Cylinder Connections; Instrument Connection - Fisher 3570 Instruction Manual

3570 Positioners
September 2015
If this maximum supply pressure value is not available, use a supply pressure that does not exceed any of the following:
D The maximum supply pressure for the positioner as shown in table 1.
D The maximum pressure rating of the actuator, from the appropriate actuator instruction manual.
D The maximum allowable valve plug stem load for the specific valve body assembly being used. Contact your
Emerson Process Management sales office
D For diaphragm actuators, refer to the actuator instruction manual for the recommended supply pressure and use
the larger value of the range listed.
The recommended supply pressure for use with piston actuators is the highest available supply pressure between
3.4 bar (50 psig) and the maximum limit determined by the actuator and positioner specifications. Selecting the
highest pressure within the limits will minimize load error and will maximize stroking speed and thrust. For the lowest
supply pressure that will assure satisfactory performance, the factors of valve plug unbalance force, valve plug seating
force, and frictional force must be considered in the following relationship:
[
(Valve
unbalance,
Supply
kg)
pressure, = 98
bar
or
[
(Valve
unbalance,
Supply
pounds)
pressure, =
psig
Consult your Emerson Process Management sales office for the appropriate values for specific actuators, valves, and
service conditions. The 0.7 bar (10 psig) is added to the equation to account for an approximate 0.7 bar (10 psi)
differential pressure loss in the positioner. For spring‐return piston actuators, the pressure required to compress the
actuator spring completely must also be considered.

Cylinder Connections

1. The connection marked CYLINDER (see figure 4) is connected at the factory to the lower part of the cylinder
(bottom) or to the lower diaphragm casing if the positioner is used with a pneumatic diaphragm actuator.
2. The cylinder top connection is a pressure passage located in the bottom of the positioner base (key 1, figure 10). On
3570 and 3570C positioners, an O‐ring (key 33, figure 10) is used between the bottom of the positioner and the top
of the actuator. On 3570P, 3570PC, 3571, 3576, and 3577 positioners, a mounting bracket (key 55, figure 12) is
required. This mounting bracket connects to the bottom of the base. An O‐ring (key 33, figure 10) is placed
between the base and mounting bracket. This mounting bracket provides a 1/4 NPT connection for the positioner
output. This connection is made at the factory if the positioner is ordered mounted to the actuator or if the
mounting bracket is installed.

Instrument Connection

The connection marked INSTRUMENT (see figure 4) connects to the output signal connection of the control device.
The positioner operates only on a pneumatic input signal; the input signal range is marked on the nameplate (key 23,
10
for valve plug stem load information, if required.
(Seating (Frictional
+ +
force, force,
kg) kg)
(Area of the actuator piston,
in square mm)
(Seating (Frictional
+
+
force, force,
pounds) pounds)
(Area of the actuator piston,
in square inches)
Instruction Manual
]
+ 0.7 bar
]
+ 10 psig
D200137X012