IET Labs 1986 Omnical Troubleshooting guide

♦PRECISION INSTRUMENTS FOR TEST AND MEASUREMENT ♦
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IET LABS, INC.
1986
Omnical
Sound-Level Calibrator
User and Service Manual
Copyright © 2018 IET Labs, Inc.
Visit www.ietlabs.com for manual revision updates
1986 Instruction Manual Dec. 2018

Email: inf[email protected]
TEL: [phone] • FAX: [phone]
www.ietlabs.com
IET LABS, INC.

i
1986
WARRANTY
We warrant that this product is free from defects in material and workmanship and, when properly used,
will perform in accordance with applicable IET specifications. If within one year after original shipment,
it is found not to meet this standard, it will be repaired or, at the option of IET, replaced at no charge when
returned to IET. Changes in this product not approved by IET or application of voltages or currents greater
than those allowed by the specifications shall void this warranty. IET shall not be liable for any indirect,
special, or consequential damages, even if notice has been given to the possibility of such damages.
THIS WARRANTY IS IN LIEU OF ALL OTHER WARRANTIES, EXPRESSED OR IMPLIED,
INCLUDING BUT NOT LIMITED TO, ANY IMPLIED WARRANTY OF MERCHANTABILITY OR
FITNESS FOR ANY PARTICULAR PURPOSE.

ii
1986
Safety Symbols
General definitions of safety symbols used on the instrument or in manuals are listed below.
Caution symbol: the product is marked with this symbol when it is necessary for the user to
refer to the instruction manual.
Hazardous voltage symbol: the product is marked with this symbol when high voltage maybe
present on the product and an electrical shock hazard can exist.
Indicates the grounding protect terminal, which is used to prevent electric shock from the
leakage on chassis. The ground terminal must connect to earth before using the product
Direct current.
Alternating current.
Frame or chassis terminal. A connection to the frame (chassis) of the equipment which
normally includes all exposed metal structures.
On supply.
Off supply.
Hot surface. Avoid contact. Surfaces are hot and may cause personal injury if touched.
Disposal
Waste Electrical and Electronic Equipment (WEEE) Directive 2002/96/EC
This product complies with the WEEE Directive (2002/96/EC) marking requirements.
The affixed label indicates that you must not discard this electrical/ electronic product in domestic
household waste.
Product Category: With reference to the equipment types in the WEEE directive Annex 1, this product
is classified as a “Monitoring and Control instrumentation” product.
Do not dispose of electrical appliances as unsorted municipal waste, use separate collection facilities.
Contact your local government for information regarding the collection systems available. If electrical
appliances are disposed of in landfills or dumps, hazardous substances can leak into the groundwater
and get into the food chain, damaging your health and well-being.
When replacing old appliances with new one, the retailer is legally obligated to take back your old ap-
pliances for disposal.
Proposition 65 Warning for California Residents
WARNING: Cancer and Reproductive Harm - www.P65Warnings.ca.gov.
This product may contain chemicals known to the State of California to cause cancer, birth defects, or
other reproductive harm

iii
1986
SAFETY PRECAUTIONS
The following general safety precautions must be observed during all phases of operation, service,
and repair of this instrument. Failure to comply with these precautions or with specific WARNINGS
elsewhere in this manual may impair the protection provided by the equipment. Such noncompliance
would also violate safety standards of design, manufacture, and intended use of the instrument.
IET Labs assumes no liability for the customer’s failure to comply with these precautions.
The 1986 complies with IEC61010-1 Safety requirements for electrical equipment for measurement,
control and laboratory use.
The 1986 is an indoor use product.
DANGEROUS PROCEDURE WARNINGS
Comply with all WARNINGS - Procedures throughout in this manual and instructions on the
instrument prevent you from potential hazard. These instructions contained in the warnings must
be followed.
BEFORE APPLYING POWER
Verify that all safety precautions are taken. Make all connections to the instrument before applying
power. Note the instrument’s external markings described under “Safety Symbols”.
• DO NOT Operate in an Explosive Atmosphere
• Do not operate the instrument in the presence of inflammable gasses or fumes
• Operation of any electrical instrument in such an environment clearly constitutes a safety
hazard
• Use Caution around live circuits and whenever hazardous voltages > 45 V are present
• Operators must not remove instrument covers
• Component replacement and internal adjustments must be made by qualified maintenance
personnel only
• DO NOT substitute parts or modify the instrument
• When working with high voltages; post warning signs, train personnel and keep unauthorized
personnel away.
To avoid the danger of introducing additional hazards, do not install substitute parts or perform
unauthorized modifications to the instrument.
Return the instrument to an IET Labs for service and repair to ensure that safety features are maintained
in operational condition.

