using the edu oscilloscope to operate sensorsuse the scale of 1/10th of a logarithmic unit called a...

Radiant Technologies, Inc.Using Sensors with the Radiant EDU 1

Using the EDU Oscilloscopeto Operate Sensors

Radiant Technologies, Inc., Albuquerque, NM [email protected]

Rev BJanuary 11, 2008


Table of Contents• Introduction

• Hardware Description

• Default Oscilloscope Operation

• Advanced Concepts– Acquisition Timing

– The Sensor Board and Sensor Die

– Advanced Control Features

– Sensing Temperature and Force

• Special Considerations

• Summary of Operating Rules


IntroductionWelcome to Radiant’s first application of thin ferroelectric filmtechnology as a force and temperature sensor designed to let you measurewhat your body’s senses actually feel. The human body has an amazingability to process minute changes over long periods of time. We designedthe EDU Sensor Board and EDU together to do something that standardtools do not: capture and present sensory information over the timescales of human perception operates! While the EDU Sensor Boardcannot possibly achieve the same level of sensory integration present inthe human nervous system, it will open for you a unique window into theenvironment in which you live.


IntroductionImagine a jazz duo with a snare drum and a double bass violin. The beatsof the snare drum have high frequency content of short duration while themusical information is carried by the combinations of beats over secondsor minutes with subtle differences in tone. Simultaneously, the listenerhears the plucking of the strings of the double bass with its owninformation envelope. The temporal range of information transmitted inthe jazz music is at least 100,000:1 and probably larger. A child canperceive the full envelope simultaneously and respond to it. A standardoscilloscope cannot. The EDU Oscilloscope function is Radiant’s firstattempt to present information of such temporal range in a useful manner.

Good Luck! Let us know what your think.


Hardware Description

• System Architecture

• EDU OSC Port

• Radiant EDU Sensor Board connection

• Telephone Cable specifications


OSC Hardware Architecture

• The EDU system architecture operating in the oscilloscope mode. The8051 captures only the single sensor channel and sends it to the host. Itcan capture up to 800 points per USB packet at a 10kHz rate.

Sensor

Amp

EDU

USB

Digital toAnalog

Converter

Analog toDigital

Converter

48MHz 8051Microprocessor

with USB engine

On-boardPower Regulators(±15V, 5V, 3.3V)

Power Pack(18V AC) Amp

HostComputer


EDU OSC Port• The OSC port on the EDU accepts 6-wire or 4-wire telephone cable.• The outside two lines carry ±15V to power the attachment.

– Do not mistake the I2C port in the center of the board for the OSC port.

OSC Port

Pin assignmentsfor the OSC portare printed nextto the portsocket.


Sensor Board Connector• The telephone socket on the EDU Sensor Board has the

same pin assignments as the connector on the EDU.

• Therefore, the connectors on the telephone cable must haveopposing orientations. (See next page for a diagram.)

• The connecting cable can be as long as you want but thelonger it is, the more 60Hz noise it will pick up.

Sensorcapacitor

Cableconnector


Sensor Board Cable• When constructing a cable to connect the EDU OSC port to

the EDU Sensor Board, the connectors must be rotated 180degrees from each other on a straight cable.

• The telephone line in the figure above is straight with notwists.

• WARNING: if your cable has connectors with the same orientation,there will be smoke and flames on the Sensor Board when you plug itinto the EDU!


Sensor Board Cable• On a properly constructed cable, the colored wires should

connect to the same pins on both connectors.


Default Oscilloscope Operation

• Configuring the Sensor Board for Force or Temperature

• Hooking the Sensor Board to the EDU

• Oscilloscope Display

• Default Operating Parameters

• Changing Operating Parameters– Y-Axis format

– Labels

– Scaling the Y-Axis


• For temperature sensitive measurements, use the sensor board with thesensor capacitor bare as delivered.

• This configuration minimizes the thermal mass attached to the sensorcapacitor, maximizing the response speed of the capacitor totemperature changes.

Bare SensorCapacitor

Configuring the Sensor Capacitor:Temperature


Configuring the Sensor Capacitor:Force

• To see changes in pressure or force, adhere a rubber, metal, or woodenpost on the sensor capacitor that extends out of the window.

– Do not touch the sensor capacitor itself with your fingers.• Place another mass on the backside of the sensor die to maximize its

thermal mass and slow down its response to temperature changes.Do NOT use

epoxy toattach thebumper to

the capacitor.


