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We are Group5 Weatherstation The team Members are : Saran Jackson Robert Howard Robert Garvey

Welcome to our presentation. We are Group5 Weatherstation The team Members are : Saran Jackson Robert Howard Robert Garvey Gene Fitzgerald Steven Dowling. Todays Presentation. Our First Variable Is A Temperature Sensor.

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We are Group5 Weatherstation The team Members are : Saran Jackson Robert Howard Robert Garvey

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  1. Welcome to our presentation We are Group5 Weatherstation The team Members are : Saran Jackson Robert Howard Robert Garvey Gene Fitzgerald Steven Dowling

  2. Todays Presentation Our First Variable Is A Temperature Sensor. We choose this mainly because of the availability of components for the circuit.

  3. Components The Temperature Sensor Consists Of 5 Components • A PT100 RTD • A Wheatstone Bridge • A Differential Amplifier (741) • Resistors • Dual Power Supply

  4. The PT100 RTD The PT100 RTD (resistance temperature detector) is a sensor that makes use of the temperature dependence of a metals resistance. In this instance it is Platinum, the resistance of which is 100 ohms at 0°c. It offers excellent accuracy over a wide temperature range and this relationship is approximately linear over a small range.

  5. The Wheatstone Bridge The Wheatstone bridge is a measurement instrument used to measure an unknown electrical resistance by balancing two legs of a bridge circuit, one leg of which includes the unknown component. It is an extremely accurate way of measuring resistances and has an unlimited array of applications in industry.

  6. The Wheatstone Bridge

  7. Differential Amplifier We can connect signals to both of the inputs at the same time producing an operational amplifier circuit called a Differential Amplifier. The Differential Amplifier circuit is a very useful op-amp circuit and by adding more resistors in parallel with the input resistors R1 and R3, the resultant circuit can be made to either "Add" or "Subtract" the voltages applied to their respective inputs. One of the most common ways of doing this is to connect a "Resistive Bridge" commonly called a Wheatstone Bridge to the input of the amplifier as shown below.

  8. Differential Amplifier Diagram

  9. Power Supplies • For the Wheatstone Bridge we have selected a 15V DC power supply. • For the Op-Amp we have also selected a 15V DC power supply.

  10. Block Diagram PT100 Wheat- Stone bridge Diff- Amp A/D Converter 92.16 Ω- 115.54Ω 100-190mV 2.8 - 5.32V -20 to 40°c

  11. Linear Graph

  12. Calculations • Low resistor ratio 1:1 = low output voltage but high accuracy and linear relationship. • High resistor ratio 1:10 = higher output voltage but lower accuracy and slightly curved relationship. • Higher output voltage means a lower gain op-amp is required.

  13. Output voltage = Va – Vb = 13.63 – 13.44 = 190 mVMinimum Temperature at -20°c Calculations Maximum Temperature at 40°c Output voltage = Va – Vb = 13.73 – 13.63 = 100 mV

  14. Resistor Values

  15. Circuit Diagram From LT- Spice LT Spice Circuit Diagram

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