ACES - Technical description: limits and resolution of measurement
This section discusses
the limits and resolution of measurements on the ARIEL CES machines. In
addition, a discussion of system checkout for the purpose of maintaining system
operation at peak accuracy will be presented. Sample test results for both the
Multi-Function and Arm-Leg machines are also included.
Each exercise station has
separate transducers which are individually calibrated. The pressure transducer
is used for calibrating force while the potentiometer is used for calibrating
position and velocity.
The analog measurement of
transducer values on the Ariel systems have an accuracy limitation by the finite
representation in a digital computer. Because data values must change by one bit
(binary digit) when represented digitally, any given transducer measurement
could have a possible error approaching one bit value.
In practical terms, the
absolute accuracy depends on the resolution of the conversion from analog values
to digital values. On the Ariel CES, one bit value typically represents 0.3
pounds of force, and about 0.01 degree of bar movement.
These accuracy levels are
entirely sufficient for the vast majority of resistive training and
resolution for the pressure transducer is a 13 bit (1/4096), and for the
potentiometer, the resolution is up to 14 bit (approximately 1/8192). These
resolution values represent a fixed percent of the value as given below:
For a Multi-Function
system with a maximum force set for 1200 pounds, a bar range of 65 degrees and a
maximum speed set to 200 degrees per second, the approximate resolution is:
As you can see, the CES
offers a wide range of force and velocity measurements, and at the same time the
system maintains very high resolution, providing the clinician with high
precision measurements. Thus, the same exercise systems can be used for
precision diagnostics in rehabilitation applications, and on the other hand as a
ï¿½heavy-dutyï¿½ training device utilized by elite athletes.
The force and velocity
transducers are easy to check and calibrate. To insure that your exercise system
performs accurately, it is important to check the force and velocity calibration
periodically. If the calibration is found to differ appreciably from the system
resolution given above, the appropriate transducer should be re-calibrated. The
system should also be re-calibrated if there is any hardware change to the
exercise station external to the computer.
FORCE calibration is
checked using the CALIBRATION CHECK option of the calibrate program. When
performing this check, a known weight will be placed on the bar and the bar will
fall through a selected range of motion. The system will record the observed
force level vs. bar position. This level should be consistent with the weight.
The VELOCITY calibration
can be checked by selecting a constant velocity exercise with one repetition. A
weight is used to cause the bar to fall through the range of motion. The
observed velocity should be consistent with the selected velocity. The velocity
measurement can be performed in a number of ways. The time for the bar to travel
the range of motion can be compared to the expected time knowing the bar range
and selected velocity. This time can be measured directly with a stopwatch.
If your Ariel computer is
configured with the optional sound board and speakers, audio instructions will
guide the user through the exercise session. Instructional commands are stored
as Microsoft compatible waveform (*.WAV) files and can be customized for each
facility if desired.
There are many methods
and programs that can be used to create *.WAV files. The instructions below are
written for the Sound Recorder program included in Microsoft Windows 95/98/2000.
Record A Waveform (WAV) File
Select START, PROGRAMS, ACCESSORIES,
ENTERTAINMENT (or MULTIMEDIA) and then SOUND RECORDER
to open the Sound Recorder program.
Make certain an audio input device is
connected to the computer.
Select FILE, NEW to create
a new WAV file.
Click the RECORD icon to begin
Click the STOP icon to stop
Select FILE, SAVE AS to
save the recording to a waveform (WAV) file. NOTE: the file must have the
same name as the one being replaced in order for the CES program to play it at
the appropriate time.
Ariel CES customers can
record ï¿½customizedï¿½ audio instructions to guide subjects through the
exercise routines. In order for the CES software to recognize the customized WAV
files, they must be created using the same names and copied to the appropriate
directory (usually the C:\PROGRAM FILES\ARIEL DYNAMICS\CESW directory).
It is also recommended to make a backup of the original WAV files prior to
Listed below are the
current file names and text contents of the currently used WAV files.