Laboratory Acquisition Software for Isometric Force Testing
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Laboratory Acquisition Software for Isometric Force Testing
Installation:
-Install DT301 card in computer and connect cable to terminal board -Install driver for DT301 (found at www.datx.com under manuals/drivers) -Install software (insert floppy#1 and run setup)
1 Experimental Setup
Whether data is to be acquired as part of clinical evaluation or for research, the collection process most often involves dividing the session into a sequence of tests. Each test involves sampling one or more signals at a specific rate for a certain duration to be repeated one or more times. In practice, each subsequent test involves some change of these parameters. Conceptually, the experimental design can be thought of as a table of tests, where each entry lists the test name and the associated acquisition parameters. The acquisition software is tailored to allow this flexibility by the use of configuration files that contain within them a series of tasks that describe each test.
The acquisition software has four main components:
-Subject database, including results for each test -Configuration files describing each experiment or group of tests -Calibration files used to describe transducer characteristics -Acquisition software used to collect data.
2 Directory Structure
The following directories are used by the acquisition program:
/acquire: main directory for this software /acquire/data: root directory for all data that’s collected. A separate subdirectory is created for each subject designated by (last name).(id number). For example, John Smith, having an id number of 12345 would have his test data stored in the subdirectory smith.12345. Under this directory is a separate directory for each test date designated by ddmmmyy (e.g. 31jan01). /acquire/subjects:directory in which the subject database is stored /acquire/config: location for experimental configuration files /acquire/calib: location for transducer calibration files
3 Subject Database
Each time a subject is tested, a new entry is placed in the database. Normally, each entry corresponds to a different day the subject was seen. However, it is possible to have multiple visits on the same day (pre- and post-medication, for example). When searching the database, the history of other visits for that subject are displayed and can be perused to check on past results.
4 Configuration Files
The data acquisition software is designed to be driven by a configuration file that contains all the information needed for the data collection process. There may be multiple files to describe different experimental paradigms (for example, different batteries of tests based on clinical diagnosis) but each file contains what is needed for each experiment or test. The files are in straight ASCII text format and can be modified with any text editor. The following nomenclature is used in the description of the experiment referred to as a configuration:
Task: A single test that can be described by what data is to be collected (channels/rate/duration) Trial: One repetition (perhaps of many) of a given task Configuration: A file that contains the descriptions of each task needed Channels: Inputs to the data acquisition hardware used to sample data Rate: Sampling rate of each signal being acquired Duration: Period of time that each channel is to be sampled Repetitions: The number of time each task is repeated before going on to the next one Analysis: The type of analysis to be applied to data after collection of each record
4.1 Use of a Configuration File
The following is a sample configuration file:
:Vital_Capacity channel#1=airflow channels=1 rate=60 duration=5 repetitions=2 :Grip_Max channel#2=dynamometer channels=2 rate=10 duration=3 repetitions=1 analysis=peak,1,1 :Grip_Fatigue duration=30
Each task is named (A line beginning with a colon is the beginning of a new task). In this case, for the task “Vital_Capacity”, an airflow transducer is connected to input 1 and it’s signal is collected for 5 seconds at a rate of 60 samples per second. This is repeated twice before going on to the next task, called “Grip_Max”. For this task, a different channel is sampled (at 10 sps) and used to measure grip force once for a duration of 3 seconds. For this task, after the data is collected, it analyzed to find the peak force as indicated by the analysis= line. Finally, the same signal is sampled for 30 seconds to check fatigue. The acquisition software automatically sequences through these tasks with no operator intervention.
5 Calibration files
When commercial data acquisition boards are used to collect data, the resulting data samples are in a binary form related to the voltage range of the board and not any real world units. A scale and offset must be determined to map the voltage to other units. This is done through a calibration procedure that is part of the acquisition software. The resulting conversions are stored in separate files called calibration files.
While each configuration file can be associated with a given experimental design, each calibration file can be associated with one or more transducers to provide the conversion values needed to map raw sample values to real world units. In this case the file consists of a table of values that consist of a task name and the resulting scale and offset required to compute calibrated values.
The calibration files are plain text files that consist of a series of lines with this format:
An example line:
Grip_Max, 2, 2.5, 2047, N
This line tells the software that for the task called “Grip_Max”, all data collected from channel #2 should use the scale of 2.5 and offset of 2047 to provide data in the units of N (for Newtons). The units field is optional and used as part of the labeling of data when needed.
Of course, this calibration is associated with a given transducer and if it is changed, a new file must be specified (contains new scale and offset values). In practice, different transducers can be calibrated in advance and if needed, can be changed in the middle of an experiment as long as the new calibration file is then specified.
Isometric testing protocol
Built into the acquisition software is an automatic analysis mode for isometric muscle testing. This is specified in the configuration file as follows: analysis=peak,
So, for the line: analysis=peak,1,1 the line is read as analyze channel 1 for peaks and display the result in display 1.
The analysis consists of finding and displaying the two largest values in the signal that was sampled and marking them with cursors. The largest value is stored with the associated task name in the clipboard. At the end of the experiment, the clipboard can be pasted into a spreadsheet to compile the data. Appendix A: Configuration files
Configuration file settings:
Parameter Argument(s) Example Function
:
channels= n1-n2,n3 channels=1,2,5-7 channel numbers to be sampled and stored
duration= time in seconds duration= specifies length of record for collection
rate= samples per second rate=100 sampling rate for all channels
repetitions= number of reps repetitions=3 number of times to repeat this task
channel#N= name for channel# N channel#2=force provides names for channels that are sampled
display= n1-n2,n3 display=1-3 channel numbers to display in display 1
displayN= n1-n2,n3 display2=4-6 channel numbers to display in display# N (N=2,3 or 4)
scale=
scaleN=
analysis=
target= level,t1,t2,t3,t4 target=10,2,5,7,9 generates a trapezoidal shaped target described by 4 turn points and a level. t1 is the time target leaves baseline, t2 is the time target reaches the level, t3 is the time target begins decrease and t4 is time target returns to baseline. In the example given, the target ramps up from 2 to 5 seconds to a level of 10 and ramps down from 7 to 9 seconds
*Unless a scale is specified, the data are scaled automatically (full data record is collected and then displayed using the data min and max as the upper and lower limits.