TABLE OF CONTENTS
INTRODUCTION …………………………………………………………………….. 1
SIMPLIFIED OPERATING INSTRUCTIONS …………………………………….. 1
Turning MICRO-15 On ……………………………………………………………… 2
Changing Battery …………………………………………………………………….. 2
Calibration ……………………………………………………………………………… 2
Pause and Run ………………………………………………………………………... 2
Reading Data …………………………………………………………………………. 2
Displayed Data ……………………………………………………………………….. 2
ON/OFF Mode ……………………………………………………………………….. 3
Reset Mode ……………………………………………………………………………. 4
Print ……………………………………………………………………………………. 4
GENERAL DESCRIPTION ………………………………………………………….. 4
SPECIFICATIONS ……………………………………………………………………. 6
PRINCIPLES OF OPERATION …………………………………………………….. 6
General ……………………………………………………………………………….. 6
Weighting Characteristics ………………………………………………………….. 8
Microphone Characteristics ………………………………………………………… 8
Internal Electrical Noise …………………………………………………………….. 8
Microcomputer Modes ………………………………………………………………. 9
Formulas and Definitions …………………………………………………………… 10
Key Functions ………………………………………………………………………... 12
Controls ………………………………………………………………………………. 13
Printer Output ……………………………………………………………………….. 13
TESTING AND CALIBRATION …………………………………………………….. 14
Battery Test …………………………………………………………………………. 14
Battery Replacement ……………………………………………………………….. 15
Calibration and Maintenance ………………………………………………………. 15
Daily Calibration ……………………………………………………………………… 15
OPERATING PROCEDURE ……………………………………………………….. 16
Effects of Operator's Presence ……………………………………………………. 17
Use with Windscreen ………………………………………………………………. 18
Determining Function Parameter Settings ……………………………………….. 19
Code Setup Procedures ……………………………………………………………. 22
INTERPRETING RESULTS ……………………………………………………….. 23
Use of L-AVG and TWA …………………………………………………………… 24
Estimating TWA from L-AVG ……………………………………………………… 25
Accuracy of Readings ……………………………………………………………… 25
Hints and Good Practices ………………………………………………………….. 25
Considerations of Measurement and Accuracy …………………………………. 27
ACCESSORIES …………………………………………………………………… 28
QUEST SERVICE AND WARRANTY POLICY ………………………………… 29
ADDENDUM
(MICRO-15)
1.) The convenience of a latching Sound Level Key means hands free
updating of the display with the current sound level. Simply press any
other key to deactivate this function.
2.) To speed operation and assure single touch response, the
keyboard is now scanned by the microprocessor 16 times per second
rather than the previous once per second.
3.) The ease of calibration has been enhanced by the use of an algorithm
for small magnitude changes. The algorithm had been averaging over a
one second period. The new algorithm averages small magnitude
changes over a 63 msec period.
4.) The overload time threshold has been changed from 115 dB Peak to 115
dB RMS.
5.) The code for switch settings is displayed automatically on the LCD
startup. This serves to confirm the proper set up of the unit and is a quick
opportunity to assure tampering did not occur during the last operation.
08/10/89
INTRODUCTION
The Quest MICRO-15 Noise Dosimeter (Figure 1) is a multifunction sound
analyzing instrument that is housed in a convenient hand-size package. It
provides information as basic as any dosimeter and may also be used as a
sound level meter, an integrating sound level meter and an exposure meter. It
has capabilities far beyond the requirements of most users.
This manual begins with a brief outline of operating instructions and then
expands into a complete analysis explanation. The user is advised to review the
entire manual to assure proper use of the MICRO-15. However, the simplified
instructions will provide basic instructions.
SIMPLIFIED OPERATING INSTRUCTIONS
This section is intended as a brief introduction to the MICRO-15. See the
appropriate section in the manual for a more detailed description of various
functions.
To operate the controls, loosen the single screw on front of unit and remove
front cover.
Turning MICRO-15 On
Press ON/OFF key. The MICRO-15 should display the internal coded switch
settings for 3 seconds and then display "----". If this sequence does not occur,
check battery.
Changing Battery
Loosen two screws on back of unit and change battery. Use a 9-volt alkaline
battery.
Calibration
Insert microphone in the calibrator adaptor and place adaptor in calibrator.
