The Electronic Thimble Algometer is made of a force sensing resistor (FSR by INTERLINK ELECTRONICS
also distributed by:Trossen Robotics
or an other type FSR with totally different characteristics: FlexiForce Force Sensors by TekScan
taped to the user's index finger before putting on a surgical glove (Notes on Interlink vs Tekscan FSR's
Any pressure applied to the finger is sensed by the resistor the resistance of which is sent to an IBM compatible computer through a USB port LabJack U12
data acquisition device. A quick calibration by means of a second force sensor (a load cell mounted with a muscle mass simulating foam) permits the user to ascertain the validity of the force readout each time the FSR is repositioned on the finger (see Calibration below
The software collects the data into a table and
can send them simultaneously to Microsoft Excel
. The data can also be
saved to a disk file
independently from Excel. New in 2008, the data are also automatically saved to
with a preset name whether or not the user needs them. In case of power failure or other malfunction,
the data can be retrieved from these log files.
To zero the strain value before a measurement is made the user can press the computer keyboard 'Z' key, or set the "Automatic Zero" option to "on" ,which
causes the strain reading to zero automatically at the end of each Inter Trial Interval (ITI).
The keyboard 'R' key can be used to reset any previous offset back to hardware baseline (not normally useful, but could be an indication
of a malfunction or need for adjustment, should a large pressure reading result).
A "Subject" switch, a "User" switch or the computer keyboard space bar can be used to store the current strain value into the table on the program main
window. If the space bar or the "User" switch are used, an asterisk is added after the strain value to indicate that the subject
did not respond to the applied pressure.
When starting, the software is in setup mode. A panel of setup controls is then visible. These controls must be used
to edit three groups of options:
|2 - The Experiment options: the "Site" columns of the table
(for more info on setting up the test options).
|3 - To change the switches, voice, auto zero options, and whether the peak force or current force
is to be recorded. This panel can also be used to test the "User" and "Subject" switches: when the corresponding switch is depressed, its
label background color turns green. If the FSR is made by Interlink, its plug has a code circuit to identify it. A label on the options
panel will display: "FSR by Interlink". If no code is present the label will read: "FSR by Tekscan".|
This panel can also be used to enable or disable the "Maximum strain reached" audio notification feature, and set the value at which it is activated.
- Subject and User switches are automatically disabled by the program if they have been disconnected
or have become defective. Once repaired and/or reconnected they can be enabled through this option.
The switches can also be disabled through this option if desired, at any time the keyboard space bar can be
used in the place of the "User" switch.
- Voice. When the computer voice is enabled, the computer will call the next location
to be tested so the user does not have to look at the display when random sequences are used.
- Auto Zero. When the computer voice is enabled, the Auto Zero can then be enabled to have the program automatically
set the zero offset at the end of the ITI, at the same time the next test site is prompted.
- Current or Peak Force. The force that is being saved can either be the maximum force that was detected during the trial:
"Peak Force", or the "Current Force" that was detected at the time the switch was depressed.
- "Reached max." notification. When checked, this option will cause an audio warning to sound, and the trial to be interrupted when the strain has reached the value
in Newton showing in the text box labeled: "Newton". The audio sound is a "wav" file called "ReachedMax.wav" that must be present in the application folder
with the other sound files: "0.wav", "3.wav", etc. Any wave file renamed: "ReachedMax.wav" can be used.
Clicking "START" switches to "Run" mode and after a delay equal to the set "Inter Trial Interval" and if the "Voice" option is
checked on, a voiced prompt calls for the first site to be stimulated.
Pressing the subject switch (if the subject switch option is checked on), the user switch (if this option is checked on) or the computer
space bar will cause the pressure reading to be stored into the "Test #" column of the table and the next ITI will start. If the peak force option is selected the
force stored is the highest force detected since the end of the last ITI.
The "Run" mode can be exited at any time. The experiment can then be restarted for test #1 trial #1, or resumed at any user selected
trial. To select the trial from which to start, click the table cell for this trial, and then "Resume" rather than "Start".
In order to perform a blind experiment, the display tubes can individually be hidden from sight and the table can be blacked out to hide the
readings. This is done through the menu "View" options
The "Force Sensing Resistor" (FSR) that fits on the finger has an estimated life of approximately 6 months depending on usage. Three FSR's are supplied with the unit but, once they are all used, it is the responsibility of the user to replace them. The FSR's can be purchased from the
Digi-Key Corporation. Their part number is: 1027-1001
Anyone familiar with soldering can easily attach the new FSR to the existing cable making sure not to apply excessive heat to the FSR plastic backing (It is recommended to use a hemostat, some pliers, or a similar tool as a heat sink). It is also imperative to insulate the exposed conductors to avoid contact with the user's hand.
