The sound level meter is the most basic noise measuring instrument. It is an electronic instrument, but it is different from objective electronic instruments such as voltmeters. When converting an acoustic signal into an electrical signal, it is possible to simulate the temporal characteristics of the human ear's response to sound waves; the frequency characteristics with different sensitivities for high and low frequencies and the intensity characteristics for changing the frequency characteristics for different loudnesses. A sound level meter is a subjective electronic instrument. It consists of a microphone, an amplifier, an attenuator, a weighted network, a detector, an indicator head, and a power supply. 1, the microphone It is a device that converts a sound pressure signal into a voltage signal, also called a microphone, and is a sensor. Common microphones are available in crystal, electret, moving coil and capacitive versions. The moving coil type sensor is composed of a vibrating diaphragm, a movable coil, a permanent magnet, and a transformer. The vibrating diaphragm starts to vibrate after being subjected to the sound wave pressure, and drives the movable coil mounted with it to vibrate in the magnetic field to generate an induced current. This current varies depending on the magnitude of the sound wave pressure that the diaphragm is subjected to. The greater the sound pressure, the greater the current produced; the smaller the sound pressure, the smaller the current produced. Capacitive sensors are mainly composed of a metal diaphragm and a close metal electrode, which is essentially a flat capacitor. The metal diaphragm and the metal electrode form two plates of the plate capacitor. When the diaphragm is subjected to sound pressure, the diaphragm is deformed, the distance between the two plates changes, and the capacitance also changes, thereby generating an alternating voltage whose waveform is within the linear range of the microphone and the sound pressure level. Forming the ratio realizes the function of converting the sound pressure signal into a voltage signal. Capacitive microphones are ideal microphones for acoustic measurement. They have wide dynamic range, flat frequency response, high sensitivity and good stability in general measurement environments. Since the capacitive sensor has a high output impedance, it needs to be impedance-converted by a preamplifier. The preamplifier is installed inside the sound level meter close to where the capacitive sensor is mounted. 2, amplifier and attenuator Many of the popular domestic and imported amplifier circuits use two-stage amplifiers, namely input amplifiers and output amplifiers, which act to amplify weak electrical signals. The input attenuator and the output attenuator are used to vary the amount of attenuation of the input signal and the amount of attenuation of the output signal so that the meter pointer is pointed at the appropriate position with an attenuation of 10 decibels per block. The attenuator used by the input amplifier adjusts to the bottom of the measurement (eg, 0 to 70 dB), and the output amplifier uses an attenuator that adjusts to the high end of the measurement (70 to 120 dB). The dials for the input and output two attenuators are often made in different colors and are currently paired with black and transparent. Since many sound level meters have a height and a bottom limit of 70 decibels, it is necessary to prevent exceeding the limit when rotating, so as not to damage the device. 3. Weighting network In order to simulate the different sensitivity of human ear hearing at different frequencies, there is a network that can simulate the auditory characteristics of the human ear and correct the electrical signal to a network similar to hearing. This kind of network is called a weighted network. The sound pressure level measured by the weighted network is no longer the sound pressure level of the objective physical quantity (called the linear sound pressure level), but the sound pressure level corrected by the hearing sense, called the weighted sound level or the noise level. The weighting network generally has three types: A, B, and C. The A-weighted sound level is the frequency characteristic of the low-intensity noise of the simulated human ear to 55 decibels or less; the B-weighted sound level is the frequency characteristic of the medium-intensity noise simulating 55 to 85 decibels; the C-weighted sound level is the analog high-intensity noise. characteristic. The difference between the three is the degree of attenuation of the low-frequency components of the noise, A is the most attenuated, B is the second, and C is the least. The A-weighted sound level is the most widely used noise measurement in the world because its characteristic curve is close to the human ear's hearing characteristics. B and C have gradually disappeared. The noise level readings from the sound level meter must indicate the measurement conditions. 