pi 2009: nanometrology, capacitive sensor, capacitance sensor ... · the change of capacitance...

Piezo • Nano • Positioning

NanometrologyCapacitive Sensors with Sub-Nanometer Resolution

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Selection Guide: Nanometrology Sensors & Electronics

Models Description Measurement Sensor Page

Range [μm]* Type

Single and Dual Probe Capacitive Nanometrology Position Sensors

D-510 PISeca™ Single-Electrode Capacitive 20-500 Single-electrode, capacitive 3-8Sensors for Sub-Nanometer Precision Measurements

D-015, D-050, Sub-Nanometer-Resolution Capacitive Position Sensors to 1000 Integrated Linearization System (ILS) 3-14D-100

Capacitive Sensor Overview

PI provides dual-plate and sin-gle-plate capacitive sensors forultra-high precision position-sensing applications. The sen-sors and special control elec-tronics with PI’s proprietary ILScircuitry were developed to pro-vide the highest linearity andresolution and have also beenemployed in PI’s reference classnanopositioning stages for manyyears.

Models Description Channels Sensor Page

Type

E-852 PISeca™ Signal Conditioner Electronics 1 Single-electrode, capacitive 3-10for Single-Electrode Capacitive Sensors

E-509 Servo Controller card for PISeca™ 1,3 Dual and single-electrode, capacitive 3-121-Plate and Dual-Plate Capacitive Sensors 3-16

D-510 PIseca™ single-platenanometrology sensors

D-015, D-050, D-100dual-plate capacitiveposition sensors

Customized capacitivesensor electronics

E-852 Signal conditionerelectronics for single platesensors

E-509 Servo controllercard for single & dual platesensors

Background Information oncapacitive sensors, p. 3-17 ffNanometrology Fundamentals

Capacitive Sensors / Signal Conditioners


Nanometrology

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Overview

One- and Two-plate Sensors

Capacitive sensors perform non-contact measurements of geo-metric quantities representingdistance, displacement, separa-tion, position, length or other lin-ear dimensions with sub-nanometer accuracy. PI offerscapacitive sensors for the inte-gration in user applications intwo-plate-capacitor versions forhighest performance and asPISeca™ single-electrode sen-sors, for more flexibility and eas-ier integration.

Measurement Principle

The measurement principle inboth cases is the same: twoconductive surfaces set up ahomogenous electric field; thechange in displacement of thetwo plates is proportional tothe signal conditioner output.Dual-plate sensors measure thedistance between two well-defined sensor plates withcarefully aligned surfaceswhich generate the most accu-rate electric field and henceprovide optimal results. Single-plate capacitive sensors meas-ure the capacitance againstelectrically conductive refer-ences, such as metallic plates,and are very convenient toinstall and connect.

Nanopositioning and

Nanometrology

PI offers the widest range ofhigh-dynamics and high-reso-lution nanopositioning systemsworldwide. The precision andrepeatability achieved wouldnot be possible without high-est-resolution measuring de-vices. Capacitive sensors arethe metrology system of choicefor the most demandingnanopositioning applications.The sensors and the equallyimportant excitation and read-out electronics are developedand manufactured at PI byexpert teams with longstand-ing experience.

Capacitive Position Metrology

Test and Calibration

PI’s nanometrology calibrationlaboratories are seismically,electromagnetically and ther-mally isolated, and conform tomodern international stan-dards.

PI calibrates every capacitivemeasurement system individu-ally, optimizing the perform-ance for the customer’s appli-cation. Such precision is thebasis of all PI products, stan-dard and customized, andassures optimum results in themost varied of applications.

E-852 signal conditioner electronics withPISeca™ D-510.020 1-plate capacitive sensor

Standard D-015, D-050, D-100 2-plate sensors(front from left) and a selection of custom sensors

Properties of PI Sensors

� Measurement Ranges from 10 up to 500 μm and More

� Sub-Nanometer Position Resolution

� Non-Contact Absolute Measurement of Displacement /

Motion / Vibration

� Immune to Wear and Tear

� Ideal for Multi-Axis Applications

� Improved Linearity with ILS Signal Electronics

� High Bandwidth up to 10 kHz

� Measures Position of the Moved Interface (Direct Metrology)

� High Temperature and Long-Term Stability (<0.1 nm/3 h)

� Vacuum Compatible

� Compact 1- and 2-Electrode Sensors, Custom Designs

� Guard-Ring Electrode Eliminates Boundary Effects

� Invar Versions for Highest Temperature Stability (5 x 10-6/K)

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Nanopositioning / Piezoelectrics

Linear Actuators & Motors

Capacitive Sensors /Signal Conditioners

Nanometrology Fundamentals

Nanometrology

Micropositioning

Index

Function, Properties, Advantages

Accuracy

Accuracy, linearity, resolution,stability and bandwidth are farbetter than with conventionalnanometrology sensors likeLVDT or strain gauge sensors.

Non-contact operation meansno parasitic forces influencingthe application and results inmeasurement free of frictionand hysteresis.

Guard-Ring Design for

Improved Linearity

Sensor design has a stronginfluence on linearity. Thesuperior PI design uses aguard-ring electrode that elimi-nates sensor electrode bound-ary effects. This ensures ahomogenous field in the meas-urement zone and results inhigher measuring linearity.

