Principles of Measurement LESSON 1 Principles of Measurement Let the Games Begin!

Objectives Measurement of temperature and pressure Units of measurement Measurement devices

References Introduction to Naval Engineering Principles of Naval Engineering

Purpose of Measuring Devices Why essential to proper operation of propulsion plants?

WHAT IS TEMPERATURE? An indication of the internal energy contained in a substance Mono-Atomic Gases: Linearly proportional Poly-Atomic Gases: translational, rotational and vibrational kinetic energy. Temp is a measure of but not directly proportional to internal kinetic energy.

Measurement of Temperature Relative Scales Fahrenheit (°F) Celsius (°C) Absolute Scales Rankine (°R) Kelvin (K) F = 1.8 C + 32 R = F + 460 C = (F - 32) / 1.8 K = C + 273 Temperature At the beginning of the renaissance many scientists recognized that the idea of the subjective sense of temperature needed to be quantified. They knew that the behavior, and sometimes the structure, of a body changed as it became hotter or colder. The most vivid example of the phenomenon is the behavior and structure of water as it is cooled to the freezing point. But, how does one quantify, or measure, a subjective feeling? Galileo, and others, tried to build various types of thermometers which were are successful to some extent, but they all lacked the essential quality of being able to measure temperature with any more repeatability than the common sense of touch. Along comes a German Physicist, Gabriel Fahrenheit, and the mercury thermometer. Fahrenheit's real contribution was a sealed thermometer that measured the expansion and contraction of mercury with temperature changes and it was independent of atmospheric pressure changes. The susceptibility of the non-sealed thermometers to atmospheric pressure changes later evolved into the barometer that is the basis of the next topic.Fahrenheit. He needed to calibrate his thermometer at some repeatable temperatures and so he selected the two most common and universally repeatable temperatures: the freezing point of pure water and the boiling point of pure water.Fahrenheit engraved a scale on his prototype thermometer before he calibrated it. When he measure the temperatures of ice water and boiling water, he came up with two of the most inconvenient numbers around: 32° and 212°.

Temperature Relationships (°F) = 9/5*(°C) +32 (°C) = 5/9*[(°F) –32] (°F) = (°R) – 459.67 (°C) = (K) – 273.15

Measurement of Pressure Definition: Force per unit area Units of measurement Pounds force per square inch (psi) Inches Hg or inches H2O (“Hg) Atmospheres (atm)

Pressure Relationships Gage pressure (PSIG) Absolute pressure (PSIA) Vacuum pressure (PSIV) or (in Hg) Atmospheric pressure (14.7 psi)

Pressure Relationships Absolute Pressure = Atmospheric Press. + Gage Press. Vacuum = Atmospheric Pressure - Absolute Pressure

Pressure Relationships 30 PSIA 15.3 PSIG GAGE PRESSURE (PSIG) ABSOLUTE PRESSURE (PSIA) Atmospheric Pressure 14.7 PSIA 0 PSIG (Average at Sea Level) 0 In. Hg VACUUM (in. Hg) 0 PSIA 29.92 In. Hg

Sensors In the late 1800s, another physicist, Bill Rankine, measured the change in thermal energy with each change in temperature for many substances and he found that each of these substances had the same theoretical temperature at which they possessed no thermal energy. That temperature is approximately -460° F. Rankine called this point absolute zero and declared the only true temperature scale to be the Rankine scale which started at absolute zero. Celsius was a little smarter than Fahrenheit when he calibrated his thermometer. He waited until after he “calibrated” his thermometer in ice water and boiling water to put the scale markings on his thermometer. He made his lower calibration point zero degrees and his upper calibration point 100 degrees. While dividing the temperature scale into 100 increments made more sense over the range of temperatures experienced in everyday life, his scale, like that of Fahrenheit, did not start at absolute zero. Kelvin fixed Celsius in the same manner as Rankine fixed Fahrenheit in that a degree Kelvin is the same as a degree Celsius except that zero degrees Kelvin is at - 273 degrees Celsius.

Principle of Operation Temperature Devices Expansion Thermometers Liquid in glass Bimetallic Filled system/distant reading Pyrometers Thermocouple Resistance Radiation and optical pyrometers

Expansion Thermometer Liquid in Glass Bimetallic Filled System/Distant Reading

Expansion Thermometer Liquid in Glass Bimetallic Filled System/Distant Reading

Expansion Thermometer Liquid in Glass Bimetallic Filled System/Distant Reading

Expansion Thermometer Liquid in Glass Bimetallic Filled System/Distant Reading

Pyrometers Thermocouple Resistance Radiation and Optical

Pyrometers Thermocouple Resistance Radiation and Optical

Pyrometers Thermocouple Resistance Radiation and Optical

Pyrometers Thermocouple Resistance Radiation and Optical

Operation of Pressure Measuring Devices Manometers Bourdon tube Bellows gage

Operation of Pressure Measuring Devices Manometers Bourdon tube Bellows gage

Operation of Pressure Measuring Devices Manometers Bourdon tube Bellows gage

Operation of Pressure Measuring Devices Manometers Bourdon tube Bellows gage

Questions?