens stopping the actuator. Thus, the damper actuator floats
between open and closed limits to maintain static pressure.
Fig. 18. Series 60 Floating Control.