Easy-to-Use Digital Oscilloscopes for Bandwidths up to 500 MHz

New from Rigol Technologies, Inc. comes the DS4000 series digital oscilloscope, a fast and versatile general purpose test instrument perfect for a wide range of applications. Available in 8 different models, the DS4000 series features bandwidths between 100MHz and 500MHz, sample rates up to 4GSa/s and 2 or 4 analog channels. The DS4000 offers a feature set unmatched by other scopes in its class, at a fraction of the cost.

Rigol’s DS4000 series digital oscilloscope incorporates many advanced technologies and processes to make detecting signal and device characteristics easier than ever. These scopes can help find system glitches with 140 million points of memory depth and 110,000 waveforms per second acquisition rate. In addition, DS4000 series can search and navigate within up to 200,000 triggered waveforms with mask tests.

DS4000 digital oscilloscopes feature Rigol’s innovative UltraVision technology and a 9 inch WVGA display to offer an intensity grading display and real-time waveform recording and waveform visualization and replay, with customizable real-time hardware filters available.

Designed to target the requirements of R&D engineers, production test engineers and advanced researchers, the easy-to-use DS4000 series is ideal for applications in the communications, aerospace/defense, research and education, industrial and consumer electronics, computing and instrumentation industries.

Pricing for the DS4000 series oscilloscopes begins at $1999, and is dependent upon configurations and quantity.

Rigol Technologies, Inc.
www.Rigolna.com

Yokogawa’s DL850 ScopeCorder

The Yokogawa DL850 is the next generation of the company’s family of ScopeCorders: versatile instruments that combine the benefits of a high speed oscilloscope and those of a traditional data acquisition recorder in a single, portable instrument.

Allion Test Labs chooses Agilent’s test solutions: Infiniium 90000A Series oscilloscopes

Agilent Technologies Inc. (www.agilent.com) recently announced that China-based Allion Test Labs (www.allion.com) has selected Agilent’s test solutions for DisplayPort and USB 3.0 compliance and certification testing.

Agilent also said that Allion Test Labs in Taiwan upgraded its Agilent test solution from HDMI 1.3 to HDMI 1.4. It also added the new symbol of J-BERT N4903B, as well as the frame error ratio measurement option to the USB 3.0 test solution.

The announcements show the continuing long-term relationship between Allion Test Labs and Agilent, as well as the ability of Agilent to provide leading-edge measurement and test solutions for USB, HDMI, DisplayPort and SATA standards compliance and certification testing.

“We choose Agilent as a strategic partner for emerging high-speed applications that cover USB 3.0, HDMI 1.4, DisplayPort 2.0, SAS/SATA 12 Gbps and TransferJet, because Agilent is recognized for its technical expertise in standards bodies and compliance programs,” said James Ou, Engineering Service Division director at Allion Test Labs (Taiwan). “We understand the importance of having the most accurate and hardware upgradeable test equipment available. We selected Agilent test equipment for our facilities because of its powerful functions in test automation, ease of use and scope bandwidth upgradeable to 32 GHz, and J-BERT supporting up to 14.2 Gbps data rates.”

As high-speed digital interfaces increase in various electronic devices, designers and test houses need the appropriate tools to ensure that their electronic designs meet newest industry standards. Allion’s testing labs will utilize the N5990A test automation software platform; 81134A pulse/pattern generator; J-Bert N4903B high-performance serial BERT; and the Infiniium 90000A Series oscilloscopes.

Pico Technology introduces PicoScope 6000 Series oscilloscopes

Pico Technology (www.picotech.com) has unveiled its all-new PicoScope 6000 Series oscilloscopes –the first USB scopes to offer a 5 gigasample per second (GS/s) real-time sampling rate. The oscilloscopes also feature a unique 350 MHz bandwidth on four channels and have a huge 1-gigasample memory buffer, unmatched on any bench-top or USB scope.

