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How to improve jaw crusher performance and productivity
Описание: How to improve jaw crusher performance and productivity Everyone wants to get the most out of their equipment, and jaw crusher operators are no exception. There are several factors that affect crusher performance and thus the whole circuit. Here are a few things that can help you avoid production losses. Avoid bridging Continuous bridging in the feeding area of jaw crushers is a common problem. WHAT IS IT? Bridging means stones blocking the flow from entering or moving down in the crushing chamber. It can be caused by just one stone that is larger than the feed opening, or then many average-sized stones of crossing against each other and blocking the crusher's feed. WHY IT IS A PROBLEM? Bridging can cause a significant loss of production that oftentimes goes unnoticed. It is relevant to keep an eye on bridging in the feeding area of a primary crusher as it can take several minutes to resolve the issue (big rock being removed, fragmented or directed to the chamber). If it occurs say ten times in a day, it quickly leads to one hour of lost production. If that happens, for instance, in one of our crusher models including stone crusher, cone crusher, etc., C130 with 352 short ton per hour (stph) working capacity and assuming a USD 12 /short ton, the daily loss can easily add up to four thousand dollars. HOW TO PREVENT BRIDGING? Bridging can be avoided by implementing a tight control of the blasting grid to avoid generating oversize material, training the truck loader operator to separate the oversize material at the pit and the primary crushing plant operator visualizing the flow of material to the crusher and controlling the stones' speed and direction by varying feeder speed and using the hydraulic hammer installed in the area. Apply the proper jaw die profile There are many kinds of rocks, differing in crushability, abrasiveness, flakiness, etc. Choosing the best combination of fixed and movable jaw dies profiles will help to optimize production when crushing difficult material. A Rock of low crushability requires a closer nip angle to keep the capacity as designed. A highly abrasive rock requires thicker and heavier jaw dies that last longer, thus avoiding loss of production due to frequent stops to replace them. Flaky rock requires toothed jaw dies to crush it into more cubical pieces, avoiding stops due to bridging and belt cutting along the crushing circuit. Having the appropriate jaw die profile saves more than 20% of production capacity that would otherwise be a loss. Let's use the same example scenario as in the first one with the C130 model. We would have approximately a 70 stph reduction in production, in other words, a decrease of USD 4000 to 8000 in revenue for one day. Monitor the condition of jaws Besides being an important item for the dryer machine's performance, the jaw crusher's jaws are responsible for front frame and swing jaw protection. Wear generally causes loss in production due to increased crushing angle, loss of tooth profile, reduction of the CSS to compensate the possible lamellar effect, etc. That is why it needs to be monitored throughout the crusher's lifecycle. As excessive wear can cause a 10–20% reduction in production, it is important to find the optimal time for the jaw turn or change in terms of cost and benefit. Again, with the same scenario with C130, we would have approximately a 70 stph reduction in production, in other words, a decrease of USD 4000 to 8000 in revenue for one day. Is an Impact Crusher right for my business? To summarise, an Impact Crusher has more versatility than a Jaw and Cone Crusher since it can simultaneously perform primary and secondary duties. We're big fans of Impact Crushers as wastes recyling because they produce excellent results for our customers and have thus far; been unbeatable as a total machine solution. Want more information on Crushing Solutions or a Consultative approach to choosing your next machine? We can help by providing a profitability calculator, production forecast and a full costing run down.
Дата Публикации: 01-11-22
7 Types Of Wound Dressings & When To Use Each
Описание: 7 Types Of Wound Dressings & When To Use Each When it comes to wound healing, it is vital to ensure that healing is as fast and effective as possible, for this using the right dressing is crucial. The type of dressing used for dressing a wound should always depend on various factors, including the type of injury, the size, location, and severity. At CLH, we have a range of different wound dressings on offer, each of which is ideal for treating different wounds. From hydrogel and hydrocolloid to alginate dressings, we have a wide range of options on offer. To make the process of choosing the right functional wound dressing for the injury, that little bit easier, we have put together the guide below, detailing what each of the seven most commonly used wound dressings should be used for. 1. Hydrocolloid Hydrocolloid dressings can be used on burns, wounds that are emitting liquid, necrotic wounds, pressure ulcers, and venous ulcers. These are non-breathable dressings that are self-adhesive and require no taping. The flexible material that they are made from makes them comfortable to wear and suitable for even the most sensitive of skin types. How these dressings work is by creating moist conditions which help to heal certain wounds; the surface is coated with a substance which contains polysaccharides and other polymers which absorb water and form a gel, keeping the wound clean, protecting it from infection, and helping it to heal more quickly. Hydrocolloid dressings are impermeable to bacteria, which is what makes them so effective at preventing infections. They are also long-lasting, biodegradable, and easy to apply. 2. Hydrogel Hydrogel can be used for a range of wounds that are leaking little or no fluid, and are painful or necrotic wounds, or are pressure ulcers or donor sites. Hydrogel can also be used for second-degree burns and infected wounds. Hydrogel dressings are designed to maximise patient comfort and reduce pain while helping to heal wounds or burns and fight infection. The cooling gel in products like Burn Soothe are what makes them so effective at reducing pain and speeding up the healing process. 3. Alginate Alginate dressings are made to offer effective protection for wounds that have high amounts of drainage, and burns, venous ulcers, packing wounds, and higher state pressure ulcers. These dressings absorb excess liquid and create a gel that helps to heal the wound or burn more quickly. Containing sodium and seaweed fibres, these dressings are able to absorb high amounts of fluid, plus they are biodegradable after use. These dressings require changing around every two days, sometimes more, due to the amount of liquid that they absorb and the nature of the wound care. Changing them too often could cause too much dryness or could lead to bacteria penetrating the wound. These should only be used for wet wounds with high liquid drainage; else they can hinder healing by drying out wounds too quickly. 4. Collagen Collagen dressings can be used for chronic wounds or stalled wounds, pressure sores, transplant sites, surgical wounds, ulcers, burns, or injuries with a large surface area. These dressings act including orthopedic external fixation as a scaffolding for new cells to grow and can be highly effective when it comes to healing. Collagen dressings encourage the wound healing process in a range of ways; these include by helping to remove dead tissue, aiding the growth of new blood vessels, and helping to bring the wound edges together, effectively speeding up healing. 5. Foam For wounds of varying degrees of severity, foam dressings can work incredibly well, as well as for injuries that exhibit odours. Foam dressings absorb exudates from the wound's surface, creating an environment that promotes faster healing. These dressings allow water vapour to enter, keeping the area moist, promoting faster healing, but prevent bacteria from entering the affected area. These dressings come in various sizes and shapes, as well as in a range of adhesive and non-adhesive options. 6. Transparent Transparent dressings are useful for when medical professionals or carers want to monitor wound healing, as these dressings cover the wound with a clear film. These make identifying potential complications much easier, such as by making infections easier to spot at an earlier time. For this reason, these kinds of dressings are often used on surgical incision sites, on burns and ulcers, and on IV sites. These dressings are breathable but impermeable to bacteria, helping to keep the wound clean and dry, preventing infection and speeding up healing. They are also flexible, which makes them comfortable to wear. 7. Cloth Cloth dressings are the most commonly used dressings, often used to protect open wounds or areas of broken skin. They are suitable for minor injuries such as grazes, cuts or areas of delicate skin. These dressings come in all shapes and sizes, from small coverings for fingers to larger ones for wounds and therapeutic patch across wider areas of the body. As well as pre-cut dressings, these also come in a roll option that is made to be cut to size.