4, detector and indicator head In order for the amplified signal to be displayed through the meter, a detector is also required to convert the rapidly changing voltage signal into a slower changing DC voltage signal. This DC voltage is proportional to the size of the input signal. According to the needs of the measurement, the detector has a peak detector and an average detector black root mean square detector. The peak detector can give a maximum value for a certain time interval, and the average detector can measure its absolute average value over a certain time interval. In addition to the pulse sounds like guns that need to measure his peak, square root detectors are used in most measurements. The rms detector can square, average, and square the AC signal to obtain the rms value of the voltage, and finally deliver the rms voltage signal to the indicator head. The indicator head is an electric meter. As long as the scale is calibrated, the noise level decibel value can be read directly from the meter head. The head level damping generally has two speeds: “fast†and “slowâ€. . The average time of the "fast" block is 0.27 s, which is very close to the physiological average time of the human ear's auditory organs; the average time of the "slow" block is 1.05 s. When measuring steady-state noise or recording the sound level change process, it is more appropriate to use the "fast" gear; when the fluctuation of the measured noise is relatively large, it is more appropriate to use the "slow" gear. The sound level meter is the most basic instrument in measuring noise. It belongs to an electronic instrument. The sound level meter is generally composed of a condenser microphone, a preamplifier, an attenuator, an amplifier, a frequency weighting network, and a RMS indicator. According to the sound level meter sensitivity can be divided into two categories, one is the ordinary sound level meter; the other is the precision sound level meter, according to the use of the sound level meter can also be divided into two categories: one for measuring stability State noise; one class is used to measure unsteady noise and impulse noise. The sound level meter uses advanced digital detection technology to greatly improve the stability and reliability of the instrument. The sound level meter has the advantages of simple operation and convenient use; it has the characteristics of large range dynamic range, large-screen liquid crystal digital display, automatic measurement and storage of various data. Sound level meter can be widely used in industrial noise measurement and environmental noise measurement of various machines, vehicles, ships, electrical appliances, etc. It is suitable for factories, building design, environmental protection, labor hygiene, transportation, teaching, medical and health, scientific research and other departments. The field of sound testing. The sound is converted into an electrical signal by the microphone, and the impedance is converted by the preamplifier to match the microphone to the attenuator. The amplifier adds the output signal to the weighting network, performs frequency weighting (or external filter) on the signal, and then amplifies the signal to a certain amplitude through the attenuator and the amplifier, and sends it to the RMS detector (or externally pressed) Flat recorder), the value of the noise level is given on the indicator head. In order to simulate the different sensitivity of human ear hearing at different frequencies (20Hz-20KHz), a network capable of simulating the auditory characteristics of the human ear and correcting the electrical signal to an approximation of the sense of hearing is provided in the sound level meter. Called the weighting network. The sound pressure level measured by the weighted network is no longer the sound pressure level of the objective physical quantity (called the linear sound pressure level), but the sound pressure level corrected by the hearing sense, which is called the weighted sound level or the noise level. Since the human ear's perception of noise in each frequency band is different, it is the most sensitive to the intermediate frequency of about 3 kHz, and the difference between the low frequency and the high frequency. Therefore, the unweighted signal-to-noise ratio is not necessarily the subjective feeling of the human ear. Good match. How to unify the measured value with the subjective sense of hearing? Then there is a balanced network, or a weighted network, which moderately attenuates both low and high frequencies, so that the intermediate frequency is more prominent. The weighted network is connected between the device under test and the measuring instrument, so that the influence of the intermediate frequency noise of the device is "amplified" by the network. In other words, the intermediate frequency noise that has the greatest impact on the sense of hearing is given a higher weight. The measured signal-to-noise ratio is called the weighted signal-to-noise ratio, which can more realistically reflect the subjective sense of hearing. The sound level meter principle technique is a technique in which a