Tekscan
I-Scan System Start-Up
for Reliable Pressure / Force / Area Data Collection
Getting Started with I-Scan:
Sensor Selection, Hardware and Software
Sensor Conditioning
Sensor Equilibration
Sensor Calibration
Data Collection
May 2003
Is Tekscan’s Tactile, Thin-Film, Array-Based Pressure
Measurement System Required for my Application?
Yes, if your application demands the following:
X and Y Pressure Distribution in Real Time
Calibrated Magnitude of Pressure and Force (absolute and / or relative)
Force Vs. Time / Pressure Vs. Time of an event
(e.g. loading a fixture with a bolt torque sequence)
Visual Location of High and Low Pressures in application interface
Thin – Film Sensor (~ .004” +/- .0002” thin)
Convenient method to measure, record, and even market results
with graphs, ASCII output, 2D and 3D color views, save your
recording as a ‘movie’ file (.fsx), and incorporate video synchronization
 System Components
–
–
–
–
–
–
–
–
Sensor pad(s)
Sensor maps (software display drivers, each sensor has its own map)
Sensor handle(s) (A/D converter) w/ 12’ standard cable (30’ & 60’ avail.)
Plug-in PCI card (each PCI card can accommodate up to four sensor
handles)
Expansion PCI unit (optional, convenient for a Notebook computer)
Tekscan Windows-based software (for most Windows OS)
IBM-Compatible PC
Color Printer (if color printouts are required)
 System Notes
– Tekscan Signal to Noise Ratio is much better than strain gauges (noisy)
since our system has a resistance range from ~ 20 KOhm up to ~ 5 MOhm.
– Dynamic response is a strong point for Tekscan
– Ink response has been matched with an Instron up to 35 Hz perfectly
– Requires an IBM-compatible computer; the more memory, processor
speed, and available hard drive space the better. Ex. 300 MHz.to1GHz
processor speed, 1GB to 40 GB RAM (memory), and a Hard Drive of
20 GB to 40 GB is an example a computer in line with the latest
technology.
 Will Tekscan Hardware Suit Application Environment?
–
–
–
–
–
–
–
–
-
Sensor handle cable lengths come in standard length of ~ 12 feet
Sensor handle standard maximum cable length is ~ 30 feet
Tekscan has tested up to 60 feet in a clean noise environment (~30 – ~ 60 Hz. max.)
Tekscan offers a Tab Extender / Clamp assembly which extends distance between
sensor pad and sensor handle by ~ 18”. Tekscan needs to assemble.
Tekscan suggests protecting the handle in a ‘horse pill’ assembly for harsh
environments. ‘Horse Pill’ offers sensor handle protection from water and drop
damage; the ‘Horse Pill” is a plastic capsule which may be fabricated with a Dremel /
Roto Zip
If noise is present, shielding the sensor with an electric ‘fence’ (conductive material)
between the sensor and the noise source. The electric ‘fence’ should be firmly
connected to the ground wire which is connected to the grounding screw on the sensor
handle
The ‘fence’ requires a high enough conductivity to adequately shield the sensor;
however, the ‘fence’ must not be too heavy or thick as it will alter the physical
pressure path of the application
Moving the sensor handle away from the noise source (isolating) will limit the effects
of the noise since the amount of capacitive coupling is directly related
to the distance of the noise source
Regarding water immersion, Tekscan sensors have been tested at 1 atm, 75 F while
immersed in water for two hours without and adverse effects to sensor performance
The sensor pads have a temperature range of ~ - 35 F to ~ + 145 F.
Will Tekscan Hardware Suit Application Environment? cont.
-
-
Tekscan sensor pads measure compressive loads (perpendicular to the sensor pad)
Shear forces may damage the sensor and are not accurately measured
The largest active region on a sensor pad is 22.7” x 34.8” with .66” symmetrical spatial
resolution
The smallest active region is ~ .5” x .5”
Data sampling speeds range from 1 Hz through ~ 10,000 Hz.; 10,000 Hz is achieved
with sensor model 9550 coupled with High Speed version of software and hardware
Video Synchronization is an available add-on feature
Tekscan manufactures several equilibrator models (pneumatic bladders); most models
have a max applied pressure of 100 PSI. One model achieves 500 PSI and another
model reaches pressures of ~ 1000 PSI over a 5” x 5” area
Some applications require the customer to construct their own bladder (hydraulic or
pneumatic)
Tekscan offers a Data-Logger which allows for remote data collection which may be
downloaded at a later time. The F-Scan (in-shoe) is available and the I-Scan version
should be available 1st Qtr. 2004 or sooner.
How to Select a Tekscan Sensor and System
 Select the Proper Sensor Size
– www.tekscan.com  Industrial  Sensor Catalog
– Load footprint should fall within sensor matrix (active area)
– Custom Designed sensors are an option
• Involves:
–
–
–
–
–
–
–
CAD electrical layout
Tooling (screens, dies)
Fabrication (printing, assembly, etc.)
Map development (unique software display)
Sensor Minimum Quantity
Initial PSAT testing
Final Product Testing (whole system)
 Select the Proper Spatial Resolution
–
–
–
–
–
–
Refers to column center to column center and row center to row center spacing
Symmetrical and Asymmetrical spatial resolutions offered
0.025” x 0.025” is the tightest spacing capability
Note: A single A/D converter accommodates 2288 sensels (52 columns x 44 rows)
Note: Eight A/D converters is the limit for a single sensor pad
To maintain a fairly tight spatial resolution (ex. 0.060”) over a large area (e.g. 10.6”
x 11.6”), multiple sensor handles are required on the same sensor pad
 Select the Proper Sampling Speed
–
–
–
–
127 Hz (frames / sec.) standard. Each sensel is sampled 127 times / sec.
Highest speed is 10,000 Hz (using 9550 model only)
A sensor pad with ~ 33,000 points will yield ~ < 32 Hz (model 8050)
A sensor pad with ~ 8,500 points will yield ~ < 63 Hz (model 8000)
– The number of sensor handles, rows, and total sensels affects sampling speed
Pre-Triggering / Triggering – Pre-triggering is available; it is a circular buffer which
will store frames of data before the Trigger point. Triggering is also a software feature
whereby you can select a ‘Start’ threshold and an ‘End’ threshold. The software will
automatically Start and Stop based upon your threshold requirements.
 Select the Proper Sampling Speed cont.
– High Speed System with Multiple Handles for a Tekscan PCI card
(frequencies may be slightly higher)
Driven
Lines
1 Handle
Max freq.
2 Handles
Max freq.
3 Handles
Max freq.
4 Handles
Max freq.
1
10,753 Hz
5,405 Hz.
5,405 Hz.
3,597 Hz.
2
5,405 Hz.
5,405 Hz.
3,597 Hz.
2,703 Hz.
3
3,597 Hz.
3,597 Hz.
2,703 Hz.
2,160 Hz.
4
2,703 Hz.
2,703 Hz.
2,160 Hz.
1,799 Hz.
5
2,160 Hz.
2,160 Hz.
1,799 Hz.
1,543 Hz.
6
1,799 Hz.
1,799 Hz
1,543 Hz.
1,350 Hz.
7
1,543 Hz.
1,543 Hz.
1,350 Hz.
1,200 Hz.
8
1,350 Hz.
1,350 Hz.
1,200 Hz.
1,080 Hz.
9
1,200 Hz.
