How to Select Your Measurement Equipment

1. Types of Measurement Equipment2. Measurement Principles3. Type of Measurement4. Information Required for Selection5. Determining the Measurement Method6. Example of Selecting a Displacement Meter or Measurement System

Displacement Meters and Measurement Systems

Selection Catalogue

2

1. Types of Measurement Equipment

The typical types of displacement meters are the 7 types listed below. The list also summarises the characteristics of each of the types.

Item Laser Displacement

Meter

2D Laser Displacement

Meter

Optical Micrometer

Instant Measurement

System

Eddy Current Displacement

Meter

Ultrasonic Displacement

Meter

Contact-type Displacement

Meter

Detection Object

Material Any object Any object Any object Any object Metals Any object Solids

Measurement Spot

Small (MIN. 2 m )

Small Small SmallStandard

(Twice the OD of head)Large

(MIN. 15 m )Small

Surface restrictions Almost none Almost none Almost none Almost none None None Soft surfaces

Measurement Range 0.2 to 3500 mm 0 to 290 mm 10 m to 120 mm 0.02 to 200 mm 0 to 10 mm 24 to 920 mm 0.8 to 30 mm

Repeatability MIN. 0.005 m MIN. 0.2 m MIN. 0.03 m MIN. 0.1 m MIN. 0.3 m MIN. 0.1 mm MIN. 0.1 m

Response FrequencyApprox.

MAX. 392 kHzApprox.

MAX. 64 kHzApprox.

MAX. 16 kHz

Approx. MAX. 18 kHz

Approx. MAX. 7 kHz

Approx. MAX. 40 kHz

Environmental Resistance (Water, Oil, Dust, etc.)

Characteristics

Advantages

- Can measure any object

- Small measurement spot

- High precision

- High-speed response frequency

- Can measure any object

- Can measure uneven surfaces and shape

- High stability

- Can measure any object

- High stability

- High precision

- Easy operation

- Can measure complex dimensions

- Can measure multiple spots

- Superior environmental resistance

- High precision

- High-speed response frequency

- Can measure any object

- Large Measurement range

- High precision

Disadvantages

- Low environmental resistance

- Low environmental resistance

- Limited to projected objects

- Limited to projected objects

- Limited work size

- Measures only metals

- Small Measurement range

- Large measurement spot

- Low accuracy

- Low response frequency

- Cannot measure soft objects

- Low response frequency

Laser displacement sensors are displacement sensors that are of superior quality in terms of the objects that can be measured, measurement accuracy, response frequency, and many other aspects.

Good, Better, Best

Coil

High-frequency magnetic fieldDetection target object

Eddy current

High-frequencyoscillator circuit

Transmitted wave

Received wave

L

Secondary winding

Secondary winding

Moving core

Primary winding

Primary winding

Primary winding

Core

Primary winding

Primary winding

Voltage output

Secondary winding

Secondary winding

Secondary winding

Secondary winding

Structure Circuit

Core Core

Det

ectio

n am

plifi

catio

n

3

2. Measurement Principles

Laser Displacement Meter 2D Laser Displacement Meter

Optical Micrometer

Eddy Current Displacement Meter

The measurement principles of typical displacement meters and measurement systems are introduced below.

The measurement principle of triangulation occurs when the position

of the target object changes, the beam spot on the receiving element

changes position. This position change is used to measure distance.

Utilises 2D laser triangulation to obtain a profile of a part for complex

measurements such as angles and radii with a single sensor.

Optical micrometers use a collimated beam of light to pass from a

light source to a receiving element. By analysing the shadow cast by

the test part, measurement is possible.

This system uses a high-frequency magnetic field. High-frequency

current is passed through the coil inside the sensor head to produce

the high-frequency magnetic field. When the measurement target

(metal) comes into the magnetic field, magnetic flux passes the

target's surface and eddy current flows in the vertical direction due to

electromagnetic induction action, causing a change in the impedance

of the sensor coil. The eddy current displacement sensor measures

distance based on the changes in oscillation caused by this

phenomenon.

