Normally, control valves for use in 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 motorised control valves is very often slow and they are subject to very high hysteresis which makes them unsuitable for many control tasks.
New motorised actuation from Schubert & Salzer
The new motorised actuation from Schubert & Salzer Control Systems has overcome these drawbacks as it sets new benchmarks in terms of resolution and positioning speed. The actuation of the 2030 series, comprising an electric stepping motor, a flexible coupling, gear box and stroke detection, is designed and manufactured to a high degree of precision. The stepping motor defines 400 steps per revolution. Every part of the gearbox is made of steel which guarantees a long service life. Therefore, each step of the motor results in a displacement of a mere 1,5 m. At the same time, the new 2030 actuator can achieve positioning speeds of up to 1,3 mm/sec.
Furthermore, the stroke detection for feeding back the position consists of extremely sturdy 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 m. Although the sliding gate valves 8038 series combined with this 2030 actuator has a stroke of only 6 mm, the resolution and, therefore, the level of control, are very high, taking just 4,5 seconds to open or close. With a standard dead band setting of a mere 0,2 %, even with these small strokes, this motorised actuator achieves a repeatability accuracy of up to 0,1 %. These values for resolution and repeatability are better by a factor of 10 than those of valve actuators available up to now on the market and are setting new standards for motorised actuators – in particular where small strokes are involved.
Quick commissioning and sturdy construction
Furthermore, this motorised actuator offers self adaptation for quick commissioning.
By pushing a button, the actuator searches for the end positions of the valve. As a result, it takes the operator just a few seconds to adapt the actuator to the particular valve. Naturally, this can also be done by using the optionally available communications software DeviceConfig. Moreover, the software also offers the opportunity to define all parameters extremely easily. Monitoring and self diagnostic functions optimise operating reliability and simplify preventive maintenance.
Its sturdy aluminium body and separate terminal box are ideal prerequisites for harsh operating conditions, which are reflected also in the high IP67 protection level. The terminals are easily accessible and enable connections for 230, 115 and 24 VAC or 24 VDC power supplies, and set point signal connections of 0-20 mA or 0-10 V. A binary actuation (On/Off/Stop) via a 24 VDC signal is also available, as is a separate manual operation mode.
The new Schubert & Salzer Control Systems motorised valve offers high speed and precision for control processes involving neutral to highly aggressive media flows in the chemical industry or process engineering.
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