Alternating current is an electric current which periodically reverses direction, in contrast to direct current which flows only in one direction. Alternating current is the form in which electric power is delivered to businesses and residences, it is the form of electrical energy that consumers use when they plug kitchen appliances, televisions and electric lamps into a wall socket. A common source of DC power is a battery cell in a flashlight; the abbreviations AC and DC are used to mean alternating and direct, as when they modify current or voltage. The usual waveform of alternating current in most electric power circuits is a sine wave, whose positive half-period corresponds with positive direction of the current and vice versa. In certain applications, different waveforms are used, such as square waves. Audio and radio signals carried on electrical wires are examples of alternating current; these types of alternating current carry information such as sound or images sometimes carried by modulation of an AC carrier signal.
These currents alternate at higher frequencies than those used in power transmission. Electrical energy is distributed as alternating current because AC voltage may be increased or decreased with a transformer; this allows the power to be transmitted through power lines efficiently at high voltage, which reduces the energy lost as heat due to resistance of the wire, transformed to a lower, voltage for use. Use of a higher voltage leads to more efficient transmission of power; the power losses in the wire are a product of the square of the current and the resistance of the wire, described by the formula: P w = I 2 R. This means that when transmitting a fixed power on a given wire, if the current is halved, the power loss due to the wire's resistance will be reduced to one quarter; the power transmitted is equal to the product of the voltage. Power is transmitted at hundreds of kilovolts, transformed to 100 V – 240 V for domestic use. High voltages have disadvantages, such as the increased insulation required, increased difficulty in their safe handling.
In a power plant, energy is generated at a convenient voltage for the design of a generator, stepped up to a high voltage for transmission. Near the loads, the transmission voltage is stepped down to the voltages used by equipment. Consumer voltages vary somewhat depending on the country and size of load, but motors and lighting are built to use up to a few hundred volts between phases; the voltage delivered to equipment such as lighting and motor loads is standardized, with an allowable range of voltage over which equipment is expected to operate. Standard power utilization voltages and percentage tolerance vary in the different mains power systems found in the world. High-voltage direct-current electric power transmission systems have become more viable as technology has provided efficient means of changing the voltage of DC power. Transmission with high voltage direct current was not feasible in the early days of electric power transmission, as there was no economically viable way to step down the voltage of DC for end user applications such as lighting incandescent bulbs.
Three-phase electrical generation is common. The simplest way is to use three separate coils in the generator stator, physically offset by an angle of 120° to each other. Three current waveforms are produced that are equal in magnitude and 120° out of phase to each other. If coils are added opposite to these, they generate the same phases with reverse polarity and so can be wired together. In practice, higher "pole orders" are used. For example, a 12-pole machine would have 36 coils; the advantage is. For example, a 2-pole machine running at 3600 rpm and a 12-pole machine running at 600 rpm produce the same frequency. If the load on a three-phase system is balanced among the phases, no current flows through the neutral point. In the worst-case unbalanced load, the neutral current will not exceed the highest of the phase currents. Non-linear loads may require an oversized neutral bus and neutral conductor in the upstream distribution panel to handle harmonics. Harmonics can cause neutral conductor current levels to exceed that of all phase conductors.
For three-phase at utilization voltages a four-wire system is used. When stepping down three-phase, a transformer with a Delta primary and a Star secondary is used so there is no need for a neutral on the supply side. For smaller customers only a single phase and neutral, or two phases and neutral, are taken to the property. For larger installations all three phases and neutral are taken to the main distribution panel. From the three-phase main panel, both single and three-phase circuits may lead off. Three-wire single-phase systems, with a single center-tapped transformer giving two live conductors, is a common distribution scheme for res
An Irrigation sprinkler is a device used to irrigate agricultural crops, landscapes, golf courses, other areas. They are used for cooling and for the control of airborne dust. Sprinkler irrigation is the method of applying water in a controlled manner in way similar to rainfall; the water is distributed through a network that may consist of pumps, valves and sprinklers. Irrigation sprinklers can be used for residential and agricultural usage. Higher pressure sprinklers that themselves move in a circle are driven by a ball drive, gear drive, or impact mechanism; these can be designed to rotate in a partial circle. Rainguns are similar to impact sprinkler, except that they operate at high pressures of 40 to 130 lbf/in² and flows of 50 to 1200 US gal/min with nozzle diameters in the range of 0.5 to 1.9 inches. In addition to irrigation, guns are used for industrial applications such as dust suppression and logging. Many irrigation sprinklers are buried in the ground along with their supporting plumbing, although above ground and moving sprinklers are common.
Most irrigation sprinklers operate through electric and hydraulic technology and are grouped together in zones that can be collectively turned on and off by actuating a solenoid-controlled valve. Home lawn sprinklers vary in their size and complexity, they include impact sprinklers, oscillating sprinklers, drip sprinklers, underground sprinkler systems, portable sprinklers. Permanently installed systems may operate on timers or other automated processes, they are installed with retractable heads for aesthetic and practical reasons, reducing damage during lawn mowing. These types of systems can be programmed to automatically start on a set time and day each week. Small portable sprinklers can be temporarily placed on lawns if additional watering is needed or if no permanent system is in place; these are attached to an outdoor water faucet and are placed for a short period of time. Other systems may be professionally installed permanently in the ground and are attached permanently to a home's plumbing system.