2D Ernostar lens

Cylindrical lens

Semiconductor lasers

HSE3-CMOS

Target

CMOS monitor camera

HL-CCD

Telecentric opticsHigh-intensityGreen-LED

Ultrasonic Displacement Meter

Ultrasonic displacement sensor emits ultrasonic from the sensor

head and receives the ultrasonic reflected off the target object. The

distance is measured by detecting and calculating the time from the

emission of this ultrasonic to the receipt of the ultrasonic.

If the detected distance is expressed as L, the time from the emission of ultrasonic to the receipt as T, and the speed of sound as C, the detected distance L can be calculated by the formula: L = 1/2 x T x C. (T is 'to-and-fro' time; thus it is multiplied by 1/2.)

[ Calculation Formula]

L = TC21

Contact-type Displacement Meter

Differential transformer is comprised of 3 coils and a moving core.

When the primary winding is excited by an AC source (constant

frequency voltage), the moving core moving along with the

measurement target causes induced voltage in the secondary

winding. This is differential coupled to obtain the voltage difference,

hence the displacement output.

Collimator lens/ Special diffuser unit

4

3. Type of Measurement

4. Information Required for Selection

There are a variety of measurements, including thickness measurement and vibration measurement. Categorising broadly, measurements can be grouped into the following 14 types.

There are primarily 5 key points in selecting a measurement system. The optimal selection can be made by gathering information based on the understanding of each point.

Measurement target object

Check the material, size, and shape. Selection is significantly affected by whether the target object is soft (in which case contact-type cannot be used) or has a complex shape (in which case laser measurement systems are suitable).

Measurement accuracy

Measurement accuracy concerns the sensors ability to provide readings that are accurate to within desired tolerances.A general rule-of-thumb is to get a sensor that is 10x as accurate as the desired tolerance.

Measurement range

Measurement range depends on the type of measurement. For 1D type sensors, the measurement range defines the maximum part deviations and part travel that the sensor can see.2D type sensors would also include a field-of-view such as the width of a part.

Measurement speedCheck the interval with which to perform measurement. To determine this, identify the travel speed of the target object and the number of desired measurements on the target.

Ambient environment Check the environment, including ambient temperature, oil, water, and dust. Also, check the space where the measurement system is to be installed.

3D3D

StrokeDistance

Positioning/Position

measurementHeight/Level

difference Depth Thickness Width

Runout/ Vibration/

Eccentricity

Outerdiameter

Wave/CurveFlatness Gap Angle/Tilt Shape

Imagemeasurement

3Dmeasurement

5

5. Determining the Measurement Method

From the above information, you can narrow your options to the optimal measurement method based on overall consideration. The chart below compares the measurement methods by key point.

We see that each sensor type has its own strengths and weaknesses depending on targets types and environmental and running conditions. Laser sensors are generally seen to be the most versatile and should be taken in high consideration when sensor flexibility may be necessary.

Good, Better, Best

[Typical Examples]

Item Laser Displacement

Meter

OpticalMicrometer

Instant Measurement

System

Eddy Current Displacement

Meter

Ultrasonic Displacement

Meter

Contact-type Displacement

Meter

Applicability to measurement object

Measurement accuracy

Measurement range

Measurement speed

Ambient environment

Overall

Measurement of the thickness of electrodes

Measurement and discrimination of pin height

Measurement of disk rotor runout

Measurement of the dimension of stamped parts

Measurement of 3D shape of forgings

Measurement of OD of super-fine wires

Measurement accuracy

There are 2 items that represent accuracy: repeatability and linearity.

Repeatability indicates the variation when performing the same measurement repetitively.

Linearity expresses the error from the ideal value.

For both, the smaller the value,

the greater the accuracy. For example,

the accuracy values for LK-H008 would be:

Repeatability: 0.005 m

Linearity: 0.5 m

(0.05% of F.S. = 0.05% * 1 mm)

If the required accuracy is 10 m,

LK-H008 fulfils the measurement accuracy,

which is 10 m x 1/10 = 1 m.

