Chapter 04A - Sensors - CHAPTER IV SENSORS/TRANSDUCERS...

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HAPTER IV CHAPTER IV SENSORS/TRANSDUCERS
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SENSOR (TRANSDUCER) SELECTION OF TRANSDUCER ± Criteria that requires to be considered when selecting a transducer: 1. Identification of an input type. Example: a pressure sensor must be able to detect an instantaneous pressure and tc t a s t at a os p s s must not be sensitive to any temperature changes. 1. Does not change the state of the process to be measured. 2. Suitable with the process and visual display unit to be used. Dr. Abdirahman CHAPTER 4 Page 2of 111
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igh accuracy SENSOR (TRANSDUCER) 4. High accuracy. 5. High precision. 6. Has a linear amplitude. 7. Has a stable response frequency. 8. Must not be induced by phase distortion or ime lag between input signal and output t e ag betwee put s g a a d output signal. 9. Has high resistance against outside elements without effecting the accuracy in certain gy limits. 10. Easy to obtain at a low price. 1 afe to be used Dr. Abdirahman CHAPTER 4 Page 3of 111 11. Safe to be used.
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peration principles of sensors/transducers Operation principles of sensors/transducers in the process industry Temperature Sensors ± Several type of temperature sensors commonly employed by the industry: 1. Bimetallic sensor hermocouple 2. Thermocouple 3. Resistive Temperature Detector (RTD) . hermistor 4. Thermistor 5. Radiation Pyrometer 6. Integrated Circuit Sensor (ICS) Dr. Abdirahman CHAPTER 4 Page 4of 111
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1. BIMETALLIC SENSOR ormall used as circuit breaker to protect ± Normally used as circuit breaker to protect electrical system from excess electrical current in the circuit. ± Usually employed in the “ON/OFF” process system. ircuit breaker is commonly connected in ± Circuit breaker is commonly connected in series with the protected circuit, allowing bimetallic strip physically connected with ne/more circuit bay. one/more circuit bay. ± Comprise from two basic material bearing two different “ thermal expansion oefficient” and onded together Dr. Abdirahman CHAPTER 4 Page 5of 111 coefficient and bonded together.
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The principle behind a bimetallic strip thermometer relies on the fact that different metals expand at different rates as they warm up. By bonding two different metals together, you can make a simple electric controller that can withstand fairly high temperatures. This sort of controller i so ften found in ovens. Here i st he general layout: Dr. Abdirahman CHAPTER 4 Page 6of 111
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Two metals make up the bimetallic strip (hence the name). In this diagram, the grey metal would be
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This note was uploaded on 05/09/2010 for the course CHE 3022 taught by Professor Abdirahman during the Fall '07 term at National Central University.

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Chapter 04A - Sensors - CHAPTER IV SENSORS/TRANSDUCERS...

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