Accelerometer and accelerometers information
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`A typical Flowmeter
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`Accelerometer Definition
`
`Accelerometer Home Page(cid:172)
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`Accelerometers: What are accelerometers? Accelerometers are devices that measures the vibration, or acceleration of motion of a
`structure.
`
`• Introduction to the Accelerometer
`What are Accelerometers?
`An accelerometer is a device that measures the acceleration, or vibration of motion of a
`structure. The force caused by vibration or a change in motion (acceleration) causes
`the mass to "squeeze" the piezoelectric material which produces an electrical charge
`that is proportional to the force exerted upon it. Since the charge is proportional to the
`force, and the mass is a constant, then the charge is also proportional to the
`acceleration.
`
`There are two types of vibration sensors (piezoelectric accelerometers). The first type is
`a "high impedance" charge output accelerometer. In this type of accelerometer the
`piezoelectric crystal produces an electrical charge which is connected directly to the
`measurement instruments. The charge output requires special accommodations and
`instrumentation most commonly found in research facilities. This type of accelerometer
`is also used in high temperature applications (>120C) where low impedance models
`can not be used.
`
`The other type of accelerometer is a low impedance output accelerometer. A low
`impedance accelerometer has a charge accelerometer as its front end but has a tiny
`built-in micro-circuit and FET transistor that converts that charge into a low impedance
`voltage that can easily interface with standard instrumentation. This type of
`accelerometer is commonly used in industry. An accelerometer power supply like the
`ACC-PS1, provides the proper power to the microcircuit 18 to 24 V @ 2 mA constant
`current and removes the DC bias level, they typically produces a zero based output
`signal up to +/- 5V depending upon the mV/g rating of the accelerometer. All
`OMEGA(R) accelerometers are this low impedance type.
`
`Accelerometers - Typical Specifications
`
`Dynamic Range is the +/- maximum amplitude that the accelerometer can measure
`before distorting or clipping the output signal. Typically specified in g's.
`
`Frequency Response is determined by the mass, the piezoelectric properties of the
`crystal, and the resonance frequency of the case. It is the frequency range where the
`output of the accelerometer is within a specified deviation, typically +/- 5%.
`
`g 1g is the acceleration due to the earth's gravity which is 32.2 ft/sec2, 386 in/sec2 or
`9.8 m/sec2.
`
`Grounding - There are two types of signal grounding in accelerometers. Case
`Grounded accelerometers have the low side of the signal connected to their case. As
`the case is part of the signal path and may be attached to a conductive material, care
`must be used when using this type of accelerometer to avoid noise from the ground
`plain. Ground Isolated accelerometers have the electrical components isolated from the
`case and are much less susceptible to ground induced noise.
`
`High Frequency Limit is the frequency where the output exceeds the stated output
`deviation. It is typically governed by the mechanical resonance of the accelerometer.
`
`Low Frequency Cut-off is the frequency where the output starts to fall off below the
`Page 1 of 3
`HAPTIC EX2011
`
`General
`Purpose Top-
`Mount
`Industrial
`Accelerometer
`ACC786A
`• 2-Pin MIL-Style Connector
`• Splashproof Design
`• Ground Isolated
`• Hermetic Seal
`• For Motors, Pumps,
`Gearboxes, and General
`Industrial Applications
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`• Dynamic Sensors
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`• Industrial Low Profile
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`• Industrial Harsh Environments
`• High Vibration General Purpose
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`• Triaxial Accelerometers
`• Dynamic Pressure Transducer
`• Dynamic Load Cell
`• Impulse Hammer
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`Accelerometer and accelerometers information
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`http://web.archive.org/web/20140817114402/https://mx.omega.com/pro...
`
`Accelerometer Tech Links
`
`• Force, Acceleration and Torque
`
`• Acceleration & Vibration
`
`• Torque Measurement
`
`• Force Sensors
`
`• Information Resources
`
`• Glossary of Terms: Force,
`Acceleration and Torque
`
`Figure 14
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`Figure 15
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`stated accuracy. The output does not "cut-off " but the sensitivity decreases rapidly with
`lower frequencies.
`
`Noise - Electronic noise is generated by the amplifying circuit. Noise can be specified
`either broad band (specified over the a frequency spectrum) or spectral - designated at
`specific frequencies. Noise levels are specified in g's, i.e. 0.0025 g 2-25,000 Hz. Noise
`typically decreases as frequency increases so noise at low frequencies is more of a
`problem than at high frequencies.
`
`Resonance Frequency is the frequency at which the sensor resonates or rings.
`Frequency measurements want to be well below the resonance frequency of the
`accelerometer.
`
`Sensitivity is the output voltage produced by a certain force measured in g's.
`Accelerometers typically fall into two categories - producing either 10 mV/g or 100 mV/
`g. The frequency of the AC output voltage will match the frequency of the vibrations.
`The output level will be proportional to the amplitude of the vibrations. Low output
`accelerometers are used to measure high vibrational levels while high output
`accelerometers are used to measure low level vibrations.
