PCB Piezotronics HT378C20 User manual

Model HT378C20
ICP MICROPHONE SYSTEM
Installation and Operating Manual
For assistance with the operation of this product,
contact PCB Piezotronics, Inc.
Toll-free: 800-828-8840
24-hour SensorLine: 716-684-0001
Fax: [phone]
E-mail: [email protected]
Web: www.pcb.com

The information contained in this document supersedes all similar information that
may be found elsewhere in this manual.
Total Customer Satisfaction – PCB
Piezotronics guarantees Total Customer
Satisfaction. If, at any time, for any
reason, you are not completely satisfied
with any PCB product, PCB will repair,
replace, or exchange it at no charge. You
may also choose to have your purchase
price refunded in lieu of the repair,
replacement, or exchange of the product.
Service – Due to the sophisticated nature
of the sensors and associated
instrumentation provided by PCB
Piezotronics, user servicing or repair is
not recommended and, if attempted, may
void the factory warranty. Routine
maintenance, such as the cleaning of
electrical connectors, housings, and
mounting surfaces with solutions and
techniques that will not harm the
physical material of construction, is
acceptable. Caution should be observed
to insure that liquids are not permitted to
migrate into devices that are not
hermetically sealed. Such devices should
only be wiped with a dampened cloth
and never submerged or have liquids
poured upon them.
Repair – In the event that equipment
becomes damaged or ceases to operate,
arrangements should be made to return
the equipment to PCB Piezotronics for
repair. User servicing or repair is not
recommended and, if attempted, may
void the factory warranty.
Calibration – Routine calibration of
sensors and associated instrumentation is
recommended as this helps build
confidence in measurement accuracy and
acquired data. Equipment calibration
cycles are typically established by the
users own quality regimen. When in
doubt about a calibration cycle, a good
“rule of thumb” is to recalibrate on an
annual basis. It is also good practice to
recalibrate after exposure to any severe
temperature extreme, shock, load, or
other environmental influence, or prior
to any critical test.
PCB Piezotronics maintains an ISO-
9001 certified metrology laboratory and
offers calibration services, which are
accredited by A2LA to ISO/IEC 17025,
with full traceablility to N.I.S.T. In
addition to the normally supplied
calibration, special testing is also
available, such as: sensitivity at elevated
or cryogenic temperatures, phase
response, extended high or low
frequency response, extended range, leak
testing, hydrostatic pressure testing, and
others. For information on standard
recalibration services or special testing,
contact your local PCB Piezotronics
distributor, sales representative, or
factory customer service representative.
Returning Equipment – Following
these procedures will insure that your
returned materials are handled in the
most expedient manner. Before returning
any equipment to PCB Piezotronics,
contact your local distributor, sales
representative, or factory customer
service representative to obtain a Return
Warranty, Service, Repair, and
Return Policies and Instructions

Materials Authorization (RMA)
Number. This RMA number should be
clearly marked on the outside of all
package(s) and on the packing list(s)
accompanying the shipment. A detailed
account of the nature of the problem(s)
being experienced with the equipment
should also be included inside the
package(s) containing any returned
materials.
A Purchase Order, included with the
returned materials, will expedite the
turn-around of serviced equipment. It is
recommended to include authorization
on the Purchase Order for PCB to
proceed with any repairs, as long as they
do not exceed 50% of the replacement
cost of the returned item(s). PCB will
provide a price quotation or replacement
recommendation for any item whose
repair costs would exceed 50% of
replacement cost, or any item that is not
economically feasible to repair. For
routine calibration services, the Purchase
Order should include authorization to
proceed and return at current pricing,
which can be obtained from a factory
customer service representative.
Warranty – All equipment and repair
services provided by PCB Piezotronics,
Inc. are covered by a limited warranty
against defective material and
workmanship for a period of one year
from date of original purchase. Contact
PCB for a complete statement of our
warranty. Expendable items, such as
batteries and mounting hardware, are not
covered by warranty. Mechanical
damage to equipment due to improper
use is not covered by warranty.
Electronic circuitry failure caused by the
introduction of unregulated or improper
excitation power or electrostatic
discharge is not covered by warranty.
Contact Information – International
customers should direct all inquiries to
their local distributor or sales office. A
complete list of distributors and offices
can be found at www.pcb.com.
Customers within the United States may
contact their local sales representative or
a factory customer service
representative. A complete list of sales
representatives can be found at
www.pcb.com. Toll-free telephone
numbers for a factory customer service
representative, in the division
responsible for this product, can be
found on the title page at the front of this
manual. Our ship to address and general
contact numbers are:
PCB Piezotronics, Inc.
3425 Walden Ave.
Depew, NY 14043 USA
Toll-free: [phone]
24-hour SensorLineSM: [phone]
Website: www.pcb.com
E-mail: [email protected]
DOCUMENT NUMBER: 21354
DOCUMENT REVISION: B
ECN: 17900

