Fundamentals of Instrumentation Flashcards
are the eyes of engineer/ operator that can see & feel the intense process variable inside the vessels
Instruments
principle measurements desired in the industry
temperature
pressure
level
flow
others (composition, pH, etc)
failure to measure effectively the level of liquid in the bottom of the tower lead to:
fire and explosion
A typical instrument has three components:
sensor
modifier
display
feel the condition and originate the signal followed by modification and amplification for effective display or transmission
sensors
measures a physical quantity and converts it into a signal
sensor (sensing section)
change the type of signal
modifier (processing circuitry)
transmitting arrangement
display (signal output)
static characteristics
accuracy
precision
repeatability
range
resolution
others (sensitivity, dead zone, etc)
dynamic chracteristics
speed of response
fidelity
lag
drift
the ability of a device or a system to respond to a true value of a measured variable under reference conditions
accuracy
expressed as “limit of error”
accuracy
is the degree of exactness for which an instrument is designed or intended to perform
precision
precision is composed of two characteristics:
conformity
number of significant figures
is the variation in measurements taken by a single person or instruments on the same item and under the same conditions
repeatability
assigning standard values to an equipment
calibration
how quickly an instrument or control system reacts to a change in the input signal or process variable and moves toward the desired setpoint or measurement
speed of response
the degree to which an instrument accurately reproduces or follows the variations of the input signal
fidelity
indicates that the output closely matches the input, without distortion or significant deviation
high fidelity
time delay between a change in the input signal and the corresponding output response from the instrument
lag
gradual deviation of an instrument’s output or reading from the true value over time, without a change in the input or process variable
drift
methods of temperature measurement
thermocouples
thermistors
electrical resistance change
expansion of materials
pyrometers
when 2 dissimilar metals are joined together to form a junction, an emfis produced which is proportional to the temperature being sensed
thermocouples
the generation of current in a circuit comprising of two wires of dissimilar metals in the presence of temperature difference
seebeck effect
thermocouples are identified by
a single letter type and grouped according to their temperature range
thermocouple groups
base metals - up to 1000 C
noble metals - up to 2000 C
refractory metals - up to 2600 C
Base metals (single letter type)
J, E, T, K
noble metals (single letter type)
R, S, B
refractory metals (single letter type)
C, D, G
a word formed by combining thermal with resistor
thermistor
a temperature-sensitive resistor fabricated from semiconducting materials
thermistor
the resistance of thermistors decreases proportionally with
increase in temperature
the operating range of thermistors can be
-200 C to 100- C
thermistors are shaped as
rod, bead, or disc
it is a positive temperature coefficient device, which means that the resistance increases with temperature
resistance temperature detector (RTD)
the resistive property of a metal is called its
resistivity
the industry standard for RTD
platinum wire RTD (Pt100)
base resistance of Pt100
100.00 ohms at 0.0 C
the de facto industry standard for temperature measurement
Platinum Wire RTDs (PRTs)
mechanical temperature measurement devices that use the principle of thermal expansion of metals
bimetallic thermometers
consist of two metal strips with different coefficients of thermal expansion that are bonded together
bimetallic thermometers
two types of bimetallic thermometers
helical & spiral type
mechanical temperature measurement devices that use the expansion of a fluid, gas, or vapor inside a sealed system to indicate temperature changes
filled thermometers
components of a filled thermometer
bulb, capillary tube, pressure-responsive element, pointer and dial
is a technique for measuring temperature without physical contact
pyrometry
an apparatus for measuring high temperatures that uses the radiation emitted by a hot body as a basis for measurement
pyrometer
types of pyrometer
radiation and optical
methods of pressure measurement
- elastic/mechanical pressure transducers
- piezoelectric pressure transducers
- pressure measurement by measuring vacuum
- pressure measurement by balancing forces produced on a known area by measured force
- manometer method
elastic pressure transducers
bourdon tube pressure gauge
bellows
diaphragm pressure transducers
operates by the deformation of a curved, hollow tube under pressure, mechanically linked to a pointer that displays the pressure on a calibrated dial
bourdon tube pressure gauge
types of bourdon tube pressure gauge
c-type
helical type
spiral type
used to measure gauge pressures over very low ranges
diaphragm pressure gauge
