Myth or Reality: The Facts about Radar, and therefore the Right Choice for Level in Solids Applications
With numerous level technologies on the market today, the selection of technology is far harder and may be confusing. Process measurement and controls are an important component for any plant attempting to evolve and abide by the strict safety and environmental regulations set forth by state agencies. Not only is it important to understand what's contained within any silo or vessel, but it's vital to understand whether a silo or flow area has material blocked. Whether that material is just too high or low within the containment is additionally critical because it can cause enormous safety hazards to plant personnel also as clean-up costs and agency fines. Additionally, installing point detection devices in transfer chutes for blockage detection is important because it is a cheap way of preempting a nasty chute blockage. These transfer chutes are everywhere the place throughout a mining site, and one plugged chute can stop production, which incurs many thousands of dollars in downtime production costs. So thereupon stated, reliable continuous level measurement and redundant point level detection are a crucial a part of any process plant, particularly at a time when improving energy efficiency and reducing operating and maintenance costs are important considerations. Plant safety and meeting stricter environmental regulations become a challenge during this tough competitive marketplace.
Many level applications pose special problems for process-level equipment and technologies. Whether the economic site may be a mine, power generation facility, or cement plant, these sites all require technologies that will withstand the tough environmental conditions also because of the harsh nature of the solids applications. These include heavy dust within the airspace, steep angles of repose, high temperatures, changing process conditions, corrosive media, abrasive solids materials, and more. additionally, numerous different sizes and shapes of containment mean that a lot of installations need to affect obstructions like mechanical bracing for structural support.
Plant personnel like reliability engineers, operations managers, facilities engineers, maintenance, and more are always trying to find ways to extend throughput, reduce downtime, and improve process efficiencies. With technology on the constant leading-edge, companies are designing process instrumentation that gives many various sorts of techniques for providing reliable level and point level detection solutions for tough applications. to achieve success during this instrumentation market, a corporation must offer solutions that are value-added to customers and offer a user-friendly configuration with high accuracy and reliability in mind. With technology love it is today, upgrading of level instrumentation at a plant location from older measurement techniques to newer designs will certainly lower maintenance costs, improve process efficiency, and supply higher accuracy devices, which can provide many benefits. With safety being most industrial company's favorite goal, any basic level measurement must be reliable, robust, and accurate and there must even be robust systems to protect against spillages from overfilling vessels.
Unfortunately, even with today's advancement in process instrumentation, no one technology will provide undaunted measurement leads to every application. Although, it's the technology of radar that has been promoted over the last several years because of the panacea for all liquid or solid level materials. is that this really the case? What went on during this instrumentation market to the thought of providing the properly engineered solution for the customer's application? Let's really check the technologies out there for liquids and solids level measurement like air radar, guided wave radar, ultrasonic, and what's being mentioned by Hawk as a sound wave. In applications, there are mechanical installation constraints, the conditions within the containment, and therefore the capabilities of the extent device will all affect the selection of measuring instruments. within the level instrumentation spectrum, there are many various technologies, but the main technology contenders are an ultrasonic or sound wave, TDR (guided wave radar), and non-contact radar. it's interesting to notice too that the technology of ultrasonic or sometimes promoted as sound wave technology has flatlined or hit a roadblock in growth. The technology of radar has been growing at the "speed of light" and is regarded, or a minimum of touted because the end all beat all technology for measuring level in liquids and solids. Well, choosing the right technology from one among these three is often a challenge, but if you are looking for top reliability, low maintenance, and repeatable performance, then look below for a few guidelines on each technology.
So, when one looks at level applications, the split is either liquids or solids. With liquids, many technologies are often applied depending upon the conditions within the application (temperature, pressure, air space conditions above the liquid surface, mounting, mechanical obstructions, and more. Liquids though aren't nearly as difficult to unravel with level technologies because the solids materials, which may range from fine powders to chunked aggregate materials, to the worst conditions of wet, moist fine powdery material that adheres to almost anything. When it involves the technologies of through-air radar, guided wave radar, or ultrasonic or acoustic, the selection of the technology is comparatively simple with a couple of exceptions. If the liquid material is water-based, with virtual conditions of a non-vaporous atmosphere, and temperatures/pressures within the ambient/atmospheric range, then ultrasonic or acoustic is suitable. With radar applied, the liquids are likely to be of a chemical or hydrocarbon formulation, probably have some excessive temperatures or pressures, and have heavy vapor conditions within the airspace. Guided wave radar is often applied also within the aforementioned conditions, with the exception maybe of the range being too lengthy for a rod or flexible cable antenna or if there's an agitator within the vessel.