microphone converts sound into an electrical signal, and then the impedance is converted by a preamplifier to match the microphone with the attenuator. The sound is converted into an electrical signal by the microphone, and the impedance is converted by the preamplifier to match the microphone to the attenuator. The amplifier adds the output signal to the weighting network, performs frequency weighting (or external filter) on the signal, and then amplifies the signal to a certain amplitude through the attenuator and the amplifier, and sends it to the RMS detector (or externally pressed) Flat recorder), the value of the noise level is given on the indicator head. The frequency weighting network in the noise meter/sound level meter has three standard weighting networks A, B and C. The A network simulates the response of the human ear to the 40-square pure tone in the equal-tone curve. Its curved shape is opposite to the 340-square equal-cord curve, so that the middle and low frequency bands of the electrical signal have a large attenuation. The B network is a response of the human ear to the 70-square pure tone, which causes a certain attenuation of the low frequency band of the electrical signal. The C network simulates the human ear's response to 100-square pure tone, with a nearly flat response over the entire audio range. The sound level measured by the sound level meter through the frequency weighting network is called the sound level. According to the weighting network used, it is called A sound level, B sound level and C sound level, and the unit is recorded as dB(A). , dB(B) and dB(C). At present, the noise measuring instrument/sound level meter for measuring noise can be divided into four types according to the sensitivity: (1) "Slow". The head time constant is 1000 ms, which is generally used to measure steady-state noise, and the measured value is a valid value. (2) "Fast". The time constant of the meter is 125ms, which is generally used to measure unsteady noise and traffic noise with large fluctuations. The fast gear is close to the human ear's reaction to the sound. (3) "Pulse or pulse hold". The needle rise time is 35ms, which is used to measure impulse noise with a long duration, such as punching, hammering, etc., and the measured value is the maximum effective value. (4) "Peak hold". The needle rise time is less than 20ms. Used to measure pulse sounds with very short durations, such as guns, guns, and explosions. The measured value is the peak value. That is the maximum. The sound level meter can be connected to a filter and a recorder to perform spectrum analysis on noise. The domestic ND2 precision sound level meter is equipped with a multiplier page path filter, which is easy to carry to the scene and for spectrum analysis. The noise meter/sound level meter can be divided into a precision noise meter/sound level meter and a general sound level meter according to the accuracy. The measurement error of the precision sound level meter is about 1 dB of soil, and the ordinary sound level meter is about 3 dB of soil. Sound level meters can be divided into two categories according to their use: one for measuring steady-state noise and one for measuring unsteady noise and impulse noise. An integral sound level meter is used to measure the equivalent sound level of unsteady noise over a period of time. The noise dosimeter is also an integral sound level meter that is primarily used to measure noise exposure. The pulsed sound level meter is used to measure impulse noise. The noise meter/sound level meter conforms to the response of the human ear to the pulse sound and the average time of the human ear's response to the pulse sound. The noise meter/level meter is noise. The most basic instrument in the measurement. The sound level meter generally consists of a condenser microphone, a preamplifier, an attenuator, an amplifier, a frequency weighting network, and a RMS indicator. Portable Projector With Battery The so-called Portable Projector, also known as pocket projector, mainly through the 3M LCOS RGB three-color projector and decoding technology, the traditional huge projector is refined and portable, making the projection technology closer to life and entertainment. A portable projector with a battery is a projector that does not need to be charged. Portable Projectors With Battery,Best Portable Mini Home Projector 2022,Battery Powered Mini Projector,Portable Projector with Built-in Battery,Best Budget Projectors with Built-in Battery Shenzhen Happybate Trading Co.,LTD , https://www.szhappybateprojectors.com
The most prominent advantage of a portable projector with a battery is that it can be used directly without being connected to a power source. You can take it to play or travel outdoors. It is very convenient. As long as you charge it well before going out, it will take time to watch a movie. There is absolutely no problem.
If you are traveling for business or personal use, you can indeed try a portable projector with a battery, it will make your life more convenient and better.