An antique sprinkler developed by Nomad called a'set-and-forget tractor sprinkler' was used in Australia in the 1950s. Water pressure ensured that the sprinkler moved across a lawn; the first use of sprinklers by farmers was some form of golf course type sprinklers. These ad hoc systems, while doing the job of the buried pipes and fixed sprinkler heads, interfered with cultivation and were expensive to maintain. Center-pivot irrigation was invented in 1940 by farmer Frank Zybach, who lived in Strasburg, Colorado. In the 1950s a firm based in Portland, Oregon Stout-Wyss Irrigation System, developed a rolling pipe type irrigation system for farms that has become the most popular type for farmers irrigating large fields. With this system large wheels attached to the large pipes with sprinkler heads move across the field. Underground sprinklers function through means of basic hydraulic technology; this valve and all of the sprinklers that will be activated by this valve are known as a zone. Upon activation, the solenoid, which sits on top of the valve is magnetized lifting a small stainless steel plunger in its center.
By doing this, the activated plunger allows air to escape from the top of a rubber diaphragm located in the center of the valve. Water, charged and waiting on the bottom of this same diaphragm now has the higher pressure and lifts the diaphragm; this pressurized water is allowed to escape down stream of the valve through a series of pipes made of PVC or polyethylene pipe. At the end of these pipes and flush to ground level are pre spaced out sprinklers; these sprinklers can be fixed spray heads that have a set pattern and spray between 1.5–2m, full rotating sprinklers that can spray a broken stream of water from 6–12m, or small drip emitters that release a slow, steady drip of water on more delicate plants such as flowers and shrubs. Use of indigenous materials recommended. In 2017, it was reported that use of common garden hoses in combination with spray nozzles may generate aerosols containing droplets smaller than 10 μm, which can be inhaled by nearby people. Water stagnating in a hose between uses when warmed by the sun, can host the growth and interaction of Legionella and free-living amoebae as biofilms on the inner surface of the hose.
Clinical cases of Legionnaires' disease or Pontiac fever have been found to be associated with inhalation of garden hose aerosols containing Legionella bacteria. The report provides measured microbial densities resulting from controlled hose conditions in order to quantify the human health risks; the densities of Legionella spp. identified in two types of hoses were found to be similar to those reported during legionellosis outbreaks from other causes. It is proposed. Drip irrigation Feynman sprinkler Irrigation Sprinkler system timer
A water timer is an electromechanical device that, when placed on a water line, increases or decreases the water flow through the use of an embedded valve. It is used in conjunction with irrigation sprinklers to form an automated or non-automated sprinkler system, capable of administering precise amounts of water, at a regular basis. An alternative to a water timer to administer precise amounts of water at a regular basis, is to calculate the needed waterflow and arrange a system composed by a Time switch and an electric pump that; the electric pump is to be arranged to be turned on and off at regular intervals by the time switch to administer precise and regular water quantities. This approach, used in DIY watering systems, allows financial savings as the water timer can be discarded. For high-end applications however, water timers sometimes allow more options. Sprinkler system timer, an electrical device? that can control water timers Solenoid valve
Irrigation is the application of controlled amounts of water to plants at needed intervals. Irrigation helps to grow agricultural crops, maintain landscapes, revegetate disturbed soils in dry areas and during periods of less than average rainfall. Irrigation has other uses in crop production, including frost protection, suppressing weed growth in grain fields and preventing soil consolidation. In contrast, agriculture that relies only on direct rainfall is referred to as rain-fed or dry land farming. Irrigation systems are used for cooling livestock, dust suppression, disposal of sewage, in mining. Irrigation is studied together with drainage, the removal of surface and sub-surface water from a given area. Irrigation has been a central feature of agriculture for over 5,000 years and is the product of many cultures, it was the basis for economies and societies across the globe, from Asia to the Southwestern United States. Archaeological investigation has found evidence of irrigation in areas lacking sufficient natural rainfall to support crops for rainfed agriculture.
The earliest known use of the technology dates to the 6th millennium BCE in Khuzistan in the south-west of present-day Iran. Irrigation was used as a means of manipulation of water in the alluvial plains of the Indus valley civilization, the application of it is estimated to have begun around 4500 BC and drastically increased the size and prosperity of their agricultural settlements; the Indus Valley Civilization developed sophisticated irrigation and water-storage systems, including artificial reservoirs at Girnar dated to 3000 BCE, an early canal irrigation system from c. 2600 BCE. Large-scale agriculture was practiced, with an extensive network of canals used for the purpose of irrigation. Farmers in the Mesopotamian plain used irrigation from at least the third millennium BCE, they developed perennial irrigation watering crops throughout the growing season by coaxing water through a matrix of small channels formed in the field. Ancient Egyptians practiced basin irrigation using the flooding of the Nile to inundate land plots, surrounded by dykes.
