1. INTRODUCTION TO ELECTRONIC INSTRUMENTATION
Chapter 3 INTC 1305 – 01
PROCESS VARIABLES
TEMPERATURE
Vern Wilson

2. OBJECTIVES Define Temp Heat Energy
Fahrenheit, Celsius, Rankine, Kelvin
Sensing Equipment
Conversions

3. DEFINITION
The average kinetic energy of a material and an indication of the heat energy available to flow between bodies
Sun’s heat dissipation
Temperature changes physical characteristics
Water to steam (vapor) or ice (solid)
As steam the molecules increase in speed and overcome surface tension to vaporize.

4. PRINCIPLE As molecules slow down the water turns to ice
Thermometers have internals that are affected by the presence or absence of heat
Hg common

5. MOLECULAR MOVEMENT Temperature is a single point reference
Heat is the amount of energy that flows over time
Heat always flow from a hotter temp to a lower temp until stable
BTU – Amount of heat required to raise the temperature of 1# of water 1°F = BRITISH THERMAL UNIT
Calorie – 1 gm 1°C

6. HEAT TRANSFER CONDUCTION CONVECTION RADIATION
Transfer of heat between solids
CONVECTION
Transfer of heat between fluids
RADIATION
Transfer of heat by emitted radiant energy

7. PHASE CHANGES – SOLID
Molecules in solids move little – forces pulling and pushing
When energy added it attempts to push them apart
As temp increases the distance between molecules increases – thus making the solid weaker
The volume increases with temp
With melting the molecules moves farther apart and lose their order
The temp remains constant until all solid melts

8. PHASE - GAS
Once all melted the temp will increase more and convert to gas – this is the boiling point
If temp still increased then it is considered super heated

9. MEASUREMENT 170 AD people concerned – Greek physician
1592 – Galileo – thermometers
1700’s – Fahrenheit defined boiling and freezing
1742 – Celsius said o° should be freezing and 100° should be boiling
IDEAL GAS LAW pv = RT
Can be catastrophic
Single, multiple or differential

10. SCALES FAHRENHEIT - 180° CELSIUS/CENTIGRADE -
RANKINE – Absolute – 492° freezing water + 180°
KELVIN – Absolute - no heat at 0 K – no molecular movement – same units as C but freeze at 273 – no degree mark used

11. BOILING AND FREEZING Rock solid or liquid? Steel? Water?
Water used as bench mark because it is easy to make
Thermal equilibrium and both freezing and boiling

12. PRESSURE AND CONTAMINANTS
Sea level – Greater than 212°F 14000’ = 195°F 150 psi = 358°F How long will it take to boil a 3 minute egg?

13. THERMOMETER THINGS THERMOWELLS THERMOMETERS
BIMETAL STRIPS - THERMOCOUPLE
RTD ( Resistance Temperature Device)
THERMISTOR
TEMPERATURE GAUGE

14. THERMOMETERS
GLASS
INFRARED – everything emits radiation in the form of electromagnetic waves or by conduction or convection
From high energy gamma rays and x-rays to long wavelength radio waves
BIMETAL STRIPS
RTD