1
PRODUCT GUIDE
377 SERIES MICROPHONES
426 SERIES PREAMPLIFIERS
Contents:
1.0 Introduction................................................................................ 1
2.0 Standards.................................................................................... 1
3.0 Setting up a Microphone Measurement System ........................ 1
4.0 Taking Measurements................................................................ 2
5.0 Accessories................................................................................. 3
6.0 Maintenance............................................................................... 3
7.0 Calibration.................................................................................. 4
8.0 Warranty and Service................................................................. 4
1.0 Introduction
Thank you for your purchase of a PCB high quality microphone. These microphones offer highly accurate
and reliable acoustic measurements and are typically used in research and design applications. They are
accurate enough for laboratory usage, yet rugged enough for field-testing.
Sound within the typical 20 to 20,000 Hz audible range of a healthy human ear can either be pleasing to
the ear, as in music, or unpleasant (or harmful), as in noise. As a result, many applications, from the de-
velopment of consumer products to research in acoustics, measure sound, even sound outside the range of
human hearing. The instrument typically used to measure sound is the microphone, which is designed,
like the human ear, to transform pressure oscillations into a corresponding voltage oscillation.
2.0 Standards
Before selecting an acoustical instrument, it is important to identify which acoustical standards are appro-
priate for the application in which the instrument will be used. Whether for legal purposes or for quality
assurance programs, these standards will help determine the required quality, accuracy and consistency of
the instrument. Standards that correspond to the performance requirements, dimensions and characteris-
tics of acoustical components are established for microphones, sound level meters, calibrators, or other
related components. The most common organizations producing these standards are the American Na-
tional Standards Institute (ANSI) and the International Electrotechnical Commission (IEC). IEC 1094-4
establishes specifications for the mechanical dimensions and certain electroacoustic characteristics for
standard industrial microphones. The performance specification sheet supplied with each PCB micro-
phone identifies the standards to which the microphone is compliant.
3.0 Setting up a Microphone Measurement System
After the proper microphone has been selected, the corresponding preamplifier, cabling, power supplies,
signal conditioning and data acquisition selections are ready to be installed. Not all of these components
are required for all test set-ups. The figures below show typical set-ups for externally polarized and pre-
polarized microphone systems.
A prepolarized microphone can be used with a standard Microphone Power Supply designed for external-
ly polarized microphones, and its preamplifier, provided the supply voltage is set to zero.

2
Externally Polarized Microphone System
Prepolarized Microphone System
4.0 Taking Measurements
The following formula is used to calculate the pressure measured by the microphone from the output volt-
age signal. The sensitivity of a microphone is typically measured at 250 Hz.
Pressure (Pa) = Voltage (mV) / Sensitivity (mV/Pa).
The lowest amplitude a healthy human ear can detect is 20 millionths of a Pascal (20Pa). Another scale
more commonly used to describe sound pressure level is the decibel (dB). To convert the output voltage
signal (measured in Vrms) to sound pressure level (measured in decibels), use the following formula:
dB
PS
V
SPL
ref
rms 















