Model 831 - Exceedance Logging

The following functions are available when the Exceedance Logging Analysis Firmware option is installed.

Exceedance Logging is performed with the Model 831 in the Event History Mode. The Optional Firmware (ELA) is required in order to measure and store data associated with exceedance events.

Event History

The Event History mode provides a detailed record for each acoustic data event providing the following metrics following an Event Trigger:

• Date and Time

• Duration

• Equivalent Energy Level (Leq)

• Maximum RMS and Peak levels

• 1/1 or 1/3 Octave Band Leq and Max Spectra

An 'Event' occurs when the measured Sound Pressure Level (SPL or Peak) exceeds a user-predefined threshold. The event occurs when a Trigger occurs from:

Level Trigger Method: where the event occurs when an Absolute SPL level from the RMS Detector (Slow/Fast/Impulse) level (SPL-1) exceeds the User-defined Absolute SPL level (SPL-1) or when the Absolute Peak Detector level exceeds the user-defined Peak Level.

     Note:

     When the signal exceeds a higher trigger level (SPL-2) is also noted.

Dynamic Trigger Method: where the event occurs when Signal-to-Background SPL level from the RMS Detector (Slow/Fast/Impulse) level exceeds the user-defined Signal-to-Background SPL level or when the Signal-to-Background Peak Detector level exceeds the user-defined Signal-to-Background Peak Level.

      Note:

     When the signal exceeds higher trigger level (SPL-2 and SPL-3) is   also noted.

For signals that are of interest two methods in the 'Time Domain' are used as an acceptance filter:

Minimum Duration: the minimum duration time is a user-selected parameter which requires that a signal exceed a duration time before it can be can be considered an event for storage logging.

Continuation Period: when a signal exceeds the Trigger Threshold requirements, as an event, the end of the event can be defined as the point at which the signal remains below the threshold level after a user-selected elapsed time. Therefore, when the signal is below the threshold level for lesser time periods it may be considered as still being part of the signal event.

Event Time History

The Event Time History will enable the following time history data to be measured as part of each event history:

• Period: defines the length of time for each time history sample (20ms to 10s)

• Spectral Mode: defines the length of time over which each Spectral Ln value is averaged for 1/1 and 1/3 Octave Band data

• Pre-trigger: defines the length of time data is stored before the occurrence of each event ( event trigger)

• Maximum Number of Samples: user selected maximum number of samples from 10 to 9,999 (default value 1000)

Event History Displays

Event History data are displayed in the following views:

• Level Displays: event records stored sequentially in time as measured Levels of Leq (A/C/Z); Lpeak (A/C/Z); Lmax (A/C/Z) & (S/F/I); LAE (Sound Exposure Level); EA (Sound Exposure) for the displayed event record

• 1/1 Octave Display: 1/1 Octave Spectrum Graph Display; Frequency (at cursor); Leq (A/C/Z); Lmax (A/C/Z) & (S/F/I); Event Data (event displayed/number of events measured)

• 1/3 Octave Display: 1/1 Octave Spectrum Graph Display; Frequency (at cursor); Leq (A/C/Z); Lmax (A/C/Z) & (S/F/I); Event Data (event displayed/number of events measured)

• Event Time History Display: Leq Graph Display; (integration time equal to user selected history period); Leq value/period (at cursor position); Time History Data (time history record displayed/number of number of time history records measured); Event Data (event displayed/number of events measured)

• Event Spectra Time History: 1/1 or 1/3 Octave Spectrum Time History Graph Display; Spectrum Selected; Frequency (at cursor); Level (at cursor); Time History Data (time history record being display/number of time history records measured); Event Data (event being displayed/number of events measured)

Links to Time History & Measurement History

When the Time History and/or the Measurement History have also been enabled a link is provided to make rapid transition from any of the Event History displays to the Time History display and/or the Measurement History display.

Measurement History Analysis

With the Exceedance Logging Analysis Firmware installed the following Run Time modes can be performed:

• Continuous ... Measures data over a user selected time interval ... initiated at 'Power On' and terminated by the 'Stop' key

• Single Block Timer ... Measures data over a user-defined time period from 'Start Time' to 'End Time'  (time/date) ... initiated and stopped manually (Run/Pause and Stop)

• Daily Timer ... Measures data over a user-defined time period from 'Start Time' to 'End Time' (time of 1/2/3 blocks within 24hr period) ... initiated and stopped manually (Run/Pause and Stop)

For each mode, the Measurement History function will perform a series of measurements over a user-defined time interval and automatically store the data. The following menus will assist in the setup:

Measurement Time Menu: duration of each measurement

Interval Time Synch: ensures that the measurement records begin at a time equal to a multiple of the measurement time

Link to Time History

When Time History has been enabled, a link is provided to make rapid transition from any Measurement History display to a Time History display