Using NI Data Acquisition and LabVIEW for Physical Ability Tests

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"With an NI USB-6008 OEM data acquisition device and LabVIEW software, we quickly developed our system with the added benefit of easy maintenance and system expansion."

- Aleksandar Popović, UNO-LUX NS d.o.o.

The Challenge:
Developing a low-cost system to evaluate physical capabilities such as speed, agility, jumping, and isometric and isoinertial strength.

The Solution:
Using NI LabVIEW system design software and a low-cost NI USB-6008 data acquisition device with a voltage converter and current driver to drive ultra bright LEDs that accept sensor signals. For precise time measurements, signals from the digital sensors connect to analog inputs.

Author(s):
Aleksandar Popović - UNO-LUX NS d.o.o.
Zoran Ignjatović - UNO-LUX NS d.o.o.

System Setup and Capabilities

Physical Ability Test 01 computer-based system to evaluate people’s physical capabilities. It tests speed, agility, jumping height (explosive power), and isometric and isoinertial strength. The system consists of a data acquisition device (see Figure 1); a set of cables; application software; three photoelectric sensors; a sensor mat; three ultrabright LEDs; camera tripods; a load cell; and a linear wire potentiometer. We based the measurement device on an OEM USB-6008 and developed the application using LabVIEW.

The front of the data acquisition device features an ON/OFF switch; a USB port to connect the device to a PC; a green light that signals a PC connection; an isometric load cell connector; and an isoinertial linear wire potentiometer connector.

The back of the data acquisition device offers a power supply unit with 230 V AC; a Sensor 1 connection to connect photoelectric sensors; a Sensor 2 connection to connect to the sensor mat; and Lights 1, 2, and 3 connections to connect the lights for measuring response time.

The USB-6008 features software-timed digital inputs, so digital signals from photoelectric sensors and the sensor mat connect to the analog inputs for time measurements. The system samples the signals at a 1 kS/s rate and analyzes the sampled data array (meaning it detects the transition state), so the time measurement has 1 ms accuracy. The signals connect to the analog inputs via a 24 V to 5 V voltage converter. To test reaction time, we used ultrabright LED stimuli. Because the digital output current is minute, an IC ULN2803 current and voltage driver turns the LEDs on and off. The signals from the load-cell conditioner and linear wire potentiometer directly connect to two differential analog inputs. The data acquisition device powers all sensors.

System software is completely configurable for defining a large number of tests. We defined a number of lap sensors to test speed. For jumping, the system can test based on duration or number of jumps. For isometric tests, the user can decide to perform compression, tension, or a combination of these two phases of contraction; how many contractions to perform; and whether the contraction frequency is arbitrary or predefined. The process is similar for isoinertial tests; defined-parameter analysis and calculation are performed for all tests. When the measurement completes, the results are stored and presented in a table. The user can define the number of repetitive measurements to perform during a single test. The system can export data to Microsoft Excel for easy measurement result storage and retrieval.

System Test Performance

The system performs the following basic tests:

  • Speed and Agility: By measuring the elapsed time at a given distance and lap times between start and finish, the system can estimate speed, as well as changes in speed over time. In addition, the system can initiate a test by a randomly generated light signal to measure response times to light stimuli. By combining the appropriate sensors, the system can perform various repeated sprint and agility tests.
  • Jumping: By measuring the elapsed time between two contacts with the ground at the start and end of the jump, the system can calculate the vertical jump height as well as the relative power (see Figure 2). The measurement starts when the subject either contacts the ground after the jump, or when he or she leaves the ground at the beginning of the jump. The measurement ends after a predefined number of jumps, or after a specified time interval.
  • Isometric Dynamometry: By measuring the force exerted against external loads and its change in time, the system can estimate isometric muscular strength, as well as the rate of force development.
  • Isoinertial Dynamometry: By measuring the distance covered by moving an external load, the system can compute dynamic movement characteristics and, based on these characteristics, can estimate muscular group isoinertial strength. The system can measure the maximal distance, speed, power, and work done in concentric (lifting the weight), eccentric (lowering the weight), and concentric-eccentric (lifting and lowering the weight) modes.

The system requires periodic calibration to validate each specific measurement technique and measuring device. It can calibrate the load cell and linear wire potentiometer and permanently store the calibration coefficients on the PC until the next calibration (see Figure 3).

Conclusion

With an NI USB-6008 OEM data acquisition device and LabVIEW software, we quickly developed our system with the added benefits of easy maintenance and system expansion.

We plan to expand the possibilities of the system, by adding support for new sensors with appropriate analysis and further development of analyzes for existing sensors. By using National Instruments tools we could reduce development time and the outcome is a scalable system so improvements require only software changes without making any changes in hardware.

Contact Information:

Aleksandar Popović

Zoran Ignjatović

UNO-LUX NS d.o.o.

Generala Milutina Vlajica 36

11147 Belgrade, Serbia

Tel: +381112511122

Email: salac@unoluxns.com

          zoki@unoluxns.com

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