Single- and Multi-Channel

Electronics

PI’s signal conditioner electron-ics are specially designed for

high bandwidth, linearity andultra-low noise and are perfect-ly matched to the various PIsensor probes. PI offers signalconditioner electronics andcontrollers for one to threechannels. The E-509 multi-channel modules plug into themodular E-500 / E-501 con-troller chassis. Bandwidth andmeasurement range can be fac-tory-set to meet the specificneeds of each application. TheE-852 one-channel signal con-ditioner electronics for PISeca™single-plate sensors are de-signed as stand-alone systemswith user-selectable bandwidthand range setting and can besynchronized to operate inmulti-channel applications.

Higher Linearity through

ILS Electronics

All of PI’s signal conditioningelectronics are equipped withthe PI proprietary ILS lineariza-tion circuit that minimizes non-parallelism errors.

Easy Handling and Integration

PISeca™ single-electrode sen-sors are particularly easy toinstall in a measurement sys-tem. On the single-channelelectronics, an LED-bar indi-cates the optimum probe-to-target gap for the differentmeasurement range settings.The multi-channel electronicscome optionally with displaysand/or a PC interface on a mod-ule in the same housing.

Ideal for Closed-Loop Piezo

Nanopositioning

Closed-loop nanopositioningsystems may be controlled bysensor / servo-controller mod-

ules of PI’s E-500 series. Suchmodules are available for con-necting up to three positionsensors, either stand-alone orintegrated into the motion sys-tem. Closed-loop operationeliminates the drift and hys-teresis that otherwise affectpiezo actuators.

For nanopositioning tasks withthe most stringent accuracyrequirements PI offers high-end digital controllers.

D-510.050 withLEMO connector

for easy handling

The P-752.11C piezo nanopositioning system with integratedcapacitive sensors provides position resolution down to 0.1 nm

Two-plate capacitive sensors D-100 (2 pairs), D-050 and D-015

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Applications for Capacitive Position Sensors

Measuring Straightness and

Flatness / Active Cross-Talk

Compensation

Excellent resolution in straight-ness and flatness measure-ments over long travel ranges isachieved with capacitive singleelectrode sensors. One applica-tion is measuring cross-talk innanopositioning. Crosstalk, off-axis motion from one actuator inthe motion direction of another,is detected immediately andactively compensated out by theservo-loops. The high sensorbandwidth provides excellentdynamic performance.

Measuring Displacement

with Nanometer Precision

Capacitive displacement sen-sors measure the shortest ofdistances with highest reliabili-ty. The quantity measured isthe change of capacitance be-tween sensor plate and the tar-get surface using a homogen-ous electric field. Accuracies inthe sub-nanometer range areregularly achieved. Absolutemeasurement is possible with awell-adjusted, calibrated sys-tem.

Nanopositioning / Closed-

Loop Systems

One application of high-resolu-tion displacement measure-ment is for nanopositioning.Two-plate capacitive sensorscan measure distance, andhence position, of a movingobject with excellent precision.The high sensor bandwidthallows closed-loop control inhigh-dynamics applications.

Parallel Metrology / High-

Precision Multi-Axis

Measurements

Closed-loop, multi-axis nano-positioning tasks are realizedwith high-performance posi-tioners that make use of directmetrology and parallel kine-matics. This allows measuringall degrees of freedom at thesame time, which compensatesguiding errors (Active Trajec-tory Control concept). Here,capacitance gauges are themost precise measuring sys-tems available, and give thebest position resolution results.

Out-of-Plane Measurement /

Constant-Height Scans /

Out-of-Round Measurement

Compensation of undulatingand oscillating motion, e.g. inconstant height scans or inwhite-light interferometry, areapplications for which capaci-tive sensors are especially wellsuited.

Tip / Tilt Measurement and

Compensation

Integrating capacitive sensorsin a system is a good way tomeasure tip/tilt motion precise-ly. The moved object’s tip angleis measured differentially, and,if required, compensated out.

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Nanometrology

Micropositioning

Index

Vibration, Flatness, Thickness

The high dynamics of thePISeca™ capacitive gauge sys-tem even allows measure-ments of vibrations and oscilla-tions with excellent resolution.Flatness of a rotating work-piece or differences in thick-ness in the nanometer rangecan be detected. One field ofapplication is in the productionof disk drives or in active com-pensation of vibration.

Force Sensors with

Micronewton Sensitivity

Single-electrode capacitivesensors, which measure sub-nanometer displacement froma distance with no contact, arefrequently used as high-resolu-tion force sensors. In a systemhaving suitably well-definedstiffness, the measured dis-placements translate to forceswith resolutions in the micro-newton range, all without influ-encing the process being meas-ured.

Layer Thickness with

Sub-Micron Accuracy

Measuring the thickness of afilm or layer of non-conductingmaterial on a moving, conduc-tive, surface (e.g. a rotatingdrum) is an ideal job for capac-itive sensors due to their non-contact operation and theirhigh dynamic performance.

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The new PISecaTM single-elec-trode capacitive sensors fromPI perform non-contact meas-urements of distance, positionor motion against any kind ofelectrically conductive target.They feature the highest reso-lution and linearity available.

The PISecaTM single-electrodecapacitive gauges are funda-mentally very temperature sta-ble, have excellent dynamicsand are easy to work with.

Capacitive Position Sensors

for Highest Accuracy and

Lifetime

Single-electrode capacitive(capacitance) sensors are directmetrology devices. They use anelectric field to measure changeof capacitance between theprobe and a conductive targetsurface, without physical con-tact. This makes them free offriction and hysteresis and pro-vides high phase fidelity andbandwidth.