types of diaphragm pressure gauge
metallic, slack
mechanical components made from thin-walled, corrugated metal or flexible material, designed to expand and contract axially when subjected to pressure changes
bellows
more sensitive that bourdon typed and used to measure low pressures
bellows
types of bellows
single and multiple
elements of electric pressure transducers
- pressure sensing element such as a bellow, a diaphragm, or a bourdon tube
- primary conversion element e.g. resistance or voltage
- secondary conversion element
AKA a strain gauge
piezoelectric pressure transducers
is a passive resistance-based pressure transducer
piezoelectric pressure transducers
what does piezoelectric pressure transducers measure
dynamic pressure (rapidly varying pressure)
what is not suitable for true static pressure measurement
piezoelectric pressure tansducers
when does piezoelectric pressure transducers produce output
when experiencing force or strain
a sensor that measures pressure by detecting changes in capacitance
capacitative pressure transducers
capacitative pressure transducers consist of two parallel plates:
one plate is fixed and the other is a flexible diaphragm that moves with applied pressure
is a resistive-type sensor that measures pressure by detecting changes in resistance
potentiometer pressure transducers
it operates using a sliding contact moving along a resistive element in response to pressure changes
potentiometer pressure transducers
measures the difference between two pressures applied at separate ports
differential pressure cell
differential pressure cell is commonly used in
flow measurement, level sensing, and filtration systems
what does electrical differential pressure transducers convert
pressure differences into electrical signals
designs that rely on mechanical movement; these types use fluid displacement, visual indicators, or mechanical linkages
non-electrical differential pressure cells
level sensors application
inventory
control
alarm
data logging
- Simple and cheap
- Can be used with any wet material and not affected by density.
- Can not be used with pressurized tanks
- Visual indication only (electronic versions are available)
dipstick
similar to a dipstick found in a car, it has weighted line markings to indicate depth or volume
rod gauge
- The pressure of the fluid in the tank causes the tape to short-circuit, thus changing the total resistance of the measuring tape.
- An electronic circuit measures the
resistance; it’s directly related to the liquid level in the tank.
resistance tape
- simple and direct method of measuring liquids through a viewing glass
- can be used in a pressurized tank (as long as the glass or plastic tube can handle the pressure)
- Good for applications where non-contact measurement is needed (like beverages)
sight glass
- Used where the sight glass level gauge can not be used
- Magneto-resistive types can provide an electrical output.
- Liquid/liquid interface (such as water and oil) can be measured by changing the buoyancy of the magnetic float
magnetic level sensor
ride the surface level to provide the measurement
floats
infer level by measuring the hydrostatic head produced by the liquid column.
hydrostatic head
- allow the indicator to be located anywhere
- air pressure in the tube varies
- with the head pressure of the height of the liquid
- Can’t be used in closed tanks or where purging a liquid is not allowed.
- Very popular in the paper industry because the air purge keeps the tube from plugging.
bubblers
is immersed in the tank and the buoyant force of the liquid produces a torque which is proportional the amount of liquid level
displacers
- a method used to determine liquid levels based on the electrical conductivity of the fluid.
- It works by detecting whether an electrical circuit is completed between electrodes when immersed in a conductive liquid. Not suitable for non-conductive fluids (e.g., oil, distilled water).
- Can detect single or multiple levels based on probe placement and requires minimal maintenance
- Ideal for high/low-level alarms and pump control applications.
conductivity level measurement
- non-contact method used to determine the level of liquids or solids using sound waves
- an ultrasonic wave is sent from a transducer, reflects off the liquid/solid surface, and returns to the sensor.
ultrasonic level measurement
- also called microwave level sensors) use radio waves to measure the level of liquids
or solids in a tank or silo - works on the principle similar to ultrasonic sensors, but uses electromagnetic waves (microwaves) instead of sound waves.
radar level measurement
placed at the bottom of the tank measure the weight and then convert it to an electrical signal.
load cells (strain gauge transducers)
Tank level is determined by the weight of the quantity of material
Load Cell Level Measurement
types of flow meters
differential pressure meters
rotary meters
point velocity meters
mass flow meters
new flow meters
- measure fluid flow by creating a pressure drop across a constriction in the pipe.
