Sound level meters: a matter of class
Since sound level meters, or slm's were invented, they have existed in various grades of accuracy. Today, accuracy is referred to as 'Class' and the reason behind all this rests with the microphone.
A microphone to measure the top 'Precision Grade' has always been very expensive. To give a scale order, a high quality precision measuring microphone has always costed many times the list price of a simple 'ordinary' meter. The difference between the two is simply the measuring accuracy. Originally, there was no international standard for sound level meters and the first one numbered IEC 123 in the late 1960's set the tone for all future standards. Soon it was realised that the accuracy of an IEC 123 meter was inadequate for research and similar tasks, so a new standard for a 'precision meter' was developed, numbered IEC 179. This was intended to represent the summit of technology at the time.
By the 1980's such a simple distinction was felt to be inadequate, so a new standard, IEC 651, added further 'types' '0' and '3'. What was originally IEC 123 became effectively a Type 3 meter and a rather more accurate device was introduced as a Type 2. In addition, a 'Type 0' or laboratory grade was listed. 'Type 0' soon faded from history, and this new standard, eventually renamed IEC 60651 remained for many years. In 2003 a new standard was published - still in use today - IEC 61672 with just two classes: Class 1 and 2.
The 'design centre' or target of the specification is the same for both classes. The only significant difference is that a Class 2 sound meter is less accurate in that it has wider tolerances. However, the superior accuracy of a Class 1 sound meter cannot be realised in a normal industrial environment due to noise reflecting from walls, ceiling and other solid objects. For this reason, the European Union mandates that a sound level meter should be 'at least a Class 2'. For more than 90% of industrial applications, especially for Noise at Work measurements, a Class 2 meter is perfectly adequate. Law enforcement officials and research labs tend to buy and use Class 1 meters, as they work may need to be scrutinised in court, but for the 'average' user, a Class 2 meter is perfectly acceptable.
Importance of Pattern Approval
However, what is far more important than the class of meter is a formal certificate of compliance, or 'Pattern Approval' certificate from a qualified government laboratory that assures the user or potential buyer that the sound level meter, whether Class 1 or 2 truly meets the standard claimed for it. Only a handful of top manufacturers can do this today. A number of low cost units currently on the market are some way away for meeting their claims and their potential errors mean that workers' hearing may be 'at risk' because of the poor accuracy.
For examples of both Class 1 or Class 2 sound level meters, please visit Pulsar Instruments' website here.
To discuss your noise measurement requirements, or your queries about Noise at Work legislation, please contact our team here or by phone on 01723 518011.