In combination with suitablesensor electronics (E-852.10)resolutions down to the sub-nanometer range and band-widths to 10 kHz can beachieved. For high-dynamicsmeasurements, a bandwidth upto 10 kHz is possible, with aresolution still down to the 1-nmrange. With sufficient mountingaccuracy, excellent linearity canbe attained (up to 0.1%).

Guard-Ring Capacitor Provides

Higher Linearity

Sensor design has a stronginfluence on linearity becausethe operating principle is basedon that of an ideal parallel-platecapacitor. The superior PIdesign uses a guard-ring elec-trode that shields the sensorelectrode from boundaryeffects. This ensures a homo-geneous electric field in themeasurement zone and resultsin higher measuring linearity.

Easy Handling and Integration

All PISecaTM sensor probes fea-ture an integrated LEMO con-nector for easy mounting andreplacement in the field. Thestandardized shaft diameterallows compatibility and flexi-bility.

Factory Calibration for

Improved Linearity

Highest possible linearity andaccuracy are achieved with fac-tory calibration of the sensorprobe together with the signalconditioner electronics. Twomeasurement ranges can becalibrated at the same time forone particular sensor probe.Factory calibration also opti-mizes parameters like ILS (lin-earization), gain and offset andeliminates cable capacitanceinfluences. The E-852.10 pro-vides two calibrated, optionallyextended measurement rangesare available.

High-Precision Machining

The measuring surfaces of thePISecaTM sensors are machinedwith diamond tools usingsophisticated process controltechniques. The result is thesmooth, ultra-flat, mirroredsurface required to obtain high-est resolution. The standardmaterial is stainless steel.

Custom Sensors / Two-Plate

Sensors

In addition to the standard sen-sors listed here, PI can offer avariety of custom versions fordifferent measuring ranges,geometries, materials match,etc. Systems with custom elec-tronics are also available.

If ultimate performance isrequired, the D-100 series two-plate capacitive sensors arerecommended (see p. 3-14 ff ).

D-510 PISeca™ Capacitive SensorsSingle-Plate Sensors with Excellent Position Resolution

Application Examples

� Semiconductortechnology / test & meas-urement

� Data storage

� Automotive industry

� Metrology

� Precision machining

� Non-Contact Measurement for Distance / Motion / Vibration

� Absolute Position Sensing

� Sub-Nanometer Resolution

� Measurement Ranges to 500 μm

� Easy Integration

� High Bandwidth

Ordering Information

D-510.020

PISecaTM Single-ElectrodeCapacitive Sensor Probe,8 mm Diameter,20 μm Nominal Range

D-510.050


D-510.100


Ask about custom designs!

PISecaTM high-precision capacitive sensor probes with E-852 signal conditionerelectronics. Sensor probes (from left): D-510.100 with 100 μm, D-510.050 with

50 μm, D-510.020 with 20 μm nominal measurement range

D-510.050 with LEMO-connectorfor easy handling

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Nanometrology

Micropositioning

Index

Technical Data

Model D-510.020 D-510.050 D-510.100 Units Tolerance

Sensor type Single-electrode, Single-electrode, Single-electrode,capacitive capacitive capacitive

Measurement accuracy

Nominal measurement range* 20 50 100 μm

Min. gap 10 25 50 μm

Max. gap 150 375 750 μm

Static resolution** <0.001 <0.001 <0.001 % of measure-ment range typical

Dynamic resolution** <0.002 <0.002 <0.002 % of measure-ment range typical

Linearity*** <0.2 <0.1 <0.1 %

Mechanical properties

Sensor active diameter 3.8 6 8.4 mm

Sensor active area 11.2 27.9 56.1 mm2

Sensor diameter 8 12 20 mm

Sensor area 50.3 113.1 314.0 mm2

Mounting shaft diameter 8 8 8 mm

Miscellaneous

Operating temperature range -20 to +100 -20 to +100 -20 to +100 °C

Material Stainless steel Stainless steel Stainless steel

Mass 8 10 16 g ±5 %

Recommended signal E-852.10 E-852.10 E-852.10 (p. 3-10)conditioner electronics E-509.E E-509.E E-509.E (p. 3-12)

*Extended measurement ranges available for calibration with E-852 signal conditioner electronics**Static resolution: bandwidth 10 Hz, dynamic: bandwidth 10 kHz, with E-852.10 signal conditioner electronics

***Linearity over nominal measurement range

D-510.020, D-510.050 and D-510.100 capacitive sensor probes, dimensions in mm.Sensor connection LEMO FFC00.650.CLA.543, triaxial, cable length 1 m

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The economical E-852.10 signalconditioner electronics is spe-cially designed for the PISeca™D-510 series of single-electrodecapacitive position sensorprobes. It provides analog out-put with very high linearity,exceptional long-term-stability,sub-nanometer position reso-lution and bandwidths up to6.6 kHz.

Measurement Principle of

Capacitive Sensors

Single-electrode capacitive (ca-pacitance) sensors are direct

metrology devices. They usean electric field to measurechange of capacitance betweenthe probe and a conductive tar-get surface, without physicalcontact. This makes them freeof friction and hysteresis andprovides high phase fidelityand bandwidth.

Selectable Bandwidth and

Measurement Range

The selectable bandwidth set-ting allows the user to adaptthe system to different appli-cations. For the highest accura-cy and sub-nanometer reso-lution, the bandwidth can belimited to 10 Hz.

For high-dynamics measure-ments, a bandwidth up to10 kHz is possible, with a reso-lution still down to the 1-nmrange.

The user can choose a measure-ment range from 20 to

500 μm, depending on thenominal measurement rangeof the selected sensor. TheE-852.10 provides differentextended measuring ranges foreach selected sensor.

