ELE 312 MEASUREMENTS AND INSTRUMENTATION by engr Dr
ELE 312 MEASUREMENTS AND INSTRUMENTATION by engr. Dr. (mrs. ) n. t. surajudeen-bakinde department of electrical and electronics engineering faculty of engineering and technology university of ilorin, ilorin LECTURE 1 Introduction to measurement AND instrumentation
OUTLINE �Introduction to Measurement units o Measurement system applications o Elements of a measurement system o Choosing appropriate measuring instruments o
Introduction to Measurement techniques have been of immense importance since the start of human civilization, when were first needed to regulate the transfer of goods in barter trade to ensure that exchanges were fair. Measurement Units They also called the International System of Units, or SI. Units of measure in the metric system. Units of physical quantities can be expressed in terms of fundamental units or derived units.
Fundamental SI Units �These are units that can neither be derived from one another nor can be resolved into any other units. They are independent of one another. There are seven(7) fundamental units. Derived SI Units �These are units that are derived from the fundamental units. They are dependent on fundamental units.
Table 1. 1 Shows Fundamental and Derived Units (a) Fundamental Units Quantity Length Standard unit metre Symbol m Mass kilogram kg Time second s Electric current ampere Temperature kelvin K Luminous intensity candela cd Matter mole mol A
(b) Supplementary Fundamental Units Quantity Standard unit Plane angle radian Solid angle steradian (c) Derived Units Quantity Standard unit Symbol Acceleration metre per second squared m/s 2 Force Newton N Pressure Newton per square metre N/m 2 Torque Newton metre Nm Work, energy, heat joule J Acceleration metre per second squared m/s 2 Derivation formula kg m/s 2 Nm
Measurement system applications Present-day applications of measuring instruments can be classified into three major areas. Ø The first of these is their use in regulating trade, applying instruments that measure physical quantities such as length, volume and mass in terms of standard units. Ø The second application area of measuring instruments is in monitoring functions as they provide information that enable human beings make decisions. Whilst there are thus many uses of instrumentation in our normal domestic lives, but majority of the monitoring functions exist to provide information necessary to allow us to control some industrial operation or process. Another important use of monitoring instruments is in calibrating the instruments used in the automatic process control systems described below.
�Use as part of automatic feedback control systems forms the third application area of measurement systems. Figure 1. 1 shows a functional block diagram of a simple temperature control system in which the temperature Ta of a room is maintained at a reference value Td. The value of the controlled variable Ta, as determined by a temperaturemeasuring device, is compared with the reference value Td, and the difference ‘e’ is applied as an error signal to the heater. The heater then modifies the room temperature until Ta=Td.
Fig 1. 1 Elements of a simple closed-loop control system.
Elements of a measurement system Ø The term measuring instrument is commonly used to describe a measurement system, whether it contains only one or many elements. A measuring system exists to provide information about the physical value of some variable being measured. Figure 1. 2 Shows several components of a measuring system. The elements in any measuring system are as follows: q A primary sensor, which gives an output that is a function of the measurand (the input applied to it). q Variable conversion elements. q Signal processing elements.
In addition to these three components just mentioned, some measurement systems have one or two other components, namely: q. Transmitter q. Signal transmission is needed when the observation or application point of the output of a measurement system is some distance away from the site of the primary transducer.
Choosing appropriate measuring instruments The starting point in choosing the most suitable instrument to use for measurement of a particular quantity in a manufacturing plant or other system is the specification of the instrument characteristics required, especially parameters like q. Desired measurement accuracy, q. Resolution, q. Sensitivity and q. Dynamic performance
Some other important factor are: q. Environmental conditions qcost and q. The extent to which the measured system will be disturbed during the measuring process is another important factor in instrument choice.
Practise Questions � Practise all questions at the end of Chapter 1 of the text book. Measurement and Instrumentation Principles by Alan S. Morris, Third Edition, Published by Butterworth Heineman , 2001.
- Slides: 14