Instrumentation-Training-Tutorial2

Instrumentation-Training-Tutorial2 - INSTRUMENTATION AND...

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D.J.Dunn 1 INSTRUMENTATION AND CONTROL TUTORIAL 2 – SENSORS AND PRIMARY TRANSDUCERS This tutorial provides an overview of instrument sensors used in process and automatic control. It is useful to anyone studying measurement systems and instrumentation but it is provided mainly in support of the EC module D227 – Control System Engineering. This tutorial is mainly descriptive. Control is a broad concept and the following might apply to an automated system such as a robot or to a process control system such as a pneumatic valve controlling the flow of steam in a pipe. On completion of this tutorial, you should be able to do the following. Explain a basic measurement system. Explain the basic working principles of a variety of temperature sensors. Explain the basic working principles of a variety of pressure sensors. Explain the basic working principles of a variety of speed transducers. Explain the basic working principles of a variety of flow meters. Explain the basic working principles of a variety of force gauges. Explain the basic working principles of a variety of displacement gauges. Explain the basic working principles of a variety of level (depth) gauges. Explain in some detail the theory and use of strain gauges. In order to complete the theoretical part of this tutorial, you must be familiar with basic mechanical and electrical science. www.PAControl.com

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D.J.Dunn 2 1. INTRODUCTION A basic instrument system consists of three elements: i SENSOR or INPUT DEVICE ii SIGNAL PROCESSOR iii RECEIVER or OUTPUT DEVICE This tutorial is devoted to input devices but you can never separate it from the rest of the system as in many cases they are all integral (e.g. a mechanical pressure gauge incorporates all of these elements). A block diagram of a basic system is shown but they are usually more complex. Figure 1 Most modern analogue equipment works on the following standard signal ranges. Electric 4 to 20 mA Pneumatic 0.2 to 1.0 bar Older electrical equipment use 0 to 10 V. Increasingly the instruments are digital with a binary digital encoder built in to give a binary digital output. Pneumatic signals are commonly used in process industries for safety especially when there is a risk of fire or explosion. The advantage of having a standard range or using digital signals is that all equipment may be purchased ready calibrated. For analogue systems the minimum signal (Temperature, speed, force, pressure and so on ) is represented by 4 mA or 0.2 bar and the maximum signal is represented by 20 mA or 1.0 bar. This tutorial is an attempt to familiarise you with the many types of input sensors on the market today. Usually such sensors are called PRIMARY TRANSDUCERS. Things that we commonly measure are:
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Instrumentation-Training-Tutorial2 - INSTRUMENTATION AND...

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