Easy Sensor Installation

The simple installation ofthe single-electrode PISeca™probes is facilitated by theE-852´s LED-bar indicating theoptimum gap between probeand target.


Improved Linearity

Highest possible linearity andaccuracy are achieved with fac-tory calibration of the sensorprobe together with the signalconditioner electronics. Twomeasurement ranges can becalibrated at the same time forone particular sensor probe.Factory calibration also opti-mizes parameters like ILS (lin-earization), gain and offset andeliminates cable capacitanceinfluences.

Integrated Linearization

System (ILS) for Highest

Accuracy

A proprietary linearization cir-cuit compensates the influ-ences of parallelism errorsbetween sensor and target andguarantees an excellent measur-ing linearity (to 0.1%).

Multi-Channel Measurements

PISeca™ sensor electronics areequipped with I/O lines for thesynchronization of multiplesensor systems.

E-852 PISeca™ Signal ConditionerFor Capacitive Single-Plate Sensors

� Cost-Effective System Solution for PISeca™ Capacitive

Position Sensor Probes

� Special Linearization System (ILS) for Maximum Linearity

� Bandwidth Adjustable from 10 Hz to 10 kHz

� Multiple Measurement Ranges per Probe

� LED-Bar Measuring-Range Display for Easy Setup & Sensor

Installation

� External Synchronization for Multi-Channel Applications


E-852.10

PISeca™ Signal ConditionerElectronics for Single ElectrodeCapacitive Sensors, 1 Channel(with Power Supply)



� Semiconductor technology /test & measurement

� Data storage


� Metrology


E-852 signal conditioner electronics with PISeca™ capacitivesensor probes D-510.100, D-510.050, D-510.020 (from left)

Output linearity error of E-852 signal conditioner / D-510.050sensor combination (nominal measurement range)

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Nanometrology

Micropositioning

Index

Technical Data

Model E-852

Function Signal conditioner for PISeca™ capacitive sensor probes

Channels 1

Sensor

Sensor type Single-electrode, capacitive

Sensor bandwidth 10 / 3 / 0.3 kHz1.1 / 0.1 / 0.01 kHz (option)

Measurement range extension factors* 1 & 2.5 (calibrated), 2 & 5 (option)

Ext. synchronization Auto master-slave

Temperature stability 0.71 ±0.25 mV / °C

Electrical properties

Output voltage -10 to +10 V / -5 to +5 V / 0 to +10 V

Output signal 1 kΩ / 1 nF

Supply voltage ±15 V (125 mA), +5 V (20 mA)

Static resolution** <0.001 % of measurement range (RMS)

Dynamic resolution** <0.002 % of measurement range (RMS)

Linearity @ nominal range <0.1 % (<0.2 % for D-510.020)

Interface and operation

Sensor connection LEMO ECP.00.650.NLL.543 socket, triaxial

Analog output BNC

Supported functionality LED bar (gap indicator)

Linearization ILS

Miscellaneous

Operating temperature range +5 to +40 °C

Mass 0.355 kg, E-852.PS1 power supply: 1.2 kg

Dimensions 80 x 130 x 40 mm, E-852.PS1 power supply: 100 x 170 x 62 mm

Target ground connector Banana jack

*Extension factors to multiply by the nominal measurement range**Static: bandwidth 10 Hz, dynamic: bandwidth 10 kHz, cable length 1 m

E-852.10, dimensions in mm

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E-509 PISeca™ Signal Conditioner / Piezo Servo Module

The analog E-509.Ex sensorelectronics is specially de-signed for the PISeca™ D-510series of single-electrode,capacitive position sensorprobes. Based on the E-500modular controller system, itprovides three channels ofanalog output featuring veryhigh linearity, exceptionallong-term stability, sub-nano-meter position resolution andbandwidths up to 10 kHz.

Two models are available:E-509.E03 is a signal condition-er module. In addition, theE-509.E3 version includes a fullservo-controller. With it, theposition values from externalsingle-plate capacitive sensorscan thus be used for servo-con-trol of piezo nanopositioningsystems.

The combination of sensor andelectronics provides a systemfor capacitive displacementmeasurement with flexiblehigh-end solutions for best lin-earity and highest resolution.

Selectable Bandwidth and

Measurement Range

The selectable bandwidth set-ting allows the user to adaptthe system to different applica-tions. For the highest accuracyand sub-nanometer resolution,the bandwidth can be limitedto 300 Hz.

For high-dynamics applica-tions, a bandwidth up to 10 kHzis possible, with a resolutionstill better than 4 nm.

Factory-set measurement rangesfrom 20 to 500 μm are possible,depending on the nominalmeasurement range of theselected sensor head.


Improved Linearity

Highest possible linearity andaccuracy are achieved withfactory calibration of the sensorelectronics for the particularmeasurement range. Factorycalibration also optimizesparameters like ILS (lineariza-tion), gain and offset andeliminates cable capacitanceinfluences.

Position Servo Control with

PISeca™

The position servo-control por-tion of the E-509 is identical forall versions, consisting of ananalog P-I (proportional, inte-gral) controller. Proportionaland integral gain can be setinternally. Control bandwidthcan also be set. A notch filterallows operation of the piezopositioning system closer to itsmechanical resonant frequency.

Multi-Channel Measurements

The three channels of thePISeca™ E-509.Ex sensor elec-tronics are automatically syn-chronized for the use in con-nected sensor systems.