Дата Публикации: 01-11-22
Marble vs Granite: Difference Between these two Materials
Описание: Marble vs Granite: Difference Between these two Materials Marble vs granite: in this article we will try to clarify the difference between marble and granite, two wonderful rocks. Both are natural sandstones extensively used in interior and exterior design, for modern and rustic furniture. They are characterized by high resistance, timeless beauty and versatility: but what is the difference between marble and granite? In order to analyze the granite marble difference, we must focus on three main aspects: geological, chemical and aesthetic difference. First of all, granite is a volcanic rock formed from molten magma that has cooled slowly over a period of time inside the earth's crust. This is the reason why granite is mainly made up of silicates, has a grain structure and is harder and more compact. On the contrary, marble is a metamorphic rock mainly made of calcium carbonate which is the result of the sedimentation on the seabed of various materials such as mud, shells, minerals and algae which, over time, following a process of transformation, have become a unique hardened material with a granular and crystalline structure. To simplify the difference between marble and granite, we can say that while marble forms in the sea, granite forms inside the earth's crust. Since granite is rich of silicates, it is tougher and more resistant especially to resistant to acid substances, scratches, wear and atmospheric agents. This is the main reason why granite is preferred in outdoors applications or in places where heavy foot traffic is expected. Yet, the processing of granite is not easy at all as it is cut and broken with difficulty and, in fact, its cost is on average higher than that of marble. The main difference between marble and granite probably lies in the aesthetic properties. On the one hand, granite is characterized by a particularly recognizable "speckled" effect and its color is determined by the variation in the percentage of minerals (such as quartz, mica, feldspar, amphibole, etc.) contained in the stone. Marble is unanimously considered more fascinating due to its irregular veins and varieties of colors based on its impurities. Difference between marble and granite: how to choose these materials in design The chemical-physical characteristics that depict the marble and granite difference also explain the use of these two materials in design. Granite, not being very absorbent and resistant to weak acids, it is largely used for the realization of countertops. Furthermore, granite is a very hard and cut resistant stone: all qualities that make it excellent for use in the kitchen. For the same reasons, granite is perfectly suitable for the production of walkable surfaces such as floors. Nevertheless, for this application granite sometimes does not adequately respond to the aesthetic criteria in vogue today; marble, instead, continues to be the preferred material in the marble vs granite flooring competition. Another difference between marble and granite in design concerns the production of pieces of furniture. Due to the difficult workability and the change in aesthetic standards, granite has been used less for furniture design compare to the 70s and the 80s when it was more popular. Today, however, it seems that a trend inversion is taking place. This is true also thanks to new types of finish available: with a matte finish, matt imported granite can beautifully adapt to more contemporary furnishing compared to the typical glossy finish granite. In conclusion, to the question granite vs marble dining table, the Customer's response may not be so obvious nowadays. Cultured marble vs granite Sometimes, when you need to realize a granite countertop, cultured marble is proposed as an alternative. Cultured marble is an industrial product and a type of faux marble which is made by the union of marble dust and a polyester resin. Even if cultured marble is generally a cheaper material which nicely mimics the look of natural stone, it is more durable than marble and it can be easily cleaned, it can still be damaged (ex. chipped, scratched or ruined by excessive heat) and maintenance or renovation operations are quite difficult. When it comes to the choice cultured marble vs granite, natural granite is still the best option as it is more durable, more easily maintained and its appearance has a charm that cannot be artificially replicated. Another quite common dispute in interior design is surely the choice between marble vs granite countertops. We do not believe that there is a better choice between the two materials but, beyond their geological and chemical difference, there are a number of aspects to consider when it comes to marble vs granite countertops. For what concerns durability, both materials are high resistant stones. However, granite is harder than Chinese marble and less porous so it is more difficult to get it cut, ruined by heat and stained. Moreover, both materials need regular sealing but marble surfaces require more careful cleaning compared to granite, this to avoid damaging the porous stone. Finally, talking of appearance, marble is unanimously recognized as the most versatile between the two. Marble veining is generally considered more elegant by designers and the infinite varieties offered by marble make this material more easily combined with styles that are also very different from each other, from rustic and traditional to luxurious and hyper-modern spaces. Marble tiles vs granite tiles When a floor must be realized, what is the best option? Marble tiles vs granite tiles? As previously mentioned, granite is very tough, scratch and stain resistant, easy to clean and perfect for heavy traffic areas (marble is not really suitable in this case as it may lose shine). However, as regards the creation of floors, marble is a stone that more easily meets the aesthetic taste of designers and customers; granite is mostly used for countertops. Lastly, both marble and granite surfaces are pretty cool and, unless the floor is installed in a very hot area (so that marble or granite can be quite pleasant underfoot), they need to be mixed with other flooring types in order to give warmth. In conclusion, marble tiles vs granite tiles? Whatever you choose, both are wonderful materials and what is certain is that nothing can substitute the natural beauty and elegance of stone.
Дата Публикации: 01-11-22
Is it worth buying a home espresso coffee machine?
Описание: Is it worth buying a home espresso coffee machine? We compare the cost and convenience of caffeinating at home versus a café. Coffee - that beverage that has most of us captured in its charm. For those of us who are official coffee addicts, we rarely go a day without having our cup (or cups). Those touch screen coffee machines that bring our coffee to our mugs are revered as sacred instruments. And the instant coffee machine rank among the many that bring us our brew every morning a€" and afternoon and evening as well! Coffee machines come in every shape, color, and configuration. Whatever level of convenience you desire; whatever brewing capacity you need; whatever time considerations are pertinent to you a€" ita€?s all out there in one machine. But for those who want a good, hot cup of coffee a€" fast a€" then the instant coffee machine is the thing to have. The instant coffee machine a€" most often seen in an office setting a€" allows the user to simply add the appropriate amount of water for one cup of coffee into the top of the machine, add the pre-measured coffee packet into the coffee compartment and press the on switch. Your coffee comes out almost immediately. The great part about the pre-made coffee packets is that they come in a variety of flavors that you can keep on hand and use depending on what you are in the mood to drink. The instant coffee machine is sold in number of retail stores. Depending on its functionality the price will vary accordingly. Most of the larger, more commercial machines are bigger and pricier. But you can also find a small instant coffee machine model for in home use as well. You can buy a large supply of the pre-made coffee packets at the same time. It may be a larger expense at the beginning but it will soon pay for itself as you save money on the pricey coffee shop lattes and espressos. The instant coffee machine is the fast way to getting the perfect cup of coffee in any flavor that you desire. Check out the varieties available on the market today and you can be well on the way to your perfect cup! 1. The cost to your pocket Given that a cup of coffee costs about $4 at a café, and as much as $5 in some areas (both regional and metro – it's not just the cosmopolitan cafés charging big bucks for their coffee), you could be spending upwards of $1500 a year if you have one cup of café coffee a day. And that number just goes up if you sometimes sneak in an extra brew or two, or get a muffin as well. So, would you be better off taking that cash and investing it in your own instant coffee machine? Let's have a look at the numbers. The cost of the machine At CHOICE, we review a wide range of coffee machines – automatic, semiautomatic, manual and pod, vending coffee machine– and they vary drastically in price from $37 to $3999. Pod or capsule coffee machines are usually cheaper than manual espresso machines (you can pick up a basic pod unit for less than $100 or splurge up to $699). But our expert taste testers agree that if you're fussy about flavour, a manual espresso machine will almost always give you the best, barista-like results. This is because it gives you the most control over the brewing process. The cost of the coffee: Ground vs pods You also need to take into account the cost of pods and capsules if you have a pod or capsule machine, or ground coffee or beans if you have a manual or automatic. This is where your cash outlay will vary wildly. Although you can pick up a bag of ground coffee from the supermarket for as little as $12 per kilogram, coffee aficionados will argue the best results will come from barista beans, which could cost you about $50 or more per kilogram. Depending on the size of your grind, a kilogram of beans should give you about 120 to 140 single shots of coffee or 60 to 70 double shots (based on eight grams for a single shot, 16 for a double). Doing the maths: Making a coffee with grinder coffee machine vs buying one We've compared coffee costs for a year below, based on buying a manual espresso machine as they deliver the most barista-like results. Keep in mind, your personal preferences (for equipment, coffee brand, even how much milk you use) will change the costs – this is a guide only. 2. The cost to the environment Unless you fastidiously use a BYO cup every time you go to a café, you're contributing to the one billion takeaway coffee cups that Australians send to landfill every year. Each cup takes thousands of years to decompose. Of course, making a coffee at home means you're more likely to use a mug or reusable cup. If you use it everyday, that's at least 365 takeaway cups you're saving from landfill every year. You can even use the grounds in your compost (just mix it with organic garden waste first, as it's too acidic on its own).
