Potential Drivers (basic circuit concepts part 2)

Question 1

Resistance Defintion

Answer 1

A property of a component that opposes electric current

Question 2

Series Connection Definition

Answer 2

Components connected end-to-end so the same current flows through each

Question 3

Parallel Connection Definition

Answer 3

Components connected so both ends of each component share the same nodes; voltage across each is the same

Question 4

Potential Divider Definition

Answer 4

A simple series circuit of two or more resistors across a voltage source; voltage is divided between the resistors in proportion to their resistances

Question 5

Direct Current Definition

Answer 5

Current or voltage that does not change direction with time

Question 6

Alternating Current Definition

Answer 6

Voltage or current that varies with time

Question 7

Impedance Definition

Answer 7

Generalised resistance for AC circuits

Question 8

Input Impedance Definition

Answer 8

The impedance presented by a measurement instrument as its input terminals

Question 9

Voltage division with input impedance

Answer 9

Measurement system only sees fraction of the source voltage that appears across its input impedance

Question 10

Dry Electrodes

Answer 10

• Higher impedance
• Used for ambulatory monitoring where long-term stability is needed

Question 11

Wet Electrodes

Answer 11

• Provide low electrode-skin impedance
• Commonly used for 12 lead ECGs

Question 12

Purpose of good skin prep

Answer 12

Reduced electrode-skin impedance and leads to stronger, cleaner ECG signals

Question 13

Large skin-electrode impedance consequence

Answer 13

Reduces signal amplitude and increases susceptibility to noise and baseline wander

Question 14

Strain Definition

Answer 14

Fractional change in length of a material when force is applied

Question 15

What are strain gauges

Answer 15

Resistive sensors bonded to structures so that when structures deform, the gauge deforms and its resistance changes

Question 16

Strain gauge in a circuit

Answer 16

Can be placed in a divider circuit so that a change in gauge resistance produced a proportional change in output voltage

Question 17

Direct measurement challenges of strain gauge in a circuit

Answer 17

• Change in resistance is typically small so direct measurement is hard
• Techniques can be used to amplify the small signal and remove thermal effects e.g. Wheatstone bridge

Question 18

Application of Wheatstone bridge

Answer 18

Measurement of pressure, flow, temperature, displacement and weight
Any application where a resistance change is used

Question 19

Quarter bridge (Wheatstone bridge)

Answer 19

Only one arm is an active strain gauge (other arms are fixed resistors)

Question 20

Half bridge (Wheatstone bridge)

Answer 20

• Two active gauges (often one increases and other decreases when strain applied)
• Better sensitivity and thermal compensation

Question 21

Full bridge (Wheatsone bridge)

Answer 21

• 4 active gauges so that 2 arms increase while the other 2 decrease
• Highest sensitivity and best compensation for temperature and common-mode interference

Question 22

Pressure Transducer Principle

Answer 22

Coverts an applied pressure into an electrical signal

Question 23

Pressure transducer and Wheatstone bridge

Answer 23

• A diaphragm deflects under pressure and bonded strain gauges on the diaphragm convert deformation to resistance changes
• Gauges arranges in Wheatstone bridge to produce small differential voltage proportional to pressure

Question 24

Sensitivity Equation

Answer 24

Output / Input

Question 25

Potential Divider Equation

Answer 25

V (out) = V (in) (R2 / R1 + R2)