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it is turned on, is reset, or the PAUSE key is pressed. Wait until the sound level has stabilized before
entering the run mode.
Always remember to press RUN.
Press PAUSE before pressing PRINT. If in the run mode, the data printed at the beginning of the
printout will not agree with the data at the end.
Considerations of Measurement and Accuracy
An integrating meter such as the M-27 Noise Dosimeter can integrate all continuous, intermittent
and impulsive sound levels within the range of the instrument. This avoids many of the potential errors
created by attempting to read and correctly interpolate sound level meter readings in fluctuating sound
fields. However, it is important to use the M-27 correctly and to understand its limits (true of any instru-
ment) to achieve its maximum accuracy.
Microphone location generally has the greatest effect on the accuracy of any noise measuring
instrument. The correct placement of the M-27 microphone has been discussed under Effects of Operator
Presence.
Threshold discontinuity can cause notable differences in readings on various meters if the noise
level is near the threshold. Since the instrument assumes that noise even slightly below the threshold is
absolute quiet, that noise level is not accumulated into the results while a noise level just slightly higher is
accumulated. This is most noticeable in the readings of dose if the threshold is the same as the criterion
level.
Peak noise levels greater than the range of the instrument are "clipped" and act as if they were at
the maximum level of either 146 dB on the 50 dB range or 126 dB on the 30 dB range.
Minimum noise levels are either at the bottom of the range or at the noise floor of the instrument.
For readings which do not have a lower threshold, the accumulated noise will be at these levels.
Crest factor is an almost meaningless term for instruments with crest factors in excess of 30 dB.
The M-27 is capable of measuring pulses as short as 1 millisecond with a peak amplitude of 143 dB and a
background level of 80 dB. This is a pulse range of 63 dB. The crest factor would depend on how often this
pulse occurred but could be greater than 60 dB.
ACCESSORIES
Model WS-5 Windscreen
Refer to page 22 on how to use the windscreen with the M-27 microphone.
Model MB-1 Microphone Bracket
Refer to page 20.
Cables
59-818 36-pin Centronics parallel cable.
59-843 25-pin serial female connector cable.
59-874 25-pin serial male connector cable.
59-758 Computer booster cable.
59-879 9-pin serial female.
Tripods
Quest supplies two models of tripods for use with the M-27 as an area monitor. For use refer to
page 21.
BX-9 Battery Change Adapter
To preserve stored data in the M-27 memory during a battery change, the BX-9 Battery Change
Adapter may be used. The BX-9 allows you to remotely power the M-27 by plugging it into the printer
output connector and therefore keeping the dosimeter powered while disconnecting the battery and
replacing it with a fresh one. The BX-9 utilizes pins number 14 and 16 on the printer connector.