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