Change_Piezoelectric Technology Review

8/3/2019 Change_Piezoelectric Technology Review

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SensorsSensors

Dave Change



General TopicsGeneral Topics• Why do we use piezoelectric sensors?

• Common uses for piezoelectric sensors

• Factory supplied documentation

• Dynamic measurement vs. static measurement

• Introduction to iezoelectricit and iezoelectric transducers

• Typical IEPE designs

• IEPE transducer characteristics•

• Transducer selection criteria

• Mounting considerations

• Impulse hammers• General handling

• TEDS

• MEMS

2Dytran Instruments, Inc.



Why do we useWhy do we use piezopiezo sensors?sensors?

• Small size • Broad frequency

• Light weight• 2-wire operation

range• Ultra low noise

IEPE

•

Wide dynamic range

• Simp e signaconditioning

• range

implementation

Dytran Instruments, Inc. 3



CommonCommon Uses for PiezoelectricUses for Piezoelectricensorsensors

• Modal Analysis • Predictive /

•Environmental StressScreening (ESS)

preventativemaintenance

• Hea t an UsageMonitoring Systems(HUMS)

•

• Aircraft groundvibration test

• Aircraft flight test




What factory supplied documentationWhat factory supplied documentationcomes with your accelerometer?comes with your accelerometer?

• Operating guide

• Outline installation drawing

•

• Calibration certificate




Outline installation drawingOutline installation drawing










Other Piezoelectric DevicesOther Piezoelectric Devices• Today’s discussion will focus primarily on

same principles to measure dynamic force andpressure




D namic vs. Static MeasurementD namic vs. Static Measurement

Dynamic Measurementynamic Measurement Static Measurementtatic Measurementynamic Measurementynamic Measurement

• The physical quantity (i.e.acceleration, force,

Static Measurementtatic Measurement

• The physical quantity beingmeasured does not change

changing over time

•Examples of dynamic events

changes very slowly)

•Examples of static

‒ ra on o ro a ng mac nery

‒ Pressure in a reciprocatingengine

‒ Force input to a structure via a

‒ Force measurement in abathroom scale

‒ Constant acceleration due to

shake table gravity




Definition of PiezoelectricityDefinition of PiezoelectricityPiezoelectricityiezoelectricity is the ability of some materials (notably

potential in response to applied mechanical stress. Thismay take the form of a separation of electric charge

. -circuited, the applied charge induces a voltage across the

material. The word is derived from the Greek wordp ez en , w c means o squeeze or press.




What is a Piezoelectric Transducer?What is a Piezoelectric Transducer?• A transducer transducer converts one form of energy into another

‒ n e case o a p ezoe ec r c rans ucer p ezoe ec r c rans ucer e rans uc on s rom

mechanical energy to electrical energy

• The prefix “piezo” is a Greek word meaning “to squeeze”

• Materials that produce an electric charge when a force is

applied to them exhibit what is known as thep ezoe ectr c e ect

• Many piezoelectric materials are known to

‒ Quartz, tourmaline, ceramic (PZT), GAPO4 andmany others




Piezoelectric TransducerPiezoelectric Transducer• The active element in all piezoelectric devices is a

.

different sensor designs based on various crystalcuts and materials.

• The common types (modes) of piezoelectric sensors

in use today are:‒‒ o age mo e o age mo e , , , ezo ron, so ron

‒‒ Charge mode Charge mode

‒ Each of these designs have their advantages and




Piezoelectric Sensin Element Desi nsPiezoelectric Sensin Element Desi ns


Compression Shear



Voltage Mode TransducerVoltage Mode Transducer

• Can utilize either quartz or ceramic

• ave u t n or ntegra e ectron cs

• Low cost signal conditioning

• Stable over broad tem erature ran e

• Limited upper temperature range due to built in

electronics• any mo ern ana yzers an a a acqu s on

systems have IEPE power built in

• Most voltage mode (IEPE) sensors available with TEDS

option• Ease of use




Input / Output Characteristics of Input / Output Characteristics of

• In ut : 18 – 24 Volts DC 2-20mA constant current

‒

Inputs other than the specified value can be harmful to thesensor

• Output : voltage proportional to acceleration orvibration

Note: The IEPE or voltage mode sensor is strictly a two wiredevice (sig / power and ground)