E-509.E3

PISeca™ Sensor / Piezo Servo-Control Module for Single-ElectrodeCapacitive Sensor Probes,3 Channels

E-509.E03

PISeca™ Modular SignalConditioner Electronics for SingleElectrode Capacitive Sensors,3 Channels

Accessories:

E-500.00

19’’-Chassis for ModularPiezo Controller System,1 to 3 Channels

E-501.00

9.5” Chassis for ModularPiezo Controller System,1 to 3 Channels

E-515.03

Display Module for Piezo Voltageand Displacement, 3 Channels

E-517.i3

Interface / Display Module, 24 BitD/A, TCP/IP, USB, RS-232,3 Channels

E-503.00

Piezo Amplifier Module,-20 to +120 V, 3 Channels

E-515.E3

Analog Output for ControllerSignal, Plug-In Module, 3 Channels

Ask about custom designs


� Semiconductortechnology / test &measurement

� Data storage


� Metrology


3-Channel Sensor Module with/without Servo-Controller, for E-500 System

The E-509.E3 module offers sensor signal read-out and servo control for three channels

� E-509.E03: 3-Channel Signal Conditioner Module

� E-509.E3: 3-Channel Sensor Module with Additional

Servo Controllers for Piezo Positioning Systems

� Integrated Linearization System (ILS) for Maximum

Linearity

� Optional: Measurement Range

� Variable Bandwidth

� Plug-In Modules for E-500 / E-501 Chassis

The E-509.E3 servo-controller module in an E-501 9.5’’ chassis withE-503 piezo amplifier module and E-516 PC-interface/display

module provides servo-control of piezo nanopositioning systemswith external PISeca™ D-510 capacitive 1-plate sensors

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Nanometrology

Micropositioning

Index

Technical Data

Model E-509.E03 E-509.E3

Function Signal conditioner electronics Sensor / Servo-Controller Modulefor PISeca™ for PISeca™

Channels 3 3

Sensor

Servo characteristics – Analog proportional-integral (P-I)

algorithm with notch filter

Sensor type PISeca™ single-electrode, capacitive PISeca™ single-electrode, capacitive

Sensor bandwidth 3 kHz 3 kHz0.3 / 10 kHz (selectable) 0.3 / 10 kHz (selectable)

Measurement range extension factors* 2 / 2.5 / 5 (option) 2 / 2.5 / 5 (option)

Synchronization 3 synchronized channels 3 synchronized channels

Electrical properties

Output voltage 0 to 10 V 0 to 10 V

-5 to +5 V, -10 to 0 V (selectable)

Thermal drift <1 mV / °C <1 mV / °C

Resolution @ 300 Hz (RMS) <0.001 % of measurement range <0.001 % of measurement range

Resolution @ 3 kHz (RMS) <0.0025 % of measurement range <0.0025 % of measurement range

Linearity @ nominal range <0.1 % (<0.2 % for D-510.020) <0.1 % (<0.2 % for D-510.020)

Interfaces and operation

Sensor connection 3 x LEMO ECP.00.650.NLL.543 socket, 3 x LEMO ECP.00.650.NLL.543 socket,triaxial triaxial

Signal output LEMO 6-pin FGG.0B.306.CLAD56 LEMO 6-pin FGG.0B.306.CLAD56

Display – 3 x Overflow LED

Supported functionality ILS ILS

Miscellaneous

Operating temperature range +5 to +40 °C +5 to +40 °C

Dimensions 7T/3H 7T/3H

Target ground connector 3 x banana jack 3 x banana jack

Operating voltage E-500 system E-500 system

*Extension factors to multiply by the nominal measurement range of the selected sensor head D-510, to be specified with order

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Measurement Method

Capacitive position sensors areanalog non-contact devices. Atwo-electrode capacitive posi-tion sensor consists of two RF-driven plates that are part of acapacitive bridge. The high-fre-quency AC excitation providesbetter long term stability thanDC excited sensors (see p. 3-19,Fig. 5). One plate (probe) isfixed, the other plate (target) isconnected to the object to bepositioned. Since the plate sizeand the dielectric medium (air)remains unchanged, capaci-tance is directly related to thedistance between the plates.Ultra-precise electronics con-vert the capacitance informa-tion into a signal proportionalto distance.

Direct Metrology, Parallel

Metrology

The sensors offered by PI arethe most accurate measuring

systems for nanopositioningapplications currently on themarket. In contrast to high-resolution sensors measuringdeformation in the drive train(see p. 2-8 ff ), like strain gaugeor piezoresistive sensors,capacitive sensors are non-contact, direct-metrology de-vices–a fact which gives themmany advantages:

� Better Phase Fidelity� Higher Bandwidth� No Periodic Error� Non-Contacting� Ideal for Parallel Metrology� Higher Linearity� Better Reproducibility� Higher Long-Term Stability

Capacitive sensors are espe-cially well-suited for parallelmetrology configurations. Inmulti-axis nanopositioningsystems, parallel metrologymeans that the controller mon-

itors all controlled degrees offreedom relative to “ground”(the fixed frame) and uses eachactuator to compensate theundesired off-axis motion ofthe others automatically (activetrajectory control). As a result,it is possible to keep deviationsin the sub-nanometer and sub-microradian range (see p.2-212 ff in the “Tutorial” sec-tion).

