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For the 3-digit code:
1. Press CODE/HL3 until 3 or less digits code are displayed. (Leading zeros are not displayed.)
2. Enter code in table.
3. Convert Hex to binary (see Table 1).
4. Look up each position in internal switch section.
3 decodes to unit 3.
F decodes to parallel printer with graph and text.
C decodes to 0A and 00 print ending and 2400 baud. (The baud rate is not used in parallel.)
TROUBLESHOOTING
Blank display.
Press ON/OFF key.
If still blank, change battery.
Unit will not start when battery changed. Try again.
Disconnect printer from unit and reconnect battery. Return for service.
Unit reads low.
Check that internal switches are in proper position.
Reset unit.
Change microphone and recalibrate unit.
Unit reads high.
Check position of internal switches.
Reset unit.
Unit is erratic.
Change microphone.
INTERPRETING RESULTS
When the M-27 is set up for OSHA compliance and for most other settings, the following are, in
general, true.
The HTL Lavg is less than the LTL and Lavg is less than Leq. The HTL Dose and TWA are less
than the LTL Dose and TWA.
If Run Time is less than eight hours, TWA is less than Lavg; if Run Time is more than eight
hours, TWA is greater than Lavg.
The SEL is greater than Leq.
The 3 dB Dose is greater than the LTL Dose if Leq is greater than the Criterion Level; it is less
than the LTL Dose if the Leq is less than the Criterion Level.
The above may not be true if the noise is below the threshold level.
If the noise is continuous or impulsive, then Lavg will be nearly equal to Leq.
If the noise is intermittent then Lavg will be several decibels less than Leq.
The time constant will cause the readings not taken with a 3 dB exchange rate to be greater than if
there were no time constant. For 3 dB it makes little difference.
The Peak Level will be greater than Slow Max unless the peak occurred while the instrument was
in PAUSE and was changed to RUN a few seconds later. Then Max Level might be greater than Peak
Level.
U.L. Time will not count unless the level has exceeded the upper limit level for a total of one
second.
In all of the above, "greater" and "less" include "almost equal."
Use of Lavg and TWA
Time Weighted Average (TWA) is measured in decibels. It is the accumulated noise dose
integrated over eight hours. The only difference