Configuring the Sensor Capacitor:Force

• Several round rubber feet with adhesive surfaces have been suppliedwith your Sensor Board.

• Using scissors or a knife, cut a rubber foot into the desired shape. Then,remove the protective paper and adhere the foot to the capacitor or diesurface.


Connecting the SensorConnect the EDUSensor Board tothe EDUOscilloscope porton the corner.

The sensorcapacitor isalready poledwhen you receiveit and is connectedto the chargeamplifier.


Default Oscilloscope OperationWhen you start the EDU V2.0software, you will find a new buttonat the bottom of the menu.

– In order to use the oscilloscopefunctions, you should have Version2.0 or higher of the EDU controlpanel.

– If you do not have the latest version,contact Radiant for an update or lookat www.ferrodevices.com.


Default Oscilloscope OperationPress START to begin capturing the sensor signal!


Default Oscilloscope Operation• The default parameters for the EDU oscilloscope program

are– 1kHz acquisition rate– 0.2 second update period on the screen

• At 5 times per second, you can visually see the delay betweeneach update

• Each update represents one transfer of data from the EDUoscilloscope input to the computer screen.

– 10 second viewing window horizontally– ±12V scale on the Y-axis vertically.

• Press STOP to stop and START to re-start where you are.• The CLEAR button erases all data on the screen to start

over. All data that passes off the left hand side of thescreen during operation is lost.


Default Oscilloscope Operation• Squeeze on the sensor to see its response.

– NOTE: Do not touch the surface of the sensor capacitor with your fingers. Put ahard, self-adhesive “bumper” over the capacitor before you apply force to thesensor capacitor.

-10.0

-7.5

-5.0

-2.5

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5.0

7.5

10.0

0 1 2 3 4 5 6 7 8 9 10

Oscilloscope(real time)

Vol

ts

Time (seconds)


Changing Oscilloscope ParametersPress Set Parameters to change the oscilloscope operation.


Changing Oscilloscope ParametersThe SetParametersmenu givesaccess to all ofthe plottingcontrols,frequencycontrols, andadvanced signalprocessingfeatures fordisplaying yoursensor data.


Y-Axis FormatThe format ofthe Y-axispresentation iscontrolledthrough these sixcontrols on themenu:


Y-Axis Format• A check in “Single Pass” forces the oscilloscope to stop after capturing

a single “Time Window” of data.

– If this control is unchecked, the acquisition continues until the STOPbutton is pressed.

• The “Y-Axis Minimum” and “Y-Axis Maximum” controls set thevertical limits of the display if the “Autoscale” control is NOT checked.Otherwise, they are ignored and the plotting routine automaticallyadjusts the Y-Axis limits real time to include the minimum andmaximum Y-Axis values contained in the “Time Window”.

– “Autoscaling” during real time can be visually disconcerting but itsolves part of the problem of visualizing data over the range ofhuman perception as it allows you to see small signals riding on largeones while ignoring the amplitude of the large signal.


Y-Axis Format• “2 Log(Y)” is another method by which to visualize large and small

signals simultaneously.

– Negative numbers cannot be plotted in log format even though thesignal from your sensor could easily be below zero as much as it isabove zero. The solution is to square the signal first, guaranteeing apositive number, and then taking the logarithm of the square.

– This function is Log(Y2).

– Under the rules of logarithms, the equation also equals 2 Log(Y).

– IMPORTANT: Many engineering and science disciplines commonlyuse the scale of 1/10th of a logarithmic unit called a decibel. Toconvert our 2 Log(Y) presentation to decibels, multiply it by 10.

• The “Use Sliding X-scale” control forces the plotting routine to printthe elapsed time on the X-axis.

– With this control off, the X-axis labels are fixed at the absolute“Time Window” width.


Labels on the GraphThe labels forthe X-Axis andY-Axis are sethere.


Graph Labels• The text displayed in these controls are displayed on the graph axes

during operation.

– The “Subtitle” is placed just below the “Title” on the plot.

• The Y-Axis Label is changed when you select the “2 log(Y)” format toadd the text “Log(“ and “ squared)” to the label.

– Formula => X-Axis Label = “Log(“ + X-Axis Label + “ squared)”

– The extra text is removed from the X-Axis label when you de-select“2 Log(Y)”.