Log20
where S is the sensitivity of the microphone in mV/Pa, and Pref is the reference pressure in air, which is
20 x 10-6 Pa. The decibel scale is logarithmic and more closely matches the response reactions of the
human ear to the pressure fluctuations. Some examples of typical sound pressure levels are shown in the
table below.
dB
Pressure
Example
0
0.00002 Pa
Threshold of Hearing
60
0.02 Pa
Business Office
80
0.2 Pa
Shop Noise
94
1 Pa
Large Truck
100
2 Pa
Jackhammer
120
20 Pa
Airplane Take-Off
140
200 Pa
Threshold of Pain
At very high-pressure amplitudes, the microphone’s diaphragm will start to distort the measured sound
pressure. The maximum rated sound pressure level of a microphone is expressed as the amplitude at
which the Total Harmonic Distortion (THD) reaches a specified amount, typically 3% THD. It is im-
portant to note that the highest sound pressure level that can be measured with a microphone system may
be limited by other parts of the system, such as the preamplifier, signal conditioner, or instrumentation.
Conversely, the Cartridge Thermal Noise (CTN) specification provides the lowest measurable sound pres-
sure level that can be detected above the electrical noise inherent within the microphone.

3
Temperature and pressure will affect the sensitivity of a microphone but these effects can be accounted
for by adjusting the recorded microphone values using the coefficients specified for each microphone
model. Simply calculate the difference in temperature and ambient pressure from those recorded during
calibration and multiply this value by the proper coefficient to determine the sensitivity offset. In most
cases, the offset will be very small and is therefore unnecessary.
5.0 Accessories
Transducer Electronics Data Sheet (TEDS)
Preamplifiers can incorporate TEDS devices, which have a built in read/write memory that contains rele-
vant information about the sensor and its use. Information includes manufacturer name, model number,
serial number, sensitivity, etc. The operation of TEDS devices is defined by IEEE P1451.4. A TEDS mi-
crophone system includes a microphone mated with a preamplifier that contains the TEDS memory pro-
grammed with both the microphone and preamplifier information. This is particularly helpful when using
large channel count systems and array set-up.
A-Weight Inline Filter
The inline filter is used in conjunction with an ICP®preamplifier to provide A-weighting for acoustical
measurements. The filter’s frequency response is weighted according to the A-weighting filter portion of
both ANSI S1.4 and IEC 60651 Type 1 Sound Level Meter Standards. ICP®signal conditioners of 4 mA
or greater are recommended when using inline filters.
Windscreens and Nose cones
Wind induced noise can be reduced by using a windscreen. This can offer some protection against dust
particles and mechanical damage. In the presence of high-speed airflow from a well-defined direction,
such as wind tunnels, a nose cone is recommended. When using windscreens and noise cones, the fre-
quency response of the microphone will be attenuated at higher frequencies.
Clamps and stands
When holding a microphone in place, it is important to minimize the influence of the stand on the sound
being measured. This can be accomplished by using low profile stands and clamps available from PCB.
Cables and Electronics
PCB carries LEMOcables as well as coaxial cables with BNC and 10-32 connectors. Traditional exter-
nally polarized microphone power supplies along with a variety of ICP®signal conditioners are available
that will fit almost any need.
6.0 Maintenance
Microphones are very stable over long periods of time, provided they are handled and stored properly.
The microphone contains fragile components that can be damaged by misuse, in particular the diaphragm,
which is made up of a very thin proprietary material and should be kept clean of dust, dirt, moisture and
free any type of imperfection (scratch, dent, etc.).
The microphone’s grid cap is designed to let the true sound pressure level through to the diaphragm while
preventing items from coming in contact with it. We do not recommend that you ever remove the grid cap
or clean the microphone. If you take the precautionary measures to keep the microphone clean and dry, it
should not be necessary. Use of accessories, like windscreens, and desiccants will help keep moisture off
the microphone and maintain the specified sensitivity level. Nose cones will help keep turbulence off the
microphone diaphragm and allow the sound pressure to be measured with greater accuracy.
Keep the microphone and preamplifier assembled while preparing for testing. Keep the rubber mainte-
nance caps on the preamplifier’s electrical connector only. Do not place these rubber caps over the micro-
phone. This will create a vacuum and undo pressure on the microphone diaphragm, which can stretch the
diaphragm and cause a change in sensitivity. Store the microphones and preamplifiers in their protective