Voltage Mode SetupVoltage Mode Setup




Alternate Voltage Mode SetupAlternate Voltage Mode Setup




Typical IEPE System DesignTypical IEPE System Design




Bias Voltage Levels in Typical IEPEBias Voltage Levels in Typical IEPE




IEPE Sensor Frequency ResponseIEPE Sensor Frequency Response

• Low frequency response is controlled by the sensorDischarge Time Constant (DTC)Discharge Time Constant (DTC)‒ Factory set and cannot be changed

‒Can be changed at time of manufacture

• g requency response s genera y a unct on osensor resonance (natural) frequency

• er ng n e sensor or s gna con on ng can a soeffect the sensor frequency response

• g sens t v ty sensors genera y ave owresonance frequency

• ow sens v y sensors genera y ave gresonance frequency




Frequency Response of PiezoelectricFrequency Response of Piezoelectric




Panel Meter ExamplesPanel Meter ExamplesTrouble Shooting AideTrouble Shooting Aide

10 BATT.O.K.

10 BATT.O.K.

BATT.O.K.

10

NORMAL

OPENSHORT

SENSOR BIASDC VOLTS

SENSOR BIASDC VOLTS

SHORT OPEN

NORMAL NORMAL

OPENSHORT

SENSOR BIASDC VOLTS

Shorted Normal Open




Discharge Time Constant (DTC)Discharge Time Constant (DTC)

•• Discharge Time ConstantDischarge Time Constant – the time required for the

its original value in response to a zero rise time stepfunction input‒ eterm nes sensor ow requency response

• Low frequency response is approximately equal to:- o nt = .

-5% = -3dB Point x 3




Charge Mode TransducersCharge Mode Transducers

• Usually ceramic based

• o u t- n e ectron cs

• Good for high temperature (+500°F)

• Ex ensive si nal conditionin

• Low noise cable required for most applications

• Charge amps are generally more difficult to use (i.e.se ng sca e ac ors, e c.




Mounting OptionsMounting Options

• Stud mounting‒ p mum requency response

• Epoxy adapter, stud mount sensor‒

• Magnetic mount‒ ,

• Magnetic mount to epoxied target‒




Frequency Response EffectsFrequency Response Effects




Transducer Selection CriteriaTransducer Selection Criteria• How much space is available for mounting the

sensor (i.e. footprint)?

•

loading)?• What is the vibration level?

• What are the frequencies of interest (max and min)?

• What is the temperature range required?

•

• Is physical clearance a problem?

• Is the environment wet or dry?

• How will the sensor be mounted (stud, wax, glue)?• What cable length will be required?

• at ca e ac et mater a w e a equate




Dynamic RangeDynamic Range

• Select proper full scale amplitude from transducer

• Full scale ranges normally listed for ±5 Volts out

• Over range capability usually set by current sourceopen circuit output voltage (not always true)

• If P.C. based data acquisition make sure board isconfigured properly for your specific measurement




Impulse HammersImpulse Hammers

• Provide a known force input (mV/Lb) to a structure

• any erent p ys ca s zes are ava a e

• For industrial use the 1Lb, 3Lb, or 12Lb sledgehammers are most popular

• Four different tip materials are provided for pulsetailoring

minimum of two channels




Typical MultiTypical Multi--Channel Modal SetupChannel Modal Setup




General care and handling of yourGeneral care and handling of your

p ezoe ec r c ev cep ezoe ec r c ev ce

• Do not‒ Drop your sensor on a concrete floor

‒ Connect a bench power supply to your sensor

‒ Remove ou sensor with a hammer

‒ Use un-calibrated accelerometers

‒ Rub your feet across the floor and touch the connector (static

electricity)




General care continuedGeneral care continued

• Do‒ If possible, store your sensor in the box it came in

‒ Connect a constant current supply

‒ Remove our sensor with a solvent and ro er tool

‒ Re-calibrate your sensor on a yearly basis

‒ Discharge yourself before handling the sensor




TEDSTEDS-- Transducer Electronic Data SheetTransducer Electronic Data Sheet



MEMS AccelerometersMEMS Accelerometers

Variable Capacitance MEMS accelerometersVariable Capacitance MEMS accelerometers

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Change_Piezoelectric Technology Review