Figure 714 shows the construction of piezo electric

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Figure 7.14 shows the construction of piezo electric transducer and the equivalent circuit of the crystal. Since the transducer has a very good high frequency (HF) response, its principal use is in HF accelerometers . When an alternating voltage is applied to a crystal, it will vibrate at its natural resonance frequency.
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47 Piezoelectric Transducer Figure 7.14: Piezoelectric Transducer
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48 Piezo Electrical Transducer Advantage: Needs no external power source self generating. Disadvantage: Can not measure static condition since it is a dynamic responding sensor. Application: HF accelerometers
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49 Temperature Transducer Temperature is one of the most widely measured and controlled variable in industry. Most of the temperature transducers are of Resistance Temperature Detectors (RTD), Thermistors and Thermocouples. RTD and Thermistor are passive devices whose resistance changes with temperature, so they need an electrical supply to give a voltage output. Thermocouples are active transducers and are based on the principle of generation of thermoelectricity.
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50 Thermal Energy 1) Solid The individual atom or molecules are strongly attracted and bonded to each other. Non-vibrate molecules – zero thermal energy (W TH =0) Vibrate molecules – finite thermal energy (W TH > 0) 2) Liquid The atoms or molecules move about in the material. 3) Gas The atoms or molecules move freely and randomly throughout the containing volume. © 2004, NORIZAN MOHAMAD.
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51 Temperature Temperature is the measurement of the average energy per molecule of a material. Temperature is measured using several temperature units such as Kelvin and Celcius. 1) Absolute temperature scales : This scale assigns a zero temperature to a material that has no thermal energy (no molecular vibration). The two common absolute scales are Kelvin (K) and Rankine ( o R). © 2004, NORIZAN MOHAMAD.
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52 Temperature The relationship between degree Kelvin and Rankine : where T is the temperature value. 2) Relative temperature scales : This scale differ from the absolute scales only in a shift of the zero axis. These two scales are Celciu s (C) – related to the Kelvin; and Fahrenheit ( 0 F) - related to the Rankine. © 2004, NORIZAN MOHAMAD. ) ( 9 5 ) ( 0 R T K T
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53 Temperature The relationship between relative and absolute temperature scales : The relationship between degree Celcius and Fahrenheit scale : © 2004, NORIZAN MOHAMAD. 6 . 459 ) ( ) ( 15 . 273 ) ( ) ( 0 0 0 R T F T K T C T 32 ) ( 5 9 ) ( 0 0 C T F T
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54 RTD RTD is Resistance Temperature Detector . RTD commonly use platinum, nickel, or copper wire whose resistance varies with temperature. The RTD resistance at temperature T 0 C is given by : where R(T) = resistance of wire at temperature T 0 C R ref = resistance at the reference temperature temperature coefficient of resistance T difference between operating and reference temperature ∆T) α (1 R R(T) ref (7-5)
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55 RTD Table 7.1 shows some common materials used in RTDs and the temperature range.
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  • Spring '18
  • Instrumentation, Transducer, NORIZAN, Linear Inductive Transducer, Angular Inductive Transducer

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