Category: Instrumentation

System Control Diagram

During plant development the process engineers specify the process through the development of the P&IDs (Piping & Instrument Diagram). Throughout this effort, the process engineers depict the total plant behavior. However, the P&IDs provide limited facilities for documentation of the overall functionality and operational aspects of the plant. It’s the control system engineer’s task to […]

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Continuous Analyzers

Other analytical instruments perform continuous analyses of a process stream for a specific parameter such as oxygen content, gas density, etc. Some continuous analyzers pump or flow a sample through a detector cell. Others place the detector element directly in the process stream. The methods of detection vary widely and may include the use of […]

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Cyclic Analyzers

Many analytical instruments are cyclic, or sampled data devices, such as the chromatograph. These automatically take a sample of the process stream, analyze it, and transmit the results to the desired device. Since most analysis cycles take from one to 20 minutes to complete, considerable “dead-time” is introduced into a control loop using this type […]

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Fieldbus

Fieldbus technology is the basis of the next generation of process control. It is an all digital, serial, two-way communication system that interconnects devices in the field such as sensors, actuators and controllers. Fieldbus is a Local Area Network (LAN) for instruments, with built-in capability to distribute a control application across the network. It has […]

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Digital Computers

Digital computers are attractive for many applications in the process control field because of their speed, accuracy, flexibility, display and logging capabilities, and ability to perform complex calculations and store and transmit vast amounts of data. Digital computers come in almost any size or shape, ranging from tiny single board special purpose devices to large […]

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Analog Computers

A process control analog computer is composed of electronic modules such as amplifiers, summers, controllers, multipliers, dividers, square and square root devices, lead and lag modules, limiters, and special dead-time devices. These modules are based around the integrated circuit operational amplifier and are interconnected to implement the desired control strategy. The process control analog computer […]

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Temperature Transmitters Calibration

Temperature transmitters are by far the most difficult to calibrate because of the difficulty in generating precise controlled temperatures. Calibration of pneumatic filled-bulb type temperature transmitters is normally a lengthy test bench procedure. Temperature calibrators for generating process temperatures are of three varieties: (1) electrically heated direct air, (2) hot oil bath, and (3) a […]

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Differential Pressure Transmitters Calibration

Differential pressure level transmitters are usually calibrated with a mercury manometer or a low level pneumatic calibrator. If remote seals are used, the seal paddle relative elevation should be the same during calibration as when the transmitter is installed. Zero elevation and suppression can be done with a bench calibrator, but if the transmitter has […]

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