Resolution

Resolution on the order ofpicometers is achievable withshort-range, two-electrode ca-pacitive position sensors (sin-gle-electrode capacitive posi-tion sensors provide less reso-lution, linearity and accuracythan two-electrode sensors).Theoretical measurement reso-lution is limited only by quan-tum noise. In practical applica-tions, stray radiation, electron-ics-induced noise and geomet-ric effects are the limiting fac-tors. For example, with the 100μm range, a D-100.00 sensorand E-509.C1A electronics,the effective noise factor is0.02 nm/��Hz. This translatesto 0.2 nm at 100 Hz bandwidth.The maximum standard band-width (jumper selectable) is3 kHz.

Figure 2 shows a D-015, 15 μm

capacitive position sensor and

an interferometer, both meas-uring nanometer-range actua-tor cycles. The graphs clearlyshow the superior resolution ofthe capacitive position sensingtechnique.


D-015.00

Capacitive Position Sensor, 15 μm,Aluminum

D-050.00


D-100.00



D-015 · D-050 · D-100 Capacitive Sensors

Fig. 1. D-015, D-050, D-100 ultra-high-resolution capacitive position sensors

provide up to 10,000 times higherresolution than calipers

Fig. 2. Piezo nanopositioning system making 0.3 nm steps, measured with PI capacitivesensor (lower curve) and with a highly precise laser interferometer. The capacitivesensor provides significantly higher resolution than the interferometer.

Notes

In addition to the standard sen-sors listed here, PI offers a vari-ety of custom versions alongwith custom electronics for dif-ferent measuring ranges, mate-rial match etc. If you don’t findwhat you are looking for,please call your local PI SalesEngineer.

Sub-Nanometer-Resolution Position Sensors

� For Applications Requiring Highest Precision

� Measuring Range to 1000 microns

� Resolution to 0.01 nm

� Linearization to 0.01 % with Digital Controller

� Bandwidth up to 10 kHz

� Servo Controller E-509.CxA, Compatible with

E-500 Controller System

� Custom Designs

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Nanometrology

Micropositioning

Index

D-015.00 (dimensions in mm) D-050.00 (dimensions in mm)

D-100.00 (dimensions in mm)

Technical Data

Model D-015.00 D-050.00 D-100.00 Units

Sensor

Sensor typ Capacitive Capacitive Capacitive

Nominal measurement range 15 50 100 μm

Extended measurement range 45 150 300 μm

Resolution* 0.0005 0.0005 0.0005 % of measurement range

Linearity** 0.01 0.01 0.01 %

Sensor active area 16.6 67.7 113.1 mm2

Thermal drift*** 50 50 50 ppm/K

Miscellaneous

Operating temperature range -20 bis 80 -20 bis 80 -20 bis 80 °C

Material Aluminum Aluminum Aluminum

Recommended sensor electronics E-509.CxA E-509.CxA E-509.CxA (p. 3-16)

Ask for custom materials*3 kHz, with E-509.C3A servo controller

**With digital controller. Up to 0,05 % typ. with E-509 analog controller***Change of active surface size in ppm (parts per million), refers to measurement range

� 1-, 2- and 3-Channel Versions

� Improves Linearity

� Eliminates Drift and Hysteresis

� Notch Filter for Higher Bandwidth

� Increases Piezo Stiffness

� ILS Circuitry Maximizes Capacitive Sensor Linearity

� Plug-In Module for E-500 System

� Prepared for Interfaces / Display Modules (optional)

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E-509.C1A

Sensor / Piezo Servo-ControlModule, Capacitive Sensor,1 Channel

E-509.C2A

Sensor / Piezo Servo-ControlModule, Capacitive Sensors,2 Channels

E-509.C3A

Sensor / Piezo Servo-ControlModule, Capacitive Sensors,3 Channels


3-Channel Servo-Controller Module for E-500 Piezo Controller System

E-509 3-channel servo-controller module fornanopositioning systems with strain gauge sensors

E-509 Signal Conditioner / Piezo Servo Module

The E-509 module is both a sig-nal conditioner for high-resolu-tion capacitive and SGS dis-placement sensors and a servo-controller for closed-loop piezonanopositioning mechanics.For more information (see page2-152).

Technical Data

Model E-509.C1A/E-509.C2A/E-509.C3A E-509.S1/E-509.S3

Function Signal conditioner & servo-controller Signal conditioner & servo-controllerfor piezo mechanics for piezo mechanics

Channels 1/2/3 1/3

Sensor

Servo characteristics P-I (analog), notch filter P-I (analog), notch filter

Sensor type Capacitive SGS

Sensor channels 1 / 2 /3 1 / 3

Sensor bandwidth 0.3 to 3 kHz (selectable with jumper); 0.3; 1; 3 kHzup to 10 kHz on request

Noise factor 0.115 ppm/Hz½

Thermal drift <0.3 mV / °C <3 mV / °C

Linearity <0.05% <0.2%

Interfaces and operation

Sensor connection LEMO EPL.00.250.NTD LEMO ERA.0S.304.CLL

Sensor monitor output 0–10 V 0–10 V

Sensor monitor socket LEMO 6-pin FGG.0B.306.CLAD56 BNC (1-ch.) / 3-pin. LEMO (3-ch.)

Supported functionality ILS (Integrated Linearization System) ILS (Integrated Linearization System)

Display Overflow LED Overflow LED

Miscellaneous

Operating temperature range +5 to +50 °C +5 to +50 °C

Dimensions 7HP/3U 7HP/3U

Mass 0.35 kg 0.35 kg

Operating Voltage E-500 System E-500 System

Max. power consumption 4 to 8 W 4 to 8 W



Nanometrology

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Fig. 1: Piezo nanopositioning system making 0.3 nm steps, measured withPI capacitive sensor (lower curve) and with a highly precise laser interferometer.The capacitive sensor provides significantly higher resolution than the interferometer

Resolution in nanopositioningrelates to the smallest changein displacement that can still bedetected by the measuringdevices.

