Extech Instruments SL120 User manual

User's Manual
Sound Level Monitor
Model SL120
Meets ANSI and IEC Type 2 Sound Level Meter Standards
Settable High Limit with large OVER indication and Alarm Output
Wall or Desk mountable
Extra large LCD display with bargraph
Maximum level display with time stamp
Optional alarm kit drives remote over limit indicators.
Test Equipment Depot - 800.517.8431 - 99 Washington Street Melrose, MA 02176 - FAX [phone] - TestEquipmentDepot.com

Version 1.2 9/05
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Introduction
Congratulations on your purchase of the Extech SL120 Sound Level Monitor. Designed for
wall mount, desk, tripod mount or hand held operation, this meter meets ANSI and IEC
Type 2 Sound Level Meter standards. Included is a High Limit Set Point with a large OVER
indication when the set level is exceeded. An Alarm Output can be used in conjunction with
the optional Alarm Module Kit to power a larger or a remote indicating device such as a
“QUIET” sign. Professional features include programmable A/C Weighting and Fast/Slow
Response time, Max Memory with time stamp, and a Clock display. The microphone can
be rotated 180 degrees to accommodate any meter location or it can be placed at a remote
location using the optional Remote Microphone Cable. A programmable ON/OFF time
extends battery life to 30 days when programmed 8 hours per day. Careful use of this
meter will provide years of reliable service.
Specifications
Applicable standards Meets IEC 60651-1979 and ANSI S1.4 1983 Type 2
SLM standards
Display 4.6” x 3.125” multifunction LCD
Frequency bandwidth 31.5 Hz to 8 KHz
Microphone 0.5” Electret Condensor Microphone (remoteable)
Measurement ranges 30 to 80dB, 60 to 110dB, 80 to 130dB
Frequency weighting ‘A’ and ‘C’ (Programmable)
Response time Fast (125ms) / Slow (1s) (Programmable)
Resolution 0.1dB
Max Hold Maximum reading is displayed with time
Alarm output 3.5mm Mono Phone Plug, Maximum: 3.4mA @ 5 Vdc,
Minimum Output Voltage: 2.5 Vdc
Limit range 30 to 130dB
Under range indication “- - -“
Over range indication “OL”
Power 8 AA Batteries; optional AC adaptor (9V@350ma)
Battery life 240hrs continuous (approx); 30 days @ 8hrs/day
Operating temperature 32 to 122oF (0 to 50oC)
Operating humidity Less than 80% RH
Dimensions / Weight 8.75x7.1x1.25" / 0.63 lbs. (22x18x3.2mm / 285g)

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30-80
LIMIT
80-130
60-110
123456
Meter Description
1. Microphone
2. Over Limit Display
3. Bargraph
4. dB display
5. OFF/ON/AUTO switch
6. Clock display
7. Max level display with time stamp
8. Set limit
9. MAX RESET button
Rear Panel
1. Range select switch
2. Time set buttons
3. Limit set buttons
4. Calibration adjustment
5. A/C select button
6. F/S select button
Test Equipment Depot - 800.517.8431 - 99 Washington Street Melrose, MA 02176 - FAX [phone] - TestEquipmentDepot.com

Version 1.2 9/05
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Sound Level Monitor Operation
Initial Configuration
1. Install 8 AA batteries
2. Setting the TIME
a) Press and Hold the Time SET button until the hours display
begins to flash.
b) Press the Time up arrow button until the hour is set.
c) Press the SET button. The minutes display will flash. Adjust as needed.
d) Press the SET button to step through and the arrow button to adjust;
Time of day Hour
Time of day Minutes
Time of day AM / PM / 24 Hour
Year
Month
Day
Auto ON Hour
Auto ON Minutes
Auto OFF Hour
Auto OFF Minute
A/C Frequency Weighting
Change the Frequency Weighting by pressing the 'A/C' button. The 'A' or 'C' icon will
appear on the display.
With ‘A’ weighting selected, the frequency response of the meter is similar to the response
of the human ear. ‘A’ weighting is commonly used for environmental or hearing
conservation programs such as OSHA regulatory testing and noise ordinance law
enforcement. ‘C’ weighting is a much flatter response and is suitable for the sound level
analysis of machines, engines, etc.
Most noise measurements are performed using 'A' Weighting and SLOW Response.
Slow/ Fast Response
Press the button to select Fast or Slow response as desired. F or S will appear in the
bottom of the LCD display.
Select FAST to capture noise peaks and noises that occur very quickly. Select the SLOW
response to monitor a sound source that has a consistent noise level or to average quickly
changing levels.
Select Slow response for most applications.
Range Selection
Slide the Range switch to the 30-80, 60-110 or the 80-130 position.
The selected range will be indicated on the LCD bargraph. If the
measured dB level exceeds the range selected “OL” will be
displayed. If the measured dB level is below the selected range “- - -“ will be
displayed.
Normally, select the range in which the upper dB level is greater than any
expected sound pressure level. The 60 to 110dB range is the most commonly
used range. Use the 30 to 80dB range in quieter areas such as offices and classrooms.
Note: When the range is changed the Max display may indicate an overload “OL”. Press
the MAX RESET button to clear the MAX display.