1,200 Hz.
1,080 Hz.
900 Hz.
10
1,080 Hz.
1,080 Hz.
981 Hz.
831 Hz.
 Select the Proper Sampling Speed cont.
Example: High Speed timing for the 5315 sensor pad
• Max data acquisition speed: ~ 216 Hz. (2016 total sensels) / dependent upon total sensels
• Time to record one frame: 1 / 216 = 0.0046 sec
• 52 driven traces:
– Time to collect data from 1 driven line = 0.0046 / 52 = 8.84 E-5 sec
• This time is broken into 64 time units:
– 8.84 E-5 / 64 = 1.38 E-6
• Scanning time for a driven line:
• Driven line needs 12 time units to apply voltage and let settle enough
– (12) (1.38E-6 ) = 1.65E-5
• After driven line is charged, all 44 intersecting rows are read sequentially
The time it takes to read one sensel is one time unit, 1.38E-6.
Time to read all 44 sensed traces  (44) (1.38E-6) = 6.08E-5
• The driven trace needs to be grounded.
– This takes eight time units. (8) (1.38E-6) = 1.10E-5
• 12+44+8=64 Time Units
Then the sequence starts over with the next driven pogo pin / trace;
the driven pads / traces are charged (activated) in sequence even if there
are no traces physically connected to the pogo pin / pad / trace.
Driven traces start at 0 and end at 51 while sensed traces start at 0 and end at 43.
 Select the Proper Sensor Full Scale Pressure Range
- Select a full scale pressure range (PSAT – saturation pressure) slightly higher than
the application’s maximum pressure to account for any pressure peaks.
- Note: Most Tekscan “55XX” (Nip / Pinch) sensor models have limited or
no standard pressure ranges
- Custom full scale pressure ranges are feasible; there are some exceptions based
upon sensel size, row and column lengths, and other variables.
- During a trial experiment, load the sensor similarly to the application and have the
Color Pressure Legend open and set to 0 to 255 (Tekscan’s eight-bit full raw digital
output scale). The maximum sensel output is 255 Raw DO (Digital Output). The
application pressure should nearly saturate the sensor output. Ex. If ~ 240 DO is
shown to be the peak pressure in the experiment, then the optimum sensor full scale
range has been selected. If a sensel reaches DO of 255, the load on it can double or
increase by a factor of ten, and no greater output will result.
Note:
Before conditioning, equilibrating, or calibration, it is recommended to check
that all components are connected properly. You can press with your finger or
a stylus to ensure the sensor responds appropriately. Apply pressure at column
end to see if any rows are shorted or open electrically, If you see red along a row
or column, the row or column may be electrically shorted. If you do not see any
color except black, then an open may be present. Always reseat the sensor and try
again. “Sensor OK” should be visible in the lower Real Time window bar.
 Conditioning the Sensor Pad
– Using, Tekscan’s equilibrator unit may be used since it imparts a uniform
load pneumatically. Most Tekscan equilibrator’s have a capacity up to 100
PSI. Maintaining similar temperature during conditioning is important.
Mimic the interface profile if feasible (i.e. roller ) and impart similar pressure
as in the application, condition the sensor for three cycles at ~ 30 seconds per cycle
at ~ 115% / ~ 120% higher than the application pressure.
– If Tekscan’s equilibrator is not feasible or available, try to implement two metal
plates with a sheet of urethane foam in between; ensure the foam is not too soft
such that it “squirms” markedly on the sensor surface.
– Conditioning the sensor pad minimizes drift, hysteresis, and improves repeatability.
– Tekscan manufactures several equilibrators (pneumatic and one electric /
hydraulic). The 0.025” thick urethane bladder applies a uniform pressure to the
sensor pad via clean, dry, shop air. An analog pressure gauge, external pressure
regulator (three-position toggle switch), and plastic tubing are included as well as a
pressure relief valve. Some models are constructed from wood and some from
aluminum. Some models incorporate OHAUS calibrated weights to apply pressure.
– Tekscan offers a cylindrical bladder which pressurizes up to ~ 600 PSI as well as
a hydraulic bladder with 5.0” x 5.0” active area and 0.5” corner radii – to fit 5101
model and smaller. One side of sensor must be peeled to fit. This bladder will be
rated to ~ 1000 PSI and will be pumped via a hand or foot pump.
 Sensor Equilibration
- Equilibration should be performed before calibration.
-Tekscan offers up to a ten-point equilibration
-In general, a sensor’s output (sensitivity) will exhibit a decrease over time, which the
Tekscan system can measure; this decrease occurs during use and is a function of the
loading conditions. A good application for equilibration, is when the sensor may
loaded repeatedly in the same physical location on the sensor pad. Typically, the
unloaded region of the sensor pad remains intact, that is it holds a higher sensitivity
than the loaded region. Equilibration compensates for for the sensor’s trends thus
provides a more even sensor sensitivity.
- Also, loading the sensor pad with rough, heavy textured materials will change the
sensitivity of each sensing element as the sensels are loaded repeatedly. In this case,
the unevenness of the sensor’s sensitivity would be more random and would not
produce a visible ‘trend’ as the case
where the sensor is loaded in the same physical region each time.
- An equilibration file may be loaded before or after the new recording
- If performing a single-point equilibration, the max pressure of interest should be
selected; this may be the range mid-point or an average Digital Output such as 125.
- Applying a uniform pressure with a bladder device is a means of inspecting the proper
sensor operation / damage.
- Scale factors range from 0.5 to 2 and the scale factor is unique to each sensel and
equilibration level (pressure).
 Sensor Equilibration cont.
-
The Black and White image in the equilibration dialog window represents:
- cold (not as sensitive sensels) with black-ish color
- hot (more sensitive sensels) with gray-ish color
The sensels with light gray-ish color represents equilibration factor values
close to 0.5
The sensels with black-ish color represents equilibration factor values close to
2.0
-
The average Digital Output is not affected by equilibration
-
Sensels with low output receive more gain to increase their Digital Output and sensels
with high output have their gain reduced to lower their Digital Output. Electronic
compensation for each individual sensel to sensel sensitivity difference, due to
manufacturing or history of use, is accomplished
-
Ensure that there is not trapped air inside the sensor which will give the ‘pillow effect’.
Sensors may be loaded a portion at a time in order to ‘milk’ any air out from inside.
Describing the Equilibration Process:
Tekscan’s pressure bladder (equilibrator) is useful in equilibrating a sensor. Equilibration is
the process of normalizing the output of each sensel (sensing point on the sensor matrix
region) to the average output of all the sensels on the pad. This is accomplished by applying
a known uniform pressure to all the sensels and allowing the software to define a scale
factor, which is applied to each sensel, resulting in a uniform output at that pressure. The
bladder device applies the known uniform pressure. This bladder may be used to equilibrate
and calibrate (in some cases).
In general, a sensor’s output or sensitivity will exhibit a decrease over time, which the
Tekscan system can measure; this decrease occurs during use and is a function of the loading
conditions. One good application for the bladder device is when the sensor may be loaded in
the same location each time. Typically, the unloaded regions remain intact but the loaded
sensels may degrade over the life of the sensor. Equilibration compensates the sensor’s
trends thus providing a more even sensor sensitivity.
