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

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

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.

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

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

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

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

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

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

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

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

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?

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

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