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Over Limit Set
Press the up or down LIMIT arrow buttons to set the OVER limit
level as displayed on the LCD. If the measured dB level exceeds
the set limit, the indication will appear in the display and the
over limit signal will appear at the alarm output connector. The
display indication and output signal will remain active as long as the
sound pressure level exceeds the set limit.
MAX Hold
The MAX display indicates and holds the highest dB level measured
since the meter was turned on or since the Max Reset button was
pressed. The time and date of the max reading is also displayed.
To clear the display and start a new measurement session, press the
front panel MAX RESET button. If the measured level exceeds the maximum for the range
selected the MAX display will indicate “OL” (overload).
Programmable OFF/ON/AUTO time
The meter is powered by 8 AA batteries or via an AC adaptor for permanent installations.
Continuous battery life is approximately 240 hours (10 days). By programming the ON/OFF
time, the battery life can be greatly extended (30 days assuming an 8 hour day). The ON
and OFF times are programmed as described in the initial configuration
paragraph. The meter will operate continuously with the power switch in
the ON position. The ON/OFF time will be controlled by the meter when
the power switch is set to the AUTO position.
Calibration
The sound level meter should be calibrated on a regular basis to assure that the meter’s
performance and microphone sensitivity has not change. Some operational directives
require daily calibration checks (OSHA). Extech offers several acoustic calibrators to
perform the calibration.
1. Set the meter to the 60 to 110dB or 80 to 130dB range.
2. Place the external calibrator over the Sound Level
Monitor's microphone and turn the Calibrator on.
3. The meter should read close to the calibrator's dB output
level. Typical Calibrator output levels are 94dB and 114dB.
4. If the meter is within ± 0.2 dB of the calibrator’s output, no
adjustment is necessary.
5. Adjust the calibration pot on the rear of the meter to the
proper level.
Test Equipment Depot - 800.517.8431 - 99 Washington Street Melrose, MA 02176 - FAX [phone] - TestEquipmentDepot.com

Version 1.2 9/05
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Meter Placement
The meter can be used Handheld, Wall mounted, Desk mounted or Tripod mounted. For
wall mount operation, orient the microphone perpendicular to the wall to minimize the
affect of acoustic reflections. For desk mounting, extend the rear legs and lock in place
with the hinged locks. The tripod mounting nut is located on the bottom of the unit.
Remote Microphone (optional)
The optional 15’ remote microphone cable can be used to place the microphone in one
location while viewing the dB levels and/or generating a high limit alarm at another
location. To remove the microphone, unscrew the holding collar and lift the microphone off
the connector. The extension cable can then be plugged into the matching connectors.
Calibration should be performed after the cable is installed.
Alarm Output (optional)
The alarm output drives the optional Remote Alarm Relay Module (cable and relay) when
the LIMIT set point is exceeded. The relay module can be used to power external warning
signs, “QUIET” signs or other indicating devices when the sound level is higher than the
programmed limit. Refer to the manual supplied with the module for connection
information.
HEARING
PROTECTION
REQUIRED
AC or DC Power
Relay Module
Indicating Device
Note: For up-to date information on this product, optional accessories and literature, call
or go to www.extech.com.

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Frequency (Hz)
Weighting Response Curves
Measurement Considerations
1. Use a windscreen (not included) to cover the microphone in windy conditions.
2. Calibrate the meter often, especially if the meter has been idle for a long period of time.
3. Do not store/operate the meter in areas of high temperature or humidity.
4. Keep the meter and the microphone dry.
5. Avoid severe vibration when using the meter.
6. Remove the battery when the meter will be stored for long periods of time.
Frequency Weighting curves
OSHA permissible levels Permissible Noise Exposure Limits
Duration per Day (hours) Sound Level db(A) Slow response
16 85
8 90
6 92
4 95
3 97
2 100
1-1/2 102
1 105
1/2 110
¼ or less 115
Test Equipment Depot - 800.517.8431 - 99 Washington Street Melrose, MA 02176 - FAX [phone] - TestEquipmentDepot.com