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3M Occupational Health & Environmental Safety Division 

Acoustic Calibrators: QC-10 and QC-20 Models 

Thank you for choosing the Quest Technologies, a 3M company, to 
meet your calibration needs. To ensure the accuracy of your sound 
measuring instrumentation, 3M Quest models QC-10 and QC-20 
Calibrators provide quick, precise calibration. The instruments 
generate a stable acoustic signal at a controlled frequency and 
amplitude to verify the accuracy of sound level meters and noise 

The purpose of this manual is to provide the user with the necessary 
information to operate the QC-10 and QC-20 Sound Calibrators. The 
entire manual should be read to fully understand the many features 
this instrument offers. 

This manual is not all inclusive and cannot cover all unique 
situations. In addition, no warranties are contained in this manual 
except as described under the warranty section. 

QC-10 and QC-20 Operator’s Manual 

Table of Contents 

1. General Description.1 

2. Theory of Operation.1 

3. Operation Procedure.2 

4. Altitude Effects .4 

5. Microphone Corrections.4 

6. Calibration Adapters.6 

7. Examples of Calibrator Use.6 

8. Battery Check and Replacement.7 

9. Calibration.7 

10. Specifications.9 

11. Service Policy.11 

12. Warranty Policy.12 

QC-10 and QC-20 Operator’s Manual 

General Description and Theory of Operation 


The Quest Model QC-10 and QC-20 are 
acoustic calibrators for calibrating precision 
type 1 as well as general purpose type 2 
sound level meters and other instrumentation 
with a microphone input. The QC-10 is a 
single frequency calibrator which generates 
1000 Hz at 114 dB SPL. The QC-20 is a 
dual-frequency, dual-amplitude calibrator. It 
generates four selectable reference tones: 
frequencies of 250 and 1000 Hz, each at lev¬ 
els of 94 and 114 dB. The calibrators are 
powered by a single 9 volt battery. 

The calibrators consist of an oscillator to 
generate the frequencies, an amplifier stage, a 
transducer and microphone coupler. The cou¬ 
pler directly accepts a standard 1” (15/16”) 
diameter microphone. Separate adapters are 
available to accommodate other sizes of 
microphones. The calibrators also provide a 
1 volt RMS signal through a 1/8” phone jack. 


Figure 2 shows the basic functional blocks of the QC-10 and QC-20. The 
oscillator is a low distortion wein-bridge type with automatic gain control and 
temperature compensation for high stability. Precision capacitors and resistors 
control the frequency, and the amplitude of each frequency is individually 
adjustable for precise calibration of the SPL. The oscillator’s output is fed 
through a temperature compensated driver circuit to the transducer where it is 
converted to sound pressure in the coupler cavity. 

The battery test circuit compares the battery voltage to a reference voltage. 
If the battery is too low for proper operation, the circuit automatically disables 
the oscillator and no sound is produced. The red LOB AT light will indicate 
this condition. 


QC-10 and QC-20 Operator's Manual 

Operating Procedure 


1. The coupler cavity of the calibrator is designed to directly accept a 
standard 1 inch diameter microphone (actual size is 15/16”). The 
proper adapter must be used for microphones whose diameter is less 
than 1 inch. Place this adapter into the coupler cavity with a slight 
twisting motion to ensure that it is fully seated. An O-ring will hold 
the adapter in place and provide an acoustic seal between the cavity 
and the adapter. 

Note: If the calibrator has recently been moved from one area to another of 

substantially differing temperature (>10°C difference), it is advisable 
to allow 1/2 hour before attempting to calibrate equipment. This is to 
assure proper temperature stabilization of the equipment. The calibra¬ 
tor does not need to be “ON” during this period. 

2. Carefully lower the calibrator over the microphone. If the adapter has 
an O-ring to provide a seal around the microphone, a slight twisting 
motion should be used to ensure proper seating of the microphone into 
the adapter. Take care not to unscrew the microphone while twisting. 

Note: If the calibrator is not lowered slowly, damage to microphone 

diaphragms may result. Be sure the calibrator is seated squarely with 
the adapter and microphone or significant error may result. 

