Electric failsafe actuator
June 2005
Valves, Actuators & Pump Control
Yokogawa SA is the sole distributor for Kinetrol in Africa. One of the products it offers is an electric failsafe actuator. This is an actuator that works with an electric hydraulic control system. This makes a solution for areas where there are no pneumatic supplies to operate a pneumatic actuator.
An electronic circuit and feedback potentiometer are fitted inside the standard actuator control box. The circuit includes a high stability linear comparator, which switches the actuator pump and solenoid valves via solid-state mains switches in response to the difference between the actual position measured by the potentiometer and the intended position given by the 4 to 20 mA signal. Limit switches prevent the actuator driving against its own end stop, whatever the signal may be. The positioner mains switches are optically isolated from the low voltage DC control circuit, which is electrically isolated from the rest of the actuator.
The feedback potentiometer is a conductive plastic servo-type unit driven by a backlash-free drive. The positioner circuit is mounted inside an insulating polymer box for safety; it is fitted with screwdriver adjustable potentiometers to allow customer turning of zero, gain and bandwidth.
The efficient design of the Kinetrol EHD actuator allows a high start frequency to be achieved, without overheating. The positioner is available on fail-safe spring return and double-acting units, and gives accurate, linear low hysteresis performance with excellent thermal stability. The intrinsic stiffness of the hydraulic system together with the backlash-free design of the Kinetrol vane actuator makes this positioner tolerant of varying or unstable loads. The complete absence of separately mounted enclosures makes installation neat, simple and economical - all external connections for power, signal and limit switches are made to normal connector block in the control box. Applications for Kinetrol Actuators would include any ¼ turn applications eg, ball valves, butterfly valves and dampers. Kinetrol also has a range of pneumatic actuators for ¼ turn applications.
For more information contact Zjaan Haarhoff, Yokogawa SA, 011 681 2560, [email protected], www.kinetrol.com
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