Fundamentals of Measurement Technology (8) Prof Wang Boxiong
Fundamentals of Measurement Technology (8) Prof. Wang Boxiong
Chapter 4 Acquisition of measurands
Chapter 4 Acquisition of measurands
4.1 Introduction Transduction implies the conversion of a measured or observed quantity, the measurand, into an electrical, hydraulic pneumatic, or any other output by means of a transducer or sensing element The device employed to accomplish this conversion is known as a transducer or a sensing element(sensor)
4.1 Introduction • Transduction implies the conversion of a measured or observed quantity, the measurand, into an electrical, hydraulic, pneumatic, or any other output by means of a transducer or sensing element. • The device employed to accomplish this conversion is known as a transducer or a sensing element (sensor)
4. Introduction Transducer and sensing element are two different concepts >Sensing element: the element or unit which directly senses and converts the measured quantities > Transducer: the whole device consisting of a sensing element with its associated auxiliary components and circuits, the sensor or sensing element being the kernel component
• Transducer and sensing element are two different concepts. ➢Sensing element : the element or unit which directly senses and converts the measured quantities ➢Transducer : the whole device consisting of a sensing element with its associated auxiliary components and circuits, the sensor or sensing element being the kernel component 4.1 Introduction
4. Introduction Since we are mainly interested in signal conversion laws of different devices and do not care for whether it is a sensing element or a transducer, so we do not distinguish between a transducer and a sensing element and generally refer to such a device as a transducer if no additional explanation is given Since a transducer is located at the input of measuring instrument, its quality will influence directly the performance characteristic of the whole instrument
• Since we are mainly interested in signal conversion laws of different devices and do not care for whether it is a sensing element or a transducer, so we do not distinguish between a transducer and a sensing element and generally refer to such a device as a transducer if no additional explanation is given. Since a transducer is located at the input of measuring instrument, its quality will influence directly the performance characteristic of the whole instrument. 4.1 Introduction
4.1 Introduction We hope to acquire measurands with no errors If the characteristic curve is a straight line the transducer is known as a linear transducer But in most cases the characteristic of a transducer is not a linear one and the transducer is called a nonlinear transducer
• We hope to acquire measurands with no errors. • If the characteristic curve is a straight line, the transducer is known as a linear transducer. • But in most cases, the characteristic of a transducer is not a linear one, and the transducer is called a nonlinear transducer. 4.1 Introduction
4.2 Classifications of transducers Different ways are employed for the classification of transducers One way is to classify transducers in terms of measured quantities Force transducers Ⅴ elocity transducers Temperature transducers
• Different ways are employed for the classification of transducers – One way is to classify transducers in terms of measured quantities: • Force transducers • Velocity transducers • Temperature transducers 4.2 Classifications of transducers
4.2 Classifications of transducers Another way is to make the classification in terms of the operating principles of transducers or the signal converting principles in transduction Structure-type transducers: transduce signals by its structural variations Capacitive transducer: changes capacitance by varying gaps between two electrode plates or the common area of the two plates Sliding-contact resistive transducer: changes resistance by changing the length of wire by moving the slide
– Another way is to make the classification in terms of the operating principles of transducers or the signal converting principles in transduction • Structure-type transducers : transduce signals by its structural variations ▪ Capacitive transducer : changes capacitance by varying gaps between two electrode plates or the common area of the two plates ▪ Sliding-contact resistive transducer : changes resistance by changing the length of wire by moving the slide 4.2 Classifications of transducers
4.2 Classifications of transducers Physical-property-type transducers based on the change in physical properties of its sensing element material to realize signal conversion Pressure accelerometer: based on the piezoelectric effect of its quartz crystal material a Photo-sensitive resistor: changing its resistance when exposed to light
• Physical-property-type transducers : based on the change in physical properties of its sensing element material to realize signal conversion ▪ Pressure accelerometer : based on the piezoelectric effect of its quartz crystal material ▪ Photo-sensitive resistor : changing its resistance when exposed to light 4.2 Classifications of transducers
2 Classifications of transducers a transducer is also an energy converting element which converts one form of the measured energy into another form of energy to a predefined accuracy or into the same energy form of other values We also divide transducers into energy-converting and energy-controlling transducers An energy-converting transducer( passive transducer) operates with the energy from the measurand An energy-controlling transducer(active transducer)is powered by external energy source, the energy variations being controlled by the measurand
• A transducer is also an energy converting element, which converts one form of the measured energy into another form of energy to a predefined accuracy or into the same energy form of other values. • We also divide transducers into energy-converting and energy-controlling transducers. • An energy-converting transducer ( passive transducer) operates with the energy from the measurand. • An energy-controlling transducer (active transducer) is powered by external energy source, the energy variations being controlled by the measurand. 4.2 Classifications of transducers