The bladder device is also beneficial in cases where the interface materials applying the load
are rough and have a heavy texture. This will change the sensitivity of each sensing element
as the sensels are loaded repeatedly. The unevenness of the sensor’s sensitivity in this
example would be more random and would not produce a visible ‘trend’ as the case where
the sensor is loaded the same each time.
Single Point Equilibration
A uniform pressure is applied to the sensor pad surface typically by one of several
Tekscan equilibrators; a 0.025” thick urethane bladder is pneumatically filled with
clean, dry, shop air which runs through our external pressure regulator and plastic
tubing. The average raw digital output of all the sensels is calculated and then a matrix
of normalization factors is derived and then applied to each respective sensel so
a uniform corrected output is given for a uniform input with higher or lower
pressure input than the single point equilibration point, uniformity output is
expected to be improved by equilibration. Equilibration is typically performed at the
pressure of the test of interest.
Single-point equilibration uses a scale factor based upon the Digital Output average of
all the sensels at the single pressure point. The scale factor is individual for each
sensel.
Multi-Point Equilibration – Offers the advantage of compensating for
sensel output over the full operating range. A piece-wise linear approach is implemented
to normalize raw digital data on a sensel by sensel basis. Multi-point equilibration treats
each sensel individually; for each sensel, a different slope exists with incremental
increase of raw digital output. Tekscan allows up to a ten-point equilibration.
Technical definition: Interpolation between inflection points of a piece-wise linear
curve; inflection points refer to Digital Output average of all the sensels at one pressure
point.
Example:
Three Sensel Values
1st Equilibration Point:
10, 16, 22
2nd Equilibration Point:
26,30,34
3rd Equilibration Point:
34,36,38
Average is taken for each equilibration point
1st Equilibration Point:
2nd Equilibration Point:
3rd Equilibration Point:
[10+16+22} / 3 = 16
[26+30+34] / 3 = 30
[34+36+38] / 3 = 36
Scale Factor is Applied to Each Sensel
1st Equilibration Point:
2nd Equilibration Point:
3rd Equilibration Point:
16/10 cold, 16/16 linear, 16/22 hot
30/26 cold, 30/30 linear, 30/34 hot
36/34 cold, 36/36 linear, 36 / 38 hot
 Multi-Point Equilibration Example cont.
Step-Wise Linear Curve Coordinates
1st Equilibration Points:
x = 10, y = 16
x = 26, y = 30
x = 34, y = 36
2nd Equilibration Points:
x = 16, y = 16
x = 30, y = 30
x = 36, y = 36
3rd Equilibration Points
x = 22, y = 16
x = 34, y = 30
x = 36, y = 36
I.E. Raw Input of x = 18, coordinates used would need to be:
x = 10, y = 16
x = 26, y = 30
Multi-Point Equilibration cont.
- The zero point is always an equilibration point
- A separate ‘piece-wise equilibration-curve’ is defined for each sensel
- An average digital value is found for each equilibration pressure (point)
- The actual digital value for each equilibrated sensel is saved
- If a sensel is not active at an equilibration pressure (point), then the overall
average digital value is used as the ‘actual’ digital value
- The highest two points are linearly extrapolated to determine the line beyond the
highest pressure (point)
- Works with a two-point calibration
Example: Application pressure range is 0 to 100 PSI
A multi-point equilibration may be implemented; equilibration points may be:
20 PSI, 40 PSI, 60 PSI, 80 PSI, 100 PSI (Five-Point Equilibration)
Application Parameters to Mimic for Calibration:
Material Interface – Application material interface should be implemented during
calibration. The same durometer rubber is very important as our sensor has a topography
which is sensitive to different durometers. Sometimes our equilibrator is used for both
equilibration and calibration. Applied load = area loaded x PSI gauge. Ensure that no
trapped air inside the sensor is acting as an air buffer when using the bladder; you will
see a low / no load area where there should be load.
Interface Profile – If at all possible try to mimic the profile of the interface.
Ex. If the interface is a roller to roller, load the roller profile and material onto
the sensor pad. I recommend comparing a flat stock and profile calibration in this case.
Temperature – Keep the temperature in your calibration similar to that of the
application. In some cases, a person’s body temperature needs to be replicated, such as
in seating applications. For every degree F the calibration temperature differs from the
application, the sensor reading will be off by ~ .25%. Note: In an automotive seat
application, where a person’s body temperature can affect the sensor output, you should
calibrate at a temperature close to 98.6 o F.
Timing - To minimize the effects of drift, mimic the time of the application in the
calibration within reason. That is if the measurement will be for 30 minutes of
recording, you may wish to calibrate for ~ 2 minutes. Our system’s drift curve levels off
after ~ 30 seconds and then our 3% per log time is effective. One can record a loading in
raw digital output and then open a Force Vs. Time graph to view the curve to see where
it begins to level off. Where the curve levels off (stabilizes) is a good indication at the
time interval needed for calibration.
 Sensor Calibration Notes:
Calibration converts the raw 8-bit digital output (0 – 255 per sensel) into engineering units such
as Pounds, Newtons, Kilograms, etc. (Force) and PSI, Kg-Cm2, etc. (Pressure). The Tekscan
reported calibrated data should be periodically compared to a known, reference load to ensure the
Tekscan calibration is still within its +/- 10% range.
A solid calibration will mimic the actual application in terms of temperature, material interface,
interface profile (application dependent), timing of test, and loading characteristics (i.e. how the load
is applied).
I-Scan uses the force imparted on the sensor pad as the calibration value; the loaded area is
automatically detected by the software. The pressure / pressure distribution is calculated from the
applied force and detected area.
Each row and column intersection is a sensel (variable resistor) with a resistive
range from < 10 MegaOhms down to ~ 20 KOhms. Calibration converts a known load’s
impedance into engineering units. A good calibration will result in good data reporting.
Tekscan’s pneumatic bladder, in some applications, may be suitable for calibration in addition to
equilibration based upon the material interface on the sensor pad
TARE Feature – Only works after a single-point or a two-point calibration has been
performed. Allows user to Tare out undesired preload. Ensure the two points in the twopoint calibration are close to linear.
Sensor Calibration Notes cont.
High Speed Post Calibration – You can perform a post-calibration (after the recording)
by utilizing the Force Vs. Time graph and applying the calibration to the highest force
point as shown by the graph as long as that force is known.
Regular Speed Post Calibration – One may calibrate the sensor after the data is
recorded by utilizing the Force Vs. Time graph or one may apply a different calibration
file as long as the new calibration was performed with the same sensor model. One must
know the force acting through the sensor for at least one frame in order to use post-cal.
Sensor Loading - Ensure the load is balanced and stable before calibrating or testing
Ensure when the sensor is loaded, that the sensor is not reporting mostly red colors nor
mostly blue colors; this would indicate the sensor is either too sensitive (red) or not
sensitive enough (blue). If mostly blue colors or orange / red colors are displayed with
our pressure legend set to full scale (0 to 255), then the sensor needs to be physically
changed out for a more suitable full scale range such that at full load the display
reports greens / yellows / oranges (3/4 of full scale allowing for any pressure peaks).
Physically load sensor in calibration fixture similarly as in the application.
Calibration pressure should be similar to application pressure. Preferably, load the entire
matrix area during calibration. Be careful no to overhang the load off the sensor; you
may need to shim if this is the case. A load frame such as an Instron, Tinius Olsen, MTS
may be implemented for high loads. Ensure the plates are free to engage in a parallel
manner.Load at least 25% of the active area for good statistical data.