- The principle is based on Bernoulli’s equation, which states that as the velocity of a fluid increases, its pressure decreases.
differential pressure flow meter
common types of differential pressure flow meter
orifice plate
venturi
flow nozzle
pitot tube
a thin plate with a hole in the center
orifice plate flow meter
a tapered tube that minimizes pressure loss
venturi flow meter
similar to a venturi but with a simpler deisgn
flow nozzle
measures flow velocity at a single point in the pipe
pitot tube
also known as positive displacement (PD) meters, measure fluid flow by trapping and displacing a fixed volume of fluid through a rotating mechanism.
Rotary Meters
They work by counting the number of times the chamber fills and empties, providing a direct measurement of volumetric flow rate.
rotary meters
common types of rotary meters
rotary vane meter
lobed rotary meter
helical(screw) meter
types of rotary meter that uses vanes that move within a rotating chamber
rotary vane meter
types of rotary meter that uses two lobed rotors that rotate in opposite directions
lobed rotary meter
types of rotary meter that uses two interlocking helical rotors for smooth flow measurement
helical (screw) meter
measure fluid flow by detecting the rotational speed of a turbine wheel placed in the fluid stream.
turbine flow meters
the rotation speed of the turbine is proportional to _____, which is used to
the velocity of the fluid, determine flow rate
common types of turbine flow meters
axial turbine meter
radial turbine meter
insertion turbine meter
type of turbine flow meter that uses a straight-flow turbine aligned with the pipe axis
axial turbine meter
type of turbine flow meter that uses a perpendicular turbine for high-pressure applications
radial turbine meter
type of turbine flow meter that has a probe-style turbine inserted into large pipelines
insertion turbine meter
- Works on Faraday’s Law of Electromagnetic Induction: A voltage is induced when a conductive fluid passes through a magnetic field.
- The voltage generated is proportional to the velocity of the fluid, which is used to calculate flow rate.
Electromagnetic Flow Meter
- Uses the Von Kármán Vortex Street effect, where fluid flowing past an obstruction creates alternating vortices.
- The frequency of vortex shedding is proportional to the flow rate.
Vortex Shedding Flow Meter
Uses ultrasonic sound waves to measure flow by detecting the time difference between signals moving with and against the flow.
Ultrasonic Flow Meter
types of Ultrasonic Flow Meter
transit-time ultrasonic meter
doppler ultrasonic meter
type of Ultrasonic Flow Meter that Measures the time it takes for sound waves to travel upstream vs. downstream.
Transit-Time Ultrasonic Meter
type of Ultrasonic Flow Meter that Measures frequency shift caused by moving particles in the fluid.
Doppler Ultrasonic Meter
Measures flow rate by analyzing time delays between signals detected at two points in the pipeline.
Cross-Correlation Flow Meter
- Uses a tracer substance (such as a dye, isotope, or chemical marker) added to the flow.
- Measures the concentration change over time to determine flow rate.
Tracer Flow Meter
- Uses swirling fluid motion generated by a fixed obstruction.
- Measures the frequency of swirling patterns to determine flow rate
Swirl Flow Meter
- Uses specially designed fluidic oscillators to create periodic flow patterns.
- The frequency of oscillation is proportional to the flow rate.
Fluidic Flow Meter
- measure the mass flow rate of a fluid based on the Coriolis effect.
- When fluid flows through a vibrating tube, it experiences Coriolis forces, causing a phase shift in vibration.
- The amount of phase shift is directly proportional to the mass flow rate.
Coriolis Mass Flow Meter
