9/29/09 Using ID Setting Files 7-190 to 255 dBExposures at higher levels than the overall criterion levelwill result in a 100% dose in less time; or, if exposurecontinues, the overall dose will exceed 100%.Criterion Time - (LOG) The Criterion Time determines how long exposure to the setTWA level can occur before 100% dose occurs for theoverall measurement.Crnt Exchange - (SSA, ISM,LOG)In the ISM instrument the CrntExchange setting is a submenu to theSLM menu selection.The Crnt Exchange rate setting sets the exchange rate(sometimes called the “doubling rate”) that calculates thecurrent TWA. The exchange rate reflects the relationshipbetween the permitted exposure levels and the exposureduration. Selecting an exchange rate of 5dB, for example,means that 5dB may be added to the permissible exposurelevel every time the exposure duration is cut in half. Thissetting provides the following four options:This setting affects the System 824’ssecondary or current buffer.3dB - The Crnt Exchange defaults to the 3dBoption. This provides a L eq time weighted average inaccordance with European common usage in additionto compliance with U.S. Environmental ProtectionAgency (EPA) regulations.4dB - The 4dB option results in the L DOD timeweighted average which complies with U.S. Depart-ment of Defense (DOD) regulations.5dB - The 5dB option results in the L OSHA timeweighted average which complies with U.S. Occupa-tional Safety and Health Administration (OSHA) reg-ulations.6dB - The 6dB option results in the L Avg timeweighted average which provides a convenient repre-sentation of the long-term average noise level asopposed to the RMS noise level.
