Positioners, converters, limit switches, position transmitters, so- lenoid valves and lock-up valves are transfer elements designed to adapt pneumatic control valves to the requirements of indus- trial plants.
Supply pressure regulators and air reducing stations are used to supply the pneumatic instruments with compressed air. Positioners ensure a predetermined assignment between the
valve position (controlled variable x) and control signal (refer- ence variable w). They compare the control signal issued by pneumatic or electric automation equipment (controller, control station, process control system) to the travel or opening angle of the control valve and supply a corresponding output signal pressure (output variable y) (pst). Positioners are often used as servo-booster as they convert low-energy signals into strong proportional signal pressures up to the maximum supply pres- sure (6 bar/90 psi). They can be used in standard and split-range operation.
Depending on the input signal, a distinction is made between pneumatic (p/p) and electropneumatic (i/p) positioners. Pneu- matic positioners accept an input signal of 0.2 to 1 bar (3 to 15 psi) and issue an output signal pressure (pst) of maximum 6 bar (90 psi).
Electropneumatic (i/p) positioners use an analog direct current signal of 4(0) to 20 mA or 1 to 5 mA as the input variable and issue an output signal pressure (pst) up to 6 bar (90 psi).
The Type 3730-3 Positioner additionally uses HART® communi- cation between field devices and the process control system. The Type 3730-4 and Type 3731-4 Positioners with PROFIBUS communication and Type 3730-5 and Type 3731-5 Positioners with FOUNDATIONTM fieldbus communication are used to inte- grate final control elements into fieldbus systems. Electropneumatic (i/p) converters convert a DC input signal (control signal) directly into a pneumatic control signal (output signal pressure pst).
Limit switches consist of two inductive, electric or pneumatic contacts. They issue a signal whenever an adjusted limit is ex- ceeded or not reached.
Analog position transmitters assign a continuous 4 to 20 mA output signal to the valve travel. They signalize both end posi- tions of the valve “Valve OPEN” and “Valve CLOSED” as well as intermediate valve positions.
Solenoid valves convert binary signals issued by electric control equipment into binary pneumatic control signals.
Lock-up valves shut off the signal pressure line of a pneumatic actuator upon failure of supply air or when the supply air falls below an adjusted value. As a result, the actuator is blocked. The control valve remains in its last position until the fault has been eliminated.
The pneumatic remote adjuster is a precision regulator that can be adjusted precisely by hand.
Air reducing stations and supply pressure regulators are used to provide pneumatic measuring and control equipment with fil- tered supply air at a constant pressure.