When you’re choosing a noise monitoring system, you want to have trust in that kit and you need to know the data that you are collecting is accurate, reliable and defensible. Sometimes behind the impressive branding and technical specs, the calibration certificate that comes with the instrument doesn’t really tell you what they seem to. In this article we explain what to look for, why IEC 61672 is the key benchmark and how type approval from PTB guarantees confidence in your data.
Class vs Type
Under the current standard of IEC61672, instruments are rated Class 1 or Class 2. The older standards such as IEC 60651 and IEC 60804 used terminology like Type 0-3. So when a calibration certificate still refers to “Type 1” it often indicates outdated or partial compliance. In the same thread if a certificate says that an instrument is Type 1 & Class 1, its mixing two different generations of standards in what could be deemed a misleading way.
IEC 61672 is all or nothing, you can’t pick and choose which parameters to test. To comply with IEC 61672, every parameter must be within tolerance:
- Frequency response
- Linearity
- Tone burst/pulse response
- Directional response
- Environmental stability
- Self-noise and overload performance
- Case corrections, windshield effects and mounting conditions
IEC 61672-3:2013 sets out how periodic calibration should be carried out. Certificates that only include a subset of these tests (for example, frequency response only) do not prove compliance to IEC 61672. A credible calibration certificate will show a clear reference to IEC 61672 with detailed results for all required parameters along with full traceability to national or international standards. The certificate will also have information around test conditions (temperature, humidity and equipment used) and will look at the whole instrument, not just the microphone.
PTB’s Role in Type Approval
To validate an instrument’s performance, manufacturers can submit their model to Physikalisch-Technische Bundesanstalt (PTB) which is Germany’s national metrology institute. PTB’s type approval is one of the most stringent certifications available. For example, the Svantek SV 307A noise monitoring station has been awarded PTB type approval, proving full compliance with IEC 61672 Class 1 requirements. This approval from PTB for the SV 307A means it has been independently verified for accuracy, durability and trustworthiness, which gives customer assurance that their data is defensible and reliable.
Common Issues with Calibration Certificates
Some certificates in circulation show some of the following problems: confusing or mixing “Class 1” and “Type 1” terminology, partial results presented as full compliance, missing traceability or equipment information can also be common along with certificates only covering the microphone and not the full system. These problems can ultimately mislead users into assuming compliance where it does not exist.
Key Advice for Clients and Buyers
Always ask, does the certificate reference IEC 61672 or only “Type 1”, check the results cover the entire system and that there is full traceability. Wherever possible pick equipment that has independent type approval. It is the clearest sign that what you are buying has been tested properly and that your data is reliable as it should be.
Sometimes the difference is in the label you can’t see. Knowing what’s behind your data is what really counts.
