User Manual

A white paper issued by Siemens  September 2015

2nd fire alarm

There are only a few seconds pre-warning time left during which final measures must be per-

formed in order to limit disruption.

 Evacuate people from the flooding area.

 Optimally prepare storage systems for the impending discharge by initiating a “panic dump.”

Flooding

During the flooding, Silent Extinguishing prevents the sensitive IT equipment from being

exposed to excessive noise levels.

Intervention

The measure plans for operation critical tasks, such as switching off the main

power supply, should be agreed in advance by the involved parties and implemented in the Data

Center Integrated Management System.

3 Questions and answers

Basics of sound measurement in decibels (dB)

dB values are frequently seen in discussions related to Silent Extinguishing. dB values are often

used in conjunction with a so-called weighting curve when the discussion concerns audible

evaluations.

The objective of the dB(A) curve is to represent the sensitivity of the human ear. The use of an

A-weighted dB value/curve does not reflect the HDD type-specific spectral sensitivity, which makes

the use of dB(A) values for HDD sensitivity not very meaningful.

 dB(A): The most common weighting that is used in noise measurement is A-weighting. Like the

human ear, this effectively cuts off the lower and higher frequencies that the average person

cannot hear.

Defined in the sound-level meter standards (IEC 60651, IEC 60804, IEC 61672, ANSI S1.4), a

graph of the frequency response can be seen below.

 dB(C): The response of the human ear varies with the sound level. At higher levels, 100 dB and

above, the ear’s response is flatter, as shown in the C-weighted response below.

Although the A-weighted response is used for most applications, C-weighting is also available

on many sound-level meters. C-weighting is usually used for peak measurements as well as in

some entertainment noise measurement, where the transmission of bass noise can be a prob-

lem.

 dB(“HDD”): This weighting curve would need to be used to depict the sound sensitivity of

magnetic hard disk drives (status of technology in 2009). The sensitivity curve has been

empirically determined by Siemens.

 dB(Z): Z-weighting is a flat frequency response of 10 Hz to 20 kHz ±1.5 dB. This response

replaces the older “linear” or “unweighted” responses because these did not define the frequen-

cy range over which the meter would be linear.

Siemens prefers to discuss noise values in spectral resolution, normally in a third-octave resolu-

tion.