Amplifier
This text is going to show how can Amplifier be used to study the free vibration of the transmitter bender element.
These data banks are loaded:
d16=read.csv("C:\\Damping\\Lab\\Bender\\Transmitter\\Amplifier\\16-02-2023\\Transmitter-Amplifier_backroom_50mm.csv",header=T)
d17=read.csv("C:\\Damping\\Lab\\Bender\\Transmitter\\Amplifier\\17-02-2023\\Trans-Amp-Air-50mm.csv",header=T)Tests are performed in air with the bender element which is installed on the 50mm diameter bottom pedestal of the stress path device.
The electric circuits which are used are as the next figures.
Up: No amplifier is used, Down: Amplifier is used
Below figure shows instead of a 20V current which directly comes from function generator, we may apply just 2V and increase that to the same level using the amplifier with Gain=10 (or other combinations).
The main difference is not the peaks that are not perfectly matched but is in the tail of the signals; the signal which is passed through the amplifier does not quickly goes to zero.
Narrowing down the range of the voltages over the vertical axis, differences becomes clear when transmitter bender element is connected to the circuit.
For the same input (20V or 2*10v), the magnitude and pattern of the detected signals are totally changed:
- Using the amplifier, the magnitude of the voltage at the beginning of the tail is quite larger compare to the other case. Other tests show existance of the bender element does not have a role on this fact but frequency of the applied signal have.
- In the case of using the amplifier noises are eliminated as well as the free vibration of the bender element. It leads to a hypothesis that amplifier applies some kind of the filter over the signal. Repeating the test will clarify the hypothesis more.
Without using the amplifier, free vibration at frequencies equal to 19, 20 and 21kHz are as below. Ignoring the magnitudes, the patterns are very similar to the vibration at fr.=6.5kHz without the amplifier (above figure).
By cross correlation, the signals are moves along the time axis to have the best coincidence.
Complete coincidence of the signals at three different but closed frequencies is very good (and suspicious at the same time!)
If amplifier is used the pattern would be as follow figure shows. Various input voltages cause different amplitudes but all of them have the same decay pattern.
the voltage on the function generator is set to 2, 3, 4 and 5 volt. In all the cases the gain of the amplifier is set to 10
In the next figure, one signal relates to the existence of the bender element and the other which does not show oscillation relates to the removing of the bender element.
In both cases amplifier is used.
Input voltage is 2V, gain of the amplifier is 10 and excitation frequency is 21kHz. 
Sending the initial excitation signal through the amplifier has these consequences:
- In some frequencies excitation last for more than a single cycle so the tail of the received signal starts from non zero values.
- In some frequencies amplifier filters the the free vibration of the bender as well as the noises so it acts as a band_pass filter.
- If free vibration of the bender does not cancel out completely, it appears as a high frequency oscillation around the exponentially decaying voltage of the tail of the signal.
- Using the amplifier, no matter input voltage be increased or amplifier´s gain, the received signal improves not only because of the stronger excitation, but because of the amplification in received signal but, what is the safe limit?: 300 Volt?
Code: Amplifier-21-02-2023.Rmd↩︎