Heat & Temperature Sensors Flashcards
It is a measure of the thermal energy in a body, which is the relative hotness or coldness of
a medium.
Temperature
It is a form of energy; as energy is supplied to a system the vibration amplitude of its molecules and its temperature increases. The temperature
increase is directly proportional to the heat energy in the system.
Heat
It is defined as
the amount of energy required to raise the temperature of 1 lb of pure water by 1°F at 68°F and at atmospheric pressure.
British Thermal Unit (BTU)
It is the quantity of heat energy required to raise the temperature of a given weight of a material by 1°.
Specific heat
It is the flow or transfer of heat from a high
temperature region to a low temperature region.
Thermal conductivity
It is the flow of heat through a material. The molecular vibration amplitude or energy is transferred from one molecule in a material to the next.
Conduction
It is the transfer of heat due to motion of elevated temperature particles in a material(liquid and gases).
Convection
It is the emission of energy by electromagnetic waves that travel at the
speed of light through most materials that do not conduct electricity
Radiation
It is the change in dimensions of a material due to temperature changes. The change in dimensions of a material is due to its coefficient of thermal expansion that is expressed as the change in linear dimension (alpha) per degree temperature change.
Linear thermal expansion
It is the change in the
volume (beta) per degree temperature change due to the linear coefficient of expansion.
Volume thermal expansion
Methods of measuring temperature
- Expansion of a materialto give visual indication, pressure, or dimensional change
- Electrical resistance change
- Semiconductor characteristic change
- Voltage generated by dissimilar metals
- Radiated energy
The most common direct
visual reading thermometer (if not the only one). The device consisted of a small bore graduated glass tube with a small bulb containing a reservoir of mercury.
Mercury in glass
It is a type of temperature measuring device that is relatively inaccurate, slow to respond, not normally used in analog applications to give remote indication, and has hysteresis. It is extensively used in ON/OFF applications not requiring high accuracy, as it is rugged and cost effective.
Bimetallic strip
These thermometers are used where remote indication is required, as opposed to glass and bimetallic devices which give readings at the point of detection.
Pressure-spring thermometers
Three types or classes of pressure-spring devices
Class 1: Liquid filled
Class 2: Vapor pressure
Class 3: Gas filled