Sensor Calibration Notes cont.
Ensure the entire calibration load is transversing through the active sensor region and
not bridging the sensor non-sensing edges. Load at least 25% of the entire sensor active area.
Ensure sensels are not saturated (red); if a sensel(s) is saturated it no longer add to any increase
in load thus a poor calibration will be accomplished if red sensels are present.
Mimic timing of application load since our sensors experience drift (3% per log time)
Most drift occurs in the first 30 seconds of loading.
Example of drift:
1 sec
10 secs
100 secs
1000 secs
10,000 secs
=
=
=
=
=
100 lbs.
103 lbs.
106 lbs.
109 lbs.
112 lbs.
Impact load calibration: Example – pendulum device for calibrating the force on the chest of an
automotive crash dummy is used since the mass of the pendulum is known and the acceleration is known
from an accelerometer in the dummy, thus the force can be calculated.
Editing a Single-Point or Two-Point Calibration is easily accomplished through the edit feature.
Sensor Calibration Notes cont.
% Active Sensing Area Vs. % Inactive Sensing Area - the less Inactive sensing area % , the
higher the output with a rubber material will be as compared to a sensor with more % active area. The
sensor with higher % inactive area will allow more off-loading of a rubber material than a sensor with a
smaller % of inactive area. It is important not only to replicate application materials during calibration but
also to think about
Sensor Stacking - Do not calibrate sensors stacked upon each other.
Metal Plates - When loading two linear surfaces (e.g. two plates of steel), it is
Recommended to insert a sheet of paper or a thin urethane sheet between the two plates.
Rubber Parts - When loading a rubber part onto the sensor, a thin sheet of teflon paper
works well to minimize shear forces which are not measured by our sensor. Our sensors
measure compressive forces.
Soft Interfaces - When loading a crash dummy or a person onto a foam / cushion, try to
calibrate with the actual materials and with the actual profiles / curvature. CAUTION needs
to be taken. For example, when sitting in a luxury automotive seat, the sensor will bend
upward on the sides thus introducing horizontal loads which can give you misleading data.
Some customers elect to use the equilibrator even though the material interface inside the
equilibrator differs from the actual application; the equilibrator offers relative repeatability
Sensor Calibration Notes cont.
Changing Area – In some applications, such as tire and seating, the area increases with
increased load thus keeping the pressure fairly constant which makes a two-point calibration
difficult since the algorithm tends to “blow-up” when the two pressures are too close in value.
The two forces should be ~ 20 % apart.
Saturated Sensels – You do not want to have all / mostly blue sensels or all / mostly
red sensels appearing on your display before you engage a calibration. If you have many red
sensels (255) you are saturated and you will not be able to resolve those points on the sensor
in the application and if you have all / mostly blue sensels on your computer screen
display, you will not be leveraging the best pressure measurement resolution you could be
with that given sensor’s saturation pressure (PSAT). Ideally, you would want to see some yellow,
orange, green, and blue colors on your display (sensor pad) before calibrating. You may need to
adjust the physical sensor for a more or less sensitive pressure range in order to find the ideal range
for the application.
Overall System Accuracy - +/- 10% of full scale (~ labeled saturation pressure on physical sensor)
Material Dependency - Do not assume that +/- 10% of the labeled PSAT on the
physical sensor will give you overall accuracy, since the sensor pads are very material
dependent. Different durometers will offload unlike a flat piece of steel; Sensel offloading
is dependent upon the % active sensor area Vs. % inactive sensor area.
Pressure Measurement Resolution – [ Saturation Pressure (PSAT) / 255 ]
Cal Files – You may generate and save many cal files for a given sensor and can load those files in
the future as long as you apply the cal files to that same physical sensor with which you calibrated and
recorded.
Sensor Calibration Notes cont.
Pressure Color Legend – Ensure the pressure legend is Open and set to full scale (0 to 255)
before calibrating or simply for testing to see if the sensor PSAT range is suitable.
Load Frame - Ensure the load frame (e.g. Inston, Tinius Olsen, etc.) is calibrated
and the plates load in a parallel manner.
Multi-Tile Calibration -If a multi-handle system (e.g. four handles each with their
own sensor such as four 5051 pads) is being used, one may calibrate each sensor
individually or calibrate all four simultaneously. If a four pad sensor is being used
(e.g. 6900 model), one may calibrate each sensor pad individually or calibrate all
four simultaneously. Requires Tekscan software version 5.10 or later.
White lines (‘boxes’) in Calibration Dialog Window - Where the white lines / ‘boxes’
intersect the calibration curve represent(s) the average raw(s) in the calibration point(s); this
is true whether it is a single or two-point calibration.
Single Point Calibration - Uses the following equation:
Digital Output
----------------------- =
# of Sensels Loaded
(Global Scale Factor) * Entered Force
-------------------Area Loaded
Typically implemented when the application’s range of loads to be measured is small
(within +/10% of the calibration load) or when the maximum load is small (< 500 to 1000
psi)
Typically implemented when system is linear; the system is linear if the sensor digital
output difference between each loading increment is similar.
Calibration Force -Calibrate at a pressure which reflects the working pressure / pressure of
interest in the application. For example, it is not recommended to calibrate at 100 psi when
you are interested in data at 10 PSI. One should select a sensor’s full scale range which
allows enough headroom for unexpected pressure peaks. Take the area into consideration
so the calibration pressure is similar to the actual application pressure.
The single-point calibration is good for ~ +/- 20% of the single calibration point.
The white line(s) in the calibration dialog window graph represent(s) the average raw output(s) of the
calibration point(s).
Two-Point Calibration – Typically implemented when application is non-linear and /
or when a wide pressure range of interest is required (~ > 1000 PSI). The two-point calibration
utilizes a sophisticated algorithm which accounts for distribution through a ‘histogram’ method.
The two-point algorithm includes zero load to solve for the two constants in the exponential Power Law
equation. Y = Axb
Y = force / load
A = scale factor
x = digital output (raw value)
b = constant, determines slope
Equations implemented:
Force 1 = [n1 * 1b + n2 * 2b + n3 * 3b + … + n255 * 255b]
Force 2 = [m1 * 1b + m2 * 2b + m3 * 3b + … + m255 * 255b]
n1 through n255 = # of sensels with digital raw values of 1…255 in the first cal point
m1 through m255 = # of sensels with digital raw values of 1…255 in the second cal point
The iteration for “b” occurs ten times; the iteration is topped if Force 1 / Force 2 is “close”
to:
[n1 * 1b + n2 * 2b + n3 * 3b + … + n255 * 255b]
-------------------------------------------------------------[m1 * 1b + m2 * 2b + m3 * 3b + … + m255 * 255b]
When “b” is solved, it is substituted back into each of the two equations in order for constant “a” to be
solved. If the system is linear, the value of “b” will = 1. If the two pressure distributions are too similar,
“b” is not solved for very well. The two pressures need to be three times apart from each other.
The DIFFERENCE between [ Force 1 / Force 2 ] and [nx^b / mx^b] should be < 0.001
Two-Point Calibration cont.
Two Loads / Forces – must be known and must generate different pressures; if the pressures
of the two applied loads are too close to each other, the algorithm may not function.