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1986
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1986
Table of Contents
Chapter 1 Introduction
1.1 Overview............................................................................................................... 1
Chapter 2 Specifications
2.1 Specifications ........................................................................................................ 2
2.2 Ordering Information ............................................................................................ 3
Chapter 3 Operation
3.1 Initial Inspection and Setup .................................................................................. 5
3.2 Dial Setting ........................................................................................................... 5
3.3 Environmental Conditions .................................................................................... 5
3.4 Storage .................................................................................................................. 5
Chapter 4 Maintenance
4.1 Maintainability and Reliability ............................................................................. 6
4.2 Preventive Maintenance........................................................................................ 6
4.3 Verification of Performance .................................................................................. 6
4.3.1 Calibration Interval..................................................................................... 6
4.3.2 General Considerations............................................................................... 6
4.3.3 Calibration Procedure ................................................................................. 7
4.4 Schematic.............................................................................................................. 7
4.5 Replaceable Parts .................................................................................................. 8

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1986
Condensed Operation
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1
1986
Condensed Operation
CONDENSED OPERATING INSTRUCTIONS
TO ACTIVATE THE INSTRUMENT:
Set 1986 controls to 1 kHz, 114 dB and
CALIBRATED SPL; listen for 1- kHz audible
tone. If no tone is present, replace battery (see para
2.4).
TO CALIBRATE A SOUND-MEASURING
INSTRUMENT:
a. Observe desiccant indicator through window; if
half (or more) has turned from pale blue to pink,
replace desiccants (see para 2.5).
b. Remove transducer from storage compartment
and mount on microphone of instrument under
test; use appropriate adaptor if necessary (see para
2.7).
c. To calibrate sound-measuring instrument
(daily procedure), perform Sensi tivity Test
outlined below; to verify conformity of sound-
measuring instrument with specifications called
out by ANSI or IEC Standards (refer to para
2.9.1). perform other 4 tests outlined below at
periodic intervals.
d. If desired, use charts on Page 6-10 (tipout) to
record results.
e. When testing is completed, replace transducer
in storage compartment.
DAILY CALIBRATION -Perform before and
after each day’s use:
Sensitivity Test.
a. Set 1986: CALIBRATED SPL, 1 kHz,
LEVEL to nearest level commonly measured .
b. Set instrument under test: LEVEL RANGE
to measure high on scale for LEVEL set in
step a, FAST or SLOW response, WEIGHTING
as desired (normally, A WEIGHTING).
c. Read level on instrument under test
and adjust its calibration control to indicate the
LEVEL selected in step a.
d. A correction must be applied to above
reading for various microphones at frequencies of
1 kHz or greater. Refer to Table A (following
these instructions) for correction.
PERIODIC VERIFICATION - Perform at regular,
periodic intervals (6 mo- 1 yr) or when trouble is
suspected:
Frequency-Weighting Test.
a. Set 1986: 1 kHz, 114 dB, CALIBRATED SPL.
b. Set instrument under test: LEVEL RANGE to
measure 114 dB high on scale, FAST or SLOW
response, A WEIGHTING.
c. Adjust sensitivity of instrument under test to
level of 114 dB (apply appropriate correction
from Table A that follows these instructions).
d. Select other five FREQUENCY settings on
1986, and note indications; apply appropriate cor-
rection each time. Compare levels to weighting
tolerances in Table 2-1 of manual.
e. Repeat step a for B and C weighting, if de-
sired, and check tolerance in Tables 2-2 and 2-3.
Linearity and Tracking Tests.
a. Set 1986: 1 kHz, 114 dB, CALIBRATED SPL.
b. Set instrument under test: LEVEL RANGE to
measure 114 dB high on scale, FAST response, A
WEIGHTING.