- Save As
- Rename Excel Sheet
- Force Tube
- Rate Tube
- Table Data
- Sending to Excel Option
Show Raw Strain Voltage (Used for calibration)
Current Calibration Data (more info)
Thimble Calibration History
- Calibrate the Load cell
- In Edit Mode when checked
Test Setup Options (Order in which the test sites are tested)
The number of the test being setup. There are 2 tests per experiment.
. Any number of the sites #3, #6 or #9 can be specified in any order (for more information)
. Specifies that the order, in which the selected sites are tested, should be randomized.
. Specifies whether the sites to be tested should be repeated the certain number of times, by trial (each trial repeated) or by test ( the test sites are repeated as a group).
. Inter Trial Interval or the amount of time in seconds between trials.
- Save This option saves the current date, time and content of the table to the file the path of
which is displayed in the window title. If the file is still "untitled" the "Save" option is identical to the "Save As" option. If a file name
has already been assigned, then the new data is appended to the current content of the file. The new data consisting of the current date, time
and table content.
(Sample data file).
- Save As This option opens a standard file dialog window that prompts the user for a file name. It
then opens the new file or deletes and reopens the file if it already existed. It saves the header information followed by the current date ,
time and content of the data table.
- Rename Excel Sheet In order to avoid accidental erasure of Excel data when the test data are automatically sent to an Excel data
sheet, it is recommended to change the Excel default name from: "Sheet#1", "Sheet#2" or whatever your Excel version default is, to a
name of your choice. To change the name in Excel simply edit the name at the bottom left side of the
sheet. In the Electronic Thimble Algometer program you can save/add the name to the list by clicking the 'Add' button after editing the text box to the
exact same name as the one used in Excel (more info).
- Exit Before exiting the program, the user is given a chance to save the table content if it has
changed and was not saved, and the current software settings are saved to a "Defaults" file called
- Force Tube, Rate Tube, & Table Data. Any of these three data displays can be hidden
through this option. The tubes, when hidden, disappear completely from sight, but the table stays visible while its
cells color changes to the same color as the text so the data are entered but not visible(
40 KB JPEG).
- Sending to Excel Option. This option permits hiding the "Not Sending/Sending to Excel" command bar to
minimize window clutter when not in use.
(Instructions on how to send the test data to Excel)
- Show Raw Strain Voltage This option displays the Analog to Digital converter raw voltage of
whichever sensor is currently being displayed before any translation to Gram or Newton. This option can be used when
calibrating the "Calibration Load Cell". During calibration, the values thus displayed go into the X column of the calibration data, and the actual weight into the Y
column. (See Calibration for more info).
- Current Calibration Data This option gives the user a chance to inspect the current calibration: the actual
log function for the FSR, and, for the Load Cell, the X (A to D voltage) and Y (actual pressure in kilograms) values and the calculated linear
function associated with each pair of points
(See Calibration for more info).
- Thimble Calibration History. Every time the program is started, the application (Algometer.exe)
folder is checked for the existence of a sub-folder called: "CalibrationHistory". If the folder does not exist it is created
and a file baring the initials: "A-C-H-" (Algometer Calibration History) and the current date as a name is also created in this
sub-folder, in which all the calibration data will be recorded until the program is exited. When the program is started again, the new
calibration data are appended to the same file if on the same date. A new file with the new date for name is created if on a
- Displayed Sensor. The same tube is used to display either the Thimble or the Load Cell. When
displaying the Thimble the tube "liquid" is red. When displaying the Load Cell the tube liquid is green.
Calibrate the Load Cell.
Before performing a load cell calibration it is recommended to check and make sure that it does need calibration:
- Load Cell Calibration Check -
- Set the software to display the Load cell in the tube display. To do this, click on: Menu/View/Displayed Sensor/Calibration Load Cell.
The "liquid" in the tube should turn to a green color. The liquid is green when the load cell output is displayed, and red when the
thimble output is displayed.
- Click on the "Newton" label below the tube to display the strain in kilogram force.
- Place a known calibration weight on the load cell, or apply a force by means of a trusted hand held algometer, and check whether the
displayed value is the same as the applied force/weight.
- Only perform the calibration of the load cell if the reading is not acceptable.