Scaling the Y-AxisThe “ScaleFactor” multipliesthe Y-Axis values.The default is x1.0which means thatthe Y-Axis reportsthe raw voltagescoming from thesensor board.Change the scaleto convert the Y-Axis units tophysical values.


• The ferroelectric capacitor on the EDU Sensor Board responds tochanges in temperature or force according to the following formulas:

– FORCE: ∆Q = p * ∆F where Q is in units of microcoulombs percentimeter squared, F is in units of newtons, and p, the piezoelectricconstant, is in units of Coulombs per Newton.

– TEMPERATURE: ∆Q = p * ∆T * Area where T is in units of degreesCentigrade, p is the pyroelectric constant with units of Coulombs perºC, and the Area is in square centimeters.

• The charge amplifier converts the change in charge to voltage.

– FORCE: Vout = (p * ∆F)/Ci where Ci is the integrating capacitor.

– TEMPERATURE: Vout = (p * ∆T * Area)/Ci

• See the discussion of scale factors and charge amplifier operation laterin this tutorial.

Scaling the Y-Axis


Quick Stop

• You now know enough to go play with Sensor Board!

• Continue with the tutorial from this point when you are ready to adjustthe acquisition frequencies and to study the Sensor Board in moredetail.


Acquisition Timing

• Definition of Parameters

• Number of Data Points

• Meaning of an Error and its Indication

• Useful Acquisition Speeds

• Detailed Description of EDU and Host Computer Operation


Acquisition Timing

These threecontrols affecthow fast thesensor boardcollectsinformation andhow much of thatinformation youcan see.


• The Sample Period is the delay in seconds between each conversion ofthe analog input voltage to a digital word.

– Minimum period = 0.0001 (10,000 samples per second)

– Maximum period = 0.0163 (61 samples per second)

• The Time Window is the length of the X-Axis in seconds on the screen.

• The Update Period determines how often the host computer returns tothe EDU to upload the measured points and re-plot the screen.

– Maximum = 3 seconds.

Acquisition Timing


• The number of points displayed in the Time Window is equal to theTime Window divided by the Sample Period.

– Example: Sample Period = 1ms. Time Window = 10 seconds.There will be 10,000 points displayed in the window when the TimeWindow is full.

• The number of points transferred to the host from the EDU at the endof each Update Period is equal to the Update Period divided by theSample Period.

– Example: Sample Period = 1ms. Update Time = 200ms. The hostwill upload 200 points after each Update Period.

• On each update, the plotting routine adds the new data to the end ofthose on the screen.

– If the Time Window is already full, the plotting routine shifts the dataset to the left the same number of points as are added, erasing the oldpoints at the beginning of the set.

Acquisition Timing


• The EDU holds the measured points in two groups of up to 800memory locations each, called buffers.

• While the EDU is storing data in one of the buffers, the host should beuploading the measured data from the other buffer.

• The data acquisition interrupt clock never stops firing and the EDUnever stops writing to the next assigned memory location.

• If the EDU is storing data in Buffer#1, then the host MUST finishuploading Buffer#2 BEFORE the EDU fills up Buffer#1 or the EDUwill switch to Buffer#2 and begin overwriting the data in Buffer#2 .The earlier data stored in Buffer#2 and not uploaded will be lost.

– When this happens, the EDU sends an ERROR flag to the host.– Whenever the host computer sees the ERROR flag, it changes the

color of the displayed data.– The change in color means that the block of data just plotted is not

complete.

ERROR Generation


• Two factors control the generation of errors:– The more points that are required to be displayed in the Time

Window, the longer it takes to redraw the window on each update.

– The shorter the Update Period, the less time there is for the hostcomputer to upload the data from the EDU and redraw the window.

• If the Time Window is too large for the Sample Period, then there willbe too many points for the host to re-draw the graph during theassigned Update Period.

– Increase the length of the Update Period to eliminate errors.

• The EDU can only upload a maximum of 800 points each UpdatePeriod. If errors are occurring and you are uploading the maximumpoints, reduce the number of points to be re-drawn each update period.

– Decrease the Time Window or

– Increase the Sample Period.

ERROR Generation


• Every computer will be different in how long it takes to re-draw thewindow on each Time Window based on the speed of the computer, thenumber of programs running in the background, and speed of its videosystem.

– Connecting the computer to a network slows down the computerbecause it has to service the network in the background.

