Ambient Sound Dosimeter
Indication of ambient sound level and total accumulated noise dose.
 
 
 Ambient Sound Dosimeter SD853m
The Ambient Sound Dosimeter is designed to measure and indicate the current sound level in an area, as well as the total noise dose (acoustic energy) received in a given day. The sound level (dBA) is the same as that which would be measured with a typical sound level meter. The energy dose (% of daily allowance) is that which would be measured with a typical noise dosimeter.

A miniature microphone is attached directly to the instrument, however an extension cable may be used for distant location of the main unit from its microphone, across a room or between rooms. The front panel LED’s indicate general sound level (70/80/90/100 dBA) and dose (25/50/75/100 %), and the backlit LCD is used for detailed readings and adjustments. Although specific measurements may be taken at any time, operation is fully automatic, including daily reset, such that no user input or adjustment is required over months or years of table-top or wall-mounted operation.
 current sound level and accumulated dose  current sound level and maximum time allowed
The primary readings of the instrument are of the sound level (L) in units of dBA, and of dose in percentage of the maximum allowed per day. The calibrated microphone signal passes through an A-weight filter, and is measured using an RMS averaging device. The level display has a standard 1 s, or 'slow', response time constant. The measured level is continuously integrated (over time from reset), and indicates the percentage dose of the maximum total daily acoustic energy dose allowed. An additional screen page displays the measured sound level with increased resolution, as well as the corresponding maximum time allowed at the current level, according to the sound exposure standard chosen. (The exposure standard is defined by parameters selected by the user.)
 Equivalent Sound Level  Average Sound Level  8h Time Weighted Average  Measurement Time  Manual Reset
Leq – is used (typically with integrating sound level meters) to indicate the equivalent or average sound level (dBA) over the time since reset. A constant level of Leq over the same time period would deliver the same total energy.

Lav – is used (typically with noise dosimeters) to indicate an average sound level (dBA), much like Leq, but where a constant level of Lav would deliver the same specific dose as defined by the selected noise exposure standard, which is not necessarily the same energy. The closer the exposure standard relates to theoretical power delivery, the more similar Leq and Lav will be. (Note that Leq ~ Lav for settings with Exchange Rate of 3 dB and a low integration Threshold Level.)

TWA8 – indicates a fixed sound level (dBA) that would result in the same displayed total dose (%) over an 8 hour period of exposure. It is an alternate way to express the dose. For example, for a set-up with Criterion Level of 85 dBA and Exchange Rate of 5 dB, at 100% dose one would have TWA8 = 85 dBA, at 50% dose TWA8 = 80 dBA, at 200% dose TWA8 = 90 dBA, and at 400% dose TWA8 = 95 dBA.

The Measurement Time is used in computation of Leq and Lav, and may be reset manually at any time, although it is normally left alone for automatic processing. (Reset results in a zeroing of both the measurement time and the total accumulated dose.)
 Criterion Level selection  Exchange Rate selection  Threshold Level adjustment
Crtn Lvl – Criterion Level (dBA) is that which would result in 100% dose after 8 hours exposure. It may be set by the user to any one of the common standards of 80, 84, 85, 87 or 90 dBA.

Exchg Rt – Exchange Rate (dB) is the increase (or decrease) in sound level that results in double (or half) the dosage rate. It may be set by the user to any one of the common standards of 3, 4, 5, or 6 dB.

Thrsh Lv – Threshold Level (dBA) is the level below which the computed dose does not accumulate, and above which the computed dose accumulates at a rate determined by the Criterion Level and the Exchange Rate. It may be adjusted and set to any level from 70 dBA to 90 dBA, in 1 dB steps.

A common industrial (older) set-up:
CL= 90 dBA, ER= 5 dB, TL= 80 dBA

A more conservative (newer) set-up:
CL= 85 dBA, ER= 3 dB, TL= 80 dBA
 Automatic Reset time interval adjustment  94 dBA mic gain calibration process  Display Contrast selection
Automatic Reset – In addition to manual reset (zeroing of dose and related variables), the user may adjust the number of idle hours after which the an automatic reset will take place. The instrument will automatically reset after this much time has passed without the sound level exceeding the Threshold Level.

Calibration – Recalibration may be performed by the user if the instrument (or its microphone if remote) can be exposed to a known constant ambient noise level of 94 dBA (or 94 dB SPL @ 1kHz).

The LCD contrast may be adjusted for extreme viewing angles, and the backlight automatically dims during extended idle time.
 
 
Architectural Specifications
 
Level Range: 65 – 109 dBA  and  75 – 118 dBA  (mic dependent)

Frequency Range: 20 – 20000 Hz

Level Display Resolution: 1 dB and 0.1 dB

Dose Range: 0% – 999%

Dose Display Resolution: 0.001% (active) and 0.1% (idle)

Sensor: detachable (short post) electret mic on powered jack

Display update rate: ~2 Hz

User interface: 8x2 backlit LCD, two buttons, two 4-LED bars

Power supply: AC adapter with 18 ft cord (200mA @ 9Vdc)