A rule of thumb is to have the two pressures be ~ three times apart. Do not saturate sensels
during calibration (saturated sensels are technically red-colored sensels with a value of 255;
I recommend no red-colored sensels present during calibration). The algorithm “blows up”
when the exponent (“b”) > 4. Typically, the Exponent, “b”, is > 4 when a nonlinear material
is used such as a rubber ‘puck’. A rough guideline for selecting the two points are 20% and
80% of the actual force; ensure you do not have saturated sensels (red colored sensels).
Note: “b” (exponent) values may be found @ Options  Settings  Calibration 
EXPONENT 0.5 to 2.0 is a reasonable (real life) range for “b”. If “b” values are
< 0.5 and > 2.0 one can be suspicious. “b” values of 2.0 for a uniformly loaded
sensor with a moderate Digital Output could be OK.
Histogram – Each of the two equations break out the distribution of data. For example,
100 sensels at 100 digital output, 50 sensels at 101 digital output, 33 sensels at 102 digital
output, etc.
Calibration Window Graph – In the graph, the calibration curve may not pass through
both calibration points due to a possible histogram shift; the mean is not always equal to the
mode / median.
Two-Point Calibration cont.
- Tare feature (located in calibration dialog box): Large tae values coupled with a non-linear calibration
will cause errors. There is not an issue for a single-point linear calibration. 3% min. of sensles is required.
- Changing Areas When performing a two-point calibration, one may experience that the second load is
similar in pressure to the first load due to the fact that the area increased as the second load point was
applied. This will result in an Error Message saying the Two-Point Calibration failed.
- Varying Loads in the same recording Example: Railroad Tie Plate : Rail Interface application.
The locomotive will impart a higher force than the passenger cars since the locomotive is much heavier.
Your Force Vs. Time graph will have similar passenger car peaks and a much higher locomotive peak.
Post Calibrate – use similar material interface, temperature, and timing if possible on a load frame
(MTS / Instron, Tinious Olsen, etc.) for imparting the calibration force. Your options are:
One-point calibration at the high peak
One-point calibration a low peak
One-point calibration; [average of low peaks] and [single high peak]
Two-point calibration; try one point at a low peak and the other point at high peak
Two-point calibration; [average of low peaks] and [the high peak itself]
OR
Repeat test with one sensor full scale pressure range suited for the passenger cars (all similar force
peaks) and another sensor suited for the locomotive. You would perform the test twice in the same
assembly; one time with a sensor range for the passenger cars and the next time with the sensor suited
for the locomotive.
OR
Insert the two sensors in the assembly in their respective interface (so not to have to reinstall second sensor if sensor
installation is time consuming or difficult. Determine if stack-up of two sensors (` 0.008”) will affect test. Take one
recording which captures both high and low peaks. Use Edit feature to cut the high peak portion from the reocrding.
Save. Take another recording which again will capture the low peaks and the higher locomotive peak. Use Edit feature
and cut the lower peaks (passenger cars) form the recording.
 Sensor & Application Tips / Software Features
- Lubrication may be achieved for shear force reduction via baby powder,
–
–
–
–
–
–
–
–
–
–
–
teflon paper, spray lubricant.
Peel sensor protective layer before using the 6220 / 6230 sensor models
Implement a sheet of regular paper, clean room wipes, or possibly silicone foam
when measuring between two metal plates. Spacer should not be too thick.
Use 3M’s Adhesive 77 when fastening sensor to a surface. Spray evenly and
lightly. No clumps should be present or a pressure artifact will exist.
Prevent sensor connector bank from getting caught inside handle by peeling
protective layer back from near connector bank assembly
Minimize sensor wrinkling and sharp bending as this will introduce artifact and
prematurely wear the sensor.
Right angle in application: use two sensors
Clean sensor after use by wiping down sensor after each application with a damp
rag / alcohol and store safely and flat (horizontal for large sensor pads) at room
temperature in a protective case.
Measure from several sensor pads with a single handle by positioning sensor
pads between a mating surface and measured one at a time by clipping and
unclipping the sensor handle down the line while taking a SNAPSHOT while
connected to each sensor pad.
Rectangular-shaped sensels are well suited for line contact (nip / pinch) – Pounds
per Lineal Inch (PLI) and Square-shaped sensel for area contact (PSI).
Shims may be used if the hard : hard interface overhangs the sensor
Applications using vacuum: our software was not written for resistance levels > 5
Mega Ohm. If vacuum causes a material to compress onto our sensor there may be
a possible correlation.
 Sensor & Application Tips / Software Features cont.
-
Placing one sensor model (PSAT ‘A’) on top of the same sensor
model (PSAT ‘B’) in order to obtain the best possible pressure
measurement resolution for an application which has a wide range is
typically not done, rather two sensors, each with a different PSAT, are
implemented separately.
Dynamic seating applications such as a foam automotive seat whereby a driver
is driving at a fair rate of speed over bumps, have many variables such as,
foam density, seat design, sensor deformation, non-linear material behavior
on our sensor, and data sampling speed up to ~ 225Hz. Further testing at the
customer facility is required for this type of application.
- The % of sensor inactive area (dead space) VS. the % of sensor active area
will influence how non-linear materials behave (e.g. rubber material such as a
mouse pad durometer). A sensor with a large active area and a very small inactive
area will yield more force output than a sensor pad with a smaller % of active area
and a higher % of inactive area.
- If tape is used to secure the sensor, be careful not to tape over the active region of
the sensor since a pressure artifact will be created.
If you trim the sensor, protect the exposed inner portion of the sensor from any
dirt or liquid from entering the sensor. Usually a piece of tape works well.
- A ‘horse pill’ may be implemented to protect the sensor from water / drop
damage; the ‘horse pill’ is a plastic capsule which may need to be fabricated with a
Dremel / Roto Zip tool.
Sensor & Application Tips / Software Features cont.
-
Nip / Pinch (roller) applications - If the line contact is narrower than the
sensor pad row and a flat plate calibration is performed, strange results most
likely occur. So, it is recommended to calibrate with a line contact and ensure
the calibrated row is placed under the nip for the measurement. If nip is wider
than the sensor pad row, calibrating with a flat stock to obtain statistically
representative data is suggested.Calibrating on one region of the sensor and
measuring from another region will compromise results / performance.
Sensor models 5501, 5560, 5570, and 5580 have wide rows (roller contact
should fall within this wide row). Force will be accurate; however, pressure
will be inaccurate since the load is a narrow line.
Example: 5580 has a 1/8” wide nip loaded on itself in the machine direction.
The row spacing is 0.54” and column spacing is 0.24” which gives a sensel
area = 0.1296 square inches. A sensel reading of 20 PSI yields a force = 20 PSI
* 0.1296 square inches = 2.592 lbs. This force acts over 0.24” (axis direction)
yielding 10.8 PLI. The force acts over 0.125”, which is 1/8”, in the machine
direction giving an average pressure of (2.592 lbs.) / (0.125” * 0.24”) = 86
PSI. Most nip pressures have a peak pressure twice that of the average
pressure, so about 172 PSI would be the expected peak pressure. Utilizing nip
sensors with a high spatial resolution (e.g. 5526) most likely would be a better
choice for narrow nips.
Nip / Pinch (roller) application example cont. –
Curved Contact Surfaces may be measured with Tekscan’s sensor models 6900,
9801, or 9830 since they have narrow sensing areas which lend themselves to
positioning on contoured surfaces with minimal artifact generated from the
geometry. Other sensor models will detect side forces generated as in an
automotive or office chair with side bolsters. Tekscan sensors respond to the
individual local normal forces, thus a seat design whereby side forces are
generated will contribute to the total load the sensor reports even though the load
is technically not perpendicular to the sensor.