• Using a Toshiba Satellite laptop with a 1GHz Celeron processor and nonetwork connection, I can execute the following acquisition rateswithout errors:

– 10KHz: Update Period = 0.08s Time Window = 1.5s

– 5KHz: Update Period = 0.16s Time Window = 10s

– 2KHz: Update Period = 0.40s Time Window = 20s

– 100Hz: Update Period = 1.00s Time Window = 600s

Acquisition Speeds


NOTE: the following three pages are for the electrical and computerengineers who are interested in how the EDU oscilloscope works.

• The oscilloscope function on the EDU requires the synchronization ofthree independent cycles:

– Two cycles run on the the EDU as part of its data acquisition.

– One cycle runs on the host computer to upload and plot the data fromthe EDU.

• One cycle on the EDU captures the data at each Sampling Period.

• The other cycle on the EDU monitors the amount of captured data inmemory. When it equals Update Period divide by the Sample Period,this cycle notifies the host that data is ready for upload.

Internal Operation of the EDUOscilloscope


EDU Data Acquisition Cycles

The Host Computer sets the “Upload Done” bit to 1 when it finishes an upload. Thus, anERROR is indicated if a buffer is being written to by the EDU before its old contents havebeen uploaded to the Host.

Hardware Timer Interrupt

Capture OSC port input voltage.

Store data at the data memory pointer.

Increment data memory pointer.

Return from interrupt.

Increment sample counter.

Wait for next interrupt.

Does sample counter equal assigned limit?

Change sample counter to zero.

Change memory pointer to start of other buffer.

Set READY bit.

Set ERROR bit?“0” if UPLOAD DONE Bit is set“1” if UPLOAD DONE Bit is not set

Clear Upload Done bit.

Yes

NoInterrupt Vector


• On the host, the operating system is notified to interrupt the program toupload data from the EDU every Update Period.

Host Computer Acquisition Cycle

EDU

On Operating System Timer Interrupt

Ask EDU if selected buffer is full.

Upload data from selected buffer on EDU.

Execute math processing of the returned data.

Add the new data to the trace and re-draw the graph displayed on the screen.

Exit to WINDOWS and wait for next interrupt.

No

Yes


The Sensor Board and Sensor Die• Charge Amplifiers

• Sensor Board Circuit

• Sensitivity

• The Sensor Die


Charge Amplifiers• A charge amplifier outputs a voltage proportional to the amount of

charge that has entered or left its “-” input. The charge coming into theamplifier on the “-” input collects on the integrating capacitor Ci.

IntegratingCapacitor (Ci)

Vout =-∆Qsensor

Ci

SensorCapacitor (Cs)

+

-Op Amp


Charge AmplifiersCharge amplifiers are naturally unstable, caused by small leakage currentsinside the amplifier collecting in the integrating capacitor. Eventually, theoutput of the integrator reaches the level of its supply voltage and it can nolonger give useful data.

IntegratingCapacitor (Ci)

SensorCapacitor (Cs)

+

-Op Amp

A feedback resistorparallel to theintegrating capacitorforces the amplifieroutput voltage back tozero volts.

The value of the resistorand capacitor togetherdetermine the rate atwhich the amplifierdecays to zero.


The EDU Sensor Board Circuit

+

-

R1

R2

R3

C1

C2

+15V

-15V

JP2

JP1

2

1

1

2

A

B

Sensor Die


• The component values are:– C1 220pF – R2 19.1 kilo-ohms– R1 10 mega-ohms – R3 49.9 ohms

• The voltage divider formed by R2/R3 boosts the feedback resistancefrom 10MΩ to 3.838GΩ.– 10MΩ is the largest value surface mount resistor available with a small

circuit board footprint.

• JP1 and JP2 allow you to pole the ferroelectric capacitor mounted onthe Sensor Board using solder bumps or metal probes.

– Put the solder bumps between [JP1:2 to -15V] on JP1 and [JP2:2 to +15V]on JP2. Plug it into the EDU for a few seconds to pole the capacitor.

– After polling, move the solder bumps to [JP1:2 to JP1:1 ] and [JP2:2 toJP2:1 ] to connect the sensor capacitor to the charge amplifier.



Physical Layout of the Sensor Board

• The Sensor Board consists of all surface mount devices.

• The top surface of the sensor capacitor faces the non-component side ofthe board through the window.

