figure 7.1 elements of the final control operation. curtis johnson process control instrumentation...

FIGURE 7.1 Elements of the final control operation.

Curtis JohnsonProcess Control Instrumentation Technology, 8e]

Copyright ©2006 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458

All rights reserved.

FIGURE 7.2 A process-control system showing the final control operations.




FIGURE 7.3 An op amp circuit for Example 7.1.




FIGURE 7.4 A pneumatic amplifier or booster converts the signal pressure to a higher pressure or the same pressure but with greater gas volume.




FIGURE 7.5 Principles of the nozzle/flapper system.




FIGURE 7.6 Using a nozzle/flapper for a current-to-pressure converter.




FIGURE 7.7 The silicon-controlled-rectifier (SCR) symbol and characteristic curve.




FIGURE 7.8 An SCR for variation of load voltage using the half-wave circuit. Only the positive half-source cycle delivers power to the load.




FIGURE 7.9 A full-wave SCR circuit. The effective rms dc voltage applied to the load is greater than that of the half-wave because the entire cycle is used.




FIGURE 7.10 An optical coupler can be used to control triggering of the SCR from an external circuit.




FIGURE 7.11 Circuit for Example 7.3.




FIGURE 7.12 Voltages versus time for Example 7.3.




FIGURE 7.13 Two common symbols for the Gate Turn-off (GTO).




FIGURE 7.14 GTO circuit for Example 7.4.




FIGURE 7.15 A TRIAC can be triggered to conduct in either direction so a true ac voltage can be applied to a load.




FIGURE 7.16 The DIAC has a bipolar breakover voltage, ±VL. After the voltage reaches ±VL, the DIAC conducts like a diode.




FIGURE 7.17 The TRIAC can be triggered from the ac line using a DIAC.




FIGURE 7.18 This modification of the triggering circuit eases calculation of a solution for Example 7.4.




FIGURE 7.19 These are the voltage waveforms for Example 7.4.




FIGURE 7.20 Bipolar Junction Transistor (BJT) symbol and characteristic curves.




FIGURE 7.21 Operating the BJT in the linear mode.




FIGURE 7.22 Operating the BJT in the switched mode.




FIGURE 7.23 Power MOSFET symbol and characteristic curves.




FIGURE 7.24 IGBT symbol and characteristic curves.




FIGURE 7.25 A solenoid converts an electrical signal to a physical displacement.




FIGURE 7.26 A solenoid used to change gears.




FIGURE 7.27 Permanent magnet dc motor.




FIGURE 7.28 Three dc motor configurations.




FIGURE 7.29 A three-phase rectifier for high power dc motors implemented with SCRs.




FIGURE 7.30 Simple ac motor with a permanent magnet rotor.




FIGURE 7.31 The induction motor depends on a rotor field from current induced by ac field coils, as shown in FIGURE 7.30.




FIGURE 7.32 ac motor control with a variable amplitude, variable frequency circuit using power electronics.




FIGURE 7.33 An elementary stepping motor.




FIGURE 7.34 The four positions of the elementary stepper rotor.




FIGURE 7.35 Stepper with 8 rotor teeth and 12 stator poles. Note that the rotor teeth line up with the A poles. With the next step, the rotor teeth will line up with the B poles.




FIGURE 7.36 A direct pneumatic actuator for converting pressure signals into mechanical shaft motion.




FIGURE 7.37 A reverse-acting pneumatic actuator.




FIGURE 7.38 A hydraulic actuator converts a small force, F1 , into an amplified force, FW .




FIGURE 7.39 A hydraulic servo system. The process-control system provides input of the setpoint to the hydraulic servo.




FIGURE 7.40 An example of a mechanical control element in the form of a hopper valve and conveyor.




FIGURE 7.41 A continuous-operation paper-thickness-controlling system using mechanical final control elements.




FIGURE 7.42 Basic control system for motor speed using a tachometer to sense the motor speed.




FIGURE 7.43 A control system varies the rotation rate of a reaction kiln based upon temperature.




FIGURE 7.44 Control of heat into a reaction vessel through an electrical power amplifier.




FIGURE 7.45 A basic control-valve cross-section. The direction of flow is important for proper valve action.




FIGURE 7.46 A pneumatic actuator connected to a control valve. The actuator is driven by a current through an I/P converter.




FIGURE 7.47 Three types of control valves open differently as a function of valve stem position.




FIGURE 7.48 Feed control to a distillation column based on temperature.




FIGURE 7.49 Figure for Problem 7.4.




FIGURE 7.52 Figure for Problems S7.2 and S7.3.




FIGURE 7.53 Figure for Problem S7.3.




figure 7.1 elements of the final control operation. curtis johnson process control instrumentation...

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