ISAT 303-Lab3-1

Measurement of Condition: Lab #3 (2005): List of parameters of condition:

– Linear distance, angular displacement, vibration, displacement, humidity, viscosity, etc

Transducer – takes input of a form of energy (characteristic e.g. light beam, magnetic field, eddy current) and generates an output that is a different form of energy (characteristic e.g. voltage) from the input

ISAT 303-Lab3-2

Measurement of Condition:Non-Contacting Displacement Sensors Displacement sensors measure the distance traveled by

a target object as it moves from one position to another. The transducers can also be used to measure external

dimensions of objects, such as thickness, height, width or diameter.

Two basic types:– Contact type: dial gages, micrometers and LVDT– Non-contact type:

» semiconductor laser displacement sensors: reflected light» inductive (eddy current) sensors: magnetic field attenuation» capacitive transducers: current decrease with plate separation» acoustic transducers: sonic waves reflection (e.g. sonar)» microwave devices: reflected -waves (e.g. radar)

ISAT 303-Lab3-3

Displacement Sensors Used in This Lab: Comparative Summary

Inductive (Eddy Displacement

CATEGORY Current) Sensor Laser Sensor

Detected object Electrically Any opaque or

conductive material translucent material

Detecting range Very short (0-10 mm) Typical (10-400 mm)

Resolution Very high (.3-1 mm) Ultra high (.01-.2 mm)

Response time Fast (0.05 -1 ms) Very fast (.001-.05 ms)

Environmental Excellent Typical

resistance

Detection point Large Very small

ISAT 303-Lab3-4

Laser Sensors: Operating Principles Displacement laser sensors consist

of a sensor head and a controller. A laser within the sensor head

emits a focused light on the the target.

Light reflected back from the target is focused on an optical position detector.

AmplifierDriveCircuit

ReferenceDistance

PositionDetector

ReceiverLens

Laser

TransmitterLens

Displa-cement

Sensor head

The unit’s output is proportional to the displacement (along the laser’s line of sight) of the target.

The controller unit contains a power supply, adjustment circuitry and signal conditioning.

ISAT 303-Lab3-5

Inductive Sensors: Operating Principles

An oscillator generates a strong focused magnetic field.

When the target enters the field, eddy currents are induced in its surface

The current produces its own magnetic field which reduces the amplitude of oscillations.

The change in amplitude is converted into a DC output of the sensor which is related to how close the target is to the sensor head.

NearFar Sensor head

Magneticfield

Metaltarget

Targetdisplacement

FarNear

Far

Oscil-lator output

Sensor output

0v

Displacement

Output,Volt

ISAT 303-Lab3-6

Inductive Sensors: Factors Influencing Sensing Range Mechanical factors

– core size and shape– material of the target– target size– manufacturing tolerance and other variations

Environmental factors– ambient temperature– electromagnetic (RF) noise– adjacent sensors or magnetic fields– electrical company power surges

ISAT 303-Lab3-7

Displacement Sensors: Sample Manufacturing Applications Non-contacting dimensional gaging: critical dimensions

in precision parts (circuit boards, engine components, sheet thickness, flatness, runout)

Motion and vibrations: small high frequency monitoring (disk head movement, machine vibration monitoring, robot motion verification and safety)

Coating and film thickness: precise measurement of thickness of coatings on metal parts (paint, resins)

Presence and absence of objects: electronic assembly, filling and packaging (damaged shrink wrapping and misfeeding)

ISAT 303-Lab3-8

Accuracy: Accuracy – closeness of agreement between a measured

value and the true value Accuracy is often given (specified) as a % of full scale

output– E.G. if device range is 0 to 5 volts and accuracy is +/-5% of F.S.– Then uncertainty is =/- 0.25 volts (.05 x 5)– Therefore at readings of below FS, % uncertainty will be

greater than 5% (per example above)– At readings close to lower end of range, % uncertainty will be

unreliable Implications for selecting measuring systems ?????

ISAT 303-Lab3-9

Inductive (Eddy Displacement

CATEGORY Current) Sensor Laser Sensor

Detected object Electrically Any opaque or

conductive material translucent material

Detecting range Very short (0-10 mm) Typical (10-400 mm)

Resolution Very high (.3-1 mm) Ultra high (.01-.2 mm)

Response time Fast (0.05 -1 ms) Very fast (.001-.05 ms)

Environmental Excellent Typical

resistance

Detection point Large Very small