• The bottom surface of the board is a ground plane. The anchor holesfor screws are also connected to the circuit ground as is the outsidecasing of the connector.

Back Sideof SensorCapacitor

ofDie

Op Amp

Resistors

C1 and C2

Probe Pad

Sensor Capacitor Window

JP1 & JP2


Sensor Die• 1.0µ 4/20/80

PNZT

• Platinumelectrodes

• TiOx/SiOx ILD

• Chrome/Goldmetallization

• 15V saturation

• Will withstandunlimitedexposure to 36V.

• Can be solderedto PC board.

4mm x 4mm PZT capacitor with 1µthick PNZT. Piezoelectric Constant ~ 500pC/N Pyroelectric Constant ~ -2.2nC/°C/cm2

Top and bottomelectrodecontacts.

0.5cm

1.0cm

Radiant manufacturers a large PZT capacitorsuitable for building simple force and heatsensors by hand.


• There are two empty contact pads (A & B) on the Sensor Board next tothe sensor die to provide contact or measurement points to the sensorcapacitor.

– To access the sensor capacitor alone, remove JP1 and JP2.

• C2 is a space with contacts for you to solder in another integratingcapacitor on the Sensor Board to reduce its sensitivity.– C2 is in parallel with C1 so it adds to the value of C1.– The theoretical formulas for sensitivities to stimuli are

• ºC/Volt = Cintegrating / (pyroelectric constant * Area)• Newtons/Volt = Cintegrating / piezoelectric constant

• Taking into consideration the nominal properties of the 4/20/80 PNZTmaterial on the Sensor Die, the default sensitivities of the Sensor Boardtheoretically should be

• ºC/Volt = -0.625 degrees per volt.• Newtons/Volt = 0.44 Newtons per volt.



• The theoretical scale factors listed on the previous page may beincorrect for the EDU Sensor Board for the following reasons:

– The sensor capacitor is suspended between two attachment points on thesensor board, allowing it to bend when a force is applied to it. Bending thecapacitor stretches it laterally and invokes piezoelectric responses frommultiple directions in the capacitor lattice.

– Changing the temperature of the sensor will not only affect the capacitor, itwill also affect the silicon die the capacitor is fabricated on as well as thesensor board. As does the sensor capacitor, they will also change their sizein response to the temperature change and apply mechanical stretching,compression, or twisting forces to the capacitor, invoking otherpiezoelectric responses in addition to the ⊥ pyroelectric response.

• Both of the factors described above may cause the sensor capacitor onthe sensor board to deviate in amplitude and direction from the simpleresponse predicted by the pyroelectric and piezoelectric constants.

Scaling Errors


• Because the amplitude and signs of the errors infringing on your sensorcapacitor are so large and unpredictable, you will have to calibrate thescale factors for your Sensor Board yourself.

– FORCE: Place a calibrated weight on the sensor capacitor on the SensorBoard and record the change in voltage reported by the oscilloscope.

• Piezoelectric Scale Factor = Weight of object / Voltage Change

– TEMPERATURE: Place the Sensor Board in a chamber or on a hot platewhere you can control the temperature and force it to change a knownamount.

• Pyroelectric Scale Factor = Temperature Change / Voltage Change

• Use small changes in temperature (~5ºC) and do not heat the Sensor Boardabove about 30 ºC.

True Scale Factors


• The poling direction achieved by using the JP1/JP2 solder jumpers issuch that the voltage will decrease if the remanent polarization of theferroelectric capacitor decreases.

– Remanent Polarization is described in Chapter 4 - Theory of FerroelectricCapacitors in the HELP files for the EDU.

– The explanations on this page assume that the Scale Factor = +1.0.

– Squeezing the capacitor reduces its thickness and forces the remanentpolarization to decrease, in turn causing the oscilloscope signal to go morenegative on the plot.

– Theoretically, reducing the temperature of the capacitor should increasethe remanent polarization and thus make the remanent polarization and theoscilloscope signal increase .

• On the Sensor Board, the opposite occurs, most likely due to mechanicalforces arising from the temperature change.

Signal Polarity


• The poled sensor capacitor has its positive terminal connected to the “-”terminal of the operational amplifier.

• When the remanent polarization decreases for whatever reason, thecapacitor electrode connected to the “-” terminal will immediately haveexcess positive charge.

• The capacitor will pull electrons with negative charge from the “-” node of theoperational amplifier to get into balance again.

