L.5 - Temperature Flashcards
Define Temperature:
the measure of the average translational kinetic energy associated with the disordered microscopic motion of atoms and molecules
Define Heat:
a form of energy associated with the motion of atoms or molecules and can be transferred through solid and liquid by conduction, through fluid by convection, and through empty space by radiation
Define Heat Capacity:
/entropy: amount of heat energy required to raise temp. of a substance by 1K
Define Specific Heat Capacity:
amount of heat energy required to raise temp. of a unit mass by 1 K
Define Thermal Conductivity:
a property of a material that describes how much heat is conducted through it for a given temp. difference
List the three common temp. transducers (w/ definitions):
1) RTD (Resistance Temp. Detectors): measures change in resistance - linear
2) Thermistor: measures change in resistance - non-linear
3) Thermocouple: creates a small voltage based on temp. difference
What is the difference between RTDs and Thermistors?
RTDs
* used for higher temp. ranges
* relatively insensitive but very linear
* higher accuracy
Thermistors
* used for lower temp. ranges
* very sensitive but non-linear
* quicker response time
What is IPTS-90?
International Practical Temperature Scale (describes temp. points based on material physical properties)
What is the difference between contact and non-contact temp. measurement?
Contact: temp. sensor needs to be within close proximity with object (immersed or touching)
Non-contact: based on measurement of electromagnetic radiation of object
List 3 temp. contact measurement techniques:
1) Simple glass thermometer: thermal expansion of glass and fill fluid
2) Resistance thermometers: response to temp. change in the form of change in resistance
3) Thermocouples: produces voltage when one terminal in the circuit is at a different temp. than other terminal if we employ 2 different metals
List 3 temp. non-contact measurement techniques:
1) Infrared thermometer: measures infrared emissions of a material
2) Spectroscopic Thermometer: reading electromagnetic spectrum of a material
3) Ultrasonic Thermometer: based on speed of sound in mediums of different temp.
What is transfer/thermal lag and what does it depend on?
it is the time delay for heat to be conducted through a material.
depend on the heat capacitance and conductance of the measurement system.
Why is an RTD enclosed in stainless steel sheath?
to protect the RTD from physical damage and hostile environments
What does the thickness of the sheath affect?
the sensor time constant
List some advantages for platinum RTDs:
- good accuracy
- repeatable
- very linear
- very fast