Turn on calibrator and press SOUND LEVEL on the MICRO-15. The display
should read correctly. If necessary adjust CAL screw while pressing SOUND
LEVEL to bring reading within these limits.
Pause and Run
When the MICRO-15 is turned on, or it is reset, or the battery is changed, or
the Pause key is pressed, the unit is automatically in the Pause mode. In the
Pause mode, only the SOUND LEVEL and PAUSE TIME functions are active. All
other functions may be read but no new data is being accumulated. Press RUN
to start or to continue accumulating data.
Reading Data
Pressing any key except ON/OFF and PRINT will cause data to be
displayed. The key must be held down for 1 second before it is read. If the key is
held down the data will be updated each second. When the key is released the
last displayed data will remain on the display. If some data cannot be calculated
(as an example, L-AVG cannot be calculated if the MICRO-15 has never been in
the run mode), then "----" will be displayed.
Displayed Data
SOUND LEVEL The current sound level in decibels.
PEAK LEVEL The highest Peak level since the unit started accumulating
data.
SLOW MAX The maximum level with a SLOW time constant.
HTL L-AVG The average sound level for the run time with a high
threshold level (HTL). For OSHA, the HTL is set at 90 dB.
(Recommended when doing short sample readings.)
HTL DOSE The accumulated noise dose expressed as a percent of the
allowable dose for all noise above HTL.
HTL TWA The high threshold time-weighted average sound
level measured in decibels. It is always based on 8 hours,
regardless of sample time. TWA will always be less than LAVG if
sample is less than 8 hours, or greater than LAVG if greater than 8
hours.
LTL L-AVG The average sound level with a low threshold level (LTL). For
OSHA, the LTL is set at 80 dB. (Recommended when doing short
sample readings.)
LTL DOSE The noise dose above the LTL.
LTL TWA Same as HTL TWA only based on the low
threshold level.
3 dB LEQ The integrated average sound level with a 3 dB
exchange rate and no threshold.
3 dB DOSE The noise dose with a 3 dB exchange rate and no threshold
expressed in percent of the allowable dose.
3 dB SEL The sound exposure level expressed in decibels
of the total integrated noise averaged over one second. It is used
to measure the sound energy of an event such as a passing
airplane.
OL TIME The time the noise level has been above the over-
load level. If the overload level has not been exceeded for a total
of 1 second the OL TIME will read ":0".
PAUSE TIME The time the unit has been in the Pause mode.
RUN TIME The time the unit has been in the Run mode and accumulating
data.
CODE An encoded number which identifies the internal
switch settings. As an example, if the display is "EE3#", the unit is
set as follows:
90 dB for 8-hour criterion level.
5 dB exchange rate.
90 dB HTL.
80 db LTL.
115 dB overload level.
"A" weighted frequency response.
50-146 dB range.
# is a number from 0 to 7 used to identify the dosimeter.
ON/OFF Mode
To put the MICRO-15 into the off mode, hold the ON/OFF key down for five
seconds until the display reads "18:8:8.8". When the key is released, the display
will be blank.
The off mode is not a mode in which the circuits are completely deactivated.
It is rather a very low power mode in which no new data is accumulated but all
accumulated data is retained.
To turn the unit back on to accumulate data, press the ON/OFF key.
The unit is completely off only when the battery is removed.
Reset Mode
To reset the unit and erase all accumulated data, hold down both the
ON/OFF and PAUSE keys for five seconds. When the unit is reset, the display
will show "---- " or ": 0".
The five-second feature is intended to prevent the loss of accumulated data
through accidental resetting.
Print
Press the PAUSE key. Connect a Printer to the PRINT jack and press the
PRINT key.
While the Printer is printing, the keys are inactive. To stop printing, press the
ON/OFF key for 1 second.
GENERAL DESCRIPTION
The microprocessor based MICRO-15 Noise Dosimeter simultaneously
monitors 15 different noise functions. It can be used as a personal noise
dosimeter, an area monitor, and as a noise survey instrument.
A hard copy printout of all data along with an expansion port for histograms
is provided.
