Process Instrumentation (Certified Automation Professional)

Explore process instrumentation as the use of instruments to measure and control a process, guided by the idea that control follows measurement, segregation, and automatic implementation whenever possible.

Define instrumentation as using instruments to control a process and recognize that process automation uses instruments for control. Begin by refreshing units and standards of measurements.

Explore the units and standards of measurement, including length, mass, time, temperature, electric current, and compare SI and English units.

Sensors convert a physical parameter into an electrical output, while transducers convert one form of energy into another, and a thermistor with signal conditioning becomes a transducer.

Classify instruments by power source, type, measurement mode, and connectivity. Active versus passive, null versus deflection, analog versus digital, and indicating versus signal summarize the four classification types.

Learn how accuracy equals the limit of error under defined measuring conditions, how precision reflects a device's freedom from random errors, and how repeatability ensures consistent readings under fixed conditions.

Explain reproducibility and repeatability in instrumentation, showing how output changes with measurement method and conditions. Demonstrate hysteresis and dead space, where output follows different paths as input increases or decreases.

Explore drift in instrumentation, including zero drift and sensitivity drift, how offset readings occur with no input, and how ambient conditions affect sensitivity. Define resolution as the smallest measurable change.

Pressure is the core measurement in process instrumentation, with four key parameters: pressure, flow, temperature, and level, driving inferential control across large plants.

Define pressure as the force acting on unit area in terms of Newton's law, and examine vacuum as total absence of pressure, not encountered on Earth, such as during spacewalks.

Explore vacuum concepts by defining vacuum as the range between total vacuum and atmospheric pressure, and learn how it is measured in process instrumentation.

Learn how atmospheric pressure is measured on earth, how absolute pressure includes atmospheric pressure from vacuum, and how gauge and differential pressures relate.

Explore pressure head, the pressure from a column of liquid, and relate it to height using the formula pressure = gamma × h (gamma being the specific gravity).

Examine primary pressure sensing elements—Bowden tube, bellows, and capsule—and compare their pressure ranges, accuracies, and cross sections, with a note on U-tube manometer use.

Measure flow with differential pressure across an orifice plate to determine volumetric flow, and review tapping types: flange, vena contracta, corner, and elbow, to feed differential pressure meters.

Compare flow nozzles with orifice plates to reveal their advantages and reliable performance characteristics. They require less upstream straight piping lengths and exhibit lower permanent pressure loss.

Henry Pitot invented Pitot tubes in 1732 to measure static and impact pressures and calculate flow.

Explore magnetic flow meters based on Faraday's law, where induced voltage in a magnetic field yields fluid velocity, which a transmitter converts to a volumetric flow rate.

Explore the nutating flowmeter, a highly accurate positive displacement meter with a simple chamber design that passes a fixed water amount per cycle, counting disk mutations to calculate flow.

Explore Coriolis mass flowmeters as the most accurate method to measure mass flow. Learn how a vibrating tube creates Coriolis acceleration, phase shift, and a twisting force proportional to mass.

Explore level measurement using direct and indirect methods, and learn zero suppression and zero elevation. Elevating the zero positions the level instrument above the liquid, starting measurement above zero.

Learn about errors in level measurements caused by overpressuring connections, sensing lines, obstructed sensing lines, and draining sensing lines.

Examine direct level measurement methods: side glass, float probes, ultrasonic, and radar. Ultrasonic uses time-of-flight, while radar uses electromagnetic waves traveling through vacuum.

Understand buoyancy and the buoyancy force on a submerged displacer and how it is used to measure level with a displacer level transmitter in a gas or liquid.

Explore indirect level measurement methods, including bubbler, displacer, radiation, strain gauge, and paddle wheel, to determine liquid levels in process instrumentation.

Explore how the bubbler method uses a gas stream into the liquid and a calibrated pressure gauge to measure liquid level via back pressure.

Explore the radiation level measurement method using a radioactive source on one side of a vessel and detectors on the other to determine material level from detected radiation.

Use a vibration level switch to measure a point of level. A piezoelectric crystal vibrates at a set frequency, and reaching the tuning fork lowers the frequency to indicate level.

Explore the main temperature scales - Celsius, Fahrenheit, Kelvin, Rankine - and their freezing and boiling points, and discuss various temperature measurement methods.

Explore methods of temperature measurement, including thermoelectric effects, resistance changes, radiative heat emission, thermography, thermal expansion, resonant frequency changes, fiber optic sensing, acoustic thermometry, and color and phase changes.

Explore expansion thermometers and how a bimetallic strip, made of two dissimilar metals with different expansion rates, bends when heated to drive dial indicators or on-off refrigerator controls.