For capacitive sensors, resolu-tion is in principle unlimited,and is in practice limited byelectronic noise. PI signal con-ditioner electronics are opti-mized for high linearity, band-width and minimum noise,enabling sensor resolutiondown to the picometer range.

Electronic noise and sensorsignal bandwidth are interde-pendent. Limiting the band-width reduces noise and there-by improves resolution. Theworking distance also influ-

ences the resolution: the small-er the working distance of thesystem, the lower the absolutevalue of the electronic noise.

Figure 1 shows measurementsof nanometer-range actuatorcycles taken with a D-015,15 μm capacitive position sen-sor and a laser interferometer.The graphs clearly show thesuperior performance of thecapacitive position sensingtechnique.

Figure 2 illustrates the influ-ence of bandwidth upon reso-lution: the PISeca™ single-electrode sensors show excel-lent resolution down to thesub-nanometer range, even athigh bandwidths.

Resolution / Bandwidth

Fig. 2: Resolution significantly below 1 nm is achieved with a 20 μm PISeca™single-electrode sensor (D-510.020) and the E-852 signal conditioner electronics.Left: 0.2 nm-steps under quasi-static conditions (bandwidth 10 Hz),right: 1 nm-steps with maximum bandwidth (6.6 kHz)

The linearity of a measurementdenotes the degree of constan-cy in the proportional relationbetween change in probe-tar-get distance and the output sig-nal. Usually linearity is givenas linearity error in percent ofthe full measurement range.A linearity error of 0.1 % withrange of 100 μm gives a maxi-mum error of 0.1 μm. Linearityerror has no influence whatso-ever upon resolution andrepeatability of a measure-ment.

Linearity is influenced to a highdegree by homogeneity of theelectric field and thus by anynon-parallelism of the probeand target in the application. PIcapacitive position sensor elec-tronics incorporate a propri-

etary design providing superi-or linearity, low sensitivity tocable capacitance, low back-ground noise and low drift. TheIntegrated Linearization Sys-tem (ILS) compensates for non-parallelism influences.

A comparison between a con-ventional capacitive positionsensor system and a PI ILS sys-tem is shown in Figure 3. Whenused with PI digital controllers(which add polynomial lin-earization) a positioning linear-ity of up to 0.003 % is achiev-able.

Figure 4 shows the linearity ofa P-752.11C piezo flexure nano-positioning stage with inte-grated capacitive position sen-sor operated in closed-loop

Linearity and Stability of PI sensors

Fig. 3: Linearity of conventional capacitive position sensor system vs. PI ILS(integrated linearization system), shown before digital linearization

Fig. 4: Linearity of a P-752.11C, 15 μm piezo nanopositioning stage operated withE-500/E-509.C1A control electronics. The travel range is 15 μm, the gain 1.5 μm/V.Linearity is better than 0.02 %; even higher linearity is achievable with PI digitalcontrollers

3-19






Nanometrology

Micropositioning

Index



mode with an analog con-troller. All errors contributed bythe mechanics, PZT drive, sen-sors and electronics are includ-ed in the resulting linearity ofbetter than 0.02 %. Even higherlinearity is achievable with PIdigital controllers like theE-710.

Stability of the measurement islimited mainly by thermal and

electronic drift. For accuracyand repeatability reasons, it isthus necessary to maintainconstant environmental condi-tions. The exceptional long-term stability of the PI capaci-tive position sensor and elec-tronics design is shown inFigure 5. Fig. 5: Measurement stability of an E-509.C1A capacitive

position sensor control module with 10 pF referencecapacitor over 3.5 hours (after controller warm-up)

Signal/Displacement

Proportionality

When a voltage is applied to thetwo plates of an ideal capacitor,it creates a homogenous electricfield. Apart from constant fac-tors, the electrical capacitanceof the setup is determined bysensor area and plate distance.Thus, a change in displacementleads directly to a change incapacitance. This value ismatched to a reference capaci-tance in a bridge circuit.

The Design of the signal condi-tioner electronics is such thatthe output signal is proportionalto the gap change. The planes ofthe sensor surface (“probe”)and the target form the two ca-pacitor plates. The target shouldnot be below a certain size be-

cause of boundary effects. Thisis important for applicationswith, say, a rotating drum as tar-get. For metallic materials, thethickness of the target has noinfluence on the measurement.

Guard Ring Geometry/Design

The proportionality referred tois based on the homogeneity ofthe electric field. To eliminateboundary effects, the superiorPI design uses a guard-ring elec-trode that surrounds the activesensor area and is actively keptat the same potential (seeFig. 7). This design shields theactive sensor area and providesfor excellent containment of themeasurement zone. Thus opti-mum measuring linearity overthe full range is achieved withinthe specified accuracy.

Principle of the Measurement

PI’s nanometrology calibrationlaboratories offer optimumconditions for factory calibra-tion. As references, ultra-high-accuracy incremental sensorslike laser interferometers areused.

PISeca™ systems are calibrat-ed at PI with a NEXLINE® posi-tioning system having a

closed-loop resolution betterthan 0.01 nm in a test standwith friction-free flexure guid-ance and an incremental refer-ence sensor featuring a resolu-tion better than 0.1 nm (Fig. 8and 9).

