Sensors 2

Question 1

What are the 3 types of contact temp sensors?

Answer 1

Thermocouples:
- Thermoelectric effect utilised
- Have the widest temp range

Thermistor:
- Resistance measured
- High accuracy
- Requires data correction to interpret data (non linear)

Resistance thermometer:

• Slower response to temp change than thermocouple.

Question 2

Compare contact and non contact sensors.

Answer 2

• Physical contact is obtrusive
• Non contact is quicker but less precise (background radiation causes errors)
• Non contact more expensive
• Non contact used in more hazardous and sensitive environments

Question 3

Give 3 examples of force sensors:

Answer 3

• Piezoelectric
• Strain gauge
• Resistive force sensor

Question 4

How do piezoelectric force sensors work, and where are they used?

Answer 4

Electrical potential generated from the piezoelectric material, which is measured.

Force plates, accelerometers.

Question 5

How do strain gauges work, and where are they used?

Answer 5

Length of wire changes length when strain applied, so does resistance.
This is measured.

Wheatstone bridge used to avoid interferance.

Strain gauges used in force plates.

Question 6

What are sources of error in strain gauge measurements?

Answer 6

Bonding faults - bonding of electrical components

Hysteresis - resistance higher when unloading than loading

Cross sensitivity - response to strain at right angles of main axis of measurement

Moisture

Temperature

Question 7

How do resistance force sensors work? What is the equation to calculate output voltage of a resistance sensor?

Answer 7

V out = V total * Rf / Rs