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Transistors Q1 and Q2 are used for sensing the wind. The relationship between thermal impedance of the transistor and the surrounding wind speed is utilized here. Transistors Q1 and Q2 are wired so that
the Vce of Q1 is higher than Q2 and therefore there will be a higher power dissipation. The wind causes cooling and so the Vce of Q1 changes. The ends in different power dissipations and different voltages across R10. This variation is detected by the opamp and amplified to produce the Vout which is proportional to the wind speed. For still air Vout will be 0V and at 75m/s wind speed the Vout will be 2.5V. A 3V FSD voltmeter connected across the Vout terminal and ground can be used as the display.
For proper working, the air must pass over both the transistors (Q1 and Q2).
The resistors used are not standard values. So you need to use the combination (series or parallel) of resistors to attain the specified values. Please note that the resistor values are very critical in this circuit.
IC LT1013 Description
Absolute maximum ratings IC LT1013
- Supply voltage : . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . .. . +22 V/ –22 V
- Input voltage range, VI (any input) . . . . . . . . . . . . . . . . . . .. . . VCC– –5 V to VCC+
- Differential input voltage . . . . . . . . . . . . . . . . . . . . . . . . . .. . . 30 V
- Duration of short-circuit current at (or below) 25 C . . . . . . . . . . Unlimited
- Package thermal impedance, θJA : D package . . . . . . . . . . . . 97 C/W
- P package . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . 85 C/W
- Case temperature for 60 seconds: FK package . . . . . . . . . . . . 260 C
- Lead temperature 1,6 mm (1/16 inch) from case for 10 seconds: D or P package . . . . 260 C
- JG package . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300 C
- Storage temperature range, Tstg . . . . . . . . . . . . . . . . . . . .. . . –65 C to 150 C
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