Guidance on performance testing

Verification that a system is fit for purpose through performance testing may require extensive checks of many parts of the system. An understanding of the measurement and the method of operation of a system will help to define the verification requirements. The level of performance testing undertaken should be appropriate to the measurement application.

This is always likely to involve performance checks immediately before a measurement or series of measurements, as well as periodic testing and individual instrumentation calibrations.

Performance checks may comprise:

• Preliminary inspection
• Electrical testing
• Acoustic testing

What can go wrong?

Considering the elements of the instrumentation part of the system. A preliminary inspection, electrical testing and acoustic checks should aim to verify that all parts of the system are fit for purpose. As a minimum, the following elements should be examined:

Microphone Pre-amplifier Cable Input channels

Filters Weighting networks Frequency response Noise floor

Preliminary inspection

Prior to any measurements, a system should be visually inspected. Check for damage to, or accumulation of foreign objects on the protection grid/diaphragm of the microphone or appropriate sensor. Operating essential controls of this system can help to ensure that the system is in working order.

Electrical testing

Where the microphone can be replaced by a suitable electrical signal, it is possible to undertake electrical tests of the system. Care must be taken to ensure that the impedance loading is equivalent to that of the microphone.

Electrical testing may then, where appropriate, consist of:

• Self-generated noise - measured in the lowest input range of the system, across the frequencies of interest
• Linearity - measured for the input ranges of interest, between the upper and lower limits
• Weighting networks - tested across the frequency range of interest at the reference range of the system
• Time weighting/averaging - tested at the reference range for each time weighting with appropriate tone bursts
• Peak response - measured with no frequency weighting, at the reference range
• RMS accuracy
• Frequency analysis - where the filters are checked in accordance with BS EN 61260

Acoustic testing

If it has been possible to electrically check parts of the system, the complete system with the acoustic sensor can then be checked.

• Microphone frequency response
• Calibration at 1 kHz - in a plane-progressive sound field, or through application of a calibrator
• Calibration at low-frequency - (e.g., 125 Hz) in a plane-progressive sound field, or through application of a calibrator, or electroacoustic actuator
• Calibration at high-frequency - (e.g., 8 kHz) in a plane-progressive sound field, or through application of a calibrator, or electroacoustic actuator

The next section discusses practical examples of performance testing by practitioners in acoustics.

Examples from practitioners >>