Analog and Digital Controllers

The part of the control loop that we will spend most of our time with in this book is the controller. The job of the controller is to compare the process signal from the transmitter with the setpoint signal and to send out an appropriate signal to the control valve. We will go into more detail about the performance of the controller in Sec. 7.2. In this section we will describe what kind of action standard commercial controllers take when they sec an error. 

Analog controllers use continuous electronic or pneumatic signals. The controllers see transmitter signals continuously, and control valves are changed continuously. 

There are three basic types of controllers that are commonly used for continuous feedback control. The details of construction of the analog devices and the programming of the digital devices vary from one manufacturer to the next, but their basic functions are essentially the same. 

PROPORTIONAL ACTION. A proportional-only feedback controller changes its output signal, CO, in direct proportion to the error signal, E, which is the difference between the setpoint, SP, and the process measurement signal, PM, 

Action of a feedback controller, (a) Proportional (b) integral (c) ideal derivative. 

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Figure A.8 Analog and digital control of a mixing process.

In the control room, process control encompasses the selection and installation of panel-mounted alarms, switches, recorders, and controllers, as well as Program Logic Controllers (PLC) and Distributed Control Systems (DCS). These include analog and digital input/output hardware, software to implement control strategies. 

Reactor process monitoring, measurement and control systems Reactor process monitoring, measurement and control systems, sub-systems and components. All analog and digital process control computers and hydraulic and pneumatic process monitoring and control instruments and equipment. 

Today, computer simulation is used extensively to analyze the dynamics of chemical processes or aid in the design of controllers and study their effectiveness in controlling a given process. Analog and digital computers have been used for this purpose, with the emphasis having shifted almost entirely in favor of the digital computers. 

Where modem autoclaves can provide analog and digital records of temperature and pressure against time, both should be provided in the permanent record and inspected diligently before product release. Manual transcription of process conditions from dial or digital gauges is not an acceptable approach to control of autoclaves. 

The primary goal of a microfluidic amplifier is to increase the pressure at a set of outlet ports by modulating some control pressures. Microfluidic amplifiers can be primarily classified into two types analog and digital. The first type uses the effect of jet interaction, whereas the second type makes use of the wall attachment effect in a fluid. 

Managing aging analog and digital instrumentation and control systems. 

Modem implementations of controllers are not analog but digital due to the widespread use of computers and digital control systems. Digital control algorithms can... 

HGH (France) TERMASCAN Modular optomechanically scanned, thermoelectrically cooled, PbSe or HgCdTe detectors, 3-5 pm, high- resolution analog and digital outputs operates with control system host computer. 

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