ISO 4412-2:1991

Overview

ISO 4412-2:1991 - Hydraulic fluid power - Test code for determination of airborne noise levels - Part 2: Motors - defines a standardized test code to determine airborne noise (sound power) radiated by hydraulic motors. Based on ISO 2204, it specifies measurement objectives, instrumentation, installation and operating conditions, measurement points and test procedures so that results are repeatable and comparable. The part applies to all types of hydraulic fluid power motors operating in steady state (practical limitation: motors above 50 r/min) and includes informational annexes (C: application guidelines; D: bibliography).

Key topics and requirements

• Measurement targets: A-weighted sound power level and octave-band sound power levels (typical octave range 125 Hz to 8 000 Hz).
• Test environment: Tests must be performed in a “free field over a reflecting plane” or in rooms meeting ISO 3744 (engineering methods) or ISO 3745 (precision anechoic/semi-anechoic) requirements.
• Instrumentation & accuracy: Acoustical instruments per IEC 651 and ISO 3744; fluid-flow, pressure, speed and temperature instrumentation per industrial testing accuracy (annex B/class C recommendations).
• Installation & mounting: Motor mounting, drives and load must minimize structure-borne and mounting-radiated noise (use high-damping materials, isolation, small flanges and flexible couplings where appropriate).
• Operating conditions: Tests carried out in the motor “as-delivered” condition under controlled, steady-state hydraulic and mechanical conditions; test parameters must be kept within prescribed tolerances.
• Measurement procedure: Includes background noise measurement and correction (per ISO 3744), defined locations and number of microphone points (per ISO 3744 methods), band and A-weighted measurements, and repeat checks for new/rebuilt motors. Note: A-weighted levels are typically determined with a standard uncertainty on the order of ~2 dB in practice.
• Reporting: Record motor ID, test environment, operating parameters (speed, torque, inlet/outlet pressures, fluid temperature and condition), instrumentation details and test results. Annex C provides guidance on application.

Practical applications - who uses ISO 4412-2

• Hydraulic component manufacturers and R&D teams validating motor acoustic performance.
• Test laboratories and certification bodies performing standardized noise measurements.
• Acoustical and mechanical engineers designing quieter hydraulic systems and specifying noise limits.
• OEMs and procurement teams comparing motor noise for equipment selection and regulatory compliance.

Related standards

• ISO 2204 (basis for code), ISO 3744, ISO 3745 (acoustic environments), IEC 651 (sound level meters), ISO 5598 (fluid power vocabulary). Annexes C and D in ISO 4412-2 give application guidance and bibliography.

Keywords: ISO 4412-2, hydraulic fluid power, airborne noise, motor sound power, noise test code, acoustic measurement, ISO 3744, IEC 651.