But, make no mistake about the very fact that when handling solids materials in an industrial environment sort of metal or coalpit, or ash during a load-out silo at an influence generation facility, the conditions for measurement are usually far more difficult. It requires a technology that will endure the atmosphere conditions like heavy dust, undulated material surfaces, wet or moist conditions from process sprayers, and sometimes hot conditions with build-up problems on any equipment installed within the application. If the peak of the fabric containment for level measurement is quite 30 to 40 feet, then it's more appropriate and practical to settle on a non-contact level measurement technology like ultrasonic, acoustic, or radar. TDR or guided wave radar can provide continuous level measurements up to 80 feet; however, in solids materials, the tensile forces and loading on the cable become extreme, and thus will potentially cause breakage and shearing. it's just not practical to outfit any solids measurement application with something of a contacting design like guided wave radar when there's any kind of build-up potential or lengths beyond 30 feet (10 meters). Also, as material shifts from one point to a different within the solids, the cable follows that line of movement. Cost also becomes an element too for guided wave radar in long measurements as cable lengths increase so does pricing. With level measurement in solids beyond 30 to 40 feet, it's a wiser option to accompany a non-contact technology.
So let's get right down to the facts about non-contact technologies, both new and older within the market place today. The technology referred to as ultrasonic has been around for several years, and it's because the name implies, sub sound technology within the kilohertz waveband. The designers of ultrasonic technology have made valiant attempts to unravel the difficult solids applications with frequencies right down to as low as 8 to 12 kHz and various transducer designs in size and shape, but the general measurement success has been inconsistent at the best. Then along comes non-contact microwave technology with the claims that it's the new "sexy" technology to live the long-range, dusty solids measurements. Great claims for something that performs well in dry materials, but induce moisture into the solids materials alongside heavy dust, water sprayers for dust abatement, and that is a formula for disaster. This new technology isn't the panacea for all level applications as many companies tout, and it definitely doesn't have authority performance within the industries like coal, metal mining, minerals, and other solids industries. With the but desirable results on solids using "ultrasonic" and therefore the through-air radar not capitalizing within the mining industries, what technology is out there to unravel these applications? Well the overlooked technology, which may be a variation on a technology theme of ultrasonic, but designed during thanks to offering significant application benefits, is sound wave technology. The magic behind this technology is that the incontrovertible fact that it utilizes audible frequencies (5 to 30 kHz) during a transducer design that's harnessed as a balanced resonant mass. the mixture of low frequency, high applied power, and variable adaptive gain control makes this sound wave technology a true solids solution that cannot be beaten and is basically underestimated. On the transducer, the low frequency with high applied pulsing power to the face creates a pressure wave that literally offers consistent and proven self-cleaning properties. Effectively, there are not any materials which will adhere to the present transducer face no matter their moisture or sticky properties.
So in mining applications, where there are wet screens from sprayers or ROM bins with dust abatement controls causing heavy build-up on anything within the area, the sound wave technology can reliably provide level measurement under those conditions. radar can't function under these moist solids conditions because it would be disastrous with material build-up adhering to the emitter on the within of the horn antenna. Or worse yet, adherence of moist, powdered ore fines on the face of a "dust" cover that's designed to stay material from entering the horn antenna, but doesn't prevent adherence on the dust cover face. Many suppliers of non-contact radar designs today will recommend the utilization of antenna purging with either water or air within the plant site. This purging option sounds great in design, but actually, the air purge causes more problems than it's worth because most instrument air supplies have moisture, and this moist air will increase the probabilities of dust build-up on the emitter within the horn. Additionally, the instrument air isn't inexpensive to provide daily.
