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Process Enginering Equipment Handbook - Claire W.

Claire W. Process Enginering Equipment Handbook - McGraw-Hill, 2002. - 977 p.
ISBN 0-07-059614
Download (direct link): processengineeringequipmenthandbook2002.pdf
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A-40 Agitators
Proportional and dynamic conversion of electrical control signals (0/4 ... 20) mA into power, regulating pressure, regulating stroke and rpm is achieved with highly versatile modular component technology:
Control unit: magnetic drive with integrated control electronics in standard and Ex-protection housings.
Sensor technology: stroke (B/s) and rpm sensors (B/n).
Servo valve to control discharge quantities.
3 Pressure reduction valves.
? Various operating cylinders.
FIG. A-29 Modular component units used for conversion of electrical control signals. (Source: J.M. Voith GmbH.)
Agitators A-41
Basic item of the modular assembly is a power-regulated electromagnet consisting of the following components: magnet housing, coil, anchor with driving rod, and the control electronics.
A regulator is used to keep the degree of linear force applied to the anchor at a rating proportional to the input signal.
This ensures that the output (force depending on pressure output) is not affected by adverse influences such as hysteresis, air gap etc (DBP-2019345).
Forces are achieved that are applied directly via the driving rod, i.e., without any hydraulic amplification, to a control piston or a stroke valve.
The diagram below shows how the neutral position magnetic force on one side of the piston is checked by a force proportional to the reduced pressure ??. The result is a direct and constant match between the input signal and the reduced pressure.
Control unit
Nominal value Magnetic
(0/4...20) mA force Pressure (PA)
fHo~
ft—^ ‘-t ,
tx!
Range matching
Main components in control unit
1 Manual adjustment
2 Spring
3 Housing
4 Anchor
5 Magnet coil
6 Sensor
7 Actuating rod
8 Socket for connecting cable
9 Control electronics
Hydraulic force (Pa x A*)
Hydraulic unit
FIG. A-30 How actuators function: power-regulated electromagnet. (Source: J.M. Voith GmbH.)
A-42 Agitators
The section diagram illustrates the main features of control regulator functioning:
¦ Drive and control pistons with failsafe spring return.
¦ Internal oil circulation as part of closedown process (rapid closedown < 0.1 sec).
¦ Inductive stroke pick-up (7) with clamp magnet coupling (8).
¦ 400 N magnet drive (1) with integrated control electronics for control pistons (3) and position of piston rod (14)
FIG. A-31 Control regulator functioning and main features. (Source: J.M. Voith GmbH.)
Agitators A-43
Electrically controllable pressure regulating valve (with or without PID controller)
consisting of ?? and El-Converts (0/4...20) mA in (0/7);
(0/16); (0/60) bar (??- 50,^)
A directly applied controlled magnetic force F is brought into exact counterbalance with a proportional hydraulic force. The appropriate output pressure in relation to the input signal iE is controlled by X0 and X1. Conversionis effected with a loss of < = 0.1%.
In the version incorporating a PID controller you can compensate for pipeline pressure losses or you can control valve positions and turbine rpm.
Parameters without integrated PID controller
Xq = pressure pA at / j = 0 or 4 mA X, = pressure pA at lg = 20 mA
Parameters with integrated PID controller
(e.g. for position regulation)
Kp = proportional amplification TN = integral action time TD = deviractive action FM = gate valve centre x0 = position of motor at it min x, - position of motor ati? max is - remote display (position)
Xo x, TP El
Directly controlled gate valve
(with or without PID controller)
consisting of B1 and Controls passage cross-sections (flow control):
(12-20) mA = (0-200) mm2 inlet (12- 0 ) mA = (0-700) mm2 return
With gate valves a controlled magnetic force F is brought into counterbalance with an elastic force, i.e., a dependent force. The input signal iE is allocated the appropriate cross-section for the valve with X0 and X1. The decisive feature is hysteresis-free control in the area around the dydraulic middle position. Symmetrical or asymmetrical controlled cross-sections A can be controlled directly up to 700 mm2. The Turcon® CTo version with protection against over-speed rpm is available as a specially adapted gate valve.
FIG. A-32 Control regulator valves. (Source: J.M. Voith GmbH.)
A-44 Agitators
(KP,TN,TD, FM)
V
Electrically controlled regulator
consisting of ??- ?? Efl El
In principle the way that regulators are controlled is via a gate valve for which the magnetic drive has both a magnetic force controller and a superimposed position regulator. The set size of the position regulator acts as the reference value for force control. The input signal iE—in this example the reference value for regulation—is allocated via X0 and X1 the appropriate stroke from the drive piston which is displayed by a (4...20) mA signal. If the control deviation is excessive this is displayedvia a potential-free optocoupler output. In order to linearize flow lines on flaps and valves the control electronics can be enlarged by the addition of a 10-stage function indicator.
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