Дата Публикации: 01-11-22
Dog Beds: Everything Pet Parents Need To Know
Описание: Dog Beds: Everything Pet Parents Need To Know Dog beds can be simple or fancy, expensive or homemade, and everything in between. How do you pick the right dog bed for your pup when there are so many on the market? Does your pooch even need a dog bed? Should you spend a lot of money when your dog is just as happy lying with you in your human bed or on the couch? Does Your Dog Need A Dog Bed? Even if your dog is allowed to sleep with you in your human bed, every dog should have a bed of their own — or two or three or four, actually. There are plenty of benefits to having dog beds. They can be used for napping during the day and sleeping in at night. Unlike the floor, a bed will keep your dog warm, support arthritic joints, and prevent calluses. And unlike a couch or human bed, dog beds are spaces that pups can have all to themselves. And if you're allergic to your dogs, then it's best if they sleep somewhere besides your bed. Dog beds can also be taken with you when you travel so that your dog feels comfortable and is able to sleep somewhere familiar. They'll rest easier and feel less anxiety. Dog pet beds are also usually easy to wash, which makes life easier if your dog has accidents, gets infested with fleas or mites, or just rolls in something stinky. A dog bed shouldn't be used as a place for punishment or confinement. It's a place of security that belongs only to that one dog, and they should always feel safe in it. A bed makes a crate more comfortable, but that doesn't mean a dog can spend twelve hours a day in a crate just because it has a bed. It's a place dogs should be able to go and relax without feeling trapped or anxious. All dogs could benefit from having a place where they can feel calm and de-stress during the day or night. What Kinds Of Dog Beds Are There? Dog beds can be as simple as your old pillow or as fancy as a wrought-iron frame with a lace canopy. Your selection depends on your taste, budget, and décor, but you may find that your dog expresses a preference by taking over another dog's bed. Keep an eye on where your dog feels most comfortable, as this can help you decide which bed will be best. Basic Styles Of Dog Beds Flat pads or mats are inexpensive and fit in crates. Nesting/snuggle beds are similar to beanbag chairs and often preferred by smaller dogs who love to curl up. Cuddler/nest beds come in the "traditional" oval bowl shape. Bolsters have one long side with a built-in pillow and are often preferred by large dogs. Donut-shaped beds are circular bolsters with a removable center pillow. Waterproof beds are good for outdoor use or incontinent pets. Homemade beds can be inexpensive and easy to customize. There are plenty of tutorials on how to make your own dog bed that you can find on YouTube or by searching online. Just make sure you're using safe materials and that it will hold up, especially if your dog likes to chew. Special Dog Beds For Seniors Or Dogs With Medical Needs Orthopedic beds support old joints or very large dogs; they usually have medical-grade foam and/or box-spring construction. Heated beds maintain body warmth. This can be beneficial for dogs who get cold easily or for dogs with arthritis that is worsened by the cold. Travel beds with cat toys are portable, so your dog can have the security of the same bed every night while on the road. For dogs who suffer from anxiety in new places, this can help them relax and get some sleep. Cot-style beds keep your dog off the ground and comfortably support joints by distributing the dog's weight evenly. They are also usually fairly easy to transport. What Is The Best Dog Bed For Your Dog? There are so many dog beds and cat beds on the market. How do you pick the best one? There are many factors to take into consideration, including size, cost, comfort, your dog's medical needs, convenience, and so much more. You should do your research and consult your veterinarian about your pup's needs before you make a decision. Here are several factors to consider when choosing the best dog toys bed: A good fit. Beyond finding something within your budget, make sure your dog fits on the bed with pet toy; heads and limbs shouldn't have to be hanging off the edge. Easy washability. Dogs eat treats, vomit, pass gas, scratch fleas, and wipe ointment-filled eyes and ears on their beds. Some dogs urinate on them — so the ability to throw the bed into the washing machine is a big help, if not downright critical. Dogs with allergies will also benefit from having their bed washed frequently. Safety. Place the bed away from high-traffic areas so no one trips on it or on the dog. If the dog chews it, then get rid of it — swallowing stuffing can lead to emergency surgery (and you thought the bed itself was expensive). Remove any buttons or ribbons the dog could chew, or look for "chew-proof" beds now available. Stuffing that works for you and your dog. Young, warm, healthy dogs can usually get by with inexpensive foam filling, but your older or arthritic dog will probably prefer more comfort and support. Some orthopedic beds use foam because it's thicker and of higher quality, so it doesn't squash flat. Thick, flexible gel has recently become more common as a bed filling; it's more comfortable than foam and distributes weight more evenly, making it excellent for geriatric dogs — but expensive. And some beds contain cedar chips to ward off pests and keep the bed smelling fresher than your dog. The environment. Some of us are concerned about using materials that won't harm the earth when we decide to replace, get rid of, or recycle a dog bed. You can check out eco-friendly dog beds if that's something that factors into your decision. Absorbent pads for dogs who wet the bed. Sick, incontinent, or geriatric dogs can benefit from washable or disposable absorbent pads (technically, you're the one benefiting because you won't have to wash the bed). Note: These flat pads won't fit well in a nesting bed.
