Motorized Valve Actuator Achieves High Control Accuracy

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Typically, control valves for process control circuits are equipped with pneumatic actuators. The advantages of this design are rapid positioning speed and high resolution of the valve position, both being prerequisites in achieving a satisfactory standard of control accuracy. However, in this case the power supply can be a cause of concern since a supply of instrument quality air is needed for the actuation of the almost always required positioner.

In principle, an electrical power supply would be less problematical for this purpose, but the positioning of motorized control valves is very often slow and they are subject to very high hysteresis which makes them unsuitable for many control tasks.

The new motorized actuation from Schubert & Salzer Control Systems has overcome these drawbacks. The actuation of the 2030 series, comprising an electric stepping motor, a flexible coupling, a gearbox and stroke detection, was designed and manufactured to a high degree of precision. The stepping motor defines 400 steps per revolution. Every part of the gear box is made of steel, which enables a long service life. Each step of the motor results in a displacement of 1.5 μm. At the same time, the new 2030 actuator can achieve positioning speeds of up to 1.3 mm/sec.

The stroke detection for feeding back the position consists of metal guides, a linear potentiometer and limit switches with Hall sensors. By using a 12-bit AC/DC converter and a special interpolation process, the position of the stroke can be detected precisely with a resolution of about 3 µm. Although the sliding gate valves 8038 series combined with this 2030 actuator has a stroke of only 6 mm, the resolution and the level of control are very high, taking 4.5 seconds to open or close.

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