– Electrons pulled from the “-” terminal will make it more positive, causingthe output voltage of the amplifier to go in the negative direction.

– The negative voltage of the output, as a source of negatively chargedelectrons, will then drive enough electrons onto the “-” node through theintegrating capacitor to make up for the electrons pulled from the “-” nodeby the sensor capacitor.

∴ The decrease in remanent polarization forced the output voltage of thecharge amplifier to move in the negative direction.

How the Charge Amplifier Works


Advanced Controls

• What the Advanced Controls do

• Correcting for the Feedback Resistor

• Integrating the Signal


The advancedcontrols allow youto correct thesignal for theeffect of thefeedback resistoror to integrate thesignal to get“velocity”information.

Advanced Controls


• The advanced controls allow you to perform two mathematicalfunctions on the measured data as it is plotted.

1. You can mathematically correct for the decay in time of thesignal caused by the feedback resistor.

2. You can integrate the measurement to convert “acceleration”into “velocity”.

What Do the Advanced ControlsDo?


• The feedback resistor creates a current input into the charge amp that is– proportional to the output voltage– inverted from the output voltage

• This inversion causes the voltage to move in the opposite direction ofits sign.

– This forces the output voltage to always move towards zero volts.– Zero volts means zero current, making the output stable.

• The correction to zero volts begins immediately any time the outputvoltage leaves zero volts so distortion in your measured signal isalways present.– The amount of distortion is dependent upon the period of your signal vs

the rate of correction.– The correction rate for the EDU Sensor Board is proportional to the

integrating capacitor multiplied times the feedback resistance value.

• 220pF • 3.838GΩ • 5 ~ 4.2 seconds.

Effect of the Feedback Resistor


• Applying a constant force to the sensor for a short period shows thecorrection function in action.

– The red line is the Sensor Board signal. The green dashed-line indicatesthe force that was applied as a theoretical step function.

– Note that the signal decays back to zero volts in 4.2 seconds after the firstapplication of the force. A little later when the force is released, it looks tothe sensor like a force in the opposite direction. This change also decaysback to zero.

Effect of the Feedback Resistor

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0.0 2.5 5.0 7.5 10.0 12.5 15.0 17.5 20.0


Vol

ts

Time (seconds)


Clicking on thiscontrol tells theoscilloscopesoftware tocalculate theamount of leakagefeeding backthrough thezeroing resistorand add it back tothe signal aftereach sample point.

Correcting the Feedback Leakage


The algorithmuses the resistorand capacitorvalues listed in thewindows. Thesematch the valuesof the componentson the SensorBoard. Do notchange themunless you changethe board.



The formula is

Voltage Loss from Feedback Resistor +=

This value is calculated for each sample point and added back to themeasured value. The correction is cumulative over time ( i.e. +=).

The feedback resistance will prevent the actual amplifier output voltagefrom saturating at +10V or -10V but the mathematical correction iscumulative and allows the plotted voltage value to exceed the ±10V limit.


)( )(Measured Output Voltage + Offset Voltage

Feedback Resistance

Sample Period

Integrating Capacitance•


Correcting for thefeedbackresistance makesthe circuit act likean integratoragain, causing it todrift linearly in apositive ornegative direction.The Offset Voltagelets you zero thedrift.



• Drift of the signal with the Feedback Resistor Correction turned on but with theOffset Voltage set to zero. Note the checkmark indication for correction.

Zeroing the Correction Drift.


• The Offset Voltage can be adjusted to reduce the drift to zero. Press theCorrect Offset button to have the software calculate the correction for you.



The corrected OffsetVoltage as calculatedby the software.

The software uses theslope of the last pointon the screen takenagainst zero plus theelapsed time tocalculate the drift anddetermine an offsetvoltage that willcounteract it.



• The sensor drift after correction. Now, the system is ready to look at signalsless than 60 seconds long (in this case).



• It might require more than one attempt to zero the drift to get thecorrection factor to the proper value.

– Each time the Correct Offset button is pressed, the new correction is addedto the old value.

– To reset the Offset Voltage to zero, press the Reset Offset button.

• Air currents and vibrations in the area can have a significant impact onthe corrected signal. Always place the sensor under a box, bowl, orother cover and let it stabilize for 10 minutes or so before executing thecorrection.

– Once the Offset Voltage is proper, you may uncover the sensor and use it.

– Covered, the sensor trace should eventually go straight with no curves.