Дата Публикации: 01-11-22
Common Types of Electrical Wire Used in the Home
Описание: Common Types of Electrical Wire Used in the Home Knowing the basic electric wire types is essential to almost any electrical project around the house. When you're installing new wiring, for example, choosing the right wire or power cable is half the battle. And when you're examining existing wiring in your home, identifying the wire type can tell you a lot about the circuit the wiring belongs to—for example, when you open a junction box and need to determine which wires go where. Wiring for modern homes is quite standard, and most homes built after the mid-1960s have similar types of wiring. Any new electrical installation requires new wiring that conforms to local building codes. Here are some common types of home electrical wire. Wiring Terminology It helps to understand a few basic terms used to describe wiring. An electrical wire is a type of -conductor, which is a material that conducts electricity. In the case of household wiring, the conductor itself is usually copper or aluminum (or copper-sheathed aluminum) and is either a solid metal conductor or stranded wire. Most wires in a home are insulated, meaning they are wrapped in a nonconductive plastic coating. One notable exception is ground wires, which are typically solid copper and are either insulated with green sheathing or uninsulated (bare). The most common type of wiring in modern homes is in the form of nonmetallic (NM) cable, which consists of two or more individual wires wrapped inside a protective plastic sheathing. NM cable usually contains one or more "hot" (current-carrying) wires, a neutral wire, and a ground wire. As an alternative to NM cable, individual wires can be installed inside of a rigid or flexible metal or plastic tubing called conduit. Conduit is typically used where the wiring will be exposed and not hidden inside walls, floors, or ceilings. These larger wires in your home are carrying 120- to 240-volt circuit voltage, often referred to as line voltage, and they can be very dangerous to touch. There are also several wires in your home that carry much lesser amounts of "low-voltage" current. These are less dangerous, and with some, the voltage carried is so low that there is virtually no chance of shock. However, until you know exactly what kind of wires you are dealing with, it's best to treat them all as dangerous. NM Cable Often called "Romex" after one popular brand name, NM cable is a type of circuit wiring designed for interior use in dry locations. Most NM cables have a flattened tubular shape and run invisibly through the walls, ceiling, and floor cavities of your home. Almost all of the wiring in outlets and light fixtures a modern home is NM cable. The most common sizes and their amperage (amp) ratings are: 14-gauge (15-amp circuits) 12-gauge (20-amp circuits) 10-gauge (30-amp circuits) 8-gauge (40-amp circuits) 6-gauge (55-amp circuits) NM cable is now sold with a color-coded outer jacket to indicate its wire gauge: White sheathing indicates NM cable with 14-gauge conductors. Yellow sheathing indicates NM cable with 12-gauge conductors. Orange sheathing indicates NM cable with 10-gauge conductors. Black-sheathed cable is used for both 6- and 8-gauge wire. Gray sheathing is not used for NM cable but is reserved for underground (UF) cable or service entrance cable (SE or SER). NM cable is dangerous to handle while the circuit conductors are carrying voltage. UF Cable Underground Feeder (UF) is a type of nonmetallic cable designed for wet locations and direct burial in the ground. It is commonly used for supplying outdoor fixtures, such as lampposts. Like standard NM cable, UF contains insulated hot and neutral wires, plus a bare ground wire. But while sheathing on NM cable is a separate plastic wrap, UF cable sheathing is solid plastic that surrounds each wire. UF cable is normally sold with gray outer sheathing. UF cable is also used for major circuit wiring, and it carries a dangerous amount of voltage as long as the circuits are turned on. THHN/THWN Wire THHN and THWN are codes for the two most common types of insulated single core wire used inside the conduit. Unlike NM cable, in which two or more individual insulated conductors are bundled inside a plastic sheathing, THHN and THWN wires are single conductors, each with its color-coded insulation. Instead of being protected by NM cable sheathing, these wires are protected by tubular metal or plastic conduit. Conduit is often used in unfinished areas, such as basements and garages, and for short exposed runs inside the home, such as wiring connections for garbage disposers and hot water heaters. The letters indicate specific properties of the wire insulation: T: Thermoplastic H: Heat-resistant; HH means highly heat-resistant W: Rated for wet locations N: Nylon-coated, for added protection THHN and THWN wires have colored sheathings that are generally used to identify their function in a circuit: Hot wires: Black, red, orange Neutral wires: White, brown Ground wires: Green, yellow-green THHN and THWN wires are circuit wires that should never be handled when the circuits are turned on. Low-Voltage Wire Low-voltage wiring is used for circuits typically requiring 50 volts or less. Several common types are landscape lighting wire, sprinkler system connections, bell wire (for doorbells), speaker system wires, and thermostat wires. Wire sizes range from about 22 gauge to 12 gauge. Low-voltage wires typically are insulated and may be contained in cable sheathing or combined in twisted pairs, similar to lamp cord wire and flat cable. It must be used only for low-voltage applications. These are typically very small wires that are much different from standard circuit wiring. Serious shocks rarely occur with low-voltage wires, but it is still always best to turn off devices before working with them. Phone and Data Wire Telephone and data wiring are low-voltage wires used for "landline" telephones and internet hookups. Telephone cable may contain four or eight wires. Category 5 (Cat 5) cable, the most common type of household data wiring, contains eight wires wrapped together in four pairs. It can be used for both phone and data transmission and offers greater capacity and quality than standard phone wire. Although data wiring does carry a small amount of voltage, anything under 30 volts is generally regarded as safe (a household circuit carries about 120-volts of power).1 However, there is always a danger of data wiring coming into contact with household wiring, so you should treat it with caution and avoid touching bare electric cable. Coaxial Cable Coaxial cable is beginning to grow less common, thanks to the use of other forms of data wiring, such as HDMI, for television data transmission. Coaxial cable is a round jacketed cable that features an inner conductor surrounded by a tubular insulating layer, surrounded by a tubular conducting shield made of braided multi-core wire. It can be identified by the threaded connectors that are used to make unions and device hookups. Coaxial cable was once the standard for connecting televisions to antenna or cable service delivery and is still often used to connect satellite dishes or to bring subscription television service to an in-home distribution point. It typically has black or white insulation and is perfectly round in shape, making it easy to distinguish from NM electrical circuit cables. The minuscule amount of voltage carried by coaxial cable signals makes it very unlikely to cause shock of any type—provided the cables are not in contact with another source of current.