Explore the three types of filled thermometers used in field systems: liquid filled, vapor filled, and gas filled.

Learn how to measure temperature without contact using a pyrometer, an instrument for non-contact temperature measurement. Explore two types of pyrometers: optical and radiation.

Discover how optical parameters measure temperature using a heated tungsten filament in an optical system. Increase filament current and calibrate it to infer the source temperature.

Explore radiation pyrometers that measure electromagnetic radiation to determine the temperature of objects. Understand emissivity at a set temperature, given by E equals k t to the fourth.

Explore ultrasonic thermometry, where the velocity of sound depends on temperature, described by v = sqrt(alpha r t / m). It traces acoustic thermometry from cryogenic services to 20,000°C.

Learn how the resistance temperature detector (RTD) uses a platinum 100 ohm resistor and measures resistance via a bridge circuit or a constant-current source.

Explore the Seebeck effect, where dissimilar metals form heated and cooled junctions to generate voltage and power thermocouples for temperature measurement, while RTDs offer greater ruggedness and wider use.

Discover density as mass per volume and how specific gravity compares density to water. Measure density with a hydrometer or induction hydrometer that uses buoyancy and electrical signals.

Explore viscosity measurement using a rotating disk viscometer to convert liquid resistance into an electrical signal for viscosity values, and learn about the Sebald instrument.

Study force measurement using strain gauges based on Newton's law, where force equals mass times acceleration, and examine a pressure sensing element fused on a silicon die.

Explore displacement measurement using a linear variable differential transformer (LVDT) with a moving core inside the secondary winding, generating a fluctuating voltage to quantify displacement.

Explore absolute and incremental position, rectilinear motion, and angular position in degrees or radians. Examine optical disc measurements with LED pulses and piezoelectric accelerometers, noting power-loss effects.

Explore humidity measurement in process instrumentation, covering relative humidity, specific humidity, and absolute humidity definitions, and explain how resistive hygrometers and dew point devices measure water vapor.

Explore optical measuring devices that measure distances in civil engineering projects like road construction and geographic mapping, and learn how theodolite delivers precise readings over large distances.

Explore the mind map of instrument types, including power instruments (active and passive) and deflection types, null type; classify by signal type (analog, digital) and indicating vs non-indicating.

Explore the terminologies used for process instrumentation, including accuracy, precision, repeatability, reproducibility, hysteresis, dead space or dead band, drift, sensitivity, offset, and resolution.

Explore mind map of errors, including static error, the difference between true value and measured value, and random error from variations, with sources such as design limitation and poor maintenance.

Explore the main process parameters to measure, including pressure, flow, level, temperature, density, viscosity, power, force or torque, dimension, and humidity.

Examine additional parameters to be measured in process instrumentation, including smoke, sound, and light, as well as position and motion.

Explore the pressure measurement mind map, covering vacuum, atmospheric, absolute, gauge, and differential pressures, liquid head, and measuring elements like Bowden tube, bellows, capsule, and u-tube manometer.

Apply Bernoulli's equation to flow measurement and examine flow elements and meters, including orifice plates with tabs, flow nozzles, pitot tubes, and magnetic, nutating disc, and Coriolis meters.

Explore level measurement concepts, zero separation, zero elevation, and errors from over pressuring and obstructed sensing lines, with direct methods (float, ultrasonic, radar) and indirect methods (bubbler, hydrostatic, displacer).

Explore temperature measurement in process instrumentation, covering scales, expansion thermometers, fill-system types, RTDs, thermocouples, pyrometers, and noncontact methods like optical, radiative, and ultrasonic thermometry.

Explore density measurement, starting with specific gravity defined as density divided by 1000. Use devices like hydrometers, thermo hydrometers, and induction hydrometers to convert density into an electrical signal.

Explore viscosity measurement by examining resistance to change in shape and employing a rotating disk viscometer and the Sebald instrument.

Explore power measurement using a mind map approach, showing how to calculate power from the equation for single-phase and three-phase four-wire systems.

Explore force measurement concepts via the mind map, noting that force equals mass times acceleration and measuring force with a strain gauge.

Explore the displacement measurement mind map and learn how to measure displacement using a linear variable differential transformer (LVDT).

Explore position measurement concepts, including absolute and incremental position, and rectilinear and angular motion. Identify sensors and instruments, such as incremental optical disk and piezoelectric accelerometer, and Hall effect instruments.

Explore humidity measurement by comparing relative humidity, specific humidity, and absolute humidity, and examine instruments like hygrometers: capacitive, resistive, piezoelectric or sorption, plus dew point devices.