– Uncovered, the signal will move in a seemingly random manner from aircurrents. You cannot get a good zero in this condition.



The second controlintegrates the signalover time.

The FeedbackResistor Correction isautomaticallyinvoked so youshould find a validOffset Voltage beforeattempting tointegrate the signal.

Integrated signals goballistic quickly!

Integrating the Signal


• What does the integrated signal mean?

• Assume that the force on the sample is caused by an acceleration.

– F = ma where m is the mass of the bumper on the sense capacitor and ais the acceleration that generated the force you measured.

• The integration of the force yields velocity.

– Therefore, applying force for a short period to the sensor capacitor isinterpreted as an acceleration that lasted for the period of the force.

– If you have the Offset Voltage and the Scale Factor set correctly, theoscilloscope signal, meaning velocity, should increase during theapplication of the force and level off when you stop applying the force.

Integrating the Signal


The Force andTemperaturepreset buttonssimply set upconvenient valuesfor the resistor,capacitor, andacquisition timeparameters fortheir respectiveacquisitionwindows.

Preset Buttons


Force Measurements

• Measurement Parameters

• Effect of Touch

• Examples of different force measurements.


Measurement Parameters for Force

• Typical forces we may measure range in speed from– Fast audio frequencies from 100Hz to 10KHz

– Intermediate speed forces such as your pulse that last a fraction ofa second

– Slow force applications executed with your fingers, arms, etc.


Audio• Set the Sample Period to the range of 1KHz up to 10KHz.

– At 1kHz, you can have a Time Window 20 seconds wide.

– At 10kHz, your Time Window can only be about 1.5 seconds wide.

• Place the sensor where it will be acted upon by an pressure wave.– A simple demonstration is to put the sensor under your laptop and then

rap on the table top!

• The Sensor Die is not suitable for picking up air pressure waves createdby your voice as they will be 10 to 100 times too weak for the 220pFintegrating capacitor to discriminate.

– Also, the acoustic impedance of the sensor capacitor to air is too high. Theacoustic pressure waves will simply bounce off of the sensor.


Heart Beat• Use the default acquisition timing.

• There will be a slight distortion of the pulse wave by the feedbackresistor.

– Set the Advanced Controls to correct for the feedback resistor and zero thesensor board to get precise results.

• My pulse at the wrist using default settings and autoscale.

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 1 2 3 4 5 6 7 8


Vol

ts

Time (seconds)


Finger Force• These types of forces take seconds to develop and release.

• You must use feedback correction and zero the sensor before makingthis type of measurement to get an accurate signal shape.

• An interesting prediction is that it will be impossible for you to hold aconstant, unvarying force on the sensor with your fingers! Try it!


Effects of Temperature on ForceMeasurements

• When you squeeze the bumpers of the sensor capacitor with yourfingers, you are also heating the bumpers and the sense capacitor withyour body heat. This heating will affect your measurements.

– Try applying the force with the eraser of a pencil.

• You can swing the sensor board through the air to see accelerationeffects if you place a heavy mass on the sensor capacitor. However, thesensor capacitor will see air currents because of its motion and you mayhave a very hard time determining if the effects you see on the signalcome from acceleration or from air-flow cooling of the sensor!

– Put the Sensor Board in a closed box and swing it around.


Temperature Measurements

• Measurement Parameters

• Examples of different temperature measurements.


• Some temperature changes can occur in a fraction of a second,especially if touch is involved.

• Temperature change by radiation or convection is slower, occurringover seconds or even a quarter of an hour.

• To make long term temperature measurements, use a Sample Period of0.01 seconds and set the Time Window to 300 seconds (5 minutes) orlonger.

• In order to see long term changes in temperature, you must use feedbackcorrection and zero the amplifier for 300 seconds or longer.

– This test takes a long time to prepare: 10 minutes under the cover plus thezeroing runs of 10 minutes each.

– Once zero’d for this long of a period, you can let the sensor runcontinuously for long periods without the measurement going unstable.

Measurement Parameters forTemperature


Some Temperature Measurements

• Leave the graph on autoscale using a Sliding Window for the X-Axis.Watch the constant changing of the signal due to air currents in theroom. A classic example of the laws of thermodynamics in action.

– You will be able to see the cooling effect from the wind created whensomeone walks by or when the air conditioning fan turns on.