The key to measuring solids materials in conditions where moist, wet, powders, ores, aggregate exist, then there must be a technology used where there are self-cleaning properties available. With sound wave technology, the facility to the transducer with low frequency is one key criterion, however, it takes tons quite just that, and that is where an Australian company has led the solids measurement charge within the extent industry. The long wavelength of the low-frequency designs also makes them appropriate for the tough stuff. Guaranteed for top performance without fail within the worst conditions known to man, the sound wave technology will absolutely amaze the doubting customer until they see in action, and "how it takes a beating, yet keeps on repeating" within the measurement.
So again, choosing between a non-contact sound wave and radar for solids materials are often challenging, but there are some simple rules to stay in mind when considering the selection for the appliance. Remember that solids materials are available in many various sizes and shapes, and no matter the particle size, the fabric is going to be very dusty within the airspace. the tactic of fill and removal from the containment also will increase the dust within the airspace which may cause further deterioration of the measurement technology's signal. During fill employing a dense phase pneumatic conveying system, which essentially blows the fabric into the silo from the highest, the airspace conditions are extremely clouded and difficult for many level technologies to perform reliably. During these conditions, the transmitted signal must be strong in power, have the proper wavelength, and have the power to penetrate the dust within the airspace without being attenuated.
For these dusty airspace conditions, let's evaluate and compare the 2 technologies of non-contact design and see which one is that the most applicable under the toughest conditions. With radar, the frequency of the device used and therefore the antenna design is extremely important in how well it'll perform in these dusty conditions. Non-contact radar designs typically operate within the waveband from 5.8 to 26 GHz, and a few even go above that, with the use of either pulse or FMCW technique. The technique of pulse wave radar seems to be most frequently used lately, and a waveband of 24+ GHz. the right size and sort of antenna are important when choosing this technology for solids level measurements. The antenna type should be a horn style and therefore the size should be as large as possible, but most manufacturers offer 2 to six-inch diameter, with some offering 10-inch parabolic dish type versions. Applying a 2 or 3-inch size horn antenna isn't appropriate for solids applications, as there's not enough of a set source at the receiving area for the microwave signal. So choosing a horn diameter of 4 inches or larger is best for penetrating the dust within the airspace, also as allowing a far better collector on the returning signals. The technology works well on measurement ranges up to 125 to 150 feet, but then, the readings become somewhat unreliable, and typically a build-up of dust becomes a serious deterrent to the propagation of the microwave energy.
The application of a Teflon fabricated dust cover is applied onto the top of the horn antenna to stop the dust from entering and build-up inside the horn. However, the dust then builds on the dust cover and overtime will impede the signal no matter its dielectric value and moisture content. Remember what was stated earlier during this article, which is when suppliers recommend the utilization of purging options like air or water. Well, this is often not a practical solution to removing the adherence of solids particles. Suffice it to mention that there aren't any self-cleaning properties for a microwave design and therefore the use of those antenna purges doesn't work properly and that they are not practical for many industrial applications. In handling long, dusty airspace measurement on solids, the larger parabolic horn antenna is suggested, but this horn size requires a gap of 10+ inches in diameter. Build-up though maybe also a sensible problem with this massive antenna because it is a large area and again has no self-cleaning properties.
When we discuss ultrasonic technology (also sound wave ) to be used in level applications, we are talking about operating frequencies within the 40 to five kHz band, and sizes of two to 9 inches in diameter. For liquid level applications, the utilization of 30 to 40 kHz frequencies is suitable because the airspace conditions aren't containing dust particulate, so propagation of the sound wave is merely then suffering from the vapor space. confine mind too, that sound wave technology is different than ultrasonic technology therein the appliance of lower frequency designs with high pulse power will create this pressure wave effect that literally atomizes any sort of condensation adhering to the rock bottom of the transducer face. the other ultrasonic design on the market today doesn't offer these cleaning values. once you are speaking about solids level applications with heavy dust within the airspace, then a coffee frequency of high power is completely essential. There also are other things to think about for the right propagation of the sound wave signal in dusty conditions. The dust particles within the airspace will most assuredly attenuate or absorb the sound wave if not properly sized to the appliance. the space of the measurement, the airspace conditions, and therefore the mounting availability are all factors to be considered when applying the proper transducer. within the case of ultrasonic technology and solids level applications, size does matter, which suggests that the lower frequency transducers will make the long-distance shots and penetrate the dust particulate with minimal attenuation. These 5 or 10 kHz frequency sound wave transducers are audible in sound and have tons of power applied to them with a variant gain scheme. The key to the performance on these difficult applications is that the application of the lower frequencies.
