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2 Design and principle of oper-
ation
The Type 3768 Limit Switch is designed forattachment to pneumatic control valves. It isfitted with inductive contact limits that issue alimit signal whenever the valve travel ex-
ceeds or falls below a certain preset limit, es-pecially when the valve has reached one ofits end positions. The limit signal is transmi-ted to alarm or indicating equipment.
The limit switch can also available be fittedwith a solenoid valve to move the valve to itsfail-safe position.
The limit switch is designed either for directatachment to SAMSON Type 3277 Actua-.tors or for attachment to actuators accordingto IEC 60534-6 (NAMUR) using an adapterhousing.
The valve travel is transmited by the pin
(1.1) to the lever (1) and converted intoa ro-tary motion. The shaft (2) transfers this rota-ry motion to two adjustable meta
which operate the associated proximityswitches (5).
The operation of the inductive limit switchesrequires switching amplifiers to be connectedin the output circuit (see section 4).
Version with solenoid valve
Version with solenoid valve
When fited with a solenoid valve, the con-trol valve can be moved to the fail-safe posi-tion, regardless of the control signal issuedby the control equipment. IF a control signalcorresponding to the binary signal '0' (OFF)is applied to the input, the signal pressure Psris shut off and the actuator is vented. The ac-tuator springs move the valve to its fail-safeposition.
When a control signal corresponding to thebinary signal 'l' (ON) is applied to the in-put, the signal pressure pa is applied to theactuator, allowing the valve to move accord-ing to the input signal issued by the controlequipment.
