Sound and Vibration Transducers Guide

An overview of the sensors and correseponding technologies including microphones, accelerometers, proximity probes, and tachometers commonly used in sound and vibration applications.

Acoustic Transducers

These sensors convert acoustical waves into electrical signals, usually a voltage, that can be measured by devices such as sound level meters and dynamic signal acquisition hardware.  The voltage output from microphones is often quite low, in the uV range and requires a preamplifier to be measured properly.  The output voltage from preamplifiers is often in the mV range and may be further amplified by the measurement device.  Review this microphone selection guide for more details on choosing a microphone for your application.

Microphones

In general, National Instruments recommends pre-polarized microphones and constant current powered (CCP) preamplifiers for use with NI devices that provide IEPE (Integrated Electronic Piezo-Electric) signal conditioning  Condenser microphones are the most common although electret type are finding wider adoption in array microphones.

• Carbon Button Microphone
• Condenser Microphone
• Electret Type Microphone
• Moving Coil Microphone
• Piezoelectric Microphone
• Ribbon Microphone

Hydrophones

Hydrophones are a microphone designed for acoustic measurements in fluids.  These normally consist of a piezoelectric crystal encased in rubber or other protective material.

• Piezoelectric Hydrophone

Additional Acoustic Sensors

• Binaural Head - a tutorial on measuring sound quality
• Ear and Mouth Couplers
• Sound Intensity Probe - a tutorial on measuring sound intensity

Vibration and Displacement Transducers

Accelerometers are used to measure vibration.  In applications that involve flight, such as aircraft and satellites, accelerometers are based on rotating mass properties. In the industrial world, however, the most common design is based on a combination of Newton's law of mass acceleration and Hooke's law of spring action.  This tutorial on accelerometer principles details the theory of these device in more depth.

Accelerometers

Accelerometers are transducers for measuring the dynamic acceleration of a physical device.  Piezoelectric accelerometers are the most common.  National Instruments recommends piezoelectric or ICP® type accelerometers for use with NI devices that provide IEPE (Integrated Electronic Piezo-Electric) signal conditioning.

• Bonded Strain Gage Accelerometer
• Hall Effect Accelerometer
• Piezoelectric Accelerometer
• Piezoresistive Accelerometer 
• Piezotransistor Accelerometer
• Photoelectric Accelerometer
• Servo Accelerometer
• Unbonded Strain Gage Accelerometer
• Vibrating Element Accelerometer

Proximity Probes

Proximity probes measure the displacement of a physical device.  Proximity probes are commonly used in machine monitoring applications because they allow users to monitor the movement of a rotating shaft.  Proximity probes are usually found in 90 degree offset pairs to map an XY Plot of the shaft movement.  This allows users to then detect imperfections such as mis-alignment of the shaft, faulty bearings, or other external factors preventing perfect rotation. 

• Eddy Current Proximity Probe 
• SMB-120 cable for connecting to proximity probes

Tachometers

Tachometers measure the rotational speed of a physical device.  Tachometers are important in sound and vibration applications because they provide rotational speed as well as phase information - this allows users to match frequency components to shaft speed and position. 

• Capacitance Tachometer
• Centrifugal Force Tachometer
• Drag Torque Tachometer
• Gyroscopic Tachometer
• Photoelectric Tachometer
• Strain Gage Tachometer
• Switch Tachometer
• Toothed Rotor Magnetic Tachometer

TEDS

TEDS or Transducer Electronic Data Sheets, based on the IEEE 1451.4 (TEDS) standard, brings plug-and-play capabilities to transducers. TEDS-compatible measurement systems can autodetect and automatically configure these “smart sensors” for measurement, reducing setup time and eliminating transcription errors that commonly occur during sensor configuration.

• IEEE 1451.4 Standard Overview
• NI Sensors Plug&Play - IEEE 1451.4 (TEDS)

Selected Models of Microphones and Accelerometers

Included here is a small selection of microphones and accelerometers from G.R.A.S. Sound and Vibration and PCB Piezotronics.  These manufacturers and others offer a much wider selection of transducers for your specific applications.

G.R.A.S. Microphones

National Instruments recommends pre-polarized microphones and constant current powered (CCP) preamplifiers for use with NI devices that provide IEPE (Integrated Electronic Piezo-Electric) signal conditioning.

• G.R.A.S. ½” Free-field pre-polarized microphone and CCP preamplifier, 50 mV/Pa, 3.15 Hz to 20 kHz, TEDS, Model 46AE
• G.R.A.S. ¼” Integrated array microphone and preamplifier, 50 mV/Pa, TEDS, Model 40PF

PCB Piezotronics Accelerometers

National Instruments recommends piezoelectric or ICP® type accelerometers for use with NI devices that provide IEPE (Integrated Electronic Piezo-Electric) signal conditioning.

• PCB General-purpose ICP® accelerometer, 100 mV/g, 0.5 Hz to 10 kHz, TEDS, Model TLD352C33
• PCB Mini triaxial ICP® accelerometer, 100 mV/g, 1 Hz to 4 kHz, TEDS, Model TLD356A32
• PCB Industrial ICP® accelerometer, 100 mV/g, 0.5 Hz to 10 kHz, Model 603C01

ICP® is a registered trademark of PCB Piezotronics.

Related Links

• NI Sound and Vibration Hardware and Software

 

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