BS ISO 13325:2019 pdf download – Tyres — Coast-by methods for measurement of tyre-to-road sound emission
7 Instrumentation
7.1 Instrumentation for acoustical measurements
The sound pressure level meter or equivalent measuring system, including the windscreen recommended by the microphone manufacturer, shall meet the minimum requirements of a Class 1 instrument in accordance with IEC 61672-1 and/or IEC 61672-3.
Alternatively, IEC 60651 1) may be used. The measurements shall be made using the frequency weighting, A, and the time weighting, F. The calibration of the sound pressure level meter shall be checked and adjusted in accordance with the manufacturer’s instructions or with a standard sound source (e.g. pistonphone) at the beginning of the measurements and rechecked and recorded at the end of them. The calibration device shall meet the requirements of Class 1 in accordance with IEC 60942. If the sound pressure level meter indications obtained from these calibrations differ by more than 0,5 dB during a series of measurements, the test shall be considered invalid.
Any deviation shall be recorded in the test report.At intervals of not more than two years, the sound pressure level meter shall be verified with the requirements of IEC 61672-1 and/or IEC 61672-3. Alternatively, IEC 60651 may be used [5] .
At intervals of not more than one year, the calibration device shall be verified with the requirements of IEC 60942. Windscreens shall be used in accordance with the microphone manufacturer’s recommendations. When no general statement or conclusion can be made about conformance of the sound level meter model to the full specifications of IEC 61672-1, the apparatus used for measuring the sound pressure level shall be a sound level meter or equivalent measurement system meeting the compliance requirements of Class 1 instruments as described in IEC 61672-3.
NOTE The tests of IEC 61672-3 cover only a limited subset of the specifications in IEC 61672-1 for which the scope is large (temperature range, frequency requirements up to 20 kHz, etc.). It is economically not feasible to verify the whole IEC 61672-1 requirements on each item of a computerized data acquisition systems model. Apparently, until today, no computerized data acquisition system available complies with the full specifications of IEC 61672-1. It is beyond the possibilities of the users of these systems to prove conformity of the instrumentation required by the test code.
7.2 Microphones
Two microphones shall be used in the test, one on each side of the vehicle. In the vicinity of the microphones, there shall be no obstacle that could influence the acoustical field and no person shall remain between the microphones and the sound source. Any observer or observers shall be positioned so as not to influence the sound reading, especially in the testing area.
The distance from the microphone positions to the centreline of travel on the test track shall be (7,5 ± 0,05) m. Each microphone shall be located (1,2 ± 0,02) m above the test area surface and shall be oriented as recommended by the manufacturer of the sound pressure level meter for field conditions for a test vehicle passing along the centreline of travel as shown in Figure 1.
7.3 Temperature measurement
7.3.1 General For air as well as test surface temperature, the measuring instrument shall have an overall accuracy of at least ±1 °C. Meters utilizing the infrared technique shall not be used for air temperature measurements.
Continuous registration via an analog output may be employed. If such an option is not available, single values are to be measured. Measurements of air as well as test surface temperatures are mandatory and shall be made in accordance with the instrument manufacturer’s instructions. Temperature measurements shall correspond reasonably over time with sound measurements. Alternatively, the average of the temperature at the beginning and the end of the set of tests may be used.
7.3.2 Air temperature
Position the temperature sensor in an unobstructed location close to the microphone, such that it is exposed to the airflow and protected from direct solar radiation. The latter may be achieved by any shading screen or similar device. The sensor should be positioned 1,2 m ± 0,1 m above the test surface level, to minimize the influence of the test surface thermal radiation at low airflows.
7.3.3 Test surface temperature
Position the temperature sensor in a location where the temperature is representative of the temperature in the wheel tracks, without interfering with the sound measurement. If an instrument with a contact temperature sensor is used, apply heat-conductive paste between the surface and the sensor to ensure adequate thermal contact.BS ISO 13325 pdf download.