Systems based on computers with data (signal) acquisition boards (often called “PC-based systems”) are becoming more common for measuring sound and vibration. Multiple-channel acquisition, flexibility in sensor selection, and custom-designed, powerful software make these systems attractive for many stationary applications. Sooner or later these systems will require calibration as an unavoidable step in acquiring the traceability of the results.
The sound measuring methods detailed in ASTM, ANSI, and ISO standards always require the use of instrumentation that is compliant with the current standards applicable to sound level meters. Consequently, if compliance with the standards is required (laboratory and field measurements) then PC-based measuring systems must comply and be calibrated based on the standards applicable to sound measuring instruments.
In the USA, the standards that must be met are ANSI S1.4-1983 (R2006)/ANSI S1.4a-1985 (R2006) and ANSI S1.43-1997 (R2007.) In other parts of the world, the IEC 61672 series of standards apply for sound measuring instruments and systems. The octave and third octave band filters should comply with ANSI S1.11-2004 (R2009) which is a counterpart of the IEC 61260: 1995.
To facilitate trade manufacturers are considering compliance with all current standards.
The ANSI S1.4 & S1.43 standards only mention the possibility of using PC-based measuring sound systems without differentiating the requirements. Responding to users’ needs, the newer IEC 61672 standard series introduces three categories of measuring equipment meant for special applications and having the minimum specific requirements:
PC-based systems that are intended for sound measurement should comply with and be tested to the standards applicable for sound measuring instrumentation. Periodic tests involve using various signals (sine, tone bursts, rectangular, step) to check the capability of the instrument (hardware and software) to correctly measure various parameters of sounds with diverse patterns.
The data (signal) acquisition boards may also have specifications from their manufacturer. These cover only a selection of the tests for sound measuring instruments, but also may contain additional parameters not included in the above standards. Also, the specifications for the acquisition boards alone may show better accuracy than required by the standards. However, testing only the acquisition part does not give assurance that the combination software-hardware (including the PC) is working properly to measure sound parameters.
A calibration plan that fully covers both the standards and the manufacturer’s requirements is long and expensive. We suggest as ideal a combination of periodic testing according to the standards for sound measuring instruments, completed with additional checks to cover the other important parameters for the acquisition board.
Scantek offers calibration for the PC-based systems in accordance with any of the applicable standards. To meet the requirements, all the components of the system (sensors & preamplifiers, cables, acquisition board and computer) must be included in the package to be calibrated. Since most of the time the software is custom developed, Scantek requires that detailed specifications for the system must be presented, along with the user manual, which itself must be compliant with the standard.
Full testing of the filters according to the IEC 61260: 1995 is also available as a separate calibration service.