THE LARGE NULL-BAR COMPRESSOR COMPARISON

THE LARGE NULL-BAR COMPRESSOR COMPARISON

Our large portfolio of compressors often leads to questions from you, which we want to clear up for you with this large-scale comparison. For this purpose, we have taken all compressors from our program and carried out some tests with them.

 

We built a small soundproof room (120 x 80 x 80 cm), in this room we poured a concrete block with a mass of about 100 kg. We then mounted the various compressors on this block using the mounting material supplied with each one. Inside the sound-insulated room, we set up a sound level meter at a distance of 50 cm from the compressor head. The pressure outlet of each compressor was placed outside and connected to a 20 L pressure reservoir. We mounted a pressure sensor on this reservoir.

 

A self-developed microcontroller took over the analysis of the pressure sensor, the communication with the sound level meter and the control of the compressor. The values determined by the microcontroller were made available in real time to a measuring computer, which recorded the data. We performed 5 measurements per compressor from 0 to 13 bar, leaving the compressors approximately one hour to cool down each time. We therefore always started with a cold compressor, which we felt was closer to everyday use. In addition, the speed varies by up to 10% with a hot compressor, regardless of manufacturer and model.

 

The compressors were each powered by a Switch Mode Power Supply with a constant 13.8 V voltage and up to 40 A current.

 

To determine the pressure curves, we used all measured values of the 5 measurement series {time[s] | pressure[bar]} in each case and combined them to create a large data pool. From this data pool we calculated an approximation by a 4th order polynomial using the " smallest squares " method. All calculated curves have a coefficient of determination R² of more than 99% and are therefore almost perfect models. The curves show the pressure versus time, the steeper the curve, the faster the compressor.

 

To calculate the average sound level, we calculated the average values of the sound level per measurement between 1 and 12 bar, then averaged all measurements of one compressor. The average sound level is given in dBA (Dezi-Bel A-weighted). The higher the value, the louder the sound source. Since Dezi-Bel is a logarithmic quantity, a 10-dB increase is already a doubling of the perceived loudness.

Pressure vs Time (20L Volume)

Performance [%]

avg. Noiselevel (1 - 12 bar)

Truth also includes repeatability and measurement uncertainty. For a total of 10 measurements on 2 different days of the same compressor, the standard deviation of the time from 0 to 12.5 bar σtime was 5.82 s, while the standard deviation of the average sound level between 1 and 12 bar σsound level was 0.45 dBA. According to the calibration of the sound level meter, the absolute value of the sound level is ±3.9 dBA, although this does not apply to the differences between the individual compressors. Here we can assume a normal distribution, which based on the standard deviation σSound level 0.45 dBA, have a 95 % certainty to the given value of ±0.882 dBA.

 

Finally, we do not want to keep the results of the individual series of measurements secret from you, of course, therefore the individual measured values in tabular form:

CompressorTime (0 - 12.5 bar) [s]Sound level (1 - 12 bar) [dBA]
min.max.avg.min.max.avg.
Streetec Comp 1 EVO55557456479.380.079.7
Streetec Comp 2 EVO42243743079.880.079.9
Viair 444C49451650679.480.880.1
Viair 480C64566165481.181.881.5
Viair 485C Gen 256958557780.381.781.1
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