PicoScope 6000 Series is the newest product line from Pico Technology’s 18 years of expertise in PC Oscilloscope design. The series packs more features and performance compared to other Oscilloscope design into a space-saving USB Oscilloscope enclosure. In addition to its headline specifications, these scopes feature an arbitrary waveform generator, a built-in function generator, switchable bandwidth limiting on each channel, mask limit testing and switchable 50-ohm and 1-megohm inputs.

PicoScope 6000 Series connects to any Windows Vista, Windows 7 or Windows XP computer with a USB 2.0 interface. The user can use one with a personal computer to save space on workbench, or link it to a laptop to create a portable device that is perfect for on-site demonstrations and field servicing. The high bandwidths and sampling rates make the scopes ideal for digital and analogue circuit designers, test installers and engineers. If the user wants to write his own application to control the scope, Pico Technology provides a software development kit that includes example code, free of charge.

Like all PC Oscilloscopes from Pico Technology, the PicoScope 6000 Series is the most efficient and cost saving oscilloscopes. “You buy only the specialized oscilloscope hardware, while your own PC looks after the standard functions such as display, disk storage and networking,” said Managing Director Alan Tong. “All of the scope’s features are included in the initial price, so there are no expensive upgrades or optional extra modules. You only need to decide whether to buy the scope on its own or with four 500 MHz compensated x10 probes.”

3D Phase Measurement Eliminates Need To Change Tip

The 3D Phase Measurement is a measurement technique that provides 3 dimensional imaging to increase accuracy and productivity in aerospace and rotating equipment applications. Paired with the XLG3 Video Borescope, this technology provides accurate 3 dimensional surface scans using a single probe tip. In effect, the 3D Phase Measurement provides accurate measurement “on-demand” by eliminating the need to change the probe tip to capture the measurement, streamlining the inspection process.

Prior to 3D Phase Measurement, videoprobe measurement was based on stereo or shadow techniques, which are complex techniques, and the tip of the probe had to be changed from a viewing tip to a measurement tip, adding time to the inspection process. 3D Phase Measurement offers Profile Views, a cross section view of a portion of the surface. With Profile View, the inspector can rotate and zoom to get a more accurate view of the defect. The ability to better visualize the shape and characteristics of an indication allows for well-informed decision of serviceability of the asset.

Tektronix Raises Bar for Oscilloscope Sampling Rates, Signal Integrity

Tektronix, Inc. announced the DPO/DSA/MSO70000C Series of digital and mixed signal oscilloscopes now deliver 100 GS/s sampling rate performance; enabling lower noise along with increased data points on 5x oversampled 20 GHz acquisitions. This world’s best over-sampling performance in a high bandwidth oscilloscope delivers significant real-world benefits including more accurate signal integrity measurements for such high-speed serial standards as PCI Express Gen 3. Other enhancements include a new, faster compute platform and a more stable timebase, ideal for radar applications.

High-performance oscilloscopes with bandwidth of greater than 4 GHz are used in a variety of high-speed serial, wideband radar, fast optical communications systems, high-end embedded systems, and high-energy physics applications. As designs move to faster and faster data rates, the margin provided by the measurement system becomes a critical factor. The DPO/DSA/MSO70000C Series, with its unprecedented 5x oversampling, delivers the performance and signal fidelity designers need to ensure that their latest cutting edge components and systems meet design specifications.

Along with a two-fold increase in sampling rate compared to the “B” Series it replaces, the DPO/DSA/MSO70000C Series features a faster compute platform. This new platform offers faster processing for longer data records such as jitter, noise, BER (bit error rate) measurements and statistics. Boot and application start up times are also significantly quicker.

“With the DPO/DSA/MSO70000C Series Tektronix delivers performance in all the right places where it will help us characterize designs with more speed and precision,” said Mark Marlett, principal engineer at Xilinx, Inc. “With adequate oversampling, we get more data points in our measurement results to accurately understand rise time performance on fast signals. With the 70000 Series, we gain confidence using real data versus having to guess with lesser sampling rates.

