Model 50 Series
Application Overview
Sonomètres Pulsar 
Lärmmessgeräte Pulsar Application Overview
This series consisting of the General Purpose or Type 2 model 52 and the Precision Grade or Type 1 model 51 and both are basic sound level meters; that is to say they measure only in exponentially averaged units. They offer all the three Time-weightings of ‘S’ (Slow), ‘F’ (Fast) and ‘I’ (Impulse) as well as Max hold.
Note:- The single letters are used today, instead of the whole word, so as to be the same in any language.
For reference, the rise and fall time constants of the three time-weightings as specified in IEC 60651 are:-
| Response | Up Tc | Down Tc |
| S | 1000ms | 1000ms |
| F | 125ms | 125ms |
| I | 35ms | 1500ms |
Usage
Such ‘simple’ or classic sound level meters, that is exponentially averaging units, were the main method of making noise measurements from about 1960 up until the Leq meter was developed as a practical tool in the early 1980’s. Even so, many traditional users still prefer the simplicity of these types of instrument.
The measurement
Because this series contains only exponentially measuring instruments, they are not usually used for ‘mainstream’ factory noise measurements for the various European Directives; for this the linear averaging units such as the 30 or 70 series are preferred. Clearly, if a very low noise level is measured in the workplace, using an exponentially measuring unit, say less than 70dB(A), it is VERY unlikely that the Leq, or LEP,d will exceed the “85dBA for 8 hours” limit. For this reason, where very low levels are involved, the 50 series is an adequate unit for this task.
Application Details and FAQ’s
The main applications of the 50 series are:-
- Vehicle Noise testing, both for racing and road use
- Product noise testing, where the output is used for Go-NoGo indication
- Machinery noise, to check changes in noise levels
- Low-level environmental noise, both rural and urban
- Factory surveys, before a full investigation
- Investigating noise complaints, usually for neighbourhood noise
Another very common ‘application’ is the use of the 50 series as a ‘head’ for complex acoustical measurements. For example, the signal output is often used to feed one channel of a multi-channel analyzer, or a tape recorder, so that the frequency weighting and signal gain control features of the 50 series can be utilized to the full. This is especially useful when the precision model 51 is used, as the full microphone performance can be utilized to give good data from about 18dB(A) to above 140dB.
Special precautions
The 50 series are so simple to use that really the only precaution is the use of a windshield if the measurement is being made in a wind speed that is likely to affect the noise readings. The normal windshield is a 90mm unit and it has little effect on the accuracy of reading. The instrument manual gives the precise corrections that need to be made, but except where the highest accuracy is needed – and only for the model 51 – the correction is insignificant.
Special Features and Functions
The 50 series have a backlit display. This simple addition makes it possible to use the instrument for night time measurements without the need for an external light that often attracts attention.
Like all the units in the standard ‘slimcase’ range a tripod mount is incorporated so that the meter can be kept away from the body of the user and thus avoid acoustic reflections and masking that hand held use often causes. This tripod mount is as near to the bottom of the case as is practical and many users complain that it is nowhere near the centre of gravity and thus care has to be taken so it remains stable on a tripod. This position is chosen deliberately as it puts the tripod mount as far away as possible from the microphone and as a result reduces the possibility of any acoustic reflection affecting the measurement.
The only precaution is that the 50 series should be calibrated before and after each usage and the Pulsar Model 100 is the designed calibrator for this series. Naturally, like any other sound level meter it should be returned to Pulsar or an approved laboratory for its annual calibration, or routine verification to ensure it remains in specification.