Noise pollution standard (audible alarm)
Mandatory automotive industry standards
Currently, inspection agencies and the environment focus on air pollution standards, but noise pollution standards are also of particular importance; noise pollution standards include sound level standards, exhaust noise, and audible alarms. In this article, based on the tests performed on Iran Khodro products, an attempt has been made to examine the standard generalities of audible alarm devices and the relevant test method.
1- Car standard, audible alarms, features and test method
Auto standard, audible warning devices, features and test method, have been prepared and compiled by the Iranian Quality and Standard Inspection Company in the relevant commissions and approved in the 29th meeting of the National Automobile and Power Standards Committee dated 02/08/81. . This standard has been published as the national standard of Iran based on paragraph one of article 3 of the law amending the rules and regulations of the Iranian Institute of Standards and Industrial Research, approved in February 1992. The purpose of this standard is to express the required features for audible alarms. All vehicles must be able to maintain these characteristics during a certain period of operation.
2- Measuring sound level
The alarm should be tested in a completely open and quiet area (background sound including ambient sound and wind noise should be at least 10 DBA below the measured sound) or in an unobtrusive chamber.
The microphone used for the measurement must be in a direction that is at the maximum level of the measured sound and is 2 meters in front of the alarm device. The microphone and alarm device should be located at a height of 1/2 meter above the ground. Sound level measurements should be made on the IEC standard weighting grid scale and by several gauges. The alarm device shall be powered by a voltage of 5.6, 13 or 26 volts, measured at the output of the electrical power source and in accordance with the nominal voltages of 6, 12, or 24 volts, respectively. The time interval between the moment of activation and the moment when the sound reaches the minimum level should not exceed 0.2 seconds. These measurements are performed at a temperature of 205 degrees Celsius.
3- Necessary environmental conditions for sound level testing
Car noise level testing must be performed in a specific environment with certain weather conditions. Some of these cases are:
3-1) The mentioned area should be an open space with a radius of 50 meters, which has a central part with a minimum radius of 20 meters.
3-2) The desired location should be smooth and leveled with concrete, asphalt or other similar materials. The test area should not be covered with snow, tall grass, ash or soft soil.
3-3) Measurements should be made in the desired weather. Also, no one should be present near the person reading the numbers near the audible alarm or microphone. If an observer is present near the device or microphone, it may greatly affect the information read from the equipment.
3-4) Hand fluctuations, an indicator that is not related to the characteristics of the general sound level, are not taken into account when reading numbers.
4- Durability tests
The alarm device shall be supplied with one of the nominal voltages specified in the standard sections and through communication wires having one of the resistors specified in the standard sections. The alarm must be operated 50,000 times, each time for one second with a 4-second pause. The alarm must be ventilated by an air stream with a velocity of approximately 10 meters per second.
If the test is performed in an echo-free chamber. The volume of the chamber must be large enough to exchange the heat emitted by the alarm during the durability test.
The ambient temperature of the test room should be between 15 and 30 degrees Celsius.
5- Acoustic tests
The test must be performed in an unobtrusive environment.
The alarm device shall be secured by the parts provided by the manufacturer to a base which weighs at least 10 times the weight of the alarm and is not less than 30 kg.
The test device and the microphone must be at the same height. The microphone should be in front of the alarm and in the direction where the measured sound level is maximum.
The resistance of the communication wires must be in accordance with the standard clauses.
The effective voltage must be in accordance with the standard.
The sound spectrum emitted from the alarm, measured at a distance of 2 meters, should resonate in the frequency band range of 1800 to 3550 Hz, the sound pressure higher than each component of the frequency above 3550 Hz. Also, the sound spectrum should not be less than 105 DBA in any case.
Start the audible alarm test when installed on the vehicle
6- Acoustic test
When verifying the type of vehicle, the warning features installed on it should be tested as follows.
The sound pressure level of the alarm, when installed on the car, should be measured at 7 meters in front of the car, in an open place and as flat as possible.
The car engine must be switched off and the effective voltage must be considered in accordance with the standard.
Measurements must be made at the IEC standard weighting grid scale.
This maximum should not be less than 93 DBA.