4
cases when not in use. With proper maintenance, the microphone and preamplifier should provide stable
and accurate results for years to come.
Dust, rain, oil, moisture or exposure to extreme temperatures may adversely affect the microphone and
preamplifier’s performance. If the microphone or the inside of the connection area of the preamplifier be-
comes contaminated, use a light pressure rubber bulb to gently blow clean, dry air onto the unit in order to
remove the dust. In the event that you absolutely must take off the grid cap and clean the microphone dia-
phragm, we recommend using a blow bulb or a light pressure, clean and dry air hose to gently blow con-
tamination off the diaphragm. The direction of the air should be parallel with the diaphragm, not directly
(0 degree incidence) pointed at the diaphragm. Do not touch the microphone’s diaphragm with your fin-
gers or let it come in contact with any sharp or pointed object. Please note that any contact to the micro-
phone’s diaphragm can negatively impact the sensitivity and long term stability of the microphone.
If the microphone is ever dropped or comes into contact with any contamination, or is exposed to extreme
temperatures, we recommend immediate recalibration of the microphone. Please note that heat from your
hands can affect the calibration results. It is always good practice to wait a minimum of 30 seconds after
placing the microphone on a test system before taking a calibration reading in order to minimize the effect
that heat from your hands has on the calibration.
7.0 Calibration
PCB offers recalibration services for our precision microphones, as well as units produced by other A2LA
manufacturers. Our internal metrology laboratory is certified to ISO 9001, accredited by A2LA to AN-
SI/IEC 17025 and ANSI/NCSL Z540-1, complies with ISO 10012-1 (and former MIL-STD-45662A), and
uses equipment directly traceable to one or more of the following National Labs (NIST, PTB or DFM).
Our investment in equipment, traceability and conformance to industry standards ensures accurate calibra-
tion against relevant specifications. We also carry a line of acoustic calibrators that can be used to cali-
brate microphone sensitivity on site as needed.
8.0 Warranty and Service
All equipment and repair services provided by PCB Piezotronics, Inc. are covered by a warranty against
defective material and workmanship under a Total Customer Satisfaction policy. If, at any time, for any
reason, you are not completely satisfied with any PCB product, PCB will repair, replace, or exchange it at
no charge. You may also choose to have your purchase price refunded. See the supplemental sheet, con-
tained with this manual, for information on our service, repair and return policies, procedures and instruc-
tions. When unexpected problems arise, call our 24-Hour SensorLineSM (716-684-0001) to speak with an
Application Engineer. Visit www.pcb.com for a complete statement of our warranty.
3425 Walden Avenue, Depew, NY 14043-2495 24-hour SensorLineSM: 716-684-0001
E-Mail: [email protected] U.S.A. Fax: [phone]
Website: www.pcb.com Toll-free (in the U.S.A.): 800-828-8840
A PCB GROUP COMPANY ISO 9001 CERTIFIED A2LA ACCREDITED to ISO 17025
2014 PCB Group, Inc. In the interest of constant product improvement, specifications are subject to change without notice.
PCB and ICP are registered trademarks of PCB Group, Inc. Sensor Line is a service mark of PCB Group, Inc. All other trade-
marks are properties of the respective owners.
Manual Number: 27042
Manual Revision: C
ECO 42502
Printed in the U.S.A.