• Place your finger within an inch of the sensor capacitor. Your fingerwill noticeably heat the sensor by radiation.

• Create a sine wave on the signal using a hot coffee cup and a cold glassof water, alternating them next to the sensor!

• In all cases, note how abruptly the temperature changes when forced buthow slowly it returns to ambient when the forcing function is removed.

– Demonstration of the rate of flow of energy governed by the temperaturedifference.


Special Considerations

• Changing the Graph while Running

• 60Hz noise

• Lock Up

• Running without the EDU


Changing the Graph While Running

• The graphics pop-up menu that you learned in IO4-Data Plotting Toolsstill apply.

• You may double-click the mouse with the cursor within the plottingarea to get the plot configuration menu.

– You can use this feature to change the plot scales or go to autoscale whilethe oscilloscope is running.

– You can also Mark Data Points to highlight the signal. Note, however,that the marked data points take longer to plot so you may start generatingacquisition errors.

• If you zoom into a signal during acquisition and subsequently STOP thetrace, the zoom will remain in force even after you START again. Youmust Undo Zoom from the pop-up menu.


60Hz Noise• The telephone cable connecting the Sensor Board to the EDU is an

antenna for 60Hz or 50Hz EMF.– You can minimize this effect by keeping the cable as short as practical.

• You are also an antenna for the 60Hz (50Hz) EMF so your body nearthe Sensor Board will inject significant noise.

– This is especially true when you touch the Sensor Board to your body tomeasure your pulse.

– The casing of the Sensor Board connector is metal and is grounded soholding the Sensor Board by the connector casing will eliminate almost allof the injected 60Hz. You, the antenna, will inject a countervening signal!

• The Sensor Board cable will distort Hysteresis measurements of smallcaps with its 60Hz noise. Disconnect the Sensor Board when runningferroelectric hysteresis loops.


Lock Up

• If the EDU locks up during operation, the oscilloscope controls will alsonot respond to your mouse commands as the computer is waiting for aresponse from the EDU to its USB queries.

• Should this happen,– Power down the EDU.

– Cancel out of the oscilloscope code using the “x” box in the upper righthand corner of the window.

– Reconnect the EDU and start over.

– In the worst case, use the Task Manager (CNTRL-ALT-DEL) to force theprogram to quit.


Sleep

• If your computer goes to sleep with the EDU attached and powered up,the EDU will go to sleep as well,

• When you take your computer out of sleep mode, the EDU will alsocome out of sleep mode. However, the operating system will no longerrecognize the EDU on its USB port.

• To re-connect the EDU in this situation, unplug the USB cable and thenplug it back in again. There is no need to power down the EDU.


Running without the EDU

• If you start the EDU software without an EDU attached, the softwarewill operate without locking up.

• You can examine all menus, recall files, and store files.– Executing a hysteresis test will yield “pseudo-data”.

– The oscilloscope function will open but will not attempt to collect data.


Summary of the Rules• Disconnect the EDU Sensor Board and its cable from the EDU when

measuring Hysteresis Loops.

• Do not touch the sensor cap with your fingers. The heat pulse effectwill swamp the force measurement.

• Hold the Sensor Board by the metal casing of its connector.

• Always cover the Sensor Board to isolate it from air currents whenzeroing the Feedback Resistor Correction mode or when zeroing forintegration.

• Make sure that the wires on either end of the Sensor Board cable go tothe same pins of their respective plugs. A mistake here will destroy theSensor Board.


Summary of the Rules• Do not touch bare connections on the Sensor Board (other than the

connector casing) when making measurements.– The circuit will not be damaged but the measured signal will be distorted.

• You may connect and disconnect the Sensor Board to the EDU with theEDU powered up.

• You may use the pop-up menu graphing controls on the oscilloscopedisplay while it is running.

– Always remember to UnZoom!


Contact InformationWe hope that you have enjoyed our tutorial about the Radiant EDUOscilloscope and Sensor Board. You may contact us withquestions or recommendations for the EDU and/or newferroelectric-based components.

– Sales information: Michelle Bell– Technical assistance: Joe Evans, Bob Howard, or Scott Chapman– Shipping instructions: Geri Martinez

e-mail: [email protected]

Telephone: 505-842-8007

Fax: 505-842-0366

web site: www.ferrodevices.com

http://www.ferrodevices.com

using the edu oscilloscope to operate sensorsuse the scale of 1/10th of a logarithmic unit called a...

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