The MICRO-15 measures the following 15 functions:
3 Noise dose percentages with different thresholds and exchange rates
3 Integrated sound levels
2 Time weighted averages Sound exposure level Sound level
Peak level Maximum sound level
3 Elapsed times
The MICRO-15 can simultaneously measure all of the following 15 functions
to check compliance with the Occupational Safety and Health Administration
noise regulations and other regulatory standards.
1. Average integrated sound level with 90 dB threshold
2. Average integrated sound level with 80 dB threshold
3. Noise dose with 90 dB threshold
4. Noise dose with 80 dB threshold
5. Time weighted average with 90 dB threshold
6. Time weighted average with 80 dB threshold
Each of the above six functions can be measured with a 5 dB exchange rate
and 90 dB, 8-hour criterion level.
7. Average integrated sound level
8. Noise dose
9. Sound exposure level
Each of the above three functions can be measured with no threshold, a 3
dB exchange rate, and a 90 dB, 8-hour criterion level.
10. Sound level
11. Peak level
12. Slow maximum level
13. Run time
14. Pause time
15. Overload time.
The MICRO-15 can be programmed by internal switches to the following
parameters:
Any 2 of 6 threshold levels (none, 70, 75, 80, 85, or 90 dB).
4 Exchange rates (3, 4, 5 and 6 dB).
4 Criterion levels (70, 84, 85 and 90 dB for 8 hours).
2 Ranges (50 to 146 dB and 40 to 126 dB).
2 Overload levels (115 or 140 dB on the high range and 90 or 115 dB on the
low range).
2 Frequency weightings ("A" and "C").
8 Identification numbers (0 to 7).
The readings can be taken at any time without destroying or resetting the
data. Even turning the unit off will not erase the internal memory. A water and
dust resistant cover protects the unit against the elements as well as tampering.
The unit is small enough to be placed in a shirt pocket or on a belt with the
microphone clipped to the shirt collar or on the shoulder. It
can be used as a sound level meter by attaching the microphone to a bracket. It
can also be mounted on a tripod for area surveys.
The MICRO-15 is powered by a single 9-volt alkaline transistor battery with
an 80-hour battery life. A low battery indication will be displayed 8 hours before
the end of life of an alkaline battery. See page 14 for method of testing battery.
SPECIFICATIONS
Standards: ANSI S1.4-1983 type 2
ANSI S1.25-1978
IEC 651 type 2 (sound level reads slow response level once
each second).
Detector: True RMS; 63 dB pulse range and crest factor.
Readout: 4-digit liquid crystal display.
Dose: .01 to 19999%.
Time: hours, minutes, and seconds.
Sound level: 0.1 dB.
Integrated sound level: 0.01 dB.
Microphone: 8 mm (1/4 inch), omnidirectional PZT ceramic with collar clip
and 36-inch cable.
Battery: Single 9-volt alkaline, 80-hour battery life.
Battery Indicator: Shows at least 8-hour battery life is available.
Calibration: External calibrator.
Temperature: -10 to +50°C operating; - 40 to +60°C storage (battery
removed).
Humidity: 0 to 95% R.H.
Magnetic Field Effects: Negligible below 4000 R/M (50 oersteds) at 50 to 60
Hz.
Size: 2.5 x 5.1 x 1.3 inches (64 x 130 x 33 mm).
Weight: 11 ounces (315 grams) including battery and coverplate.
Construction: CMOS microprocessor in rugged aluminum housing with
tamper-, water-, and dust-resistant security cover.
PRINCIPLES OF OPERATION
General
The MICRO-15 Noise Dosimeter uses an 8-mm omnidirectional
ceramic" microphone buffered by a high impedance FET input stage. The
electronics utilizes low power circuitry for long battery Hie, maximum stability,
and high reliability over a wide range of environmental conditions. A block
diagram of the MICRO-15 is shown in Figure 2.
Weighting Characteristics
The MICRO 15 has both "A" and "C'" weighting characteristics
as shown in Figure 3. For OSHA and most noise measurement requirements, the
"A" weighting should he used. The "A" weighting has a similar response to the
human ear. The "C" weighting is used for measuring noise reduction in hearing
protectors and other scien-ific purposes.
Microphone Characteristics
The microphone used on the MICRO-15 Dosimeter is a Model
1845 ceramic microphone designed tor use in sound level measuring
instruments. An integral FET amplifier and controlled acoustical construction
provide the transduction sensitivity level, frequency range, and flat frequency
response necessary for ANSI S1.4-1983 Type 2 sound level meter requirements.
