Author: John Mulindi
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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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Input & Output Modules of a PLC – Types & Applications
The input/output modules act as the signal interface between the monitoring sensors and actuators, and the controller. Additional they provide electrical isolation, if needed, to convert the input signals into an electronic format appropriate for evaluation by the controller; the I/O modules provide the memory storage and format the output signals for displays and control…
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How to Calibrate an AC Ammeter & an AC Voltmeter
An instrument calibration is performed by comparing its reading with that of a more accurate instrument when both instruments are measuring the same quantity. In this case, the more accurate instrument is employed as a standard for comparison purposes. To calibrate ac ammeters and ac voltmeters, ac supply and an ac standard instrument must be…
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The IEEE-488 Instrumentation Bus (GPIB)
A bus in computer systems means a collection of unbroken signal lines that interconnect computer modules; these connections are usually made by taps on the lines. Examples of parallel bus architectures and protocols include: IBM PC bus (IBM PC/XT/AT), the Intel iSBX bus, the MicroVAX Q-bus, the Intel Multibus (IEEE-796 bus), the IEEE-488 instrumentation bus…
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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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4 Common Arrangements of Distribution Substations
The general technique of supplying large quantity of power to factories or other complexes is by means of high-voltage (HV) supply, typically at 11 kV, occasionally at 6.6 kV. The installation consists of a main substation at the point of entry, with HV cables to supply subsidiary substations located near load centres. Where necessary, it…
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AC Transmission and Distribution Systems
Electrical energy is generated, transmitted and distributed in the form of AC. Since, alternating voltage can be changed in magnitude by means of a transformer; it is possible to transmit AC power at high voltage which reduces the current in the conductors hence the line losses. The conductors system is the means by which electric…
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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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Gunn Diode – Features, Operation & Applications
Features of a Gunn Diode A gunn diode is made up of only N-type semiconductor which is typically sandwiched between two metal conductors. The central section is usually lightly doped N– surrounded by heavily doped N+ layers. The central section is N-gallium arsenide whereas the two outer sections undergo epitaxial growth from GaAs with increased…