In any digital oscilloscope, there is a strong correlation between sampling rate and internal noise — a high sampling rate results in less noise which in turn leads to more margin for the user. As shown by extensive comparison testing, the DPO/DSA/MSO70000C Series with 100 GS/s operation delivers up to 20 percent reduction in noise compared to the 50 GS/s setting on the same instrument.

High Stability Timebase for Wideband Radar System Verification
Modern radar designs use frequency and phase modulation within the radar pulses to increase a radar’s range resolution and target identification capabilities. Maintaining the same modulation characteristics from pulse to pulse is key to the system’s operation. Performance oscilloscopes are the tool of choice for radar pulse measurement, but must have a stable timebase able to stay on frequency for long captures.

The DPO/DSA/MSO70000C Series meets this requirement with a new high-stability timebase that provides for lower long term jitter, phase and frequency stability. When combined with the pulse and frequency settling measurement capabilities of SignalVu vector signal analysis software, the DPO/DSA/MSO70000C Series gives designers of frequency agile radios and radars the ability to accurately verify system performance.

Tektronix Leads in Serial Data Test
The DPO/DSA/MSO70000C Series oscilloscopes provide the bandwidth and sampling rates needed to debug serial data signals up to 12 Gb/s on all channels simultaneously – ideal for multi-lane applications including PCI Express 3, SATA 6 Gb/s, SuperSpeedUSB , HDMI, DisplayPort, and 10 Gb Ethernet. The FastAcq acquisition mode provides a capture rate greater than 300,000 waveforms per second – about 100 times faster than competing alternatives – delivering both critical insight into signal behavior and in-depth analysis.

Tektronix offers a broad range of software packages for high-speed serial data design, debug, and compliance verification. This includes DPOJET for jitter and timing analysis, SDLA for testing transmitter, interconnects and receivers, and standard-specific packages for DDR, DisplayPort, PCI Express, USB, HDMI, SATA, Ethernet, Fibre Channel and others. In addition, Tektronix delivers the widest variety of oscilloscope probing accessories, including innovative TriModeTM probes, for making both analog and digital connections to the device under test (DUT) with minimal disruption.

Highest Performance Mixed Signal Oscilloscope
Winner of the “Best in Test” 2010 Award, the MSO70000 Series is the industry’s highest performance family of integrated MSOs and provides up to 20 channels of measurement capture (4 analog and 16 digital) with analog bandwidth ranging from 4 to 20 GHz. The MSO70000C combines the signal visibility and timing features of a high performance logic analyzer with the analog precision, probing and usability of a high performance real-time oscilloscope. This makes it the ideal debug and verification tool for such demanding high-speed design applications as DDR memory, high performance ASICs, FPGAs, system-on-a-chip devices, and digital RF.

Tektronix
www.tektronix.com

Oscilloscope supports MIPI and SATA Standards

Agilent Technologies Inc. expands its mixed-signal and digital-storage oscilloscope portfolio with two lower-cost 600-MHz Infiniium 9000 Series models, three new application packages and GPIB compatibility. The 9000 Series is the industry’s first oscilloscope family to offer bandwidths from 600 MHz to 4 GHz, and it includes the industry’s first mixed signal oscilloscope to support MIPI and SATA industry standards.

Oscilloscopes are the primary tools engineers use to test and debug electronic designs, and engineers need increasingly broad measurement capability to deliver robust products in a timely manner. Agilent’s lower-cost Infiniium 9000 Series 600-MHz models incorporate advanced viewing and analysis for debugging and testing a wide variety of traditional signals and buses used in embedded designs. In addition, they offer optional logic and protocol analyzer capabilities.