Дата Публикации: 01-11-22
How To Choose a Harmonica
Описание: How To Choose a Harmonica When it comes to easy playability, affordability and portability, it's hard to beat a harmonica. Despite their modest size and cost, harmonicas are capable of producing an amazing array of tones, and this versatility is reflected in the music genres in which the mighty little mouth harp plays a part. From the more obvious categories such as blues, country, and rock to more surprising musical territory such as jazz and classical music, the harmonica with its often human-like voice easily fits in. In this guide, we'll look at the many types of harmonicas that are available and pinpoint those that make sense for beginners as well as harp players and other musicians looking to expand their repertoires. Types of harmonicas Though there are a number of specialty harmonicas, the three most common varieties fall into one of three categories based on how they are tuned: diatonic, chromatic, and tremolo harmonica. We'll focus mainly on these while touching on a few of the less common harmonica types. If you want to dive right in, you can browse the huge Musician's Friend selection of all types of harmonicas here. Diatonic harmonicas The most common type of harmonica you'll encounter in pop, blues and folk music—diatonic harmonicas are designed to play in a specific key. That said, overblowing and note-bending techniques plus playing in alternate "positions" makes it possible to play a diatonic in keys and modes other than its "official" key. A couple of players, Howard Levy and Carlos Del Junco, have developed an overblowing technique with which they play chromatically using a humble 10-hole diatonic harp. Blues harp players usually perform in what's called "cross harp" or "second position." This involves playing a harmonica that's tuned to a perfect fourth below the key the music's written in. If a song is in the key of C, an F harmonica will be used. Most blues use the notes of a pentatonic scale, and playing a G-tuned harp gives you access to notes that complement the pentatonic C scale, especially on draw notes—those on which you inhale to produce those wailing "bent" notes that are a cornerstone of blues harp technique. There are a number of other positions that skilled harp players use to mesh with other instruments and create various effects. Cupping your hands around the harp and using your tongue to block and unblock holes are some of the ways to create rhythmic chordal effects and tones. You'll find numerous online resources as well as harmonica books and tutorials that explain these techniques in detail. We'll make several recommendations on excellent harp tutorials below. A diatonic harmonica's simplicity makes it a great choice for the beginner. Most harmonica teachers recommend starting out with a 10-hole diatonic harmonica tuned to the key of C. As you shop the huge selection of harmonicas at Musician's Friend, you'll come across many variations on the basic diatonic harmonica.Take for example the Lee Oskar line of harmonicas. Designed by the harp player who gave the band War its distinctive sound, some Lee Oskar models are tuned to minor and other non-standard scales. Many harp players like their bright, penetrating sound and the fact the company sells replacement reed plates so you can refurbish an older harp rather than buying a new one. Most harp players end up with a collection of diatonic harmonicas from various makers in a range of keys. Since their cost is far more modest than say, guitars, building a collection of harps to suit various styles of music and situations is easy to do. We recommend you try a number of different models to discover which instruments suit your playing style and the sound you're going for. Chromatic harmonicas Most chromatic harmonicas have a button-activated lever that directs air to two separate reed plates that include all the notes in the 12-tone western scale. With sufficient skill, you can play just about any scale or mode using the chromatic's "gear shift." The larger reeds in the chromatic are somewhat harder to bend and overblow than their diatonic counterparts. But thanks to their heft, the chromatic is capable of producing some very rich-sounding chords and effects. Many blues harp players such as Little Walter, Rod Piazza and George "Harmonica" Smith have used chromatics to generate fat tones that have led to the blues fan term "Mississippi saxophone." In the hands of a virtuoso like Toots Thielman, a chromatic harmonica can be used to play complex jazz scales with lightning-fast melodic runs that you'd more likely associate with a saxophone. Stevie Wonder is another master of the chromatic harmonica. His harp solos on "Isn't She Lovely" offer a master class in overblowing techniques. Chromatic harmonicas are more difficult to play than diatonics. Therefore, we recommend beginning with a diatonic and stepping up when you're ready to take on a more challenging instrument. Learning to first play in all positions on a diatonic will allow you to graduate more easily to a chromatic. Even though chromatics are nominally tuned to the key of C or G, in actuality, if you learn all the appropriate scales and positions, you can play virtually any music that uses the standard 12-tone scale. Tremolo harmonicas Tremolo harmonicas, also sometimes referred to as "echo" harmonicas, produce their distinctive warbling sound through the use of two reeds per note, one tuned slightly sharp, the other slightly flat. The difference between the waveforms created by the paired reeds causes the beating effect that's somewhat akin to the shimmering sound of a 12-string guitar that has paired strings tuned an octave apart. Chromatic tremolo harmonicas are popular in Asian rock and pop music. Diatonic tremolo harps are sometimes used in folk and pop music, and produce a rustic tone that's ideal for playing cowboy songs like "Red River Valley" around the campfire. Specialty harmonicas Though far less common than the types we've already discussed, specialty children's harmonicas are popular for use in harmonica ensembles and orchestral settings. Here's a brief overview: Chord harmonicas These are usually large instruments that can produce up to 48 different chords and are typically laid out in blocks of four-note clusters. Each note usually has two reeds tuned an octave apart. Chord harmonicas provide rhythmic and melodic support in harmonica ensembles. Orchestral harmonicas Also made to be played in harmonica ensembles, these come in various pitch ranges and note-layout arrangements. You'll find both diatonic and chromatic models. Tools to hone your harp skills Whether you're looking to spice up your acoustic guitar performances with some harp playing or going for the big, honking sound of electrified blues harp, there's a great selection of harmonica tutorials at Musician's Friend. To whet your appetite, here are a few top sellers that have helped everyone from beginners to intermediate and experienced harpists develop and polish their chops: A smart choice for the absolute beginner, the Mel Bay Easiest Harmonica Book will teach you the basics of playing a diatonic harmonica. You'll also learn a simplified form of notation used in many harmonica methods books and other media. Once you've developed your basic blues harp skills, the Hal Leonard Blues Harmonica Collection Songbook offers a great way to master songs recorded by icons such as Little Walter and Sonny Boy Williamson. Using easy-to-follow tablature, it provides accurate transcriptions of 40 blues harp classics. Intended for the advanced harmonica player who wants to learn chromatic harmonica techniques from a virtuoso, the Hal Leonard Toots Thielemans - The Jazz Master Class Series DVD is a rosetta stone. Toots demonstrates his enormous facility on the chromatic, discusses teaching approaches with students and performs some jazz classics. Going electric As blues bands became increasingly electrified in the 1950s, harp players such as Little Walter began using inexpensive "bullet" microphones with crystal elements that were designed for police and taxi dispatch use. They plugged these mics into various tube guitar and bass amps, then by cupping their hands tightly around the harp and mic, produced a fat, distorted sound that has become the holy grail for Chicago-style blues tone. Harmonica-friendly mics The modern harmonica player has a lot of options where mics and amps are concerned. Country and acoustic blues harp players often simply play through the band's PA system using various types of dynamic vocal mics mounted on a stand. They use their hands and head-shaking techniques to create vibrato and trill effects on sustained notes. Electric blues and rock harp players more typically play with the the mic cupped in their hands forming a tight seal. In conjunction with their lips and mouth this creates a sound chamber that can be manipulated to create soulful, heavy tones. As with blues and rock electric guitarists, the electric blues harp player typically seeks a punchy, distorted tone with plenty of midrange. In part this is achieved by overdriving the preamp stage of the amplifier to produce pleasing overtone-rich harmonics. The downside of this approach is that the mic is prone to pick up frequencies from PA and amp speakers, resulting in howling feedback. Experienced blues harpists combat this by keeping the harmonica tightly enclosed in their hands and avoiding stage positions that are likely to trigger feedback through the mic. Some harp mics include a volume knob that can help prevent those dreaded squeals while others, by virtue of their small size, can easily be shielded by the player's hands. Harmonica-friendly amplifiers Back in the day, harp players used whatever amps were available—typically small tube amps intended for guitar. The larger Fender Bassman Combo with its four 10" speakers was also a popular choice since it generates plenty of punchy volume to compete with drums and heavily amplified guitars and is sensitive to playing dynamics. (More on this killer combo in a minute.) Today, things haven't changed too much. Most harp players still look to smaller tube guitar combo amps to generate the sounds they love. In larger venues, they usually close-mic their combo's speaker(s) sending the signal to the PA system via the mixing console. Here are some of the more popular amp choices: The Fender Super-Champ X2 Guitar Combo Amp has a 15W power stage that gets really loud, and when overdriven produces the harmonically rich distortion that's ideal for creating the towering "Mississippi saxophone" sound pioneered by artists like Little Walter Jacobs and Big Walter Horton. It's very portable, and can be easily miked when playing in larger venues. If you're looking for more power and have a bigger budget, the Fender 65 Princeton Reverb is an authentic re-creation of the original beloved by both harp players and guitarists for decades. It's equipped with three 12AX7 tubes and a 12AT7 in the preamp, dual Groove Tubes 6V6s in the power stage, and a single 5AR4 rectifier tube that together with the 10" Jensen speaker pour out retro "blackface" tone.