2
1986
Condensed Operation
c. Note reference reading on instrument under
test.
d. Indicator Linearity. Decrease 1986 LEVEL in
10 dB steps, and note if reading on instrument
under test responds in corresponding 10 dB steps.
Tolerances are listed in Tables 2-4, 2-5 of manual.
e. LEVEL RANGE Control (Attenuator)
Tracking Accuracy. Repeat steps a through c;
decrease LEVEL RANGE control on instru-
ment under test in 10 dB (or 20 dB) steps,
and make corresponding changes with 1986
LEVEL control. Readings should agree, within
tolerances listed in Table 2-6 of manual.
Dynamic-Characteristics Test.
a. Set instrument under test : LEVEL RANGE
as desired, FAST response, A WEIGHTING.
b. On 1986: set VARIABLE SPL to set fast/slow
(reference), any FREQUENCY (1 kHz is auto-
matically generated for this test), adjust LEVEL
and SPL ADJUST to set reference level at 4 dB
below upper limit of indicator.
c. On 1986, set VARIABLE SPL to fast to pro-
duce 200 ms tone bursts to test FAST indicator
response. Note maximum reading. (HINT: To
check maximum meter response, it may be
helpful to slide a card parallel with needle
over meter scale to point at which MAXIMUM
excursion of needle just becomes visible.)
d . Set instrument under test to SLOW re-
sponse. On 1986, set VARIABLE SPL to slow
to produce 500 ms tone bursts to test SLOW
response. Note maximum reading.
e. Compare both FAST and SLOW maximum
readings with tolerances in Table 2-7 of manual .
RMS-Accuracy (Crest-Factor-Capacity) Test.
a. Set instrument under test: LEVEL RANGE as
desired ( 100 dB maximum upper limit) , FAST or
SLOW response, C or FLAT WEIGHTING.
b. On 1986: set VARIABLE SPL to set crest fctr
(reference), any FREQUENCY (2 kHz auto-
matically generated), adjust LEVEL and SPL
ADJUST controls to set reference level at 2 dB
below upper limit of indicator.
c. On 1986, set VARIABLE SPL to crest factor
to produce a tone-burst signal with crest factor
of 3; this tests rms accuracy of instrument under
test. Note change in reading.
d . Compare change in reading with tolerances in
Table 2-8 of manual.
MICROPHONE CORRECTIONS.
The following table (Table A) lists corrections,
for various microphones, that are to be applied to
the reading of an instrument being calibrated by
the 1986; these corrections are only applicable at
the high frequencies (1 kHz, 2 kHz and 4 kHz) of
the 1986. The corrections listed for microphones
designed for free-field response (either perpendicu-
lar or random incidence) incorporate pressure-
to-free-field, high -frequency and microphone-
volume corrections; corrections listed for micro-
phones designed for pres sure response incorporate
high-frequency and microphone-volume correc-
tions. These corrections are discussed in para 2.11
and 2.12, and must be applied when either a
Sensitivity Test or a Frequency-Weighting Test is
performed. The applicable correction (in dB) is
to be added to the reading of the instrument under
test before comparing it with the calibrated output
of the 1986 (shown on its panel by the posi-
tion of the LEVEL switch)

