Chapter 10 Flashcards
What are two examples of devices that use electromechanical transduction?
Accelerometer and force-plates (among others)
What are the two commonly used force sensors in biomechanics?
1- Piezoelectric sensor which uses quartz crystals
2 - Stain gauge which consists of a thin metal foil
Both generate a change in electric potential difference
To measure changes in electrical potential of a straying gauge it must be either .. ?
Stretched or compressed
What are the two types of load cells that contain strain gauges?
What force do each of these measure?
S-type Load Cell (names for its shape) measures both tensile and compressive forces
In-line Load Cell (typically on weight machines) only measures tensile forces
What is the first step when using electromechanical transducers?
What is the purpose of this step?
Calibration - determine the relationship between the voltage and the magnitude of the physical phenomenon (force, acceleration)
Given an electromechanical transducer, how would you go about finding the calibration coefficient?
Place known weights onto the transducer and measure voltage. Do this for multiple weights until a relationship is formed. Graph this relationship.
The calibration coefficient is the slope of the line.
*must have a perfect relation with R^2=1.0
Measuring voltage involves what type of conversion?
Analog-to-digital conversion.
What is the most important feature within analog-to-digital conversion?
The sampling frequency or conversion rate
What might an analog voltage-time data series look like?
A smooth arced line
How does converting analog data into digital data influence the data?
Analog data is continuous, but when its converted into digital voltage time-series data, the data is represented as discrete points sampled at specific time intervals.
How many load cells are in a multi-axis force platform?
6 Load cells - gives 6 pieces of information
What is the definition and equation of pressure?
Pressure is when a force is distributed over an area.
Pressure = Force/Area
What is the centre of pressure?
The centre of pressure is the location that a single total force acts through that has the same moment as sum of the moments of all the distributed forces in the pressure
gradient.
Measuring changes centre of pressure on a force platform after balancing will give data about _________.
Postural Sway
What may indicate someone has good balance when looking at the data of COP from a force platform?
Increased postural sway indicates the person has more control over their balance. Someone with poor balance may have less postural sway as they must restrict their body to a smaller area by contracting their muscles.
