ENGN-3220 Engineering Measurements Introduction PDF

Introduction Measurement Systems ENGN-3220 Engineering Measurements Introduction Fall 2024 ENGN-3220: Engineering Measurements 1/15  Introduction Measurement Systems Introduction Diff...

Introduction Measurement Systems ENGN-3220 Engineering Measurements Introduction Fall 2024 ENGN-3220: Engineering Measurements 1/15  Introduction Measurement Systems Introduction Different types of measurements are at the core of the industry as well as our every day life. There is a need for accurate and cheap measurement devices. There are two types of measurement systems: 1 Metric System, (a.k.a. the SI units), e.g. km, meter, and kg 2 Imperial System, e.g. mile, yard, pound, ounce ENGN-3220: Engineering Measurements 2/15  Introduction Measurement Systems Introduction Fundamental SI Units ENGN-3220: Engineering Measurements 3/15  Introduction Measurement Systems Introduction Some Derived SI Units ENGN-3220: Engineering Measurements 4/15  Introduction Measurement Systems Measurement Systems A measuring system (or a measuring instrument) provides information about the value of some physical quantity or variable being measured. Elements of a Measuring System ENGN-3220: Engineering Measurements 5/15  Introduction Measurement Systems Measurement Systems: Primary Sensor The first element in any measuring system is the primary sensor; this gives an output that is a function of the measured quantity (i.e. the input applied to it). For most (but not all) sensors, this function is approximately linear. Some examples of primary sensors are a liquid-in-glass thermometer,a thermocouple, and a strain gauge. ENGN-3220: Engineering Measurements 6/15  Introduction Measurement Systems Measurement Systems: Primary Sensor A strain gauge is a device used to measure strain on an object. Most commonly, it consists of an insulating flexible backing which supports a metallic foil pattern. The gauge is attached to the object by a suitable adhesive. As the object is deformed, the foil is deformed, causing its electrical resistance to change. Strain Gauge ENGN-3220: Engineering Measurements 7/15  Introduction Measurement Systems Measurement Systems: Primary Sensor In the case of the mercury-in-glass thermometer, the output reading is given in terms of the level of the mercury, and so this particular primary sensor is also a complete measurement system in itself. However, in general, the primary sensor is only part of a measurement system. The types of primary sensors available for measuring a wide range of physical quantities will be presented in this course. ENGN-3220: Engineering Measurements 8/15  Introduction Measurement Systems Measurement Systems: Primary Sensor One or more secondary sensors are needed if the characteristics of the primary sensor are affected by the environmental conditions in which the primary sensor is operating. Secondary sensors measure the environmental conditions and allow the appropriate correction to be made to the measurements provided by the primary sensor. Such correction is done automatically in the so-called intelligent sensors. ENGN-3220: Engineering Measurements 9/15  Introduction Measurement Systems Measurement Systems: Conversion Element The second element of a measurement system is the conversion element. Conversion elements are needed where the output variable of a primary transducer (i.e. primary sensor) is in an inconvenient form and has to be converted to a more convenient form. For instance, the strain gauge has an output in the form of a varying resistance which cannot be easily measured and so it is converted to a change in voltage by a bridge circuit, which is a typical example of a conversion element. In some cases, the primary sensor and conversion element are combined, and the combination is known as a transducer. ENGN-3220: Engineering Measurements 10/15  Introduction Measurement Systems Measurement Systems: Signal Processing The third element of a typical measuring system is the signal processing element (analog or digital). The signal processing elements improve the quality of the output of a measurement system in some way. A very common type of signal processing element is the electronic amplifier, which amplifies the output of the primary transducer or conversion element. ENGN-3220: Engineering Measurements 11/15  Introduction Measurement Systems Measurement Systems: Signal Processing This is particularly important where the primary transducer has a low output. For example, thermocouples have a typical output of only a few millivolts. Other types of signal processing element are those that filter out induced noise and remove mean levels, etc. ENGN-3220: Engineering Measurements 12/15  Introduction Measurement Systems Measurement Systems: Transmission and Utilization Transmission of the measured quantities is needed in many practical situations where, for instance, we have numerous sensors whose output is to be aggregated in a “control-room”. Also, transmission of the measured quantities might be needed if there are physical inaccessibility or environmental unsuitability of the site. The measured quantities are usually displayed, recorded and used an inputs to automatic control systems. ENGN-3220: Engineering Measurements 13/15  Introduction Measurement Systems Measurement Systems: Transmission and Utilization Elements of a simple closed-loop control system ENGN-3220: Engineering Measurements 14/15  Introduction Measurement Systems References 1 Morris, Alan S., and Reza Langari. Measurement and instrumentation: theory and application. Academic Press, 2021. 2 Morris, Alan S., “Measurement and Instrumentation Principles”, 3rd Edition, Butterworth-Heinemann, 2001 3 https://en.wikipedia.org/wiki/Strain_gauge ENGN-3220: Engineering Measurements 15/15