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Process Instrument of Week 12, Juthatip Youchang 61010162 - Coggle…
Process Instrument of Week 12
Level Measurement
Capacitance
The oldest form of measurementis often used in filler bowls, oil reservoirs, and short chemical storage vessels
The capacitance level sensor works like an electronic capacitor
Types of capacitive level probes
Conductive liquids
It cannot be used as the dielectric (insulating) medium of a capacitor
Capacitive level probes designed are coated with plastic or some other dielectric substance
Nonconductive liquids
It used as the dielectric itself, with the metal wall of the storage vessel forming the second capacitor plate
The probe is just a bare metal cable or rod
Applications
Measurement electronic level for interface applications involving layers
Advantages
It quick response speed
The wide variety of media that it can measure
limitation
It only works with a ground reference point
Criteria used for measuring the appropriate level
Range or height of measurement
Accuracy and repeatability
Material to be measured
Type of measurement (continuous level, interface or point level)
Physical or chemical changes to material in container
Vapors in the air space with temperature changes or heavy dust
Material of container
Pressure and temperature
Dielectric constant
Desired output or information from field device
Solids or liquids to be measured
Analytical Measurement
pH measurement
The measurement of the hydrogen ion activity in a liquid solution
Types of pH meter
Colorimetric pH measurement
The simplest to measure the pH of a solution is by color
In general litmus paper is used in the laboratory to find the pH value
Natural pH indicator
This hydrangea plant indicates acidic soil by the violet color of its blossoms
Red cabbage is chopped and cooked the cabbage juice comes out is pH sensitive.
Potentiometric
Use is electrochemical
Special pH -measurement electrodes
Manufacture with closed end made of this glass, a small quantity of buffer solution contained within the glass bulb
The measurement and reference electrodes provide a voltage-generating element sensitive to the pH value
To always keep the glass electrode wet
Buffer solution inside the bulb formulated to maintain a constant pH value of 7.0
Viscosity Measurement
Types
Capillary viscometer:(Laboratory type)
Liquid passing through a capillary tube is directly proportional to its absolute viscosity
Cannon-Fenske Routine
Is a rugged and inexpensive viscometer
The works well if the liquid to be measured is transparent or translucent
Ubbelohde
Used to measure transparent liquids
Suitable to measure with liquids with high viscosity
Suspended level viscometers possess the same viscometer constant at all temperatures
Reverse Flow Viscometers
Designed for testing opaque liquids
Must be cleaned, dried, and refilled before a repeat measurement can be made
Dilution Viscometers
Estimates of the molecular size and shape of large polymer molecules
Diluted polymer solutions show a change in kinematic viscosity as the shear rate changes
Vacuum Viscometers
The liquid is too viscous to flow under gravity can measured viscosity by vacuum viscometer
Require a vacuum that is very accurately controlled
Efflux cup viscometers: (Saybolt viscometer)
Used for fieldwork to measure the viscosity of oil, syrups, vanish, paint, and bitumen emulsions
The standard instrumentation testing petroleum products
Types of orifices
furol
Road-oil
Universal
Most commonly used
Efflux time
Measured through fixed orifice at the bottom of a cup
Designed as Saybolt Universal Second(SUS)
Falling ball viscometers
Operates on Stoke’s falling-ball principle
Measurement of high viscosity fluids
Measurement is made by timing the ball of the ball through the accurately calibrated distance between two marks on the glass tube
Rotational viscometers
Its ease of operation
Spindle geometries
Disc spindles
Is the most prevalent
Cylindrical spindles
This type of spindle does not require large samples
Polymer manufacturers often choose this spindle geometry
Cone spindles
The benefit of accommodating even smaller sample sizes
Vane and T-bar spindles
Both used to measure soft solid-like materials that flow with some difficulty
Spiral spindle
Can be rotated at different speedsty
The typically used at a single rotational speed and provideonly one data point for viscosity
Use a spring to measure the torque required to rotate a spindle immersed in a sample liquid
The measured viscosity depends on the geometry of the spindle (shape and size) and the speed of rotation
Measurements provide a wealth of information about a material
Humidity Measurement
Two terms
Humidity
Connected with the amount of water vapor present in air or gas
Measuring humidity is determining the amount of water vapor in a gas
Moisture
Used to indicate the amount of water vapor adsorbed in liquid or absorbed by a solid
Methods of humidity
Sorption methods
Changes of the dimensions
Hair hygrometer & hair hygrograph
Changes of electrical properties
Electronic hygrometer
Psychrometric methods
Dry-bulb
Wet-bulb
Condensation methods
Llithium chloride dewpoint hygrometer
Chilled-mirror dewpoint hygrometer
Psychrometer
Measures the actual air (dry-bulb) temperature
Types
Sling Psychrometer
The simple design, low cost, and portability
Is constructed of two thermometers secured to a frame
This thermometer is reffered the wet bulb while the other thermometer is termed the dry bulb
Aspirating Psychrometer
Is a mechanized unit, compact and easily transportable
Accuracy, less chance for procedural error, and usefulness in confined areas
The other one is covered with a wet-bulb temperature
Hair hygrometer & hair hygrograph
The change of length of certain organic or synthetic fiber when these are exposed to a moist atmosphere
The expansion and contraction of fiber creates a change in length
Electronic hygrometer (capacitive type)
Capactive type sensors
Consists of hygroscopic dielectric material sandwiched between a pair of electrodes forming a small capacitor
Use a plastic or polymer as the dielectric material
Very linear and hence can measure RH from 0% to 100% require complex circuit and also need regular calibration
Resistive type sensors
The sensor element changes in response to humidity changes, and the capacitance changes are extracted as electrical signals
The difficulty in measuring low values (below 5%RH)
The change is impedance is too high and difficult to control the dynamics
Temperature effects the properties significantly
Chilled-mirror dewpoint hygrometer
By noting the temperature of polished metal surface(mirror) when the first traces of condensation(fogging) appear
The temperature of the metallic mirror is measured using a platinum resistance thermometer
Condensation used a photo-detector with the reflection of a light-emitting diode (LED) on the mirror
Lithium chloride dewpoint hygrometer (Dewcel)
Used to determine the dewpoint
Consists of temperature sensor covered with wicking soaked in a solution of lithium chloride, and over which is wound a pair of bare gold wires
The electrical potential applied to the wires
The flow of current through the lithium chloride solution
Raises the temperature of the solution
Juthatip Youchang 61010162