In addition to extending its lineup with lower-cost models, Agilent has added new applications that capitalize on higher-bandwidth 9000 Series models. Emerging serial bus standards in the wireless mobile industry have created the need for teams to debug and test devices that meet MIPI-DPHY physical-layer standards. Agilent’s 9000 Series is the first mixed-signal oscilloscope to offer MIPI-DPHY compliance test and protocol analysis enabling faster development of wireless mobile products employing MIPI standards. Teams can quickly move from physical-layer to protocol-layer measurements and can use the compliance application to automate testing to ensure compliance with MIPI-DPHY standards.

Development teams working on electronic products that include storage may have cost constraints or legacy requirements that make SATA 1 a better choice than other interface technologies. Engineers using Agilent’s 9000 Series scopes can quickly see SATA 1 information at the physical and protocol layers. For development teams using the faster 3-Gbs SATA II standard, Agilent offers both compliance and protocol support with its Infiniium 90000 Series.

While LAN and USB IO have reduced the need for traditional programming over GPIB interfaces, many engineers continue to rely on programmatic interaction with oscilloscopes via GPIB. Agilent’s new GPIB-to-LAN adapter enables GPIB applications on a computer to interface transparently to an instrument with a LAN interface as if it were a GPIB instrument. This adapter broadens the number of test environments that are ideal for the Infiniium 9000 Series scopes.

“We’ve received great customer reviews on our Infiniium 9000 Series introduced earlier in the year,” said Scott Sampl, vice president and general manager of Agilent’s oscilloscopes business. “Now we’ve extended the family so more customers can use the scope with the industry’s broadest measurement capability.”

Source Measure Unit from Agilent Technologies, Inc.

SANTA CLARA, CA – Agilent Technologies Inc. introduced a three-channel source
measure unit (SMU) that can simultaneously provide power and perform
measurements in applications such as parametric testing of diodes, LEDs, CMOS
integrated circuits and other semiconductor devices. The U2723A USB modular
SMU`s compact size saves benchtop space, and its improved throughput saves time.
It is the latest addition to Agilent`s family of paperback-sized USB modular
instruments.

The compact U2723A, which supplies voltage (± 20 V) and current (120 mA) on all
three channels, can operate in four-quadrant mode and also provides accurate
current measurements down to nanoamp levels. With 15 ms rise time, the SMU
improves throughput, especially during mass testing of semiconductor devices. It
also simplifies automated testing with up to two embedded test scripts per
channel.

The Agilent U2723A can be used as a standalone instrument or as a module plugged
into the compact U2781A USB modular-products chassis. For standalone use, the
U2723A can be connected to a PC via USB, and testing can be performed with the
bundled Agilent Measurement Manager (AMM) software. To simplify integration into
new or existing test systems, AMM includes a code-conversion capability that
translates commands into forms compatible with popular programming languages
such as C#, C++, Agilent VEE and Microsoft® Visual Basic.

Testing Provides Roadmap to Intelligent Assembly

“Intelligent assembly” is an approach to quality that shifts the focus from ever-tighter dimensional tolerances to consistent function in the final assembly. It’s based on the use of servo devices and sensors to monitor the assembly operation in real-time, and computer software to determine when the product meets acceptable functional parameters.

Proponents of Intelligent Assembly claim that many components and products could be produced at lower cost with no sacrifice in performance by simply changing the way quality is defined, and adopting intelligent assembly systems. But, the necessary systems aren’t exactly staple items on the shelf of every supplier and that has been one of the factors keeping intelligent assembly from more widespread adoption.

There’s a bit of folk wisdom that says, if the only tool you have is a hammer, it doesn’t take long for everything to start looking like a nail. Since at least the 70’s, manufacturers have been doggedly pursuing “quality” improvements with the only tool available, tighter and tighter tolerances.

Fig. 1-New Promess integrated torque functional test TFT 1/200 is rated at 1 N-m (9 in.-lb) with a maximum rotational speed of 200 RPM in either direction.  TFT systems are used by test equipment builders and end users in a broad range of testing and measuring of torque applications, including automotive steering and drive train component testing and assembly, manual window crank final testing, seat testing, bearing pre-load, and torque-to-turn testing.