Model Number
HT378C20 Preliminary ICP MICROPHONE SYSTEM Revision: NR
ECN #:
Performance ENGLISH SI
Nominal Microphone Diameter 1/2 1/2
Frequenc Response Characteristic Random Incidence Random Incidence
Open Circuit Sensitivit 50 mV/Pa 50 mV/Pa [3]
Open Circuit Sensitivit (+/-1.5 dB) -26 dB re 1 V/Pa -26 dB re 1 V/Pa [3]
Frequenc Range(+/-1 dB) 6 to 6300 Hz 6 to 6300 Hz
Frequenc Range(+/-2 dB) 3.5 to 16,000 Hz 3.5 to 16,000 Hz
Lower Limiting Frequenc (-3 dB) 1.0 to 2.75 Hz 1.0 to 2.75 Hz
Inherent Noise(Linear) <32 dB re 20 µPa <32 dB re 20 µPa
Inherent Noise <17 dB(A) re 20 µPa<17 dB(A) re 20 µPa
D namic Range(3% Distortion Limit) >137 dB re 20 µPa >137 dB re 20 µPa
D namic Range(Maximum without Clipping) 140 dB re 20 µPa 140 dB re 20 µPa [2][4]
TEDS Compliant Yes Yes [5]
Environmental
Temperature Range(Operating) -40 to +248 °F -40 to +120 °C
Temperature Coefficient of Sensitivit (+14 to +158°F (-10 to +70°C)) 0.005 dB/°F 0.009 dB/°C [2][3]
Static Pressure Coefficient -0.01 dB/kPa -0.01 dB/kPa [2][3]
Humidit Coefficient of Sensitivit (0 to 100%, non-condensing) ± 0.001 dB/%RH ± 0.001 dB/%RH [3]
Influence of Axial Vibration(0.1g (1 m/s²)) 63 dB re 20 µPa 63 dB re 20 µPa [2]
Electrical
Polarization Voltage 0 V 0 V [1]
Excitation Voltage 20 to 32 VDC 20 to 32 VDC
Constant Current Excitation 2 to 10 mA 2 to 10 mA
Output Bias Voltage 10 to 14 VDC 10 to 14 VDC
Maximum Output Voltage +/-7 Vpk +/-7 Vpk
Output Impedance <55 Ohm <55 Ohm
Physical
Housing Material Stainless Allo Stainless Allo
Venting Rear Rear [6]
Electrical Connector BNC Jack BNC Jack
Mounting Thread(Grid) 0.5 - 60 UNS 0.5 - 60 UNS
Size (Diameter x Height)(with grid) 0.52 in x 3.88 in 13.2 mm x 98.6 mm
Size (Diameter x Height)(without grid) 0.50 in x 3.84 in 12.7 mm x 97.5 mm
Weight 1.74 oz 49.2 gm [2]
All specifications are at room temperature unless otherwise specified.
In the interest of constant product improvement, we reserve the right to change specifications without notice.
ICP® is a registered trademark of PCB Group, Inc.
TLD - TEDS Capable of Digital Memor and Communication Compliant with IEEE 1451.4
Optional Accessor : Model ACS-63 Calibration (with TEDS) of Precision Condenser
Microphones and Preamplifiers together (mated pair). (1) replaces Model ACS-42
NOTES:
[1]Prepolarized
[2]T pical.
[3]re 250 Hz
[4]Peak.
[5]TEDS Capable Digital Memor and Communication, compliant with IEEE P1451.4
[6]Venting through Preamp.
[7]See PCB Declaration of Conformance PS064 for details.
S PPLIED ACCESSORIES:
Model ACS-42 Calibration of microphone with preamplifer (1)
3425 Walden Avenue, Depew, NY 14043
Phone: [phone]
Fax: [phone]
E-Mail: info@ cb.com
[7]
OPTIONAL VERSIONS
Optional versions have identical specifications and accessories as listed for the standard model
except where noted below. More than one option ma be used.
Entered: AP Engineer: NJL Sales: MV Approved: MT Spec Number:
Date: 10/15/2014 Date: 10/15/2014 Date: 10/15/2014 Date: 10/15/2014 59950