3. Turn the unit on. Allow 15 seconds after turning on for the output to 
stabilize. If no sound is apparent after 15 seconds or the LOB AT light 
is lit, refer to the section on battery replacement (page 7). 

4. QC-20 only: Select the frequency and amplitude desired. When 
selecting the frequency and amplitude combination, consider the 

a. Background noise must be more than 20 dB below calibrator out¬ 
put for accurate readings, e.g., 74 dB or less for 94 dB position. 

b. Meters with needle movement displays should typically be cali¬ 
brated at or near full scale deflection. 

c. Manufacturers usually state optimum frequency and amplitude 
for calibration of their instrument. 

QC-10 and QC-20 Operator's Manual 


Operating Procedure 

d. The 250Hz tone is useful for checking the frequency response of 
instruments. When comparing meter response at 250 and 
1000Hz with “A” weighting, the nominal reading at 250Hz 
should be 8.6 dB below the reading at 1000Hz. With “B” 
weighting, the reading should be 1.3 dB less. For both “C” 
and LINEAR (or FLAT) settings there should be no difference 
between readings at the two frequencies. 

5. Verify the sound level meter’s accuracy by comparing its reading with 
the calibrator’s output. Following the manufacturer’s instructions, 
adjust the sound level meter for a correct reading. If attitudes or 
microphone corrections are necessary, refer to the most recent revision 
of ANSI SI. 10. 

6. After calibration is complete, slowly remove the calibrator, and switch 
off the unit. For further details of calibration, refer to the most recent 
revision of ANSI SI. 10. 

7. NEWER calibrators, beginning in 1998, have an automatic shutoff 
feature. This prevents draining the battery by accidentally leaving the 
calibrator turned on. A timer circuit will automatically shut the cali¬ 
brator off after approximately two minutes. To restart the calibrator, 
turn the power switch OFF and then ON again. 


QC-10 and QC-20 Operator's Manual 

Altitude^ Effects and Microphone Corrections 


Most calibrators are affected by changes in altitude and the resulting 
change in barometric pressure. The vibration of the calibrator’s diaphragm 
causes cavity volume variations which thus cause pressure variations. Changes 
in ambient air pressure and density can change the actual sound level produced. 
The calibrators are set at the factory to produce their rated SPL at standard 
barometric pressure at sea level (760mm Hg). 

Newer design calibrators, beginning in 1998, have negligible altitude cor¬ 
rection requirements. The newer calibrators have a convex profile to the cou¬ 
pler cone, with a slightly extended “chimney” for the bleed hole. 

Older calibrators, which have a straight conical profile to the coupler 
cone, require altitude compensation. Figure 3 shows correction factors for dif¬ 
ferent attitudes and barometric pressures. 



Different models of microphones have differing air volumes between the 
grid and diaphragm and also have diaphragms that vary in stiffness. Because 
of this, the generated sound pressure at the microphone diaphragm may vary 
from the nominal level of the calibrator. Also, free field microphones have 
reduced high frequency output when calibrated in a pressure chamber. A cor¬ 
rection is thus necessary for some microphones. 

Refer to the manual for your sound level meter or microphone for the 
proper correction values. 

QC-10 and QC-20 Operator's Manual 


Altitude Effects 

Figure 3. Effect of Altitude/Barometric Pressure 


QC-10 and QC-20 Operator's Manual 

Calibration Adapters and Examples of Calibrator Use 


The QC-10 and QC-20 cavity directly accepts a standard 1-inch measure¬ 
ment microphone (actual diameter 0.936”). Smaller microphones require an 
adapter for proper calibration. Quest provides the following adapters for vari¬ 
ous microphone sizes. 

056-990 Standard 1/2 inch (0.52” actual) measurement microphone 
056-988 Standard 1/4 inch diameter measurement microphone 
056-989 Quest 8mm diameter dosimeter microphone 
056-160 10mm diameter microphone for Quest model 208 meter 
056-162 0.725 inch diameter microphone for Quest 261 

056-163 0.827 inch diameter microphone used on older model Quest 

2400/2500/2700/2800 meters 


Example 1. You are calibrating a sound level meter with a 1/2” pressure 
response microphone which requires no correction. You are using an older 
design QC-20 at a barometric pressure of 530mm Hg, corresponding to an 
elevation of approximately 9,500 feet. With the calibrator set at 114 dB 
and 1000 Hz, the meter reading, from Figure 3, should be .2 dB above the 
calibrator setting, or 114.2 dB. 

