Foam
F0am is made up of trapped bubbles in a liquid or solid, separated from one another by films of liquid. Although foam is fragile, the liquid films are resilient and have a plastic quality. The bubbles are spherical when the liquid films are quite thick, approximately 0.01mm.
Manufactured foams have special properties, such as low density, lightness and compressibility, that make them suitable as thermal insulators, flotation devices, and packing material. Liquid foams are often used to extinguish fires and are called fire retardant foams. However many foams are simply a by-product formed in chemical processes through agitation or aeration of liquids. So foam controllers are used to remove the foam.
Foam Controllers
Foam can cause many problems in process equipment by fouling level sensors leading to overflows, as well as reducing the speed of machinery. Foam can reduce pump efficiency, reduce the capacity of the tank, allow bacteria to grow, formation of dirt deposits, reduced effectiveness of the liquid solution, drainage problems for sieves and filters, and additional costs of cleaning, downtime and imperfect products. Factors that may produce foam include leaky seals on pumps, high pressure pumps, or poor system design for the inlet and outlet of a tank.
To sense foam in a tank or in the process equipment a specialised foam sensor and controller should be used. Specialised foam sensors will ensure that they are not fouled up and still work reliably even when covered in foam. A defoamer is also used to reduce and prevent the generation of foam through adding chemicals to the process liquid. Defoamers can address both surface foam and entrained air. A defoamer is insoluble, has low viscosity and an ability to spread rapidly on foamy surfaces. It causes the rupture of air bubbles to break down foam. However in food and pharmaceutical processes chemical defoamers cannot be used because of risk of contamination, so mechanical methods are used.
What are transmitters?
A transmitter is an electronic gadget that sends information to a receiver through electromagnetic signals. An example of a non-electronic transmitter would be a person’s vocal cords- the vocal cords create a signal (sound) that transmits information to another person (who receives it through their ears). Electronic transmitters usually consist of a power supply, an oscillator (a circuit that generates a repetitive signal), a modulator (modulates the signal from one waveform to another), and an amplifier (increased the strength of the signal).
All telecommunication devices- phones, radios, televisions, computers- contain a transmitter to send information. Devices that contain both a transmitter and a receiver (to receive the signal and interpret it), are called transceivers. For example, a mobile phone is a transceiver because it both sends and receives signals.
Level Transmitter
In industrial applications transmitters are used to convert measurements from a sensor to a display for a user. Level transmitters measure the level of both liquids and solids within a defined space (such as a tank) and send the information via a signal to a receiver (either a computer-controlled device or a user). Level transmitters can measure levels at determined points (such as when a specific level is reached or at certain intervals) or continuously (measuring within a specified range and providing a continous reading of the level). Between these is a multiple point level transmitter.
Level transmitters use a range of different techniques and technologies to determine levels such as ultrasonic , electrical conductivity, magnetic floats, pressure, capacitive and optical. Some examples of different types of level transmitters include Hydrostatic Tank Gauging, Magnetostrictive Tank Gauging, Interface Level monitoring (Oilset), Guided Microwave Level Transmitter and Hydrostatic Bubblers.
Fuel Terminals
Fuel Terminals provide fuel for vehicles, whether petrol or diesel. Today there is an increasing market for alternative fuels as well, giving rise to eco-friendlier fuel terminals providing ethanol fuel, biodiesel, natural gas, hydrogen, or electricity. Natural gas includes be liquified petroleum gas (LPG) and compressed natural gas (CNG). Sometimes fuel is blended before being dispensed. For example, blending is used to produce an intermediate octane rating, rather than have just high or low octane fuel (octane ratings measure the resistance of gas to detonation in spark-ignition internal combustion engines, defined through the ratio of iso-octane to heptane).
Fuel Terminal Equipment
Fuel dispensers are known by different names across different continents- from gas pumps in the USA, to petrol pumps in UK-influenced countries, and bowsers in Australia, New Zealand and Canada. The components used for dispensing fuel at a fuel terminal include the pump, dispenser, tank gauge, POS, electric motor, meters, pulsers and valves. Some fuel dispensers also have ‘pay at the pump’ devices. Basically, a fuel dispenser is divided into an embedded computer and a mechanical unit. The computer contorls the pump action, its displays (price, litres), and communicates with the vendor (POS- Point of Sale). The mechanical section does the actual pumping of the fuel and controls the physical fuel flow.
Other fuel terminal equipment includes the hose and nozzle. A fuel dispenser may have several nozzles dispensing different fuels, so the nozzles are usually colour coded to distinguish between, for example, high octane fuel, an ethanol blend and unleaded gas. The hoses used are designed to endure tough treatment whether being driven over or yanked from the dispenser to prevent accidents. This means they use heavy duty springs or coils for extra durability. Most dispensers also have an automatic cut-out to stop the flow of fuel once the tank is full. A sensing tube in the nozzle senses the level of fuel by detecting the change in pressure when displaced air is no longer being drawn up the sensing tube.