But adding extra zeros to a tolerance specification, also adds extra zeros to production costs, and there are limits to how much consumers will pay for “quality” achieved that way. Perhaps it’s time to stop looking for perfection, and start looking for some new tools.

Intelligent assembly systems
An intelligent assembly system gives you a whole new toolbox. Intelligent Assembly is based on the idea that function is the consumer’s ultimate measure of quality. Under that definition it doesn’t matter if the components are perfect, as long as they work properly and deliver acceptable value to the user.

If the assembly system is smart enough to tell the difference between good products and bad products as they are being made, then it’s quite possible to loosen tolerances in the supply chain – or at least stop tightening them. That can be done today using a combination of servo-controlled, instrumented assembly equipment, and sophisticated, real-time computer analysis of the process data.

Custom-engineered Intelligent Assembly systems have been available for more than 20 years. Some use a technology called “signature analysis” to monitor and qualify the assembly process.

What this means is that the assembly system records the force/distance, force/rotation, force/time or other critical relationships of a known good assembly to create a profile or “signature” of the process that produced it. By comparing each subsequent operation to the “signature,” and setting upper and lower tolerance limits, production of good functions or tolerances can be assured without the need for subsequent inspection.

The signature is typically represented as a pair of curves on the system’s display. As long as the results of any individual assembly operation fall within the area between the two curves, the product can be expected to perform as specified.

The exact shape of the signature also provides information about the individual parts being assembled, which can be used as input to control strategies for other processes. For example, parts that are too soft or too hard will produce a distinct change in the signature, as will parts with out-of-tolerance assembly details such as hole or shaft diameters.

The technology has been applied in hundreds of different applications ranging from automotive hood latches, to medical catheters, and including many items traditionally thought of as requiring extremely tight dimensional tolerances.

In the hood latch application, for example, the assembly system cycled the latch while the rivet holding it together was peened. It stopped the peening process when the force required to move the latch reached a specified value. That way, all of the latches produced functioned identically, despite wide variations in rivet dimensions and properties.

Medical catheters have a small diameter metal tube crimped to a larger tube that’s attached to the flexible portion of the catheter. If the crimp fails, the catheter either comes apart or closes off, both of which are unacceptable.

A hydraulic press previously used for the crimping operation produced inconsistent results. It was replaced by an Intelligent Assembly system that provides a 100% effort test certification for every catheter produced, and virtually eliminates crimp failures in the field.

Promess builds Intelligent Assembly systems based on a line of proprietary servo-controlled electromechanical presses; a series of precision torque units; and a line of computer-based controls running Windows(tm)-based software. Other suppliers use similar products, most of which are proprietary as well. Until recently, that meant that anyone wanting to use Intelligent Assembly technology was essentially limited to a custom-engineered system.

Assembly components
The situation is changing, though, as the components required to build intelligent assembly systems become standard, and readily available to end users who want to experiment with the technology before committing to it. Promess, for example, in recent years has made a number of individual components available to customers who wanted to build their own systems. These include a small (1 Nm) torque functional test (TFT) integrated torque-monitoring-and-control systems, Fig 1, and a line of customizable servo-press workstations intended to offer a semi-standard solution for high-precision assembly and test applications, Fig. 2.

Fig. 2-New customizable servo-press workstations offer a semi-standard solution for high-precision assembly and test applications, based on Promess’ electromechanical assembly press (EMAP), intelligent control, and integrated sensor technologies. Typical applications include assembly and testing of springs, check valves, anti-lock brake components, shock absorbers, oxygen sensors, and a broad range of fluid measurements.

