A sound level meter is an instrument that can measure the noise level of industrial noise, living noise and traffic noise in an approximate manner according to the auditory characteristics of the human ear. The noise level is the sound pressure level (dB) or loudness level (phon) measured with a sound level meter and corrected for hearing. According to the sound level meter, the accuracy of 1000Hz pure tone is measured under standard conditions. In the 1960s, the sound level meter is divided into two categories, one is called precision sound level meter, and the other is called ordinary.
This method is also adopted in China. Since the 1970s, some countries have introduced four types of divisions, namely, type 0, type 1, type 2, and type 3. Their accuracy is ±0.4dB, ±0.7dB, ±1.0dB and ±1.5dB. Depending on the power source used in the sound level meter, it can be divided into two types: AC type and DC type sound level meter with dry battery. The latter can also be portable. Portable has the advantages of small size, light weight and convenient use in the field.
Generally composed of a microphone, an amplifier, an attenuator, a weighting network, a detector, an indicator head, and a power source.
(1) 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 generated; the smaller the sound pressure, the smaller the current generated.
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) Amplifiers and Attenuators Many domestic and imported ones in the amplifier circuit 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 can be adjusted to the bottom of the measurement (eg 0~70 dB). The attenuator used by the output amplifier can be adjusted to the high end (70~120 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) In order to simulate the different sensitivity of human ear hearing at different frequencies, the weighting network has a network that can simulate the human ear's auditory characteristics and correct the electrical signal to an auditory approximation. Right 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 to display the amplified signal through the meter, a detector is also needed to convert the rapidly changing voltage signal into a slower 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. In order to meet the needs of the measurement site, the sound level meter generally has a triangular bracket so as to be fixed on the triangular bracket as needed.
There are also some jacks on the panel. If these jacks are connected to the portable octave band filter, they can form a simple spectrum analysis system for small field use. If combined with the recorder, the scene noise can be recorded on the tape and stored. More detailed research will be carried out later; if combined with an oscilloscope, the waveform of the sound pressure change can be observed, and the waveform can be taken by the camera; the analyzer, the recorder, etc. can be combined with the sound level meter and used together. This depends on the test conditions and test requirements.
1. Check the calibration of the sound level meter with a sound calibrator
2. Set the range switch to the appropriate gear according to the size of the sound to be measured. If the size cannot be estimated, set it to “85-130â€.
3. Place the time weighting switch in the position specified by the standard; when the sound level is relatively stable, set it to “F†(fast); if the sound level changes drastically, put it in “S†(slow) 4. Read the reading mark Placed in "5S" or "3S"
5. Set the power switch to “onâ€; display the number when the instrument starts working.
6. If the excessive mark “▲†(the under-remark “▼â€) is displayed at the right end of the display, the range switch should be moved up or down to make the range mark disappear. If the range marker cannot be disappeared, the measured sound level is outside the measurement range of the instrument.
7. After adjusting the range of the sound level meter, the measurement result can be read from the display.
8, make a good measurement record
9. After the measurement is completed, it is recommended to check the sensitivity of the sound level meter with a sound calibrator to ensure accurate and reliable measurement data.
10. Set the power switch to “Offâ€. If the instrument is no longer used for a long time, be sure to remove the battery.
1. When measuring, the instrument should select the correct gear position according to the situation. Both hands should hold the sound level meter on both sides, the microphone points to the sound source to be tested, and the extension cable and extension rod can also be used to reduce the sound level meter and human body measurement. Impact. The position of the sound level meter should be determined according to relevant regulations.
2. The sound level meter is powered by battery. It should be checked whether the battery voltage meets the requirements: the meter function switch is set to “battery†file, and the “attenuator†can be set arbitrarily. At this time, the indication on the meter should be within the rated battery voltage range. Otherwise Need to replace the battery. Install the battery or external power supply to pay attention to the polarity, do not reverse the connection. Do not remove the battery for a long time to avoid leakage of the instrument.
3. Read the instructions before use to understand the usage and precautions of the instrument. Preheating is performed according to the warm-up time (for example, 10 minutes) specified in the instruction manual of the sound level meter.
4. When the battery voltage used by the sound level meter is insufficient, it should be replaced.
5. Calibration amplifier gain: The meter function switch is set to “0†and the “attenuator†switch is set to “calibrationâ€. At this time, the meter pointer should be in the red line position, otherwise the sensitivity potentiometer needs to be adjusted.
6. When you don't know how big the measured sound level is, you must put the “attenuator†at the maximum attenuation position (for example, 120dB), and then gradually adjust to the attenuation position required by the measured sound level during measurement to prevent the measured position. Sound level exceeds range, bad sound level meter
7. Do not disassemble the microphone to prevent it from falling and put it properly when not in use. 8, the sensor is extremely delicate and vulnerable to more expensive parts, pay attention to light handling throughout the experiment. After the experiment is completed, remove the sensor and place it in the designated place.
9. The instrument should be kept away from high temperature, humidity, sewage, dust and air or chemical gas containing high levels of hydrochloric acid and alkali.
10. Do not disassemble the instrument without authorization. If the instrument is not normal, it can be sent to the repair unit or the factory for maintenance.
The 1080P high-definition projectors on the market can be roughly divided into three grades: high, medium, and low. The low-end products are mainly aimed at the entry-level market. In terms of performance, they can fully meet the needs of watching various HD videos. In terms of adjustment, it tends to be simpler, mainly to allow entry-level users to quickly set up the projector, but the contrast of such projectors is generally not very high, and the overall picture effect is relatively general; mid-range projectors mainly have certain projector knowledge. , the projection picture also has a better performance, the most important contrast of the cinema projector has also been greatly improved, the projector adjustment tends to be more professional, and it is also equipped with various additional functions to improve the projection effect; high-end products are Mainly aimed at enthusiast players, both price and performance are the symbol of flagship. For commercial use, in addition to satisfying home entertainment applications, 1080P high-definition standard projectors can also support clear and delicate text and table content projection for business office applications that often conduct office text, PPT presentations, and video presentations. .
4k meeting room projector,video projector for meeting room,conference room led projector,lcd meeting room projector,business 1080p HD projector
Shenzhen Happybate Trading Co.,LTD , https://www.szhappybateprojectors.com