3
1986
Condensed Operation
Table A
MICROPHONE CORRECTIONS*
1·kHz 2-kHz 4-kHz
Microphone GR Adaptor Correction Correction Correction
Mfr.& Type Used (dB) (dB) (dB)
------------------------------------------------------------------------------------------------------------------------------------
Random-Incidence-Response
Microphones:
GR 1961-9610 or -9601 none 0.0 0.1 1.2
(1 in. electret)
GR 1962-9610 or -9601 1987-7061 0.0 0.1 1.0
( 1/2 in. electret)
GR 1971 (1 in. ceramic) none 0.0 0.1 1.2
GR 1983 Sound-Level Meter 1987-7061 0.0 0.2 1.1
(1/2 in. ceramic)
GR 1954 Noise Dosimeter 1987-7076 & 0.0 0.1 0.5
(3/8 in. ceramic) 1987-7095
Shure Bros. Model 98108 1987-7066 0.0 --- ---
(1-1/8 in. ceramic)
------------------------------------------------------------------------------------------------------------------------------------
Perpendicular-Incidence
Response Microphones:
GR 1961-9611 or -9602 none 0.3 1.0 3.5
(1 in. electret)
GR 1962-9611 or -9602 1987-7061 0.1 0.4 1.8
(1/2 in. electret)
B & K 4131/45 (1 in. condenser) 5855-6920 0.3 1.2 3.5
(O-ring)
B & K 4133/65 (1/2 in. condenser) 1987-2050 0.0 0.3 1.0
B & K 4135 (1/4 in. condenser) 1987-2060 0.0 0.0 -0.2
------------------------------------------------------------------------------------------------------------------------------------
Pressure-Response Microphones (GRID ON)
Western Electric 640AA, none 0.0 -0.2 -0.5
B & K 4160 (1 in. condenser)
Tokyo Riko MR103 none 0.0 -0.2 - 0.5
(1 in. condenser)
B & K 4132** (1 in. condenser) 5855-6920 0.0 0.2 0.6
(O-ring)
B & K 4134 (1 /2 in. condenser) 1987-2050 0.0 0.0 0.2
B & K 4136 (1/4 in. condenser) 1987-2060 0.0 0.0 -0.4
------------------------------------------------------------------------------------------------------------------------------------
* Measurement Conditions: Atmospheric Pressure, 760 mm (30 in.) of Hg., Temperature, +20°C (68°F).
** Additional microphone-volume corrections required at lower frequencies; refer to Table 2-13.

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1986
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1986
Introduction
Chapter 1
INTRODUCTION
1.1 PURPOSE
The GR/IET 1986 Omnical is a comprehensive
sound-level calibrator capable of testing all the ba-
sic characteristics of a sound-measuring instrument
with the exception of directivity. It is intended for
use, in field or laboratory calibration, on a wide
variety of sound level meters, analyzers, or sound
measuring systems that use microphones adaptable
to its cavity.
1.2 DESCRIPTION
The GR/IET 1986 Omnical produces 6 steady-
tone octave frequencies in the range of 125 Hz
to 4000 Hz, at 5 calibrated sound-pressure levels
(SPL) that increase in 10 dB steps from 74 dB
to 114 dB. In addition, it generates various tone
bursts to verify the dynamic characteristics and
rms accuracy of a sound-level -meter detector and
indicator. The cavity of the 1986 will accommodate
all GenRad 1 in. electret-condenser microphones,
GenRad l in . ceramic microphones, the Western
Electric 640AA (or equivalent) microphone, and
the Tokyo Riko MR103 microphone. The 1986
is also supplied with an adaptor that mates with
GenRad 1/2 in. electret-condenser microphones. An
optional adaptor set is available to accommodate
the 3/8 in. microphone used on the GR 1954.
Noise Dosimeter, the Bruel and Kjaer 1 in., 1/2 in.,
and 1 /4 in. microphones, and the Shure Brother’s
Model 98108 1-1/8 in. microphone.
1.3 CONTROLS, INDICATORS AND
CONNECTORS
Figure 1-1 illustrates controls, indicators and con-
nectors on the GR/IET 1986; Table 1-1 describes
these items.
The 1986 is powered via a 9 V alkaline battery. This
should be checked if there is no output.
There is an internal PICO II Very Fast-Acting Fuse
0.125 A, 125 Vdc axial fuse soldered to the main
PCB board. Littlefuse part number 0251.125MXL.
This should only be replaced by qualified personnel.
1.4 ACCESSORIES
Model GR/IET 1986-9700 signifies the instrument
and some included accessories that are delineated
in Table 1-2;
Figure 1-2 illustrates these accessories (the optional
carrying case shown is not included in the GR
1986-9700 package).
Figure 1-3 illustrates the optional GR 1987-9600
Microphone Adaptor Set, an accessory available by
order from GenRad; the adaptors in this set are
described in Table 1-3.