The new TFT 1/200 is rated at 1 Nm (9 in.-lb) with a maximum rotational speed of 200 RPM in either direction. Each system consists of a torque module containing a servomotor, encoder, torque transducer, and output shaft plus a Promess EMAC electronic controller/monitor.

The torque module can produce output rotation in either direction, and the integral angular encoder provides shaft-angle feedback to the control. Mechanical overload stops to protect the transducer. The TFT replaces the traditional inline motor/transducer torque-sensing system with a single, fully integrated unit.

The workstations are based on the field-proven Electro-Mechanical Assembly Press (EMAP), with intelligent control, and integrated sensor technologies integrated with Windows-based, icon-driven software. They provide a custom foundation for sophisticated assembly and test systems.

The EMAP, which is also available as a component, consists of a ball-screw driven by a servomotor and equipped with an array of force and position sensors. The unit provides precise monitoring and control of force and position during assembly and test operations. Because the EMAP is servo-driven, the entire system is easily programmed either on or off-line, and easily reconfigured to handle a variety of different parts and/or operations.

Standard workstations are available with press capacities ranging from 40 kN to 120 kN, with larger and smaller sizes available as special orders. Both press to force/position and pull-to-force/position operations are possible with the Promess servo-press workstation. Typical applications include assembly and testing of springs, check valves, antilock brake components, shock absorbers, oxygen sensors, and a broad range of fluid measurements.

Both the TFT and the workstation used the Promess Electro-Mechanical Multiaxis Controller (EMAC). This is an easily programmed, fully integrated, multiaxis motion controller and data-acquisition-and-analysis system that performs the analytical functions using Promess-developed software.

These capabilities deliver the final piece of the intelligent assembly system, providing real-time monitoring and analysis using signature analysis technology. In simple terms, the system records the force/position signature of a known good operation, and then compares subsequent operations to it. The net result is that ability to replicate known good assemblies or processes.

None of this is earthshaking news to those who have been following the development of intelligent assembly technology, but the fact that the necessary components are now available as stand-alone products is something relatively new. The upshot is that these systems are now within reach of more potential users who don’t need a custom-engineered solution, but who can still benefit from the technology.

Promess, Inc.

Test and Measurement Basics of Microphones

Microphones are familiar sensors that transform sound pressure waves into electrical signals over a broad range of frequencies and amplitudes. They are an integral part of a variety of devices including tape recorders, hearing aids, telephones, and computers. They are also used in radio and television broadcasting and audio engineering. But another specific class, perhaps not as well known, is intended for the scientific measurement of certain types of sounds and noise levels, including ultrasound. Sounds monitored for test and measurement purposes are recorded, analyzed, and typically assigned somewhat different quantitative and qualitative values than voice and music in the entertainment industry. The most common types of microphones include carbon, magnetic, piezoelectric, and condenser.

Each type is best suited for a specific application. For example, carbon microphones were first used in telephones and for radio communications. They are relatively low-cost, rugged, two-terminal devices that contain a small cartridge of lightly packed carbon granules, usually biased with current or voltage. When acoustical pressure waves hit the microphone, the carbon granules compact and relax thus modulating the terminal resistance. The continuously changing resistance then generates an output signal of varying voltage or current in step with the sound pressure waves at the microphone’s input.

Magnetic microphones are dynamic transducers that contain a moving coil, and are based on the principal of magnetic induction. Here, a coil of wire attaches to a lightweight diaphragm, which is in the presence of a magnetic field. The coil moves and generates a voltage proportional to the applied acoustical pressure.

The third type, a piezoelectric microphone, uses either a natural quartz or manmade ceramic crystal. Although these microphones have relatively low sensitivity levels, they are durable and can measure high amplitude pressures. Conversely, their noise-floor level is generally high, which make them particularly suitable for shock and explosive-type pressure measurements.