Example 2. You are checking a meter with a free-field microphone whose 
pressure response is 0.1 dB less at 250 Hz and 0.2 dB less at 1kHz than 
it’s free field response. You are using “A” frequency weighting at Denver, 
Colorado with an elevation of 5,200 feet. You are also using an older 
design QC-20 so altitude correction is required. 

Set the calibrator at 1000 Hz and 94 dB. The microphone correction from 
the sound level meter manual states that the meter will read 0.2 or 
93.8 dB. Also, from Figure 3 the altitude correction is +.1 dB. Therefore 
set the meter to read 93.9 dB. 

As a check only, you may wish to switch the calibrator to 250 Hz. The 
corrections now are as follows: 

“A” Weighting -8.6 dB 

Microphone -. 1 dB 

Altitude -.6 dB 

Total -9.3 dB 

Check to see that the meter reads 84.7 dB (94 - 9.3 = 84.7). 

QC-10 and QC-20 Operator's Manual 


Battery^ Check & Replacement and Calibration 


No operator judgements are needed to determine the condition of the bat¬ 
tery. If the battery is so low (approximately 7 volts) as to affect the unit’s cali¬ 
bration, a battery-condition detector circuit disables the oscillator, lights the 
LOB AT indicator, and no sound is produced. Please note that the QC-10 and 
QC-20 have a circuitry stabilization time of 3 to 5 seconds, and no sound is 
produced during this time. This “warm-up” time should not be misconstrued 
as a low-battery condition. If, however, after 15 seconds no tone is heard, 
replace the battery with a fresh NEDA Type 1604 9 volt transistor battery. 
Newer units with the automatic shutoff feature will run for shorter lengths of 
time as the battery weakens. 

To change the battery in newer units, remove the two screws in the cover 
plate. Remove the cover plate and metal sleeve to expose the battery. Pull the 
battery away from the snap connector and remove. To install a new battery, 
press its flat end into the foam retainer, compressing the foam. Slide the con¬ 
nector end of the battery in line with the battery socket and snap it into place. 
The battery will not “snap-in” in the wrong direction. Reinstall the sleeve, 
cover plate and screws. 

To change the battery in older units, grasp the coupler (black cone) end in 
one hand and the gray sleeve in the other. Turn the sleeve counterclockwise 
until it can be slid off. When the sleeve has been removed, pull the battery 
away from the snap connector and remove. To install a new battery, press its 
flat end into the foam retainer, compressing the foam. Slide the connector end 
of the battery in line with the battery socket and snap it into place. The battery 
will not “snap-in” in the wrong direction. Reinstall the gray sleeve, making 
sure that it is firmly seated. 


The QC-10 and QC-20 are calibrated at the Quest laboratory with a type L 
standard microphone (B&K 4144) and special instrumentation traceable to 
NIST. The QC-10 or QC-20 is very stable; but since it is used to calibrate 
other equipment, it should be checked periodically against laboratory stan¬ 
dards. It is recommended that the calibrator be returned to the factory at least 
yearly for recalibration, or whenever there is a question as to its accuracy. 


QC-10 and QC-20 Operator's Manual 


Figure 4 depicts the calibrator with the sleeve removed. Calibration is not 
affected by removing the sleeve. Calibration potentiometers are indicated 
for adjusting the SPL and the 1 volt output. The 1 volt adjustment is the 
master output adjustment and as such affects the SPL. 

Note: These adjustments are for laboratory calibration only and should not 

be readjusted by the user. 

QC-10 and QC-20 Operator's Manual 





ANSI SI.40-1984 and IEC 942:1988 Class 1 

Output Frequency: 

QC-10: 1000 Hz 

QC-20: Selectable, 250 Hz, 1000 Hz ± 2% 

Output Amplitude: 

QC-10: 114 dB 

QC-20: Selectable, 94 dB (1 pascal) or 114 dB ref. 

