CH10: Force Measurement

Question 1

What is Electromechanical Transduction?

Answer 1

Electromechanical transduction occurs when a mechanical action results in a change in electric potential.

Question 2

What is electrical potential commonly known as?

Answer 2

Voltage (or electromotive force)

Question 3

What is the electrical potential?

Answer 3

It is the force that causes electrons to flow from one part of a circuit to another part of a circuit.

Question 4

The flow of electrons is also known as…

Answer 4

Electrical current

Question 5

What do electromechanical transducers create?

Answer 5

Create a change in electric potential – they either increase or decrease the electrical current flowing through a circuit

Question 6

What is a common electromechanical transducer?

Answer 6

Potentiometer

Question 7

What is a potentiometer used in?

Answer 7

Potentiometer’s are used in volume dials, dimmer switches, etc.

Question 8

What are other commonly used electromechanical transducers?

Answer 8

1. Potentiometer
2. Accelerometers
3. Gyroscopes
4. Force sensor

Question 9

What is an accelerometer used for?

Answer 9

Measures acceleration

Question 10

What is a gyroscope used for?

Answer 10

Measure angular velocity in 3 axes

Question 11

What are the two commonly used force sensors in biomechanics?

Answer 11

1. Piezoelectric sensor
2. Strain gauge

Question 12

What is a piezoelectric sensor?

Answer 12

• Uses quartz crystal
• Compressing crystal generates change in electric potential difference
  Example: Force platforms: Kistler

Question 13

What is a strain gauge?

Answer 13

• Uses thin metal foil
• Stretching or compressing metal foil generates change in electric potential difference
  Example: Force platforms: AMTI, Bertec

Question 14

Electrical circuits will always have a minimum of __________ electrical contacts.

Answer 14

two

Question 15

What are load cells?

Answer 15

Strain gauges are instrumented in a load cell for force measurement. There are many designs for load cells, but they generally consist of a steel or aluminum body that the
strain gauge is laminated to.

Question 16

What are the two examples of load cells?

Answer 16

1. “S-Type” load cell: tensile or compression
2. “Inline” load cell: tension

Question 17

What can electromechanical transducers be used for?

Answer 17

1. Calibration: Determine relation between voltage and magnitude of physical phenomenon
2. Measure voltage
3. Calculate magnitude of physical phenomenon

Question 18

What is the calibration coefficient?

Answer 18

An increase of 1.0 V is equal to an increase in 447.43 N – or put another way there are 447.43 N/V.

Question 19

What is one major feature that is important in analog-to-digital conversion?

Answer 19

Conversion rate or sampling frequency

Question 20

What is a multi-axis force platform?

Answer 20

A multi-axis force platform has 6 load cells, configured in a manner to measure forces in 3 axes and moments of force about 3 axes. The multi-axis or “true” force platform provides a lot of information, which is not possible form a “single-axis” or “vertical-only” force platform.

Question 21

What is the centre of pressure (COP)?

Answer 21

The point of force application. The coordinate system not only defines the direction of the forces, it is part of determining the point of force application.

Question 22

What is the pressure formula?

Answer 22

Pressure = Force / Area

Question 23

What are the types of standing balance?

Answer 23

1. Double-limb standing
2. Single-limb standing

Question 24

Motion of body’s mass is reflected in changes what?

Answer 24

centre of pressure location

Question 25

What is postural sway?

Answer 25

Measuring COP provides an indicator of the amount and magnitude of this motion,