The flood water remained until the fertile sediment had settled before the engineers returned the surplus to the watercourse. There is evidence of the ancient Egyptian pharaoh Amenemhet III in the twelfth dynasty using the natural lake of the Faiyum Oasis as a reservoir to store surpluses of water for use during dry seasons; the lake swelled annually from the flooding of the Nile. The Ancient Nubians developed a form of irrigation by using a waterwheel-like device called a sakia. Irrigation began in Nubia some time between the third and second millennia BCE, it depended upon the flood waters that would flow through the Nile River and other rivers in what is now the Sudan. In sub-Saharan Africa irrigation reached the Niger River region cultures and civilizations by the first or second millennium BCE and was based on wet-season flooding and water harvesting. Evidence of terrace irrigation occurs in pre-Columbian America, early Syria and China. In the Zana Valley of the Andes Mountains in Peru, archaeologists have found remains of three irrigation canals radiocarbon-dated from the 4th millennium BCE, the 3rd millennium BCE and the 9th century CE.
These canals provide the earliest record of irrigation in the New World. Traces of a canal dating from the 5th millennium BCE were found under the 4th-millennium canal. Ancient Persia used irrigation as far back as the 6th millennium BCE to grow barley in areas with insufficient natural rainfall; the Qanats, developed in ancient Persia about 800 BCE, are among the oldest known irrigation methods still in use today. They are now found in the Middle East and North Africa; the system comprises a network of vertical wells and sloping tunnels driven into the sides of cliffs and of steep hills to tap groundwater. The noria, a water wheel with clay pots around the rim powered by the flow of the stream, first came into use at about this time among Roman settlers in North Africa. By 150 BCE the pots were fitted with valves to allow smoother filling as they were forced into the water; the irrigation works of ancient Sri Lanka, the earliest dating from about 300 BCE in the reign of King Pandukabhaya, under continuous development for the next thousand years, were one of the most complex irrigation systems of the ancient world.
In addition to underground canals, the Sinhalese were the first to build artificial reservoirs to store water. These reservoirs and canal systems were used to irrigate paddy fields, which require a lot of water to cultivate. Most of these irrigation systems still exist undamaged up to now, in Anuradhapura and Polonnaruwa, because of the advanced and precise engineering; the system was further extended during the reign of King Parakrama Bahu. The oldest known hydraulic engineers of China were Sunshu Ao of the Spring and Autumn period and Ximen Bao of the Warring States period, both of whom worked on large irrigation projects. In the Sichuan region belonging to the state of Qin of ancient China, the Dujiangyan Irrigation System devised by the Qin Chinese hydrologist and irrigation engineer Li Bing was built in 256 BCE to irrigate a vast area of farmland that today still supplies water. By the 2nd century AD, during the Han Dynasty, the Chinese used chain pumps which lifted water from a lower elevation to a higher one.
These were powered by manual foot-pedal, hydraulic waterwheels, or rotating mechanical wheels pulled by oxen. The water was used for public works, providing water for urban residential quarters and palace gardens, bu
Rain Clox was the trade name given to a series of electromechanical irrigation controllers produced by the Rain Bird Corporation from 1962 to the late 2000s, were responsible for giving rise to the widespread use of automatic irrigation. The first model was the ME11AB, capable of running 11 stations on two schedules. A scaled-down residential model, the RC-8, was formally introduced in 1968 and was marketed as the "first appliance for the garden"; the Los Angeles Times reported in 1967 that architects incorporated the RC-8 into a suburban housing development in Glendale, planning on adding the cost of the system to the mortgage. The controllers were used in controlled experiments of swine waste lagoon systems; the product line would range from compact 3-station mechanical units to 23-station multi-program devices. The Rain Clox series controllers were known for their durability. In 1997, Rain Bird held a contest to find the oldest functioning controller locating an RC-8 manufactured in 1964, still functioning after it survived a tornado.
A considerable online aftermarket for the controllers has appeared following their discontinuation. Dual-schedule controllers with individual switches for each station to run on either B program. Rain Bird resurrected this design as the "Turfmaster". RC-3 RC-8 RC-12 RC-18 RC-23 These featured a single 14-day watering schedule and 23 possible on-the-hour start times; the RC-A series controllers were replaced by the RC-B and RC-C series following improvements in mechanical design. RC-4A - 4 stations, 1–60 minutes. RC-7A - 7 stations, 1–60 minutes. RC-1230A - 12 stations, 1–30 minutes in 1-minute increments RC-1260A - 12 stations, 2–60 minutes in 2-minute increments These consisted of two RC-A series controllers in one unit which operated in sequence, with the capability of switching off the lower controller on a given day. Zones requiring less watering would thus be assigned to the lower unit; the 12th station on the upper unit was replaced with a tripper mechanism to start the lower unit. RC-1830AB - 11 stations, 1–30 minutes in 1-minute increments.
RC-1860AB - 11 stations, 2–60 minutes in 2-minute increments. RC-2330AB - 11 stations, 1–30 minutes in 1-minute increments. RC-2360AB - 11 stations, 2–60 minutes in 2-minute increments. Master control units for golf courses, consisting of a single RC-A unit which operated three separately timed sets of stations. MC-3S - Three sets of 12 stations, 1-10 minutes