Overall diameter is 8 mm Typical sensitivity is 70 dB below 1 volt per microbar
measured at 1 KHz, Figure 4 is a diagram of a typical microphone response .
Internal Electrical Noise
The internal electrical noise of the MICRO-15 is equivalent to an
acoustical level of approximately 40 dB. On the 5O-146 dB range the internal
noise has a negligible effect on the reading. On the 40-126 dB range the internal
noise determines the lowest reading of the meter.
Microcomputer Modes
The MICRO-15 is controlled by a MC146805 CMOS Microcomputer. The
MC146805, in addition to being a general purpose microprocessor, has32 input
output lines, 112 bytes of RAM, 2106 bytes of ROM, a counter, an interrupt, a
low power wait state, and a very low power stop state. The MICRO-15) operates
in one of the following six modes.
Reset Mode
The MICRO-15 enters the reset mode when the unit is reset or a battery is
connected. In this mode power is applied to the unit, all previous data is cleared,
the internal switches are read, the counter is cleared, the pause register is set,
four dashes are placed on the display, and the unit enters the wait mode.
Wait Mode
In this mode the microcomputer waits for an interrupt to occur. During the
wait mode it continues to gather data from the voltage to frequency converter.
Otherwise the microcomputer is in a low power state. When the 1/16 second
interrupt occurs, the unit enters the pause or run mode depending on the pause
register.
Pause Mode
In this mode the SLOW time constant sound level is computed and the
pause time is counted. Every second the keyboard is checked to see if any key is
pressed. If a key is pressed the computer enters the compute mode. Otherwise it
returns to the wait mode.
Run Mode
The same as the pause mode except the data necessary to compute Lavg,
Leq, DOSE, TWA, SEL, PEAK, MAX, RUN TIME, and OVERLOAD is
accumulated.
Compute Mode
If a key has been pressed with the unit in the pause or run modes, the
MICRO-15 will compute and display the desired function. If the key is held down
it will recompute it each second using the data accumulated during the preceding
second. If the data will not compute (as an example, Lavg will not compute if the
sound level never exceeds the threshold level) the display will show four dashes.
If the print key has been pressed the processor will compute one line of print
every other second and send the data to the printer output. The printer output
may be terminated by pressing the ON/OFF key for one second. The computer
continues to accumulate data during a printout. For best results the computer
should be placed in the pause mode during a printout.
When computing is completed the processor returns to the wait mode.
Stop Mode
If the ON/OFF key has been depressed for 5 seconds, the MICRO-15 enters
the stop mode. In the stop mode the processor stops accumulating, but does not
erase data. Power is removed from the analog circuitry, and the display circuitry.
The 32,768 Hz oscillator is stopped as is the processor's oscillator. Only a few
microamps of current is drawn from the battery to maintain the microcomputer's
memory and to power the ON/OFF key.
When the ON/OFF key is then pressed the computer returns to where it was
before it was turned off except it will be in the pause mode.
Formulas and Definitions
The MICRO-15 uses the following formulas to calculate the accumulated
data:
Where:
LS = Sound level in dB with SLOW time constant if the sound
level is greater than the threshold level and is -∞ if the level is less than
the threshold level.
L3 = Sound level in dB without SLOW time constant.
TC = Criterion time in seconds or 28800 seconds.
RTIME = Run time in seconds.
ER = Exchange rate in dB.
CRIT = Criterion level in dB.
HTL = High threshold level.
LTL = Low threshold level.
Key Functions
SOUND LEVEL The sound level, at the end of each second, with slow (1
second) time constant. SOUND LEVEL and PAUSE TIME are
the only functions active during pause time.
PEAK LEVEL Peak sound level detected in any 1/16 second interval plus 3
dB. For impulses longer than 100 milliseconds the error is
less than -2 dB.
SLOW MAX The maximum sound level with slow time constant.
HTL L-AVG The integrated average of the slow time constant sound level
and an internal switch determined exchange rate and high
threshold level measured in decibels.
HTL DOSE The percent dose of HTL L-AVG with a selectable 8
hour criterion level.
HTL TWA The time weighted average in decibels. It is equal
to an 8 hour continuous sound level which would produce
HTL DOSE.
