Tag: process control
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Centralised vs. Decentralised Control Systems
Centralised control is usually carried out via computer software, having as inputs all the available sensors and producing signals for all the available actuators in the system. This control strategy is the most powerful, at least in theory, capable of … Read more
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Actuators as Automation Components
An actuator is normally controlled by the controller. The actuator, in turn, changes the output of an automated process. The actuator in an automated process may in actual fact be several actuators, each of which provides an output that … Read more
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Hierarchical Control Strategies for a Process Plant
In a process plant, we typically have a number of control goals that require different algorithms and types of information from the process; from the level closest to the process to the plant-wide control. All these activities ought to be … Read more
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Manipulating Devices & Actuators in Process Instrumentation
The function of the manipulating device is to influence the process variable. Its main purpose is to regulate a mass or energy flow. Mass flows can be either in gaseous or liquid state e.g. steam, natural gas, fuel oil, etc.… Read more
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Analog vs. Digital Controllers
Analog signals pass continuously through a full range of values for example a measuring device converts the process variable (PV), say temperature, into a signal corresponding to this temperature. Each temperature value corresponds to a value of the electrical signal. … Read more
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Steam-heated Reboiler Control System
When steam-heated reboilers are used in distillation columns and the heating medium is steam, a flow control loop for the steam will typically be incorporated. The control valve can then be placed either in the steam or condensate line. Steam … Read more
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Furnace Control System for a Rapidly Changing Demand
Let’s consider the figure below: Figure 1.0 Typical single-fuel cross-limited combustion control system In the system above, the output of temperature controller TC represents the process demand, and this signal is applied as one of the inputs, each to a … Read more
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Industrial Process Temperature Control System
Let’s consider the industrial process control system shown below: Figure 1.1 Industrial Process Temperature Control System The requirement is to control the temperature ϴ in the tank. The voltage r, obtained from a potentiometer, is calibrated in terms of the … Read more
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How to Perform Mass flow Measurements with DP sensors
Let’s assume we are measuring flow by differential-creating primary device for example an orifice plate and a DP cell as illustrated in Figure 1 below: Figure 1 Liquid mass flow measurement The differential head across the primary device is corrected … Read more
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Instrumentation and Controls for a Steam Desuperheater
A steam generator is an item of plant equipment that is found in almost every manufacturing site, and its output of steam has many critical uses in a variety of production processes. Steam has been assigned a measurement quality and … Read more