`
`Temperature Sensitivity is the voltage output per degree of measured temperature.
`The sensors are temperature compensated to keep the change in output to within the
`specified limits for a change in temperature.
`
`Temperature Range is limited by the electronic micro circuit that converts the charge to
`a low impedance output. Typically the range is -50 to 120C.
`
`Accelerometers How to Select? When selecting an accelerometer for your
`application many parameters must be considered.
`
`What is the vibration amplitude to be monitored?
`What is the frequency range to be monitored?
`What is the temperature range of the installation?
`What is the size and shape of the sample to be monitored?
`Are there electromagnetic fields?
`Is there a high level of electrical noise in the area?
`Is the surface where the accelerometer is to be mounted grounded?
`Is the environment corrosive?
`Does the area require Intrinsically safe or explosion proof instruments?
`Is the area a wet or a wash down area?
`
`Additional Considerations:
`The mass of the accelerometer should be significantly smaller than the mass of the
`system to be monitored.
`The accelerometer dynamic range should be broader than the expected vibration
`amplitude range of the sample.
`The frequency range of the accelerometer should fit the expected frequency range.
`The Sensitivity of the accelerometer should produce an electrical output compatible
`with existing instrumentation. Use a low sensitivity accelerometer to measure high
`amplitude vibrations and conversely use a high sensitivity accelerometer to measure
`low amplitude vibrations.
`
`Mounting
`The sensor must be mounted directly to the machine surface to correctly measure the
`vibrations. This can be accomplished by several types of mounts:
`
`Flat Magnet Mount
`2-pole Magnet Mount
`Adhesives (Epoxy/Cyanoacrylate)
`Mounting Stud
`Isolating Stud
`
`Magnet Mounts are generally temporary mountings.
`Magnetic mounts are used to mount accelerometers to ferromagnetic materials
`commonly found in machine tools, structures and motors. They allow the sensor to be
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`Accelerometer and accelerometers information
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`http://web.archive.org/web/20140817114402/https://mx.omega.com/pro...
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`easily relocated from site to site for multiple location readings. Two-pole magnetic
`mounts are used to mount an accelerometer to a curved ferromagnetic surface.
`
`Adhesives, and threaded studs are considered permanent mountings.
`Adhesives such as epoxy or cyanoacrylate have proven to provide satisfactory bonding
`for most applications. Keep the film as thin as possible to avoid any unwanted
`dampening of the vibrations due to the flexibility of the film. To remove an adhesive
`mounted accelerometer, use a wrench on the case's wrench flats and twist to break the
`adhesive bond. DO NOT USE A HAMMER. Striking the accelerometer will damage it.
`
`Mounting studs are the preferred mounting technique.
`They require the structure to be drilled and tapped but provide solid reliable mountings.
`Be sure to follow the specified torque settings to avoid damaging the sensor or stripping
`the threads.
`
` Accelerometer Types Vary
`
`ACC793 Premium
`Grade Accelerometer
`
`ACC101 Industrial
`Accelerometer
`
`ACC103: Laboratory
`Accelerometer for
`High Vibration Levels
`
`Premium Grade
`These accelerometers are made from premium selected crystals and use low noise circuitry to product a
`premium, low noise, accelerometer. Their 316L Stainless steel case is hermetically sealed against the
`environment so they can survive harsh industrial environments. They also have FM and CSA Intrinsically
`safe options available. The ACC793 is a standard top cable configuration and the ACC797 is a low-profile
`side cable configuration.
`
`Industrial Grade
`Industrial grade accelerometers are the workhorses of industry. The are used on everything from machine
`tools to paint shakers. OMEGA has four models to choose from. ACC101 (shown) is a high quality low
`cost accelerometer for general purpose applications. ACC 102A is hermetically sealed for harsh
`environments, has a fixed cable and weighs only 50 grams. The ACC786A, top cable, and ACC787A,
`side cable, are hermetically sealed and have detachable cables sealed against the weather.
`
`High Vibration
`Accelerometers used to monitor high vibration levels have a lower output (10 mV/g) and lower mass than
`industrial accelerometers. The ACC103 weighs 15 gms and can monitor vibration levels up to 500 g's. It is
`a stud mount design and is designed for use on shaker tables, vibration labs and heavy industrial
`machine tools. The ACC104 weighs only 1.5 gms and is designed for adhesive mounting. Both models
`have a Frequency range of 3 to 10 kHz and a dynamic range of +/- 500 g's.
`
`ACC301: Triaxial
`Accelerometer
`
`Triaxial
`Triaxial accelerometers measure the vibration in three axes X, Y and Z. They have three crystals
`positioned so that each one reacts to vibration in a different axis. The output has three signals, each
`representing the vibration for one of the three axes. The ACC301 has lightweight titanium construction
`and 10 mV/g output with a dynamic range of +/-500 g's over a range of 3 to 10 kHz.
`
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