20 //N/m 2 (20 //Pa) 

Output Accuracy: 

±0.3 dB @ 20°C 760mmHg 


Less than 1 % within temperature and humidity oper¬ 
ating ranges 

Electrical Output: 

1 volt RMS sine wave, ±5% (0.4 dB) 

Output impedance = 1000 ohms. Phone jack (1/8”) 
compatible with Switchcraft 780 plug or equivalent. 


Operating range -10 to +50°C. 

1 KHz: within +/-0.3 dB from +5 to 50°C 

Below +5°C coefficient of SPL is 0.0 to 
+0.01 dB/°C ref. 20°C 

250Hz: within +/- 0.3 dB from +5 to 40°C 

Below +5°C coefficient of SPL is 0 to 

0.02 dB/°C max ref. 20°C 

Storage temperature -40 to +65°C with battery 

Coupler Volume 

A lcc increase in coupler volume will result in a 
typical decrease in output of .27 dB @ 1kHz and 
.67 dB @ 250 Hz. 


Relative humidity 5 to 95% with less than 0.1 dB 
change in output. 


QC-10 and QC-20 Operator's Manual 


Effects Due to 
External Fields: 

60Hz: No measurable effect up to 5 Oersted 
(1 Oe = 80 A/m) 

400Hz: No measurable effect up to 2 Oersted 
(Stated field strengths are magnetic test chamber 
limits) Tested for RF susceptibility with no effect at 
field strengths to 65 V/m over the frequency range 
of 10MHz to 500MHz. 


Battery operated, 9 volt transistor battery, NEDA 
1604 type. Projected battery life greater than 25 
operating hours with intermittent use. Battery life is 
affected by temperature. Consult battery manufac¬ 
turer’s data for specific battery life at a current draw 
of 10mA. 


4.1” (10.4 cm) long, 2.4” (6 cm) dia. 


12 oz. (0.35 kg) 

QC-10 and QC-20 Operator's Manual 


Service Policy 

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) 567-4047 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. 


QC-10 and QC-20 Operator's Manual 

Warranty Policy 

Warranty Policy 

Quest Technologies warrants our instruments to be free from defects in 
materials and workmanship for one year under normal conditions of use and 
service. For U.S.A. customers we will replace or repair (our option) defective 
instruments at no charge, excluding batteries, abuse, misuse, alterations, 
physical damage, or instruments previously repaired by other than Quest 
Technologies. Microphones, sensors, and printers may have shorter warranty 
periods. This warranty states our total obligation in place of any other 
warranties expressed or implied. Our warranty does not include any liability 
or obligation directly resulting from any defective instrument or product or any 
associated damages, injuries, or property loss, including loss of 
use or measurement data. 

For warranty outside the U.S.A., a minimum one year warranty applies to 
the same limitation and exceptions as above with service provided or arranged 
through the authorized Quest distributor or our Quest European Service 
Laboratory. Foreign purchasers should contact the local Quest distributor 
for details. 

QC-10 and QC-20 Operator's Manual 




Quest Technologies, a 3M company, is a manufacturer of durable, reliable instrumentation 
and software systems that help monitor a variety of health and safety hazards, including 
noise, vibration, heat stress, indoor air quality and toxic/combustible gases. The 3M-Quest 
brand of instrumentation is used by safety and industrial hygiene professionals to help 
comply with worker safety and environmental regulations and standards around the world. 
Quest Technologies, a 3M company, is part of the 3M Occupational Health & Environmental 
Safety Division, a global leader in respiratory, hearing, eye, head and fall protection, visibility 
and protective clothing, and detection products. 

To learn more, call us at 262.567.9157 





now part of 3M 

Occupational Health & 
Environmental Safety Division 

Quest Technologies, a 3M Company 
ISO 9001 Registered Company 
ISO 17025 Accredited Calibration Lab 
1060 Corporate Center Drive 
Oconomowoc, Wl 53066 
Customer Service: 262-567-9157 
Toll Free: 800-245-0779 

Please recycle. Printed in USA. 

©2011 3M 

All rights reserved. 

056-144, Rev.J 7/11