MARINE AUTOMATION AND CONTROL (TOPIC 2)

Marine Automation and Control Lesson 2 - Measuring Instruments

Learning Objectives  Comprehend the measurement of pressure, temperature, level and flow.  Comprehend the units of measurement  Comprehend various measurement devices

What Do We Measure?  LENGTH (in, ft, yd, mm, cm)  AREA (sqin, sqft, sqm, )  VOLUME (cuft, cum)  MASS (lb, kg)  FLOW (gal/h, l/s, m3/hr)  TIME (s, min, h)  PRESSURE (psi, cm of Hg, bar, kg/cm2, )  TEMPERATURE (F, C)  SPEED (Knots, rpm, km/h, m/s)

TEMPERATURE  A measure of a substance’s internal kinetic energy  [Simply stated] The degree of hotness or coldness of a substance, as measured on a thermometer

Temperature Measurement  Scales  Conversions  Fahrenheit (F)  F = 1.8*C + 32  Rankine (R)  R = F + 459.67  Celsius (C)  C = (F-32) / 1.8  Kelvin (K)  K = C + 273.15 Fahrenheit and Celsius based on boiling and freezing points of water Rankine and Kelvin based on absolute zero - more precise thermodynamic study.

Temperature Measuring Devices  Expansion Thermometers  Liquid in Glass  Bimetallic  Filled System / Distant Reading  Pyrometers  Thermocouple  Resistance  Radiation and Optical Pyrometers

Liquid in Glass Thermometer

Bimetallic Expansion Thermometer

Distant Reading Thermometer

Thermocouple

Resistance Temperature Device

Radiation Pyrometer

Thermometers

PRESSURE  Force exerted on a unit area  Measured in psi (other units include atm, in Hg, mm Hg, bar, kg/cm2)  Atmospheric pressure at sea level is 14.7 psia, 0 psig, 1 atm, 29.92 in Hg, 760.0 mm Hg  absolute pressure (psia) = gage pressure (psig) + 14.696

Pressure Relationships  Pressure Relationships Pa = Patm + Pg Patm = 14.7 psi or 29.92 in. Hg or 1 bar.  Barometric Pressure - A measure of air pressure that correlates with weather and altitude.

Pressure Measuring Devices  Manometer  Bourdon tube  Bellows gage

Manometer

Bourdon Tube

Bellows Gauge

Pressure Gauges

Level Gauges

Flowmeters  Mechanical flowmeters measure flow using an arrangement of moving parts, either by passing isolated, known volumes of a fluid through a series of gears or chambers (positive displacement) or by means of a spinning turbine or rotor.  All positive displacement flowmeters operate by isolating and counting known volumes of a fluid (gas or liquid) while feeding it through the meter. By counting the number of passed isolated volumes, a flow measurement is obtained.

Flowmeters