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NOTE
When the unit is off, the battery still powers the memory. If the unit is not going to be
used for a few days, the battery should be removed.
Microphone Replacement
The microphone is field replaceable. To unscrew the microphone, grip the knurled nut on the top
of the dosimeter and gently turn it counterclockwise. Do not twist or turn the cord or black strain relief.
Replace with new microphone and recalibrated unit.
Calibration and Maintenance
The M-27 should maintain its accurate calibration for many months of use. However, to insure
consistently accurate operation it is recommended that the unit be returned once a year for a complete
checkout and calibration. The calibration standards for the equipment in Quest's laboratory are traceable to
the N.I.S.T.
The M-27 should be checked each day before it is used. It is recommended that one of the Quest
calibrators be used, with the proper 8 mm microphone adaptor.
Daily Calibration
1. Turn M-27 on and press any key. If LOBAT is displayed, the battery is low and should
bechanged.
2. Turn on the calibrator and check the battery indicator. Replace the battery if required. If the
calibrator has multiple frequencies or levels, set it to 1000 Hz. Listen to see if the calibrator is producing a
tone.
3. Remove the windscreen from the microphone. Carefully insert the microphone in the
microphone adaptor and place the adaptor in the calibrator. Make sure the microphone is inserted all the
way in the adaptor and the adaptor rests flush on the inner rim of the calibrator. Turn on the calibrator. If
the calibration is done at high altitudes see Altitude Corrections below.
4. Press CODE/HL3 until CAL is displayed. Press SOUND LEVEL. If the level is correct, press
PAUSE/RESET until CAL is displayed.
5. If the reading is off slightly, insert a small screwdriver in the hole above CAL and slowly turn
the CAL screw until the display reads correctly. Press PAUSE/RESET until CAL is displayed.
6. The M-27 is now calibrated and ready for use.
7. If a calibrator is used at any frequency other than 1000 Hz, then the proper correction for that
frequency weighting must be made (see Figure 4).
Altitude Corrections
The effects of atmospheric pressure on the M-27 are negligible. However, calibrator sound levels
are affected by pressure and corrections must be made. For the Quest Calibrator the correction is -.1 dB for
each 2000 feet above sea level.
OPERATING PROCEDURE
As a Personal Noise Dosimeter
1. If display is blank, press ON/OFF to turn unit on.
2. Clear the M-27 memory by pressing and holding down the PAUSE/RESET key until it counts down
from P-5 to P-0 and - --.
3. If LOBAT is displayed, replace the battery and continue.
4. Check the calibration of the unit (see Calibration and Maintenance).
5. Check CODE to see if correct.