7-18 824 Reference Manual 9/29/09exposure level every time the exposure duration is cut inhalf. This setting provides the following four options:The formulas for TWA can be foundin "Integrated Level Calculations"on page B-1.3dB - The default 3dB option is the most commonlyused and results in the L eq time weighted average.(When a threshold of 0 is used.) It is used internation-ally and for measurements that comply with U.S.Environmental Protection Agency (EPA) regulations.4dB - The 4dB option results in the L DOD timeweighted average which is used for measurementsthat comply with U.S. Department of Defense (DOD)regulations.5dB - The 5dB option results in the L OSHA timeweighted average which is used for measurementsthat comply with U.S. Occupational Safety andHealth Administration (OSHA) regulations.6dB - The 6dB option results in the L Avg timeweighted average which is merely a convenient rep-resentation of the long-term average noise level asopposed to the RMS noise level.Ovll Threshold - (LOG)This setting affects the System 824’sprimary or overall buffer.The Ovll Threshold setting sets the threshold for computingthe overall time weighted average (TWA).As per the requirements of various regulatory agencies, onlythose sound levels which are above a certain threshold levelare used when computing the TWA. Accordingly, thissetting can take on any integer value within the followingrange:0 - 255 dBFor hearing conservation measurements, set the threshold to80dB. For most community noise measurements, set thethreshold to 0dB. (When set to 0, all levels are included)Ovll Criterion - (LOG) The Ovll Criterion setting sets the TWA level whichconstitutes 100% dose for the overall measurement. The100% dose occurs if a person is exposed to that level for thecriterion time. Accordingly, this setting can take on anyinteger value within the following range:
