Tag: Process instrumentation
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Instrument Installation – Mounting & Accessibility Guidelines
Before we look at the instrument installation – mounting and accessibility guidelines, it is important to ensure that installation is carried out using the best engineering practices by skilled professionals in Instrumentation and Control, Electrical, Industrial Automation, etc. These professionals should be fully conversant with the safety requirements and regulations governing a plant site. Generally…
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Demand Mode vs. Continuous Mode Safety Function
Demand Mode Safety Function Demand mode safety function is where a specified action is taken in response to process conditions or other demands. In the event of a dangerous failure of the SIF, a potential hazard only occurs in the event of a failure of the process of BPCS (Basic Process Control System). Demand mode…
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What are Virtual Instruments?
Virtual instruments (VI) are instruments based on computer software whose controls and displays are presented on a computer screen and whose operation and settings are controlled by the keyboard and mouse. Instead of purchasing a number of expensive, dedicated, standalone instruments, users find it less costly to purchase a computer with a multichannel, analog-to-digital converter…
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Instrument Piping Systems Installation Guidelines
The right installation ensures the long term instrument system reliability. In this article we look at the general guidelines for the installation of instrument piping systems. Piping Systems/Tubing Runs Before we can proceed, it is important to state the difference between piping and tubing; tubing can be regarded as thin-walled seamless pipe that cannot be…
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What is the Safety Instrumented Function (SIF)?
The safety instrumented function (SIF) is used to monitor a selected process parameter and takes an executive action to make the process safe, if certain limits are exceeded. An illustration of safety instrumented function in a process plant is shown below: The figure above illustrates a gas pipeline which supplies a feed to a power…
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Combustion & Temperature Control for a Direct-Fired Process Heater
The figure below shows the control schemes applied to a direct-fired process heater. From the diagram above, the heat from the burning fuel is applied directly to the tubes carrying the process fluid in similar way as the water tubes in a steam generator. This type of heater is usually used as a reboiler in…
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Passive vs. Active Sensors
Sensors are normally used to convert physical variables like pressure to signal variables. Sensors are also often termed to as transducers since they are devices that convert input energy of one form into output energy of another form. Sensors can be classified into two broad classes depending on how they interact with the environment they…
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Furnace Control System for a Rapidly Changing Demand
Let’s consider the figure below: 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 high (>) and a low (<) signal selector block (module). The second input to the high (>) selector is obtained from the measurement…
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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 a scale based on what is known as its dryness, which indicates how much “free”…
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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. From the figure above, the temperature of the heat-transfer medium is the parameter that sets the demand on the heating system. The amount of heat required is manually…