6
1986
Introduction

7
1986
Introduction
Fig 1-1
Reference Name Description Position(s) Function
1Transducer
Assembly
Extendable assembly
containing electro-
magnetic transducer
Stored or
extended
Provides acoustical
output to calibrate
a sound measuring
instrument
2 Desiccant Window 4.5 cm 1 3/4 in.
circular window
Allows observation of
desiccant indicator
3Storage
Compartment
Allows storage of
extension cable and
transducer assembly
4Battery
Compartment
Recessed in housing
access via cover
9 V alkaline battery that
powers instrument
5 FREQUENCY 6 position rotary
switch
4 k, 2 k, 1 k,
500, 250, 125
Hz.
Selects frequency of
calibrated output level
in CALIBRATED SPL
mode, disable in other 5
VARIABLE SPL modes
6 LEVEL 6 position rotary
switch
POWER OFF,
114, 104, 94,
84, 74 dB
Disconnects instrument
from battery, Selects
calibrated output level
in CALIBRATED SPL
mode; selects nominal
output in 4 VARIABLE
SPL modes.
7 AC output
Miniature phone jack,
0.097”, Switchcraft
Type TR-2A. Accepts
Switchcraft Type 850
miniature phone plug
Provides nominal output
output of 230 mV for 114
dB SPL
8 Variable SPL 6 position rotary
switch Calibrated SPL
Selects calibrated
output level at selected
FREQUENCY and
LEVEL
Set fast/slow
Calibrator generates
continuous 1 kHz tone at
selected nominal LEVEL
fast
Calibrator generates
continuous 1 kHz tone
bursts, each burst has
200 mS duration every
2 s.

8
1986
Introduction
Fig 1-1
Reference Name Description Position(s) Function
slow
Calibrator generates
continuous 1 kHz tone
bursts, each burst has
200 mS duration every
10 s.
set crest factor
Calibrator generates a
continuous 2 kHz tone at
LEVEL selected. Adjust
with SPL ADJUST knob
to set reference for crest
factor test
crest factor
Calibrator generates a
series of pulses with a
crest factor of “times 3”
9 SPL ADJUST 1 turn continuous
potentiometer
Used in conjunction with
LEVEL control, allows
continuously variable
level from 72 dB to 118
dB in fast and slow mode
or from 75 dB to 111 dB
in crest factor mode
10 Extension cable 61 cm (2 ft) cable
Allows extension of the
transducer assembly
to the instrument being
calibrated
11 Adaptor (supplied
with 1986-9700)
1/2” GR microphone
adapter
12 cavity 1” microphone cavity