Sensor & Application Tips / Software Features cont.
Using Sensor in a Wet Environment – I have found a ‘Horse Pill’ capsule
which will assist in wet environments.
Using Sensor on a Contoured Curve – Tekscan has designed narrow sensors
(‘fingers’) such as the 6900 and the 9801 / 9830 which lend themselves to
contoured surfaces in that the effects of the curve are minimized.
ASCII Data – May be exported very easily in two different formats
Web Demo – Allows Tekscan to run our system while a prospect views the
computer screen of the Tekscan engineer giving the web demo
Verify Pressure Pattern – Rotate sensor pad and if ‘anomaly’ follows sensor
then it is a ‘bad’ sensor. If ‘anomaly’ stays in the same location, then it is from
the part being tested
Virtual Maps - In order to create a real-time window with a virtual map in our
software, you definitely need to have as many handles connected as are required for the
virtual map.
Group Recordings – Allows recording of groups of frames as a single
‘movie’ using multiple start and stop events.The software will continue to
stop and start recording based upon the selected triggering events until
manually stopped or frames specified is reached.
Sensor & Application Tips / Software Features cont.
ASR (Automatic Sequential Recording) – Allows a new recording to
automatically start when the current one is complete, without the need to manually
open new real-time windows and start new recordings. The software would
automatically save and close the current movie, open a new Real-time window,
and begin a new recording. This will continue until stopped manually or until the
total frame count is reached.
Drift – The sensor exhibits drift with an applied constant load. The drift is ~ 3%
per log time. If a 100 pound load is applied to the sensor, after 1 second the load
would read ~ 100 pounds, after 10 seconds the load would read ~ 103 pounds,
after 100 seconds the load would read ~ 106 pounds, and after 1000 seconds the
load would read ~ 109 pounds.
Since most drift occurs at the beginning of the loading period, it is suggested to
calibrate ~ 30 seconds after the load is applied or longer. Impact loads (High
Speed) may be calibrated after the recording with our Post Calibration software
feature.
Sensor & Application Tips / Software Features cont.
TARE Feature – Only works after a single-point or a two-point calibration has
been performed. Allows user to Tare out undesired preload. Ensure the two points
in the two-point calibration are close to linear. 3% minimum of sensels is required.
TARE Example: 3” diameter (circular) image is the preload whereby all 200
sensels which comprise this circular image are all blue in color (assume the same
shade of blue thus the same raw count for each sensel). I wish to TARE all 200
sensels, that is completely remove them so they do not factor into my
measurement calculations. Assume each of the 200 sensels have a raw count value
of 40. A TARE will reduce the value of each of the 200 sensels. Since the max
output of each sensel is 255, the reduced value of each of the 200 sensels will be
255 – 40 = 215. 215 becomes the equivalent of ‘255’, thus 215 is the ‘new’
saturating point for the 200 sensels.
Pressure Measurement Resolution The I-Scan handle has an 8-bit A/D converter
which offers 255 discrete levels. Pressure measurement resolution is differnet for
each sensor pad. For example, a sensor with a saturation pressure (PSAT) of
200 PSI, will yield a pressure measurement resolution of 200 / 255 = .784 PSI /
Digital Output. The vertical Pressure Legend (color bands) consists of thirteen
colors; each of the thirteen colors represents all 255 levels of a sensel thus each
color will have a range of values.
Sensor & Application Tips / Software Features cont.
Sensor Turn-On Threshold – Tekscan software is factory default setting for
noise threshold is 3 digital raw counts (out of 255). If a significant amount of
random noise present, it is recommended to increase the lower limit (field) in the
Pressure Color Legend. The noise is captured in the recording but will not be
displayed; the Pressure Color Legend is a ‘visual filter’. The TARE function can
remove any preload or pattern seen from the displayed image.
Sensor Turn-ON Pressures
Full Range
Press Meas. Resolution
Turn-ON Pressure
5 PSI
25 PSI
250 PSI
2,500 PSI
Depends upon sensel size
0.3 PSI
3 PSI
30 PSI
0.02 PSI
0.1 PSI
1 PSI
10 PSI
Sensor & Application Tips / Software Features cont.
Shim Stock – Can minimize the effects of shear forces. A rubber block being loaded onto
our mylar substrate sensor which in turn sits on a solid metal surface would tend to impart
shear force and could damage the sensor in addition to yielding erroneous sensor data. Shim
stock, such as Lexan (.005”.010”,.020”) Teflon paper, loose leaf paper or a thin piece of metal foil
(stainless steel / beryllium copper), will offer more consistent sensor output. Calibrate with the same
shim stock material as in the application. (Note: http://www.gelexan.com/gelexan/features.html)
Another example is our sensor pad inserted between two metal plates; without any shim
Stock such as a piece of paper, the sensor would most likely report more pressure peaks than
if a piece of loose leaf paper was inserted in the interface. The piece of loose leaf paper
would maintain the integrity of the pressure distribution pattern while filling in the ‘valleys’
thus ‘smoothing’ the ‘peaks’.
Sensor Protective Cover – Most Tekscan sensors are constructed from two 0.001”
mylar substrates and have a total thickness of ~ 0.004” +/- 0.0002”. Most sensors are also
shipped with a 0.001” mylar protective layer which can add life to the sensor due to the extra
protection it offers; it is recommended that the calibration includes the protective cover as
well. Exception: Model 6220 / 6230 should have the protective mylar shipping cover
removed for calibration and measurements. The cover has an adhesive and release agent
on the sensor side; if a high load is applied, the cover may “set” in certain areas which can result in
artifact load, that is load contributed by the cover itself. The added 0.001” thickness of this cover can
cause the sensor to get caught inside the handle on the pogo pins; if pulled out, pogo pins will be
damaged. Fold the cover back so it does not insert into the handle.
Sensor & Application Tips / Software Features cont.
Saturating – If a sensor is loaded beyond its PSAT (labeled saturation pressure, which is a
guideline since the material interface Tekscan tests with may be different than the
customer’s material interface. The PSAT is a saturation pressure guideline. The best method
to determine if the standard sensor PSAT is suitable for the application is to load the sensor
in the actual application and set the vertical Color Pressure Legend to 0 to 255, which is full
scale uncalibrated. The color image on the computer display should not be all blue in color
nor al red or mostly red. There should be a mix of colors (some blues, greens, yellows, and
maybe orange and brown).The average Digital Output should be ~ 220 which allows for
pressure headroom for any pressure peaks. Reading from a sensor with a display of
mostly red or all red does not leverage our thirteen colors in our Color Pressure Legend
scale.The thirteen colors assist in resolving the pressure into different levels. If a sensor is
pierced, cut, severely sheared, wrinkled, creased, or repeatedly bent in the same location,
the sensor will exhibit an electrical open and / or electrical short or may simply report
artifact pressure.
A sensor should be inspected visually and after connected to the sensor handle to ensure no
damage exists and that it is working properly. Pressing by hand or using a load frame to test
if all sensels are reporting is common. A blank column or row may be corrected by reseating
the sensor in the sensor handle.
Sensor & Application Tips / Software Features cont.