Measurement range

There are 2 items that represent measurement range: reference distance and

measurement range.

Measurement range indicates the range width that can be measured.

Reference distance is the distance from the frontal face of the measurement part to

the central position of the measurement range.

Reference distance: 8 mm

Measurement range: 0.5 mm

In conclusion, the measurement range in this case is 7.5 to 8.5 mm, on the basis of

the whole face of the sensor head.

Measurement speed

Measurement interval is calculated based on the sampling cycle and line speed.

Sampling cycle: 392 kHz

Measurement interval: Approx. pitch of 2.5 m

((1000 mm/s) / 392 kHz = 2.5 m)

The minimum requirement of 0.1-mm pitch can be met with this specification.

Ambient environment

Assuming a clean environment with a 5 degrees Centigrade fluctuation of

air-conditioning, the temperature drift is calculated below.

Temperature characteristics: 0.2 m/C (0.02% of F.S./C = 0.02% * 1 mm/C)

Temperature drift: 1 m (0.2 m/C * 5C = 1 m)

1 m is on the margin of the required accuracy, which indicates that temperature control

may be necessary.

6

6. Example of Selecting a Displacement Meter or Measurement System

Check the key points and narrow down the options to those that satisfy the required specifications.Here, we are using an example of a laser displacement meter specification to find if it meets the given measurement requirement.

Measurement target: Solar cell substrate Application: Thickness measurement Measurement accuracy: Tolerance decision with 10 m read accuracy Measurement range: Thickness standard t = 0.7 mm

(Measurement distance should be as far apart as possible) Measurement speed: Line speed is 1 m/s. Measurement should be

performed in a 0.1-mm intervals. Ambient environment: Clean environment with air-conditioning system

Measurement Requirement

Specifications

< Linearity Graph >

Distance

Ideal line

Measuredvalue

Linearity

Vol

tag

eVoltage

7

Specifications of Laser Displacement Meter (LK-H008)

Model LK-H008

Installation mode Specular

Reference distance 8 mm

Measurement range*1 0.5 mm

Light source

Red semiconductor laser

Wavelength 650 nm

Laser class(JIS C 6802)

Class 1

Output 0.3 mW

Spot diameter (based on reference distance)

20 m (LK-H008)20 m x 550 m (LK-H008W)

Linearity*2 0.05% of F.S. (F.S. = 1.0 mm)

Repeatability*3 0.005 m (0.001 m)

Sampling cycle 2.55/5/10/20/50/100/200/500/1000 s (variable with 9 levels)

Temperature characteristics 0.02% of F.S./C (F.S. = 1.0 mm)

Environmental resistance

Enclosure rating IP67

Ambient operating illuminance Incandescent lamp or fluorescent lamp: 10000 lux max.

Ambient temperature*4 0 to +50C

Operating Ambient humidity 35 to 80% RH (No condensation)

Vibration resistance 10 to 55 Hz 1.5 mm double amplitude in X, Y, and Z directions, 2 hours respectively

Material Die-cast aluminium

Weight (including cord) Approx. 240 g

*1 Measurement range is for when the sampling cycle is 20 s is greater.*2 Value is based on measurement of KEYENCE standard targets (mirrored metal workpiece) in standard mode. *3 Value is based on measurement of KEYENCE standard targets (mirrored metal workpiece), with an average

repeat of 16384 times with reference distance. Value in parentheses is based on a typical example measuring an average of 65536 times with a sampling cycle of 200 s.

*4 If the ambient temperature is 40C or higher, the meter must be installed on a metal plate.

Ultra High-Speed/High-AccuracyLaser Displacement SensorLK-G5000 Series

Sensor head for transparent/mirror surfaceLK-H008

WW1-1013

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Copyright (c) 2013 KEYENCE CORPORATION. All rights reserved. Measurement-WW-EN0827-GB 1083-1 E 600C49 Printed in JapanThe information in this publication is based on KEYENCEs internal research/evaluation at the time of release and is subject to change without notice.

* 6 0 0 C 4 9 *

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