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1986
Introduction
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10
1986
Introduction
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11
1986
Introduction
For convenience to the user, the pertinent specifica-
tions are given in an OPERATING GUIDE affixed
to the case of the instrument. Figure 2-1 shows a
typical example.
Output sound-pressure levels: 74, 84, 94, 104,
or 114 dB re 20 μPa *
Nominal output frequencies: 125, 250, 500, 1000,
2000 or 4000 Hz
Actual output frequencies: Preferred per ANSI
S1.6-1960 and ISO R266: 125.9, 251.2, 501.2,
1000, 1995 or 3981 Hz ±3%.
Reference conditions:
Temperature: 20°C (68°F)
Atmospheric pressure: 1013 mbar (760 mm
of Hg)
(30 in. of Hg)
Relative humidity: 65%
Microphone effective volume: 0.5 cm3
(0.03 in.3) (nominal for GR 1961 Electret-Condenser
Microphone)
Accuracy of sound-pressure Level: Understated
reference environmental conditions;
114 dB SPL all frequencies, except 4 kHz , for
cavity alone or when used with any adaptor
(except 1
⅛” adaptor): ±0.25 dB
114 dB SPL at 4 kHz: ±0.5 dB
At output levels other than 114 dB SPL, tolerance
is increased by: ±0.1 dB
1
⅛” adaptor: ±0.5 dB at 1 kHz only
Temperature coefficient of sound-pressure level:
Less than ±0.02 dB/°C for all frequencies except
4000 Hz
Tone-burst signals: Test signals provided as pre-
scribed by ANSI S1.4-1971; IEC Publications 123-
1961. 179-1973 and 179A-1973;and Consolidated
Revision of IEC Publications 123 and 179. In tone
burst modes,output can be either continuous (SET
FAST/SLOW or SET CREST FACTOR) or series
of bursts (FAST, SLOW or CREST FACTOR), as
selected. Level is uncalibrated and continuously
adjustable.
In FAST or SLOW, peak amplitude of tone burst is
identical to that of continuous signal.
In CREST FACTOR, rms value of tone burst se-
quence is identical to that of continuous signal.
FAST: repeated tone bursts at 1 kHz, 200 ms duration
every 2 s, for measuring sound level meter FAST rise
response;amplitude is continuously variable from 72
dB to 118 dB re 20 μPa; background level is 20 dB
below burst level.
SLOW: repeated tone bursts at 1 kHz, 500 ms dura-
tion every 10 s, for measuring sound-level-meter
SLOW rise response; amplitude is continuously vari-
able from 72 to 118 dB re 20 μPa; background level
is 20 dB below burst level.
CREST FACTOR : repeated tone bursts at 2 kHz,
5.5 ms duration, 40-Hz repetition rate, crest factor 3,
for measuring rms detector-indicator accuracy and
amplifier crest-factor capacity ; rms amplitude is
continuously variable from 75 to 111 dB re 20 μPa.
Variable sound-pressure-level control: Enabled
only in tone-burst modes. Provides 11 dB of
adjustment
Chapter 2
SPECIFICATIONS

12
1986
Electrical output: Outputprovided fromnominal 600Ω
shortablesource.Voltage proportionaltosound pressure;
230 mV ±30 mVrms nominal output corresponding to
114 dB SPL
Distortion: <1% THD acoustical or electrical
Power: Powered by 9 V alkaline battery; battery
provides at least 8 h continuous operation
Battery test: Internal circuitry checks condition
of battery continuously with automatic instrument
shutdown when battery voltage falls below accept-
able range
Microphone coupling: Transducer cavity accom-
modates following 1” microphones: GenRad 1961
electret-condenser, and GenRad 1971 ceramic
Temperature:
Operating: -10°C to +50°C (+14°F to +122°F)
Storage: -40°C to +70°C (-40°F to +140°F),
with battery removed
Humidity: 0% to 90% R.H. non-condensing,
operating
Dimensions: (wxhxd): Approximately 280 x 67 x
165 mm (11 x 2.625 x 6.5 in.)
Weight: Approximately 1 kg (2.2 lb)
Battery test: Internal circuitry checks condition of
battery continuously. Automatic instrument shutdown
when battery voltage falls below acceptable range.
Microphone coupling: Transducer cavity accom-
modates following 1-in. microphones: GenRad 1961
electret-condenser, GenRad 1971 ceramic
Accessoriessupplied:Coupler-adaptor to accommo-
date GR 1962 1/2-in. electret-condenser• microphone
and GR 1983 Sound-Level Meter microphone;
battery; instruction manual.
Accessories available: Adaptor set that in-
cludes coupler-adaptor for 3/8-in. GR 1954
Noise Dosimeter microphone; coupler-adaptors
and “O” ring for 1 in., 1/2 in. and 1/4 in.
Bruel and Kjaer microphones. Carrying case.
-------------------------------
Environmental:
This product complies with the WEEE
Directive (2002/96/EC) marking
requirements. The affixed label indicates that
you must not discard this electrical/electronic
product in domestic household waste.
Product Category: With reference to the equipment types
in the WEEE DirectiveAnnex I, this product is classed
as a “Monitoring and Control instrumentation” product.
* In the international system of units (SI) the unit
of pressure is the pascal (Pa); 1 Pa = 1 N/m2= 10
dynes/cm2= 10-2 mbar.
REF: “The International System of Units (SI)”, U.S.
Dept. of Commerce, National Bureau of Standards,
NBS Special Publication 330. SD Cat. No. C13.
10:330/2, U.S. GPO, Washington, D.C. 20402.
*U.S. Patent 4,070, 741.