Cutting Sensors – Some sensors lend themselves to being cut, that is some sensor
designs allow for removing part of the sensor with an exacto knife, hole punch, or
scissors resulting in no loss of data from the physical sensor region left after the
cut. Sensor models 62220 / 6230 lend themselves to being trimmed from the
inside outward in order to accommodate sliding the sensor over a bolt or part
diameter.
Model 5250 may be cut to be 5” x 10” based upon its electrical trace routing.
Each sensor would be treated differently; sometimes it is easier to cut the sensor
and insert the sensor into the handle and view the screen image when the sensor is
loaded.
Sensor & Application Tips / Software Features cont.
API (Application Programming Interface) – Tekscan offers a product, API 2 ,
which is a High Level interface and is outlined below:
Requires Tekscan software version 5.X
Writes equilibrated and calibrated data to a buffer for user program access
API 2 is an add-on software module
API 2 may be programmed with C++
Customer would write their own programming code using Tekscan’s library of commands
API 2 is built into I-Scan’s top level (high level interface)
API 2 is capable of exporting Real Time data
LabView compatible (LabView has its own DLL (library) / user procedure)
LabView can be written such that LabView “grabs” data from Tekscan sensor pad / software
continuously by setting up a loop
API 2 allows Tekscan’s software to send data to Client’s computer as well as allow Client’s
software to “grab” data from Tekscan software
Note: The DLL performs the job of communicating; transferring collected data from the
Server (Tekscan) to the Client (customer) computer.
The DLL may be loaded into the customer’s software to serve as a convenient bridge for graphing and
transferring sensor data from Tekscan software to Client’s (customer’s) software
The customer can modify Tekscan’s sample DLL (Fsx User)
Microsoft Com is a protocol which may be implemented to transfer data from Server to Client via custom
/ commercial software
Can be used with a RealTime window or a recording
Quick Start Check List
Connect all Tekscan hardware to computer before starting-up computer
Ensure all connections are secure
Ensure proper sensor is selected for application
Proper shape, size, spatial resolution, and full scale pressure range
Test PSAT selection for proper range / best pressure measurement resolution
Determine if a “shear protector / load transmitter” is required
E.g. metal foil, teflon paper, piece of mylar, piece of loose leaf paper
Start-up computer
Launch Tekscan from Desktop / Windows Explorer
If you receive handle not found error message, reboot or try downloading latest
software driver from our website: www.tekscan.com  Support. Call Tekscan
at 800-248-3669 and ask for Technical Support or call Vince Carrara x 268.
Ensure you know how sensor is physically orientated in the application
e.g. determine sensor’s physical orientation with respect to the computer screen image
Equilibrate if Tekscan equilibrator is available or if a custom produced one is available
Calibrate while ensuring material interface, temperature, and timing are similar to the
application . Save recordings. Post analysis.
Embedded Video Capture
Minimum Required Hardware :
DV (Digital Video) format camcorder with FireWire (iLink, or IEEE1394) port.
Desktop computer:
FireWire PCI card
Notebook Computer:
PCMCIA card with Firewire
Firewire cable:
Usually shipped with Firewire card
Processor Speed:
600 MHz Intel Pentium III or AMD Athlon 600 Mhz
Note: Sony’s newer proprietary Micro MV format is not supported.
Required Windows Operating System :
Windows 98 SE
Win ME
Windows 2000
Windows XP
Steps for Capturing Real Time Video and Synchronizing
1)
Plug in FireWire to camera and computer FireWire Card
2)
Turn ON camera
3)
Aim camera at desired area for video capture
4)
Open Real Time window
5)
Select “Capture Video” button (camcorder with three lines in front of lens icon) on
tool bar to open a Real Time video feed from camcorder lens
6)
Check to see if “Movie Recording” button (sensor handle / camera icon) is selected
7)
Select “Record” button (red diamond icon – Main Toolbar) which will record both
the sensor data (.fsx file) and the Real Time video feed from the camcorder lens.
8)
A playback window will automatically open when the recording has been manually
stopped or the frame count has been reached
9)
Select “Separate Movie / Video” button (two white sheets moving apart icon)
10)
Use play forward and play back buttons (video window) in order to
determine by eye the best synch’d sensor image with video.
11)
Select “Synchronize Video” button (two rectangular blocks moving in
opposite directions icon)
Note: Canon brand camcorders tend to slow the refresh rate on a Real Time
Tekscan display.
Note: You may playback the video either from the Main Toolbar or from the
Video window. If you play from the Main Toolbar, then you need to
stop from the Main Toolbar. The same for the Video window.
Note: The playback speed from the Video window is fixed at 30 Hz. The playback
speed from the Main Toolbar is adjustable under “Playback Speed” pulldown icon on the Main Toolbar.
Note: Playback Speeds
Fast – ~ 1000Hz or less depending upon computer processor speed & # of sensels
Midfast - ~ 33 Hz
Normal - ~ 18 Hz
Midslow - ~ 3 Hz
Slowest - ~ .5 Hz
Note: Right mouse click on the video window for playback options such as
“Repeat Forever”, sound volume, etc.
Video Synch Tips
Example: Motorcycle rider is a the test person say for a seat comfort and person with video camera
is away from track (sidelines). The rider can stand on foot-pegs and then sit quickly onto the
sensor. Repeat a few times. Then one can synch the video with the Tekscan recording.
Example: F-Scan Mobile product. Subject can switch from left to right foot (marching in place) or better
yet, jogging in place. This will allow a synch of the video and the Tekscan recording.
Video Capture with Four Camcorders –
Description:
Four camcorders could input (analog) separately to a Quad Processor and Switch unit; this unit would
be processing in Real Time. The Quad Processor and Switch unit would send a single analog output
signal to a Converter Box (analog  DV format). This converter would send out a continuous image
from the camcorder lens as a single DV formatted signal to the computer. Tekscan software can accept
a single DV formatted signal. A Firewire card as well as Tekscan software version 5.20 are required.
A quad screen (four images) would appear on the computer screen.
Analog to DV converter –
Video Miscellaneous
A computer screen refreshes ~ > 70 Hz (good for the human eye)
A video camera refreshes at ~ 30 Hz. (NTSC)
Note: European (PAL standard, 25 Hz)
A slight video delay exists on computer screen due to the nature of FireWire
Tekscan DV capture utilizes Microsoft libraries
External Trigger / Synch Hardware Box
Trig / Synch Box
External Triggering – Customer can build their own trigger circuit or purchase Tekscan’s Trigger Box
The Trig / Synch Box can accept an External signal generated from customer’s equipment which triggers
Tekscan’s software to begin a recording.
Synchronization – This unit can send a signal out to a few pieces of customer equipment to establish
Time Zero with Tekscan’s .fsx recording
COM Port Synch
Synchronization Triggering Only Software – Allows Tekscan to send out a pulse to an external
device after each frame (need an oscilliscope to read the signal) May be accomplished simply through the
COM port. Tekscan software must be enabled for external triggering through the COM Port.
External Triggering refers to an external piece of equipment sending a signal to the computer on which
Tekscan software resides. Synchronization refers to Tekscan sending out a signal to an external device.
Video Synch Software
Required if customer would like to synch captured video (Mini DV format) with Tekscan .fsx recordings.
Requires Tekscan software version 5.20. Also, helpful if customer wishes to synch data from a force
plate.
Miscellaneous
Tekscan has tested sensor pads up to 24 V DC.