- When done set the software back to display the Thimble output.
- Load Cell Calibration -
The load cell is a linear precision load cell, therefore a two point calibration to correct software offset and factor should be sufficient. However, the
software was designed to handle calibrations with any number of points should it be judged necessary to do so.
- Click on Menu/Tools/Calibrate the Load Cell
- You will first be informed of what to do should you want to save the calibration results to an Excel file (see below left).
- The front panel will then change somewhat (See the calibration front panel):
- The strain tube will be displaying the load cell output.
- The rate tube will be hidden.
- A calibration table will replace the trial table.
- Step by step instructions will be presented at the top left corner of the front panel.
- You will then be presented with an editable list of weights from which to chose (See below right).
- Follow the step by step instructions at the top left corner of the front panel.
- Once the calibration is completed, we recommend performing another "Calibration Load Cell Check" just in case something unexpected had happened.
- Load Cell Calibration Results -
Typical load cell calibration data are shown at right, as displayed by the software when using the menu:
"View >> Current Calibration Data >> Load Cell", and below as recorded in the defaults file: "AlgometerDFT.ini":
1=0.0100, 0.0000, 2.0795, -0.0208
2=0.4500, 0.9150, 0.0000, 0.0000
Both should be interpreted thus: the calibration function is a linear function passing through points (X = 0.01, Y = 0.0) and (X = 0.45, Y = 0.915)
which translates to the function:
Weight in kilogram = 2.0795 x the Voltage + (-0.02).
- Help on the WEB This is it, you are here.
Test Setup Options
Test # The "Test #" specifies
which test is being setup, or rather which test will be filled up with the setup selections when the "Enter" command bar is clicked. It
automatically switches to the next test after the "Enter" command is used.
- Selecting a preset group: Click the down arrow to get access to a list of previously saved groups of sites to be tested.
Click the desired group in the list. The selected group will be used by the program to define the trial sequence for the test being edited.
- Removing a group: Select the group to be removed, then click "Remove".
-Adding a new group: Type the new group into the text window above the list. You must separate the test sites with some character
other than spaces and numerals, any character will stay in the list display but will be ignored when transferred to the table. The newly
defined group can then be added to the list by clicking the "Add" button. If not "Added" to the list, this new group can be used but will
not be saved for use at a later date. The groups are automatically placed in alphabetical order, and , if preceded with a name can more
easily be retrieved if the list becomes long enough.
Randomized When this option is checked the sites in the selected group are randomized.
Repeat Mode Three options are available: 1-each trial is repeated , 2- the whole group is repeated as
a unit, 3- no repetition, the sites are only tested once. In the example, Test#1 was repeated "by Trial" and Test#2 was repeated "by Test"
ITI Each test can have a different Inter Trial Interval that is specified by typing a time in
seconds into the ITI text box.
Once all the options are selected, clicking the "Enter" bar will make the computer fill the trial sequence into the table and save the ITI.
The FSR resistance is sensitive to the curvature as well as the pressure applied to the sensor.
This is the reason a foam, simulating the tested object is used as an interface between the calibration load cell and the FSR.
In order to properly use the algometer on a different surface, it is imperative that the foam be changed to one with characteristics closer to the new object to be tested
It is the responsibility of the user to find such substitute and affix it to the calibration load cell apparatus.
Attempting to test the system accuracy using any other force producing device such as another algometer or scales is futile unless the same type of interface is used between the two units.
The accuracy of the "INTERLINK ELECTRONICS" force sensing resistors and their stability are somewhat questionable (
FSR publication p5 and
FSR publication p6).In order to ascertain the validity of the measurement a quick
re-calibration is needed each time the FSR is placed onto the finger or any time deemed necessary. A second force sensor, an
LC8100-200-10 load cell is fitted with a layer of plastic foam to simulate the muscle mass.
Pressing the FSR onto the load cell foam causes the software to take a series of samples of both, the thimble FSR and load
cell force readings thus creating a translation table. The resulting best fit curve is subsequently used to translate the
input voltage from the Thimble FSR into a force in Kgf or Newton. This calibration procedure takes no more than a couple of seconds.
For this calibration to be accurate, it is necessary to ascertain that the precision load cell is itself properly calibrated.