Calibration for Best Accuracy

Fig. 6: Capacitive sensor working principle. The capacitanceC is proportional to the active sensor area A, �0 is constant,�r is the dielectric constant of the material between the pla-tes, generally air

Fig. 7: Capacitive sensors with guard ring design providesuperior linearity

Fig. 8: Output linearity error of a PISeca™ single-electrodesystem is typically less than 0.1% over the full measurementrange

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Direct Metrology / Parallel

Metrology with Two-Plate

Capacitive Sensors

Capacitive sensors are the idealchoice for nanometrologyapplications in positioning,scanning and metrology requir-ing the highest possible accura-cy. Two-plate capacitive sensorsachieve the highest linearity andlong-term stability. The meas-urement probe can be attacheddirectly to the moved surface(direct metrology) and provideabsolute, non-contact displace-ment values against a reference

surface, with no influence what-soever on the motion per-formed. These sensors are par-ticularly well-suited for parallel-kinematics nanopositioning sys-tems. There, in a multi-axis sys-tem, motion in all degrees offreedom is measured against acommon reference, and therunout of the various actuatorscan be compensated out in realtime (active trajectory control).In this way, motion accuracies inthe subnanometer and submi-croradian ranges can beachieved.

Direct Metrology, Parallel Metrology

Fig. 9: Ultra-high-precision NEXLINE® positioning system with incremental sensorin a calibration and test stand for PISeca™ sensors. The resolution is significantlybetter than that of a laser interferometer

Fig. 10: Capacitive position sensors in anultra-high-accuracy, six-axis nanoposition-ing system designed by PI for theGerman National Metrology Institute(PTB). Application: scanning microscopy

When measuring distance bydetection of capacitancechanges, fluctuations in thecable capacitance can have anadverse effect on accuracy.This is why most capacitivemeasurement systems onlyprovide satisfactory resultswith short, well-defined cablelengths.PI systems use a special designwhich eliminates cable influ-

ences, permitting use of cablelengths of up to 3 m withoutdifficulty. For optimum results,we recommend calibration ofthe sensor-actuator system inthe PI metrology lab.Longer distances between sen-sor and electronics can bespanned with special, loss-free,digital transmission protocols.

Special Design Eliminates Cable Influences

During sensor production, greatcare is taken to maintain criticalmechanical tolerances. Meas-uring surfaces are diamondmachined using sophisticated

process control techniques. Theresult is the smooth, ultra-flat,mirrored surfaces required toobtain the highest resolutioncommercially available.

Electrode Geometry, Sensor Surface Flatness

and Finish

For optimum results, target andprobe plates must remain paral-lel to each other during meas-urement. For small measure-ment distances and small activeareas, any divergence has astrong influence on the meas-urement results. Tilt adversely

affects linearity and gain,although not resolution orrepeatability (see fig. 12).Positioning systems with multi-link flexure guidance reduce tipand tilt to negligable levels (seeFig. 13) and achieve outstandingaccuracy.

Parallelism of Measuring Surfaces

Fig. 11: Digital sensor-signal transmis-sion (DST) allows a distance up to 15 mbetween positioning unit and controller,here an E-710 multi-axis digital piezocontroller

Fig. 12: Nonlinearity vs. tilt. Resolution and repeatability are not affected by tilt

Fig. 13. Flexure-guided nanopositioning systems like the P-752 offer submicroradianguiding accuracy and are optimally suited for capacitive sensors

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Nanometrology

Micropositioning

Index

Glossary

The measurement range de-pends on the size of the activesensor area as well as on theelectronics used.Due to PI’s proprietary signalconditioner electronics design,the mid-range distance isalways identical to the selectedmeasurement range. The probe-to-target gap may vary from

50 % to 150 % of the measure-ment range (see Fig. 14).The sensor capacitance is thesame as that of the referencecapacitance in the electronics.Different reference capacitancescan be used to extend the nom-inal (standard) measurementrange (see Fig. 15).

Measurement Range

Two-electrode capacitive sen-sors consist of two electrodes,named probe and target.Single-electrode sensors meas-ure against a surface that iscalled the target. The target sur-face is, in principle, a conductivematerial electrically connectedto ground. Measurement againstsemi-conductors is possible aswell.

While two-plate capacitive sen-sors consist of two well-defined

high-quality planes, with single-plate sensors, target surfacecharacteristics can influence theresults. A curved or rough sur-face will deteriorate the resolu-tion because the results refer toan average gap (see Fig. 16 and17). Surface shape also influ-ences the homogeneity of theelectric field and thereby themeasurement linearity. For fac-tory calibration, a target planethat is considerably larger thanthe sensor area is used.

Target

Precision measurement withnanometer accuracy requiresminimizing environmental influ-ences. Constancy of tempera-ture and humidity during themeasurement are as essentialas cleanliness.Electronics from PI are basical-ly very temperature stable. Tem-perature drift is under 0.2% offull measurement range with achange of temperature of 10 C°.Temperature changes alsocause all material in the systemto expand or contract, thus

changing the actual measuredgap.The influence of a change in rel-ative humidity of 30 percentagepoints is less than 0.5% of themeasurement range. Conden-sation must always be avoided.Dusty or damaged sensor sur-faces will also worsen the meas-urement quality.Environmental conditions atthe time of calibration arenoted on the calibration sheetPI provides with each indi-vidual system.

Environment

Fig. 14: Definitions: measurement range and mid-rangedistance have identical values

Fig. 15: Measuring ranges of different PI capacitive positionsensors (standard ranges in blue, extended ranges in black)

Fig. 16: Roughness of the target surface downgradesresolution and linearity

Fig. 17: Curved surfaces lead to an averaged distancemeasurement



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