Condenser microphones come in two types, externally polarized, and pre-polarized. They transform the sound pressure waves into capacitance variations, which are then converted to electrical signals. The unit’s cartridge comprises a small thin diaphragm spatially in parallel with, but not electrically contacting a stationary metal back plate connected to a voltage source. In the presence of oscillating pressure, the diaphragm moves and changes the gap between the diaphragm and the back plate. This produces an oscillating voltage output, which is proportional to the original pressure signal.

The voltage source for an externally powered condenser microphone is usually a 48 to 200 V power supply. By comparison, a newer pre-polarized microphone has an “electret” layer of charged particles deposited on its backplane to supply the polarization. The electret microphone can use inexpensive constant-current supplies instead of costly polarized power supplies. Also, more economical BNC coaxial cables or 10-32 connectors can be used instead of the LEMO-type, 7-pin connectors and cables. Coaxial cables can carry the signals over long distances without significant degradation. Modern pre-polarized microphones are becoming the preferred type for laboratory test, measurement, and field applications.

Selecting and specifying microphones
Most types of microphones can measure broadband sound pressure levels from a variety of sources, but high-precision condenser microphones characterize the sound better than most. When choosing the optimum microphone, a number of factors must be considered:  the application, the sound source, and the operating environment. Also, investigate the type of response (application) field, dynamic response, frequency response, polarization type, sensitivity required, and temperature range needed. A variety of condenser microphones are available for specific applications.

Precision condenser microphones work well in three common application fields: free-field, pressure-field, and random-incident (diffuse) field. Free-field microphones are intended for measuring sound pressure variations that radiate freely through a continuous medium, such as air, from a single source without any interference. The microphone is typically pointed directly at the sound source (0º incidence angle). Free-field microphones measure the sound pressure at the diaphragm; however, the sound pressure may be altered from the true value when the wavelength of a particular frequency approaches the dimensions of the microphone. Consequently, correction factors are usually added to the microphone’s calibration curves to compensate for any changes in pressure at its diaphragm due to its own presence in the pressure field. These microphones work best in anechoic chambers or large open areas where hard or reflective surfaces are absent.

The second type is called a pressure-field microphone. They measure sounds from a single source within a pressure field that has the same magnitude and phase at any location. In order to simulate a uniform pressure field, they are usually calibrated in enclosures or cavities, which are small compared to their wavelength. This minimizes any alterations in measurements due to the presence of the microphone in the sound field. They are also supplied with a pressure versus frequency-response curve. Such microphones measure the pressure exerted on walls, airplane wings, or inside structures such as tubes, housings, and cavities.

The third type is called a random-incident or a diffuse-field microphone. They are omni-directional and measure sound pressure from multiple directions and sources, including reflections. They come with typical frequency response curves for different angles of incidence and compensate for the effect of their own presence in the field. An appropriate application for this type of microphone is measuring sound in a building with hard, reflective walls, such as a church.

Dynamic response
The main criterion that describes sound is based upon the amplitude of sound-pressure fluctuations. The lowest amplitude that a healthy human ear can detect is 20 millionths of a Pascal (20µPa). Since the pressure numbers represented by Pascals are generally extremely small and not easily managed, another scale is more commonly used, called the decibel (dB). This scale is logarithmic and more closely matches the response of the human ear to pressure fluctuations. Some examples of typical sound pressure levels used as a reference include the following:

Typically, the maximum decibel level is based on the physical characteristics of the condenser microphone. The specified maximum dB level refers to the point where the diaphragm approaches the back plate, or where total harmonic distortion (THD) reaches a specified amount, about 3% or less. The maximum level in dB that a microphone outputs in a certain application depends on the voltage supplied and its sensitivity. In order to calculate the maximum output for a microphone, use a specific preamplifier and its corresponding peak voltage, and then calculate the pressure in Pascals that the microphone can accept. The amount of pressure is determined from the following equation:

Where: P = Pascals, Pa
Voltage = the preamps output peak voltage, V.