Дата Публикации: 01-11-22
The Do's and Don'ts of Metal 3D Printing
Описание: The Do's and Don'ts of Metal 3D Printing Star Trek aficionados are well versed in the wonder of the "Replicator," a machine that initially synthesized meals on demand, but eventually evolved to magically produce any number of complex objects, from clothing to the USS Enterprise's spare parts. 3D printing, and in particular, recent advances in metal additive manufacturing (AM), have many likening what's possible with the technology to the sci-fi promises of the Star Trek universe. Proponents of metal 3D printing are bullish on the potential, touting the ability to accommodate complex structures, decrease materials waste and reduce lead times for specific classes of traditionally manufactured metal parts. However, the general lack of understanding of the process, especially the need to redesign parts to achieve the true benefits, remains a significant hurdle to adoption as well as an ongoing inhibitor to metal AM return on investment (ROI). While metal 3D printing is indeed a game changer, most companies haven't fully capitalized yet because they aren't taking the opportunity to redesign parts, contends Tom Houle, director of LUMEX NA for Matsuura USA. "When we see parts that are designed to be metal 3D printed instead of converted to metal 3D printing then the result is a part that is lighter, uses less materials, creates less scrap and waste and runs on a machine 24/7, lights out," he explains. "Those are four game-changing aspects of metal 3D printing and why the technology will eventually be commonplace." Designing for Metal AM is Key For now, metal AM is not exactly a manufacturing floor or engineering department staple, but it is making headway. A recent survey from Market Reports World projects the metals 3D printing market to grow at a compound annual growth rate (CAGR) of almost 22% from 2021 to 2025, increasing revenue by $1.3 billion. Grandview Research is projecting 27.8% CAGR growth between 2020 and 2027, fueled by increased adoption in the medical, automotive, and aerospace and defense sectors. Despite the uptick, the high-cost and complex nature of traditional metal 3D printers have put them out of reach for a large segment of manufacturers and engineering shops. That dynamic has shifted over the last few years as prices have declined and a spate of next-generation models have made the technology more accessible. Yet, as companies start to test-drive metal 3D printing, they encounter an array of challenges that leave many disappointed with results. "The core challenge of metal 3D printing is education and expectation setting," says Lishan Mu, product manager at Markforged. "Because of the novelty of metal 3D printing, the manufacturing world doesn't know what to print or how to design for the metal AM process. They are taking parts meant for machining and expecting the same results from metal 3D printing. It just doesn't work that way as metal 3D printing is a completely new fabrication process that has its own capabilities, strengths and shortcomings." To help counter that scenario, Markforged advises engineering teams to embrace a redesign approach, reevaluating parts by drilling down into why a particular feature was designed the way it was. "Ask yourself, 'Why is the hole round? Is it because it's a through hole for a screw or because the drill to create the hole is round? Does it actually need to be round?'" asks Mu. "Most conventionally-designed parts are concepted to require as little material removal as possible, which is the exact opposite of what Design for AM (DfAM) suggests. If you ask enough of the right questions, you'll quickly find areas to optimize for a successful output with metal 3D printing." To assist customers in this process, the Markforged University program helps identify the right parts to print as well as how to implement DfAM techniques to ensure print success. Best Practices for Metal AM Beyond the No. 1 best practice of redesigning parts for metal AM, experts in the field have various recommendations for what measures to avoid along with guidelines to ensure the best value and to optimize printed parts. Among them are: Don't underestimate post-processing. Because it's still relatively unknown in broad market circles, many companies tend to look at metal 3D printing, and metal AM in particular, as a black box. Experts say it's a misconception to assume most offerings are a plug-and-play machine and that there won't be significant machining and finishing work required to ensure a part comes out finished as intended. Companies diving into metal AM need to cultivate an understanding about how particular materials operate in terms of structural integrity as well as gain a clear picture of what's required for surface finishing and heat treatment to ensure there is no deformation and that parts will meet required tolerances. Often, companies don't factor in the need for machine shop capabilities as an integral part of the metal AM process. Those firms that go into metal AM with a strategy that starts with design and goes all the way through inspection and testing have better results with implementation, Houle says. "Those that have a plan from the ground up for implementing metal 3D printing have a strong track record of ROI," he says. "Those that bring in the technology and try to find different parts or applications they can convert do not." Matsuura's LUMEX Avance-25 and Avance-60 metal laser sintering system focus on a hybrid approach, which streamlines post-processing work, Houle contends. The systems combine a powder bed metal AM platform with subtractive machining capabilities to ensure quality parts are finished with maximum precision. SPEE3D's supersonic 3D powder deposition (SP3D) process also helps defray post-processing challenges while operating up to 100 to 1,000 times faster than traditional MJF 3D printing processes, according to Bruce Colter, vice president and general manager for the Americas region of the company. SPEE3D is based on cold spray technology, typically used for parts repair and coating, which combines high-pressure carrier gas with metal powders and operates below the melting point of the metal in use so it achieves a high density of deposits and low residual stresses. The resulting process requires far less heat treatment or post-processing work to get a quality finished result. "The dirty little secret of metal AM is that often 60% of the process time is spent at the back end, de-stressing, heat treating or HIP (Hot Isostatic Pressing) parts as part of the finish work," Colter says. HIP refers to a process that exposes components to simultaneous application of heat and high pressure to help form the part by compacting the metal powder and eliminating porosity. Make use of simulation to help optimize print processes. As companies expand use of simulation, simulation can also play a role in helping companies understand the metal AM process, specifically to optimize the printing process. SPEE3D just released SPEE3D Craft, a 3D printing simulator that takes users through the entire process, from part design to picking materials and removing parts from the build plate. It also provides instruction for use of the equipment. Desktop Metal also sees simulation as a critical step for successful metal AM. The company's Live Sinter software simulates the complex forces and deformation of parts during sintering, helping users with limited experience with the technology to achieve defect-free parts. To foster better parts design for metal AM, the company offers Live Parts generative design software. "We focus on simulation before and during the simulation process," says Jonah Myerberg, Desktop Metal CTO. "We want the designer to only put materials where they need to be and design the part around the manufacturing process, and Live Sinter shows how parts distort and change so engineers can make minor tweaks and get better results." Don't forget metal AM is an end-to-end process, not just a machine. The specific features and functions of a metal AM system are important, but it's critical to look at how the platform addresses the entirety of the process to ensure the best results. At Velo3D, for example, the Sapphire 3D printer is integrated tightly with Flow print preparation software and Assure, a quality assurance and control system. Flow employs simulation to ensure predicable print outcomes directly from a native CAD workflow. The software also features standardized recipes for parts, negating the need to develop new process parameters for every print job, saving time and reducing the need for SLS 3D printing specialists. Assure uses a multi-sensor defect detection system to predict bulk material properties for each part and to determine print health in real time, ensuring companies can move to production with verifiable part-to-part consistency. "Historically, engineers have had to wait for something to be printed to scan and check results," says Zach Murphree, vice president of technical partnerships at Velo3D. Do embrace an iterative approach to design and manufacturing. That's at the heart of the benefits of SLA 3D printing of all types. "Don't be afraid to put something on the machine," says Patrick Dunne, vice president of advanced application development at 3D Systems. "Maybe it doesn't work, maybe it breaks, but it's the ability to iterate at a high frequency and embrace Agile as a design approach that's so interesting." Do get your feet wet with a service bureau. To determine whether metal AM makes sense for your applications, consider enlisting the help of a service bureau that has already gone through the learning curve and codified best practices to address complexities like part orientation or how to best plan for supports. "We've already been through the growing pains," contends David Bentley, senior manufacturing engineer for FDM 3D printing at Protolabs, a contract manufacturer. "Right now metal 3D printing isn't a dark art, but there's definitely some art to it. We can look at a part and come up with a solution that works on the first print and avoid a lot of that trial and error."