LTL L-LAVG Same as HTL L-AVG with a low threshold level.
LTL DOSE Same as HTL DOSE with a low threshold level.
LTL TWA Same as HTL TWA with a low threshold level.
3 dB LEQ The integrated average sound level measured in
decibels with a 3 dB exchange rate, no time constant, and no
threshold.
3 dB DOSE The percent dose with a selectable 8 hour criterion
level.
3 dB SEL The total sound exposure level in decibels inte-
grated over 1 second.
PAUSE TIME Length of time unit has been in pause mode. The MICRO-15
is in pause mode after the PAUSE key, the ON/OFF key, or
reset keys have been pressed or the battery has been
connected.
RUN TIME Length of time the unit has been in run mode.
OL TIME Length of time the unit has exceeded the overload
level. Overload data is revised up to 16 times a second. Only
complete seconds are displayed.
CODE (See code section.)
Controls
ON/OFF When pressed for 5 seconds unit turns off and dis-
play becomes blank. When unit is off pressing the key will
turn it back on in the pause mode. Memory is not erased
when unit is turned off. When off the battery drain is very low.
PAUSE Stops accumulating data. Only sound level and
pause time functions are active. When key is pressed, the
pause time is displayed.
RUN Starts or continues accumulating data. Display
shows run time.
PRINT Causes 15 functions and 8 parameters to be
printed. Unit should be in pause mode to stop accumulating
data while printer is operating. Pressing ON/OFF key will
cause printer to stop.
RESET Pressing both PAUSE and ON/OFF for 5 seconds
will cause the unit to reset. After the unit has reset a "0" will
be displayed and the unit will be in the pause mode.
Printer Output
The printer output is compatible with many RS232-C serial printers and the
serial inputs of computers. The data is sent in ASCII code. It is sent
asynchronously at 600 baud.
The printout consists of 29 lines with 15 characters in each line. See Figure
5.
The top section of the printout details the internal parameter switch settings.
The lower section gives the results of the 15 readouts. The SPL (Sound
Level) printout is the only function that prints the instantaneous value at the time
of printing; it may not be a meaningful number. This is because the unit is always
measuring as a sound level meter even if it is in the pause mode.
Each line is terminated with an 0A HEX line feed character.
Each character consists of 11 bits sent at 600 baud made up of 1 start bit at
5 volts, 8 ASCII character bits sent least significant bit first with zero set at 5 volts
and one at 0 volts, a parity bit always set to 5 volts, and 2 stop bits set at 0 volts.
Lines are sent at a rate of 1 line every 2 seconds. The busy line from the
printer is not checked. There is a delay of at least 1.5 seconds between the line
feed character and the start of the next character.
TESTING AND CALIBRATION
Battery Test
Press SOUND LEVEL and check the display for a single decimal point
(example 72.9). If additional colons and decimal
points appear (example :7:29), the battery is low and requires replacement. If this
indication is observed after having accumulated data to 8 hours or less, the data
is still accurate but new measurements should not be made.
Battery Replacement
Loosen the 2 screws on the back of the unit and remove the back. Remove
the battery from the cavity and carefully unclip the battery. Replace with a new
battery. Take care to observe the polarity of battery and do not reverse the
terminals. For best results use a 9-volt alkaline battery. Replace the battery in the
compartment and check the display. If it displays 4 dashes replace the back
cover. If not check the connections on the battery. The MICRO-15 is now operating in the Pause mode.
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, remove the battery.
Calibration and Maintenance
The MICRO-15 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
N.I.S.T.
The MICRO-15 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 MICRO-15 on, press SOUND LEVEL, and check to see if only one
decimal point is on the display. If two colons and a decimal point are on, the
battery is low and should be changed.
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 determine if the calibrator is producing a tone.
3. Remove the windscreen from the microphone. Carefully insert the
microphone into the coupler and place the coupler into the calibrator. Make sure
the microphone is inserted all the way into the
coupler and the coupler rests flush on the inner rim of the calibrator. Turn the
calibrator on and push down the SOUND LEVEL key on the MICRO-15. The
MICRO-15 should display correctly.
