Tag: Process automation
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How PLC Systems are Protected from Plant Voltages
Internally a PLC typically operates at 5 V dc. The external devices such as solenoids, limit switches, motor starters, etc. operate at voltages up to 110 V ac. The mixing of these voltages will cause irreparable damage to the PLC … Read more
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Key Requirements for Industrial Control Computers
A computer is often used as part of a control system. The input data is typically from the operator’s commands and signals from the plant (flows, pressure, temperatures, limit switches, etc.). The output data comes in form of … 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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The Instrumentation for Furnace Control
The figure below shows a typical basic furnace used to raise the temperature of a heat-transfer medium that is used on other equipment in a plant process. Figure: Single-fuel combustion control system From the figure above, the temperature of the … Read more