Process Variables and Sensors

Parts and materials needed for today (instructor will provide): DP transmitters Thermocouples Filled-bulb temperature sensor RTDs Heat source (e.g. cigarette lighter) Vortex flowmeter Thermal flowmeter Magnetic flowtube Turbine flowmeter Orifice plates Coriolis flowmeter Multimeters

Process Variables and Sensors Documents you will need for today: “Realistic Instrumentation Diagrams” worksheet (from the Socratic Instrumentation project website)

Fundamental Principles Brainstorm all the fundamental principles of physics you can recall that are relevant to the sensing of process variables such as pressure, level, temperature, and flow!

Pressure Measurement

Level Measurement

Temperature Measurement

Temperature Measurement: filled-bulb sensor

Temperature Measurement: RTD

Temperature Measurement: thermocouple

Flow Measurement: orifice

Flow Measurement: vortex

Flow Measurement: magnetic

Magnetic Flow Meters n Process must be a liquid n Minimum conductivity n Meter must be full

Magnetic Flowmeters MAGNETIC ADVANTAGES No Moving Parts Very Wide Rangeability Ideal For Slurries Unobstructed Flow Path DISADVANTAGES Liquid Must Be Conductive Physical Pressure and Temperature Limits

Magnetic Flowmeters n No moving parts n No pressure drop n Flowrate independent of viscosity, temperature, and density n Minimum upstream piping requirements n Electronics interchangeable without regard to size n Measure dirty liquids with solids n Measure highly corrosive fluids n Very large turndown n Linear output Advantages Over Other Technologies

Vortex Meter

Principle of Operation Q = V x A

Vortex

ADVANTAGES No Moving Parts For Liquid, Gas, or Steam Uneffected by Pressure, Temperature, or Density Changes. Wide Rangeability DISADVANTAGES Span Limitations Due to Viscosity Flow Profile Sensitive (Vortex) VORTEX / SWIRLMETER

Turbine Meter Principle of Operation Rotor velocity is proportional to fluid velocity

Turbine Meter n High accuracy (.5% of rate) n High rangeability (up to 50:1) n Compact design n Fast response time n Broad range of sizes n Clean water applications only n NIST Traceable Factory Calibration n Low cost, Easy to install n In and out of line, under pressure

Turbine Meter n Straight pipe run requirements n Process fluid lubricity n Reynolds number constraints ä Viscosity ä Density n Maintenance & recalibration Performance Considerations

Turbine Flowmeters TURBINE ADVANTAGES High Accuracy Suitable for Extreme Temperatures and Pressures Can Be Used On Gas or Liquid DISADVANTAGES Only For Low Viscosities Moving Parts Sensitive to Flow Profile

Flow Measurement: turbine

Flow Measurement: ultrasonic

Ultrasonic Flowmeters n Doppler n Time of flight Types

Doppler Flowmeter Ultrasonic Flowmeters Principle of Operation

Transit-Time Flowmeter

Ultrasonic Flowmeters n Reynolds number constraints n Entrained gas or particles for doppler n Clean liquids for time of flight n Installed without process shut down n Straight upstream piping requirements Performance Considerations

Flow Measurement: true mass

Application: distillation process

Extra: hydrostatic level sensor calculation