Atmospheric pressure has virtually no effect on the MICRO-15. However,
calibrator sound levels are affected by altitude; and if the MICRO-15 is calibrated
at high altitudes, corrections must be made. For the Quest Calibrator the
correction is -.1 dB for each 2000 feet above sea level.
4. If the reading is off slightly, insert a small screwdriver in the hole marked
CAL and slowly turn the adjustment screw until the display reads correctly.
5. The MICRO-15 is now calibrated and ready for use.
6. 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).
OPERATING PROCEDURE
1. If display is blank press ON/OFF to turn unit on.
2. Clear the MICRO-15 memory by pressing and holding down both the
ON/OFF key and the PAUSE key for five seconds until the display shows a
single zero and a single colon.
3. If 2 decimal points and a colon are displayed replace the battery and
continue.
4. Check the calibration of the unit. (See preceding section, Calibration and
Maintenance.)
5. Check code to see that it is correct. (See Setting Internal Switches and
Code Setup Procedures in following pages.)
6. Attach the microphone to the collar of the operator (see Effects of
Operator's Presence in following paragraph).
7. Press the RUN key.
8. Install the security cover and attach the unit to the operator's belt or
pocket.
9. At the end of the workday, remove the security cover and press PAUSE.
10. Remove the unit from the operator.
11. Press each function key and record the results or connect a printer to
the printer jack and press PRINT.
12. Press and hold the ON/OFF key until the display becomes blank. If the
unit is not going to be used for several days, remove the battery.
Effects of Operator's Presence
Any object or surface can act as a reflector or absorber of sound. An
operator or person wearing the dosimeter is also a reflector or absorber of sound
and affects the microphone performance. The MICRO-15 is designed to read
correctly with the microphone in a random incidence sound field without the
presence of reflecting objects.
The recommended placement of the microphone for personal noise
monitoring is on the shirt collar, high on the shoulder, and away from the neck as
far as practical (see Figure 6). If the noise is directional it is generally the best
practice to place the microphone near the ear which receives the most noise
exposure.
If the MICRO-15 is to be used as a hand held instrument the microphone
should be mounted on the 58-863 microphone boom (see Figure 7). It may be
either clipped to the boom or the clip removed and the microphone screwed to
the boom. The boom is then attached to the belt clip on the back of the
instrument. If desired the complete
unit can be mounted on a tripod (see Figure 8). The microphone should be
pointed upward forming approximately a 70-degree angle with the noise source.It
should not be pointed directly at the noise source.
Use with Windscreen
To prevent wind from blowing across the microphone and causing an
erroneous measurement of sound level, the Model WS-5 Windscreen (for 8 mm
microphones) should be used (see Figure 6). It is recommended that the
windscreen be used at all times in that it helps support the microphone in an
upright position when worn. It will also help protect the microphone under dusty,
oily, and humid conditions. The windscreen is made of reticulated polyurethane
foam. The screen is simply pushed onto the microphone when needed. The
acoustic attenuation effect of the windscreen on the dosimeter is very small and
for all practical purposes can be neglected. Maximum attenuation occurs at high
frequencies and is approximately 0.5 dB at 8 KHz, .25 dB at 5 KHz, and 0 dB at
frequencies below 2.5 KHz.
Determining Function Parameter Settings
There are over 15,000 options for setting function parameters on the
MICRO-15. The parameters are set by means of the two 8-position switches (see
Figure 9) in the battery compartment.
The setting of these switches and the corresponding parameter values can
be determined externally by pressing the CODE key on the front panel and
decoding the display by using Figure 10.
Figure 10 consists of a central column showing the display code characters
and two main columns on each side showing the values of the selected
parameters and the settings of the 8-position switches — up or down — to obtain
the selected parameters.
The two main columns on the left relate to the left hand switch and to the
third and first characters respectively in the display code. The third character
indicates the overload, weighting, and the range setting. The first character
indicates the criterion level and exchange rate.
The two main columns on the right relate to the right hand switch and to the
second and fourth characters in the display code.
The second character indicates the two thresholds. The fourth character
indicates the number of the dosimeter. Any number from 0 through 7 can be
selected. It is used only to identify the dosimeter and does not affect operation of
the MICRO-15.
As an example, to use Figure 10 to determine the values of the selected
parameters, suppose that the display code is "EE35". Proceed as follows:
1. Locate E, the first character, in the central column.
2. Read across and in the column entitled "First Character" note that the
criterion level is 90 dB for 8 hours and the exchange rate is 5 dB.
