Author: John Mulindi
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How cycloconverter is used as a direct frequency converter
The cycloconverter provides direct ac to ac transformation with control over both the output voltage magnitude and output frequency. It employs phase-angle-controlled bridges to synthesize voltages. The most common form is the three-phase to three-phase converter illustrated below: Each output needs two three-phase thyristor bridges. One bridge is used to synthesize positive voltages at the…
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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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Basic Features of a Hartley Oscillator
The primary LC oscillator circuit does not have the option of controlling the amplitude of the oscillations. A weak electromagnetic coupling between first inductive coil L and second inductive coil L2 results in insufficient feedback and the oscillations would eventually die away to zero. Equally, a strong feedback causes the oscillations to increase in amplitude…
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Industrial Process Temperature Control System
Let’s consider the industrial process control system shown below: The requirement is to control the temperature ϴ in the tank. The voltage r, obtained from a potentiometer, is calibrated in terms of the desired temperature ϴc. This voltage represents the input quantity to the feedback control system. The actual temperature ϴ, the output quantity, is…
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What is a Microprocessor Clock?
The CPU clock dictates how fast the processor can process the data, and a microprocessor having a clock speed of 3 MHz means that it can process data internally 3 million times a second at every clock cycle. The crystal quartz oscillator is the most appropriate frequency determining device in virtually all microprocessors, microcontrollers, PICs…
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Basic Features of Crystal Oscillators
The crystal oscillators are implemented using the piezo-electric effect. This is actually realized when a voltage source is applied to a small thin piece of crystal quartz. The quartz crystal begins to change shape. This piezo-electric effect is the property of a crystal by which an electrical charge produces a mechanical force by changing the…
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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: The differential head across the primary device is corrected for temperature variation in the first calculation block, but there is no need for pressure correction because a liquid is virtually…
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Key factors to consider when selecting flowmeters
Selecting the right flow measuring instrument for a given flow application can be a challenging task given the numerous measurement techniques available. In this article, we look at some of the key pointers that can help you in the decision making process. What is discussed here isn’t exhaustive in itself but should act as some…
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Optical Time Domain Reflectometer (OTDR)
The commonly employed technique for analysing the state of a fibre optic is to test it with an Optical Time Domain Reflectometer (OTDR). The OTDR uses backscattered light of the fibre to imply loss. The OTDR works is similar way to RADAR, sending a high power laser light pulse down the fibre and looking for…
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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”…