Parallel System: Adjustable Gain does not amplify the signal but rather changes the
resistance.
Piezo refers to a device which discharges; Tekscan can measure both Static and
Dynamic pressures / forces. Discharging is not part of our technology.
Flexiforce (single button sensor pad, 3/8” diameter standard) is a passive device with an
analog output. Our example excitation circuit will output 0 to 5 VDC. Another excitation
circuit could be made whereby 4 to 20 mA is the output.
High Speed sensor pad 9550 has one driven trace (serpentine) and 42 sensed traces;
the electrical routing plays an important role in maximizing the data sampling.
Wireless pressure mapping devices currently transmit less data throughput than Tekscan
non-wireless
Our sensor data is conditioned (smoothed) before it is converted to a digital signal
Miscellaneous
Application pressures < 1 PSI, may still be able to utilize Tekscan’s system;
it is recommended that you focus on ‘trends’ in the pressure patterns in application
pressures less than 1 PSI.
Sensor Carrying Case
Miscellaneous
Increasing the voltage (semi-conductive ink) or increasing the resistance will make the
sensor more sensitive
ELF Adjustable Gain should be set such that the dynamic range should be ~ 80% of the
range
The Trigger feature works on the sum of raw sum of two Real Time windows if two are
open
Calculating sensor dimensions:
Example: If you wish to have 0.025” spatial resolution in both X and Y directions and
one direction of the sensor needs to be 0.200” 
0.200” / 0.025” = # of rows = 8
52 columns max wide X 0.025” = active width of sensor = 1.3”
Sensor Screen Printing (block style): There are some cases where a sensor design requires
block printing (ink is deposited in a single swath) and the electrical traces are matrixed.
Some sensor designs are ‘block’ printed on both substrates while other designs are ‘block’
printed on one substrate. ‘Block’ printing can be an issue if the saturation pressure is too low
(cross talking). ‘Block’ printing is dependent upon a few variables such as sensor geometry,
sensor size, sensel size, saturation pressure, active area : dead area ratio, and electrical trace
width. ‘Block’ printing (one substrate or two) may be required if pressure shorts occur
with a normal stripe (rows and columns) printing design. ‘Block’ screen printing is on a
case-by-case basis.
Batch converting .FSX files to ASCII files: Windows scripting may be an option whereby
A script would open each .fsx file (Tekscan ‘movie’) in our software and run the Save
ASCII feature on each file and then close the file.
MatLab may be able to do this.
If Tekscan could write software to accomplish this for New Product fee.
Miscellaneous
Spray Nozzle applications: spray nozzle fluid onto sensor for 30 seconds minimum
to
ensure most of the sensels have had time to register a value (impact)
Seating Applications: (Other forces at work)
Most end users perform a two-point calibration with our bladder out
of convenience and repeatability of a uniform load (pneumatically loaded 0.025” urethane).
The materials of the bladder do not mimic a person’s / water dummy’s / regular dummy’s
buttock and the car seat; the bladder’s mating surfaces are either metal / wood and pliable
urethane. A person sitting in an automotive seat involves pliable buttocks and usually a foam
seat (foams vary in their densities). Our sensor measures compressive forces which may be
imparted in the vertical and / or horizontal position depending upon if the seat has side leg
supports and / or thigh supports. A luxurious seat imparts side forces which are recorded by
our sensor. Our sensor does not measure shear forces. A two-point calibration requires our
pneumatic bladder assembly.
The two calibration points typically used are .5 psi and 2 psi
Compressive forces from side supports will tend to ‘add’ body weight; however, Force
reported in lower right-hand corner of Real Time window or “movie” window will typically
be more or less than actual person’s body weight.
Two-Point Calibration for Seat Minimizes Error:
Railroad Train [Rail : Plate ] and [Plate: Tie] Application:
Note: Locomotive and passenger cars passed over a section of track under which Tekscan
sensors were positioned; one sensor was inserted between the rail and tie plate and the
other sensor was positioned between the tie plate and the tie (wooden).
The passenger car pressures on our two sensors were similar compared to the higher
magnitude of the locomotive pressure due to its heavier weight.
It is a good practice to cover the top and / or bottom of the sensor pad with a thin yet
strong shim material such as General Electric’s Lexan which will help protect the
sensor from punctures / tears due to high pressure imparted over uneven surfaces.
With respect to calibration, one option is to perform a two-point calibration;
one point could be the average of the similar passenger car amplitudes (forces) and the
second point could be the amplitude (force) of the locomotive. Calibrate with the same
shim stock as used in the measurement.
Ensure you are covering as much of the contact surface as you can with the sensor
pad. Also, ensure the full scale pressure range (PSAT) of the sensor is suitable for the
measurement.
Tekscan Train Pressure Images:
The lower peaks are the passenger cars and the higher peaks are the locomotive.
Tire Bead:
It is important to determine if the proper full scale pressure range has been selected.
Use WD40 to clean wheel of any grease
Use a soap solution to lubricate the tire bead itself and the top surface of the sensor.
Use duct tape to adhere the sensor pad to the wheel; do not tape on active area of sensor
5101 at 0 – 2000 PSI is a good sensor to begin testing; the sensor was cut in half (parallel to
the sensor neck) and the cut was taped so no soap solution would migrate into the active
Area. The sensor was cut to minimize crinkling due to the compound curve
If you are filling the tire instantly (“Cheetah” tank), make sure the fill tube is on the
opposite side of the sensor location or the sensor may tear.
If you are using a ‘air ring’ too fill the tire (slow fill), tape the holes which are in line with
sensor so the air will not move the sensor out of position.
Wear ear protectors in case of a tire blow-out
Catalytic Converter Canning:
Clamshell
Turnicate
Canning / Stuffing
– two halves (top and bottom)
– one seam ./ single piece
– brick with vermiculite blanket wrapped on it is stuffed into a single
piece can
Ensure the proper full scale pressure range has been selected for the application by setting
the color pressure legend to its full raw scale 0 – 255, 0 being the bottom field and 255 being
the top field. Then position the sensor in the application and load to determine how much of
the full raw scale of the sensor pad you are actually using. A good rule of thumb is to have a
mix of colors such as blues, yellow, green, and possibly brown and some reds. You do not
want to see all red or all blues.
Some canning applications have a full scale range of ~ 0 – 50 psi while others are ~ 0 – 350
psi.
Leaving the protective layer on the sensor will improve sensor durability; however, test the
sensor with and without the protective layer to determine if there is a significant difference
in sensitivity.
Miscellaneous
Poisson’s Ratio:
Ratio of strains
V = E transverse = ratio of transverse contraction strain to longitudinal extension strain
--------------in the direction of the stretching force.
E longitudinal
V is typically negative (compressive). Tensile is positive.
Stress = Force per unit Area = F / A = lbs. / in.^2 = PSI
Miscellaneous
Young’s Modulus:
E = Stress = [ F / A ]
= [ F / A ] * [Lo / Delta L ]
-----------------------Strain
[Delta L / Lo]
Note: Lo = equilibrium length
Foams:
Impact Foams
Flexible PVC foam 5230 / E = 100 kPa / Poisson’s Ratio = V = 0.5
EVA Foam (ethylene vinyl acetate) – Density = 30 kgm^3
Foam Blend – ESI (40% Dow ethylene styrene interpolymer / 60% lower density
polyethylene). Density = 53 kg / m^3