3. Locate E, the second character, in the central column.
4. Read across and in the column entitled "Second Character" note that the
high threshold level (HTL) is 90 dB and the low threshold level (LTL) is 80 dB.
5. Locate 3, the third character, in the central column.
6. Read across and note that the overload level (OL) is 115 dB, the
dosimeter is set for "A" frequency weighting and the 50-146 dB range.
7. The fourth character is 5, the number of the dosimeter.
To select different parameters, set the switches as shown in Figure 10.
As an example, if 90 dB overload "A" weighting, and 40 to 126 dB range is
desired, set the left switch positions 2, 3, and 4 to up, down, and up respectively.
To set the criterion level to 70 dB and the exchange rate to 3 dB set positions 5,
6, 7 and 8 to up. For a high threshold of 80 and a low threshold of 70 set the right
switch positions 1, 2, 3 and 4 to down, down, down, and up respectively.
To identify this dosimeter as unit 0, set switch positions 5,6 and 7 to up.
All the switch positions in a row must be set as shown to set the correct
settings. Note as an example, the 115 dB overload switch (position 2, left switch)
could be up or down depending on the range setting. Also the threshold settings
are encoded.
The two outermost switch positions are not connected and may be left in
any position.
The MICRO-15 reads the switch positions only when the unit is reset or a
battery is reconnected. If the switch positions are changed when the unit is
operating, the change will be ignored.
Code Setup Procedures
The MICRO-15 is set at the factory to the current OSHA requirements
unless otherwise specified. When the CODE key is pressed and automatically at
start-up, the display shows a coded display of the current internal switch settings.
As an example, if the display is "EE3#" then the unit is set to a criterion level of
90 dB for 8 hours, an exchange rate of 5 dB, a high threshold level of 90 dB, a
low threshold level of 80 dB, 115 dB overload level, "A" frequency weighting, and
the 50 dB to 146 dB range.
The last number is the unit identification number (indicated here as #) and
does not affect the setup of the unit.
To change the overload level from 115 dB to 140 dB, move the left switch
position 2 from up to down and reset the unit. The code will now be"EE7#".
To change to "C" frequency weighting, move the left switch position 3 from
down to up and reset the unit. The code will now be
"EE5#".
Some examples of common switch settings and codes are as follows:
INTERPRETING RESULTS
When the MICRO-15 is set up for OSHA compliance and for most other
settings, the following are, in general, true:
The HTL L-AVG is always equal to or less than the LTL. LEQ will always be
equal to or greater than HTL and LTL readings.
The HTL DOSE and TWA are less than the LTL DOSE and TWA.
If run time is less than 8 hours, TWA is less than L-AVG. If run time is more
than 8 hours, TWA is greater than L-AVG.
The SEL is greater than LEQ.
If LEQ is greater than the criterion level, the 3 dB DOSE is greater than the
LTL DOSE. If LEQ is lower than the criterion level, the 3 dB DOSE is less than
the LTL DOSE.
The above may not be true if the noise is below the threshold level.
If the noise is continuous or impulsive, then L-AVG will be nearly equal to
LEQ.
If the noise is intermittent, then L-AVG will be several decibels less than
LEQ.
The slow time constant will cause the readings taken with other than a 3 dB
exchange rate to be greater than if there were no time constant. For 3 dB it
makes little difference.
If the unit has not been in the RUN mode, PEAK LEVEL and SLOW MAX
will be at their minimum values.
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 SLOW MAX might be greater than PEAK LEVEL.
OL TIME does not count until the peak level has exceeded the overload
level for a total of one second.
In the preceding statements a reading which is "greater than" or "less than"
can be taken to mean the same as "almost equal to."
Use of L-AVG and TWA
Time Weighted Average (TWA) is measured in decibels and is equal to a
continuous level for 8 hours which would produce the same noise dose as the
dose accumulated over the run time. The average integrated sound level (LAVG) will be equal to TWA at 8 hours. If the time is less than 8 hours, then TWA
will be less than L-AVG. If time is greater than 8 hours, TWA will be greater than
L-AVG.