Interlink vs Tekscan FSR's
The Tekscan A201-1 sensor has a better size (1cm in diameter) than the Interlink sensors (choice
between two diameters: 5mm and 13mm
However the main difference between the Interlink and Tekscan FSR's is their
impedances: while the Interlink FSR impedance is in the order of the Kilo-Ohms, the Tekscan FSR
is in the Meg-Ohms. Insulation of the Tekscan leads and connectors is very
important for the slightest touch will make the force reading
jump around the whole usable range. A jumper was added inside the Interlink plug to change
the biasing of the FSR's (See schematics) depending on whether it is made by Interlink or
Tekscan. Although the size of the Tekscan FSR is more appropriate for small fingers, the Interlink FSR has a more linear response and should
probably be used whenever possible. The "Calibration Data" graph above
is pretty much typical of the Interlink FSR's. Two near perfect
calibration graphs: Interlink
Sending to Excel
1- Open Excel and edit the sheet name to change the Excel default to whatever name you desire. We highly recommend changing
the Excel default in order to avoid accidentally erasing valuable data. The Algometer program automatically sends the data
to Excel without checking for proper transfer nor errors.
2- "Copy" the name to the clipboard then press 'Enter' to validate the new name otherwise the data will not transfer from
the Algometer program.
3- In the Electronic Thimble Algometer program, select the menu option: "File/Rename Excel Sheet". The small window
shown at right will appear. This File option is only available when the menu "View/Sending to Excel Option" is checked (the
"Sending / Not Sending to Excel" command bar is then visible).
4- Select the whole text currently inside the text box, then "paste" the Excel sheet name previously saved to the clipboard
(You can also edit the name without copying and pasting). Click "Add" if you want to add it to the list for future use.
5- Clicking the 'Remove' button will delete the currently selected name from the list.
6- Clicking the 'OK' button will validate the selection and close the window. If you have selected the option of 'Sending to
Excel' by clicking on the command bar, you will notice that the caption of the bar has changed to reflect the current name of
the Excel sheet.
7- Clicking the 'Close' button will close the window without changing any previously selected name.
8- You should now make sure that the data are being sent to Excel before running the experiment.
a- Click the button bar with the caption: "Not Sending to Excel" which should change to: "Sending to Excel - " followed
by the Excel sheet name to which the data will be sent.
b- Click the "S T A R T" button
c- Press the 'Subject' switch or the keyboard space bar and observe that whatever is being saved into the Algometer program
table, also appears on the Excel sheet.
d- Clicking on the "Clear Test Results" will clear the data in Excel as well as the data in the table.
Table & sample Log file
Every time the [Start] button is clicked, a log file is created with the name: ThimbleAlgometerLog#1.txt ( or
WagnerAlgometerLog#1.txt or VonFreyAlgometerLog#1.txt for the other types of Algometers). If the file already exists it is
renamed: ThimbleAlgometerLog#2.txt. If that one already exists it is also renamed with the #3, etc. up to #9 at which time the
file that would be called #10 is deleted. So the latest log file is always #1.
Log File as of February 25, 2008
T H I M B L E A L G O M E T E R L O G
All timings start when the strain reaches 0.5 Newton
The Rate = (Peak Strain - 0.5N) / Peak Time
Peak Peak End Total
Date Time Test# Trial# Site Strain Time Rate Strain Time User
2/25/2008 3:57:54 PM 1 1 6 6.26 11.82 0.47 6.11 11.92 *
2/25/2008 3:58:07 PM 1 2 9 6.35 8.16 0.72 6.35 8.16 *
2/25/2008 3:58:23 PM 1 3 3 10.46 10.33 0.96 10.46 10.33 *
2/25/2008 3:58:34 PM 2 1 6 9.58 6.34 1.43 9.58 6.34 *
2/25/2008 3:58:50 PM 2 2 3 8.58 4.20 1.92 8.58 4.20 *
2/25/2008 3:58:59 PM 2 3 9 10.11 3.93 2.39 10.11 4.02 *
And its corresponding saved "Experiment Table" data
Algometer Experiment Data
Subject ID: qwe
Test # 1 Test # 2
Site Strain Rate Duration Site Strain Rate Duration
1 6 6.1* 0.47 11.92 6 9.6* 1.43 6.34
2 9 6.4* 0.72 8.16 3 8.6* 1.92 4.20
3 3 10.5* 0.96 10.33 9 10.1* 2.39 4.02
- Blank rows are inserted to alert of the fact that the experiment was
stopped and then resumed, and that the trial following the blank row
may not necessarily be the next one showing in the table, as is the
case for the second blank row in the sample above.
- The asterisk in the "User" column indicates that the trial was ended
using the "User" switch or the keyboard spacebar.
2005 September 30
Last update: 2011 December 19