SPL Meter

Since the calibration standards were set up in the second half of the 20-th century here has been a growing necessity for regular calibration control of the instruments used. Depending on the kind of the instrumentation there can be 6 classes of calibration. Depending on the sphere of use of the instrument, it may belong to a certain class, registered, labelled (for example, “calibrated” if it is class l or “out of service” if it is class 6), each instrument gets its own file with the information about the device, its history, first operation, possible malfunctions. Calibration checks need to be repeated with the time. Each calibration result is examined by the particular authority and the next check is scheduled after the calibration is satisfactory and confirmed.

A SPL meter which can be used as a standard reference model is referred to as Class l. Class ll comprises those SPL meters that are for test or measurement and recorded inspection.

As a rule, only the results of the measurements and the time may show when it is appropriate to recalibrate or conduct the next calibration of the SPL meter. The manufacturer’s recommendations on the calibration of an SPL meter are not usually taken into consideration, and the calibration is usually performed by the designated authority in order to get the objective results. A very important point is also how often and how the noise level meter / SPL meter is used. This is especially important for a Class l SPL meter. If an SPL meter has been used excessively during a short time interval, it may make sense to recalibrate the SPL meter to make sure that all the functions are correct and the accuracy corresponds. Depending on the environment, the calibration time intervals may also be changed. Laboratory conditions may differ a lot from the measurements on-site, it means that humidity, temperature, contaminants may have a negative influence on the SPL meter and the new calibration may be desirable.

In reality, many modern SPL meters are as stable as calibrators themselves. In the past, all the instruments required calibration, nowadays some of them, for example, a SPL meter, is very precise and stable. Of course, in the process of operation different kinds of damage are possible, especially with fragile and vulnerable instruments (like microphones) and then calibration is applied to restore or verify the correctness of the of the SPL meter.

Class l calibration is the most accurate type with a very small uncertainty (or tolerance), class ll allows a bigger deviation. Depending on the SPL meter class, different kinds of calibration can be applied. For example, when it comes to sound meters / SPL meters, Class l should give +/-0.3 dB, Class ll +/- 0.5 dB or when it comes to weights, Class l gives 2.5 mg tolerance for 1 kg weight, at the same time Class ll gives 5 mg.

The SPL meters and instruments must have a calibration certificate nowadays. A calibration of a decibel meter / SPL meter helps, if not to avoid, then to minimize the risk to get uncertain results and measurements.

One more step which may follow calibration is getting a Type Approval from the PTB. SPL meters should also be applied for PTB (Physikalisch-Technische Bundesanstalt) approval. It is the German International Metrology Institute. This Institute is one of the main test and verification institutions, that gives scientific and technical services. One of its main responsibilities is to give or not to give the National Type Approval of measuring instruments and all the auxiliary mechanisms and devices which have to be legally verified. The UK equivalent to the PTB is the NPL (National Physical Laboratory) and the US equivalent is the NIST (National Institute of Standards and Technology).

A SPL meter is often tested by the PTB, NPL or NIST to get the Type Approval Certificate. This document confirms that a certain noise level meter / SPL meter has been tested in accordance with all the relevant requirements of the Type Approval System.

To apply for type approval, it is necessary to present all the technical information about the SPL meter, manufacturer contact information, purpose, name and application area of the noise level meter / SPL meter, including the type of calibrator used. As a rule, for a class l sound meter or SPL meter, a class l calibrator should be used and not less. For a class ll noise meter / SPL meter, a class ll calibrator is enough. The calibrator used for the calibration of the SPL meter also needs to get an approval from the PTB, NPL, NIST or other authority. Only after all the information about the SPL meter is studied and checked, after all types of tests, mechanical and electrical, are conducted and the results analysed, the above-mentioned certificate for the SPL meter may be issued.

Accredited calibration laboratories work in close cooperation with the PTB, NPL or NIST organization. The main task of that cooperation is to guarantee and ensure the uniformity of all measurements taken.

Nowadays it is near to impossible to find a place in a town or city where there would be an absolute and total silence. Too much traffic, too many people, factories, plants, railway stations, airports and so on – from the one side, life is unimaginable without all these things, from the other – life may turn into torture, if they get out of control and do not meet any requirements. Outdoor noise or sound – is one of the stress causing factors and that is why the permissible level of the sound emission is under permanent control by a spl meter. Any equipment used outside (vehicles, devices, machinery) should meet the requirements of the EU directive concerning noise and outdoor equipment. Especially when it goes about living districts, there are particular time periods when the works by means of the drills and other noisy equipment, can be carried out. Even though these sounds are transient and do not last permanently, their level is extremely high for a normal unprotected human ear and that is why is strictly regulated and must measured by a spl meter. Problems with noise level are also experienced by those who live in the proximity to the railway stations, airports, noisy streets or even hospitals and police stations. Excessive and long-term exposure to high-level noise may have dramatic negative impacts on the human health (hearing damage, raised nervousness and irritability, unstable phycological condition), and in some areas noise monitoring and control by use a spl meter is an essential task! Thus, noise level of 120-150 dB /decibel (airport noise, planes taking off and landing, road drills) is absolutely dangerous to the human beings and that is why continuous presence or living very close to the sources of such kinds of noise may have consequences. The perfect level of 30-50 decibels, which is quite a favorable atmosphere with the sounds of a more quire and pleasant character, is sometimes not reachable any more.

To understand how bad the noise really is just by description of your physical perception is impossible - You have to use a spl meter. Different people percept noise in different ways, and what is perfect for some people, is unbearable for the others. Therefore, the limits of noise exposure have been set based not on individual opinions, but on scientific conclusions concerning healthcare. It applies to all people who are exposed to noise, not depending on their personal preferences: workers operating drilling equipment and similar should wear protective clothes, airports should mostly be built outside the living areas, the sirens should be adjusted to an acceptable level and many other similar points.

That is why a special spl meter has been created: allows not only measuring and, thus, monitoring the environment “noise pollution” permanently, but enables to carry out the necessary changes, either in planning, or in already existing processes, for improving the surrounding atmosphere. This spl meter is weather proof, which means that is can be used even under harsh environmental weather conditions and the measuring process will not be interrupted. Since the measurements are to be carried out outside, near the airports or construction sites, a long-lasting battery pack is provided and there is no need to search for a power source when measuring on site. The possibility of mounting the spl meter on a tripod provided makes the measuring process easy and convenient and there is no necessity to hold the spl meter. The readings collected after a certain period of time may be processed and an absolutely clear picture of the noise level in a particular area / region is received.

It is necessary to remember that there are noise limits, for both, its level, as well as for its duration. The measurements received with the help of the spl meter show discrepancy between the desirable and real values and thus, any problem connected with the noise emission can be solved in a correct way, so that all the requirements were met and the working process (construction, airport, vehicles with sirens) was not stopped anyways.