The MICRO-15 automatically computes the TWA of a worker if the unit is
worn by the worker for a full workday. Even if the worker does not work exactly 8
hours the TWA measurement will read the correct TWA for that worker.
L-AVG can be used with short term sampling to estimate the worker's TWA.
If the noise exposure during the sample period is representative of the noise
throughout the workday and the workday is 8 hours, then the TWA for that
worker is equal to the L-AVG measured with the short term sample.
Estimating TWA from L-AVG
A short term sample can be used to estimate worker exposure even if the
workday is other than 8 hours by adding or subtracting a correction factor from
the L-AVG reading.
As an example, if a worker has a L-AVG of 85.58 dB after a 10 minute
sample, and the sample is representative of the noise throughout the workday,
and the workday at that position is 7 hrs., 15 min., then from Table 1 under a 5
dB exchange rate read across from a work day of 7 hrs., 15 min. to the 5 dB
column and note the correction factor of -.71. Subtracting .71 from 85.50 gives a
TWA of 84.79 dB.
Accuracy of Readings
There is a tendency to overestimate the accuracy of digital readings. In the
MICRO-15 some values such as L-AVG and TWA are computed to 0.01 dB. The
absolute accuracy of the reading is not 0.01 dB. (See specifications for accuracy
and tolerances). However, the resolution of 0.01 dB is useful in determining the
sample time required for a short term sample. As an example, if L-AVG reading
is increasing 0.03 dB every second then additional sample time may be required.
If the L-AVG reading remains stable within a few 0.01 dB's, then the sample time
may be long enough.
Hints and Good Practices
The MICRO-15 is in the pause mode after each of the following: the battery
is replaced; the unit is turned on; it is reset; or the PAUSE key is pressed. Wait
until the SOUND LEVEL reading 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.
The SOUND LEVEL on the printout includes the noise of the printer, and
should therefore be ignored.
Table 1. Corrections for Computing TWA from L-AVG.
Values in this Table were computed from the formula:
Considerations of Measurement and Accuracy
An integrating meter such as the MICRO-15 Noise Dosimeter integrates all
continuous, intermittent and impulsive sound levels within its range. This avoids
many of the potential errors created by attempting to read and correctly
interpolate the readings of sound level meters in fluctuating sound fields.
However, it is important to use the instrument properly and to understand its
limits in order to achieve the maximum accuracy.
Microphone location generally has the greatest effect on the accuracy of any
noise measuring instrument. The correct placement of the MICRO-15
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 of the units. Since the
instrument does not measure noise that is even slightly below the threshold, such
noise 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 40 dB range.
Minimum noise levels are either at the bottom of the range or are 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 MICRO-15 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 18 for instructions on using the windscreen with the MICRO15 microphone.
58-863 Microphone Boom
Refer to page 17.
Tripod
Quest supplies two tripod models for use with the MICRO-15 as an area
monitor.
Printers
The MICRO-15 can be used with a serial, 600 baud printer.
Service Policy
The Quest product you have purchased is one of the finest acoustic instruments available. It is backed by our full one year warranty which seeks complete
customer satisfaction. This is your assurance that you can expect prompt
courteous service for your equipment from the entire Quest service organization.
Should your Quest equipment need to be returned for repair or recalibration,
please contact the Service Department at (800)245-0779 (USA) or Fax (262)5674047 for a Return Authorization Number. The RA number is valid for 30 days,
and must be shown on the shipping label and purchase order/cover letter. If you
are unable to return instruments in that time call for a new RA number. Send it
prepaid and properly packed in the original shipping carton directly to Quest
Technologies, 1060 Corporate Center Drive, Oconomowoc, WI 53066 U.S.A.
Repair or replacement work done under warranty will be performed free of
charge, and the instrument will be returned to you prepaid. Your copy or a
photocopy of the Quest Registration Card will serve as proof of warranty should
the factory require this information.
If for any reason you should find it necessary to contact the factory regarding
service or shipping damage, please direct your calls or letters to the attention of
the Service Manager, Quest Technologies, (262) 567-9157 or (800) 245-0779.
Office hours are from 7 AM to 6 PM (Central Standard Time) Monday through
Friday.
For service or recalibration outside the U.S.A., please contact your local
Quest Dealer or fax Quest U.S.A. at 1-262-567-4047.
Loading...