Ultrazvukový anemometr

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Práce popisuje principy a problémy při realizaci ultrazvukového anemometru. Je popsán princip výpočtu rychlosti větru a následné korekce výpočtu. Pro realizaci jsou využity ultrazvukové sensory a microcontrolér ARM Cortex-M3. Práce se zabývá generováním PWM signálu, jeho analogovou filtrací, zesílením a odvysíláním. Na přijímací straně jeto nízkonapěťový zesilovač a komparátor. Vyvíjený kód je popsán pomocí vývojového diagramu.

Vydal: FEKT VUT Brno Autor: Michael Dvořácek

Strana 22 z 49

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2 PWM filter and amplifier Signal from PWM generator has high level 3,3 and low use whole potential transmitter have adjust this PWM signal obtain kHz harmonic signal with amplitude peak peak. Instead evaluation board PWM generator takes place artificial pulse generator. Used filter has dual attenuation. So we would like eliminate 120 kHz, 200 kHz and higher harmonic components. Slew rate V/μs and permit amplify frequencies till MHz [6]. set amplification with resistor and 80kΩ feedback resistor R2. We can see connection this circuit image below.Temperature sensor used correct airspeed reach better precision calculated wind speed. Square wave signal composed from many harmonic components. It’s commonly using low noise power amplifier with power supply voltage till ±18 [6]. 3. For elimination component was chosen high pass filter. Used capacitor has nF and resistor 390 This values shift cutoff frequency 40,8 kHz. First harmonic component frequency kHz. Another ones are odd multiple the first one. For this purpose was designed second order low pass filter. and volts set low and high level pulse. TR and are rising and falling edge width. 14 . For amplification used operational amplifier TL071 Texas Instruments. Our PWM signal square wave signal with component 1,65 DC component not suitable for usage with symmetrical power supplied amplifier. PER period the generating signal and its width, both μs. These values amplify signal by 28. This was created Pspice software Orcad for the purposes simulation. Cutoff frequency with capacitor and resistor 470 33,9 kHz. Lower frequencies will attenuated. Results measurements and calculation wind speed are printed the TI evaluation board built Screen. That’s amplification. will use symmetrical power supply with non-inverting connection. That’s per octave, the third harmonic component will be attenuated [7]