Дата Публикации: 01-11-22
Powerful Trucks with Powerful Howo parts
Описание: Powerful Trucks with Powerful Howo parts Introduction: Everyone has a dream to have big luxurious car, jeep, van or even a truck that shows the strength and dominance in the society we move in. The gigantic trucks in today's modern automobile industry plays a vital role in the development of infrastructure, building, extreme civil projects, and many other construction and building work. The Howo trucks and Howo parts, are the symbol of power, mobility and speed, through which customers in the domain of mining, construction and logistics get the best services in very smooth and professional way. In this article we would be focusing on the Howo spare parts. Some of them are listed below Dump Truck: The dumper truck to load unload any raw material like stones, rocks, sand used in mixing material for construction purpose, charcoal and similar material. These trucks are 371 HP, Cargo capacity of 7300*2300*1700 mm3 or 28.54 CBM. Front Axle can bear 2×9000 Kg weight while Rear Axle can bear 2×16000 Kgs. Please check the howo truck parts include fast transmission assembly catalogue for reference Tractor Truck: A tractor truck is the one that pulls a very heavy trailer, with multiples wheels in the tractor. The 18 wheel tractor truck has the 10 wheel tractor and 8 wheel trailer. Example is the Sinotruk tractor truck with 420 HP, dimension 6985*2550*3800 mm, front axle 1×9000 Kg and rear axle 2×16000 Kg weight capacity. Cargo Truck: Transportation of goods and materials, heavy duty truck with 371 HP engine, front and rear axle 2×9000 and 2×16000 Kg respectively. Cement Mixer Truck: 290 HP, front and rear axle 1×7000 Kg and 1×13000 Kg respectively. SPARE PARTS: Water Temperature Sensor: This auto part is used to measure the water temperature of the Sinotruk Howo truck in radiator WD615 Engine Howo truck engine has large torque, and reduced fuel consumption by more than 10%. They have broader power range 196-323KW, high reliability up-to 10,000 hrs without major overhauling. The WD615 engine and WD618 engine can be interchanged thus reducing the running cost. Optimized combustions and fuel supply system makes them environmental friendly. The reference can be found in howo electric spare parts catalogue Wheel HUB: The Sinotruk assembly known as wheel HUB is used to attach the wheels to the truck and it include the wheel studs. 25 Valve This auto part is the double H valve. It is gear type and have gear assembly. Clutch Plate: This is the transmission system auto part with clutch disk material type steel. Please check the howo engine spare parts catalogue for reference Planetary Carrier: This is the auto part gearing used in tractors to give high torque to wheel driving system. OIL PRESSURE SENSOR Up-to 600 bar, MEMs based auto part oil pressure sensor, the howo trucks wiring diagram will be useful to check the functionality of this oil pressure sensor Magnetic Valve: This is the electromagnetic solenoid valve, power combining mode, semi linkage working state. This auto part is operated with 24V and its electrical connection is shown in howo trucks wiring diagram Mileage Sensor: The mileage sensor is another auto part, is also known as odometer, used to measure the speed of howo truck with transmission parts. Operated on 8-12V, gear box assembly type. Air Filter: The K2841 air filter is important auto part, used in heavy duty excavator, loader, and forklifts. It has excellent performance on moist, hygroscopic or agglomerative dust. It blocks fumed silica, metallic fumes, metallurgical powders etc Howo Truck Relay: This is the 24V and 30/20 Ampere, relay, with silver alloy contacts, sealed and dust cover. Commonly used in trucks and other vehicles. Find the howo trucks wiring diagram online to check its coil and contacts connection.
Дата Публикации: 01-11-22
COVID-19 diagnostic testing
Описание: COVID-19 diagnostic testing Nurse knowledge can improve test administration, ensure efficacy, and increase result accuracy Takeaways: Three COVID-19 diagnostic testing methods are available: molecular, antigen, and antibody. Each method has unique advantages and disadvantages. Nursing knowledge can help ensure accurate testing use, interpretation, and application. Editor's note: This is an early release of an article that will appear in the June 2021 issue of American Nurse Journal. In response to the COVID-19 pandemic, the healthcare industry has created several testing methodologies to detect the SARS-CoV-2 virus in those who currently are infected and antibodies in those who were previously infected. These tests were developed in record time. However, their accuracy continues to evolve as we learn more about the virus. To ensure proper test administration, procedural efficacy, and accurate results reporting, nurses must fully understand each method. Testing methods Various nations and certifying organizations—including the World Health Organization (WHO), Conformité Européenne, and the U.S. Food and Drug Administration (FDA)—have approved over 400 molecular, antigen, and serological antibody diagnostic tests for SARS-CoV-2. When determining which test is appropriate, nurses should consider method of sample collection, processing procedure, length of time for results, test sensitivity and specificity, test limitations, and results interpretation. Testing methods fall into three categories: molecular, antigen, and antibody. Molecular testing Molecular tests detect RNA from the SARS-CoV-2 virus to diagnose an active or acute COVID-19 infection. Examples include the nucleic acid amplification test (NAAT), real-time reverse transcription-polymerase chain reaction (RT-PCR), and loop‐mediated isothermal amplification (LAMP). Sample collection routes include nasopharyngeal, deep nasal, anterior nares, and oropharyngeal. Depending on laboratory capability, molecular test results can be obtained in 3 to 4 hours or up to a week; the average time is 1 to 2 days. Hanson and colleagues recently suggested a strategy of initially obtaining an upper respiratory tract sample (nasopharyngeal swab) for SARS-CoV-2 molecular testing in hospitalized patients with suspected COVID-19 infection. If the initial sample is negative and suspicion for the disease remains high, the panel suggests collecting a lower respiratory tract sample (sputum, bronchoalveolar lavage fluid, tracheal aspirate) rather than another upper respiratory sample. Antigen testing Antigen tests detect surface proteins from the SARS-CoV-2 virus to diagnose an active or acute infection. Specimens are obtained from the nasopharynx and anterior nares. Antigen tests and uncut sheet are recommended for individuals with symptoms during the first 5 to 7 days of infection. However, a Cochrane systemic review of 22 antigen test studies found that their sensitivity varied considerably, from 0% to 94%, with the average sensitivity being 56.2%, which is why a confirming RT-PCR test is recommended. Antibody testing Antibody testing, which requires a blood sample either from a vein or a finger prick, is used to detect a past infection. These tests are conducted using lateral flow or immunoassay tests, such as the ELISA (enzyme-linked immunosorbent assay) and the CIA (chemiluminescent immunoassay). Antibody testing can determine the presence of immunoglobulin M (IgM) or immunoglobulin G (IgG) antibodies developed in response to infection. On average, it takes up to 3 weeks after infection for antibodies to develop and be detected in the serum. The FDA doesn't formally evaluate the performance of antibody tests that aren't commercially marketed before use. However, emergency use authorization is required for commercially sold antibody tests. A study by Iyer and colleagues found that COVID-19 antibody levels remain in the blood up to 2 to 3 months after the initial infection Another study by Dan and colleagues reported that COVID-19 specific B and T cells also remain in the blood for several months after the individual has recovered. This finding suggests some possible immunity if re-exposure occurs. However, the extent and degree of immunity is unknown, with active studies currently underway. Test advantages and disadvantages Each of the testing methods has advantages and disadvantages. Molecular testing Advantages. Molecular tests, specifically the RT-PCR, are considered