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lsli12.4up - 12-1 12-1 12-2 12-2 Chemical Sensors Detect...

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12-1 12-1 Chemical Sensors Detect presence and concentration of chemicals. Two types will be discussed: Humidity. Measure humidity in air. Oxygen. Measure amount of oxygen in air. Model functions will not be given for any transducer described in this set of lecture notes. 12-1 EE 4770 Lecture Transparency. Formatted 13:26, 23 December 1997 from lsli12. 12-1 12-2 12-2 Humidity Transducer Two common types, capacitance and resistance. Construction and Operation, Capacitance Type Capacitor Plates Humidity-Sensitive Dielectric Lead Lead Transducer is a capacitor. Capacitor’s dielectric is exposed to environment. The dielectric’s permittivity changes with humidity ... and so the capacitance changes with humidity. 12-2 EE 4770 Lecture Transparency. Formatted 13:26, 23 December 1997 from lsli12. 12-2 12-3 12-3 Construction and Operation, Resistance Type Lead Humidity-Sensitive Resistor Lead Transducer consists of leads placed on a special material. Water from the air adsorbs onto the surface. This causes a change in resistance, which is measured. Output of both types are highly temperature dependent. Sensors usually sold with integrated conditioning circuits. 12-3 EE 4770 Lecture Transparency. Formatted 13:26, 23 December 1997 from lsli12. 12-3 12-4 12-4 Oxygen Sensors Construction and Operation Platinum Electrode Zirconium Oxide Lead O -2 Reference Gas Test Gas Platinum Electrode Lead O -2 O -2 O -2 O -2 Consists of zirconium oxide, ZrO 2 , between platinum electrodes. One side exposed to reference gas other side exposed to test gas. Gases come in contact with both platinum and zirconium oxide. On both sides O - 2 adhere to zirconium oxide’s surface. Reference gas has a known concentration of oxygen. Test side exposed to gas being measured. Test gas oxygen concentration determined from electrode voltage. 12-4 EE 4770 Lecture Transparency. Formatted 13:26, 23 December 1997 from lsli12.
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lsli12.4up - 12-1 12-1 12-2 12-2 Chemical Sensors Detect...

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