After the maximum pressure level that the microphone can sense at its peak voltage is determined, it can then be converted to dB using the following logarithmic scale:

Where: P = Pressure in Pascals, Pa
Po = Reference Pascals, Pa (Constant = 0.00002 Pa)

The microphone’s cartridge thermal noise (CTN) rating indicates the lowest measurable sound pressure level that it can detect above the electrical noise inherent within the microphone. The inherent noise level of a microphone and preamplifier combination is highest at both the lower and upper limits of the microphone. Each microphone has a unique noise characteristic, and the diameter of the microphone strongly influences its frequency response and noise level.

Frequency response
After the microphone’s field response and dynamic range have been determined, find the usable frequency range from its specification sheet. Proper selection requires that the measured pressure levels fall between the microphone’s low-end noise level (CTN), and the maximum rated dB level of the microphone. In general, the smaller the microphone diameter, the greater the high-end dB level expected. The larger diameter microphones are recommended for lower frequency range amplitude (dB) measurements since the inherent noise or CTN specifications are typically lower.

Manufacturers typically specify a ± 2 dB tolerance on the frequency versus output amplitude. When comparing microphones, check the tolerance in the specific frequency range most needed. When an application is not critical, select a wider frequency range with a higher allowable output (dB) tolerance from the manufacturer’s specification sheet.

Polarization type
Condenser microphones are further classified in two categories; traditional externally polarized and pre-polarized microphones. Either type works well for most applications, but the pre-polarized units tend to produce more repeatable output in humid surroundings. Pre-polarized microphones are recommended where temperature changes can promote condensation and short circuits on the internal components of externally polarized microphones. Conversely, at temperatures between 120 and 150º C, externally polarized microphones are better suited, because their sensitivity level is more consistent in this range.

Microphone sensitivity is inversely proportional to temperature. Microphones operated or stored in high temperature environments may require calibration more frequently. However, a probe microphone is specifically intended for withstanding these kinds of harsh environments. It combines a microphone with a probe-type extension tube for mounting close to the sound source. The probe tip contains the microphone, and the signal-conditioning module may be remotely located, either in a less harsh environment or where access to the sound source is too small for a typical condenser microphone.

Special applications
Microphones are often designed for special applications. For example, corrosion-resistant microphones called hydrophones are used for testing, monitoring, and measuring sounds under water. Different models are available for different sensitivities, frequencies, dB levels, and operating depths.

Another particular type, sound level meters, are special instruments intended to read sound pressure levels quickly and conveniently. Portable units are usually small, handheld instruments, which include the microphone, preamplifier, power source, software, and display. They measure ambient noise levels on the street and artillery ranges; in factories, power generating plants, shopping malls, office buildings, and numerous other places.

Intensity probes are usually the best choice for measuring the magnitude and direction of a sound. The set up usually consists of two phase-matched microphones with a spacer between them. They measure the pressure level as well as the speed and direction of the propagating sound waves. The higher frequencies typically require a smaller spacer, while larger spacers are used for lower frequencies or where sounds might reverberate.

Array microphones are used for near-field, acoustic holography (NAH). These are applications where 3D field values are studied. A number of array microphones are placed in a predetermined pattern and combined with appropriate software to map the acoustic energy flow of a complex sound pressure field. Array microphones work especially well where a large number of microphones are used concurrently. Also, Transducer Electronic Data Sheet (TEDS) are recommended to be used with arrays, since they let the user quickly and easily identify a particular microphone within the array. TEDS chips and firmware are typically stored electronically in each microphone and list its model number, serial number, calibration date, along with the specifications of the microphones sensitivity, capacitance, impedance, and other information that can be downloaded to help ensure accurate test results.

Finally, outdoor microphones can withstand rigorous environmental exposure, such as in airports and on highways. Noise measurements here are crucial to providing information for improving human safety conditions. Environmental and outdoor microphones provide different levels of protection for the internal components, while maintaining their high-accuracy specifications.

PCB Piezotronics Inc

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