the Gold Standard for diagnosing SARS-CoV-2 virus. Molecular tests also are used as confirmatory tests after antigen testing because they're highly accurate with a sensitivity and specificity greater than 95%. Research demonstrates that RT-PCR is less likely to yield false negatives compared to other testing modalities. The RT-PCR test also is beneficial in determining whether an individual has an active COVID-19 infection detectable within their test sample. If so, they're presumed to be infectious when the sample is collected. WHO guidelines seem to offer a more collectively inclusive recommendation for determining infectious correlation using RT-PCR testing results. Most people who test positive will test negative after isolating for 13 to 14 days, as recommended by the WHO; the CDC recommends 10 days. Individuals who test positive for longer than that are rare. Studies indicate that some who test positive for 2 to 3 months are immunocompromised or experiencing symptoms. More evidence is needed to determine if a direct correlation exists between the viral load found within a sample and the individual's ability to spread the infection. Disadvantages. Reports indicate that accuracy of RT-PCR results rely heavily on sample collection timing, type, storage, handling, and processing. The tests diagnose active infection only; they can't detect whether an individual was infected previously. A false negative result is possible if the sample isn't properly obtained or if an individual is tested too early after exposure to the virus or too late in their infection. In the later stages of the disease (>7 days postexposure), samples from the lower respiratory tract (sputum, tracheal secretions, bronchoalveolar lavage) may yield higher rates of detection but are more invasive for the patient. The deep nasopharyngeal swab technique has been reported to be very uncomfortable for some adults and small children. New minimally invasive methods have emerged, such as nasal, throat, saliva, and self-administered swabs available at major pharmacies throughout the United States. These minimally invasive testing methods have been crucial in detecting and tracking infection, but they have limitations, which nurses should be aware of. For example, molecular diagnostic tests are complicated and expensive to perform. They require laboratory personnel who are competent using specialized lab equipment and reagents. With public health emphasis on testing to decrease virus transmission, the increased molecular testing volume has resulted in some labs becoming backlogged with reporting test results, some taking as long as 14 days. Long turnaround times create the potential for individuals infected with COVID-19 and awaiting test results to transmit the virus unknowingly to others, which also creates challenges for contact tracing. Antigen testing Advantages. Antigen tests produce results faster than molecular tests do; point-of-care tests yield results in as little as 15 to 30 minutes. In addition, antigen tests are less expensive compared to RT-PCR tests and don't require specialized laboratory technique. Antigen testing offers quick screening and detection of COVID-19 among high-risk groups and in high-congregate environments (such as prisons and long-term care facilities). According to the Centers for Disease Control and Prevention (CDC), the sensitivity for antigen testing varies among the tests that have received emergency use authorization. The WHO recommends a minimum of 80% sensitivity and 97% specificity for antigen-detecting rapid diagnostic testing. Disadvantages. Despite the fast-turnaround time for antigen testing results, a significant disadvantage is the lack of widely available and affordable at-home testing kits in some communities. Most antigen tests are performed at a hospital, clinic, or pharmacy and require travel time to and from the testing site. The FDA recently issued an alert about the potential for false positives. In addition, a Cochrane systematic review of 22 antigen test studies found that sensitivity varied from 0% to 94% (average 56.2%). False negative results also can occur if samples don't have a sufficient amount of viral protein to yield a positive test, making these tests less sensitive and less accurate than molecular tests. In addition, because antigen tests are qualitative, they can be inaccurately interpreted due to reader error. If an antigen test is negative, a confirmatory RT-PCR test is recommended. Antibody testing Advantages. Antibody testing can identify previously infected individuals who are asymptomatic. This information is essential for guiding transmission control measures such as quarantine, isolation, and social distancing, as well as the closure of schools, places of worship, and businesses. Another benefit of antibody testing is that it can aid in vaccine development and efficacy. The testing can identify which parts of the virus the immune system responds to and should be targeted during vaccine development. Disadvantages. A significant limitation of antibody tests is that the correlation of antibody levels with immunity is uncertain. Testing positive for IgG antibodies, which indicates recovery from COVID-19 infection, doesn't guarantee immunity from re-infection. Because individuals with IgG antibodies may still carry and transmit the virus, they should continue to follow CDC guidelines regarding mask wearing, hand hygiene, and social distancing. To further complicate antibody testing, some individuals don't develop detectable IgG or IgM antibodies after infection. This means that the absence of detectable antibodies doesn't rule out a previous COVID-19 infection. Currently, over 100 antibody tests are available or in development. They don't all have the same level of sensitivity and specificity. The lack of standardization for validating antibody tests in the United States makes their quality variable and test interpretation complex. Relying on antibody tests to make decisions about individual immunity or back-to-work orders is problematic. Nursing implications Nurses should possess the fundamental skills and knowledge to perform COVID-19 diagnostic tests as ordered, especially as the need for expanded testing continues to increase. In addition, they should learn to detect infections during symptom screening and how to interpret test results. Given continually emerging information about the virus and testing guidelines, nurses must stay current with evidence-based recommendations. (The information in this article is current as of April 10, 2021.) Following the ongoing research will help ensure nurse competency regarding COVID-19 testing methodology and aid them in understanding regional epidemiological and local surveillance data. In addition, nurses can contribute to enhancing nursing practice by participating in COVID-19 research focused on practice implementation and policy development. As members of the frontline healthcare team, they also can support research by collecting and analyzing data. The COVID-19 pandemic has shifted the nursing education landscape. Nursing schools have begun to revamp their curricula to include concepts relevant to the pandemic. The American Association of Colleges of Nursing released a document recommending that U.S. schools of nursing address COVID-19 preparedness and response, including diagnostic test interpretation, symptom assessment, and evaluation and intervention for patients diagnosed with a current or previous COVID-19 infection. Stay armed The increased demand for COVID-19 testing has led to the rapid development of testing methods and the parallel growth in knowledge, including limitations and advantages of each method. COVID-19 testing is a pivotal component of public health strategies for curbing the spread of the disease. Nurses armed with information about COVID-19 testing are well-positioned to screen patients, provide education, advocate for patients and families, and prevent transmission. Francisca-lenae Egbuna is the owner of NAIE LLC, in Binghamton, New York. Jean McHugh is an associate professor and director of the Accelerated BS in Nursing Program at SUNY Downstate Health Sciences University College of Nursing, in Brooklyn, New York. Myriam Jean Cadet is adjunct nursing faculty at SUNY Downstate Health Sciences University College of Nursing.
Дата Публикации: 01-11-22