Oversizing the transducer supported frequency and knowing the conditions within the measurement will convince achieve success. The lower frequency with power will affect the tough conditions of dust, build-up, and moisture within the airspace, and far more. With long-range measurements beyond 50 feet and really dusty airspace conditions, the choice of the transducer frequency is vital and will be at a minimum, 15 kHz or lower. Remember though, it's not only the frequency for succeeding in these applications, but the facility applied, the transducer design, and therefore the dynamic gain circuit. With the proper transducer selection, the subsequent thing to think about is that the build-up potential of the solids materials within the application. As we discussed within the previous paragraph with radar, there are not any self-cleaning properties related to that technology, so build-up is often an element in impeding the energy from the sensor to material surface. The sound wave technology uses high energy applied to a radio receiver which causes mechanical vibration on the transducer surface, thus leading to a movement enough to stay solids particles of dust off of the transducer face.
This self-cleaning technique allows for correct propagation of the low-frequency signal even under the dustiest of airspace conditions as no build-up will adhere to the transducer face. Also, the reliable, continuous performance of the sound wave system depends upon the adjustability of the gain circuit. because the acoustic signal decreases in amplitude, the dynamic gain circuit automatically increases gain to the signal so that there's a rise within the amplitude and therefore the level is often maintained. This ability to vary the gain dynamically throughout the measurement proves to be a robust point when having a lower frequency and high power grid also. It takes equally of technology-savvy to accomplish a reliable level measurement on solids applications.
Level measurement on liquids applications is considered to be much easier with regards to a reliable acoustic signal as compared to solids measurement on things like coal, lime, mined ores, cement, and gypsum. the selection of the proper technology for these difficult solids applications doesn't need to be a brain teaser. Most companies are astute at assisting within the applicability of their designs, but it's important for you because the user to know the restrictions of the technologies. Below may be a summary chart for the technologies discussed during this article along with side others and therefore the various conditions under which there might be exposed. It is a guide for the choice of technology for your application conditions.
Now for each continuous level application in your facility, you ought to be considering the appliance of a reliable point level technology. The practice of using an alternate technology point level device with endless level measurement should be adopted with every company. And no, it isn't because the suppliers want to form or sell more products, but because it only makes logical sense. believe it, if you've got a malfunction or an application upset together with your continuous device, and there's no point level shut-off for top-level, then you'll have a spill which spill requires clean-up, which ends up in unnecessary costs, and potential fines by governmental agencies just like the EPA. Additionally, these spills could also end in a security violation with the harm caused to employees or the method. additionally, to the high-level back-up, there should be precaution is taken and applicability of some extent level switch for a coffee level shut-off also as point detection during a chute with solids material. Using point level technologies for back-up protection provides a high degree of cost prevention to replacing damaged pump systems, screw conveyors, valves, and other process control devices. With the value of point level switches being anywhere from $200 to $2000 depending on the severity of the appliance, these are relatively low cost and supply a coffee cost of ownership as they serve to stop problems.
With the importance of getting some extent level back-up to your continuous level technology, it's knowing to choose an alternate technology from what your continuous device is within the application. So as an example, if you've got a sound wave system for measuring coal in your loadout silos, then you'll apply some extent level technology of vibration, capacitance, rotating paddles, or microwave. With now level in mind, there are many various technologies to settle on from. the foremost common used for solids applications would be capacitance, vibratory forks, rotating paddles, acoustic waves, and microwave designs. With solids materials, the abrasive and heavy loading of the fabric is often an element in causing more problematic issues with some extent level device, especially on low level or high flowing materials, so choosing the proper one is vital. Other factors like build-up on the probe elements or impact from falling material also can affect the performance and reliability of the merchandise.
The technologies of microwave and sound waves lend themselves to the harder solids applications, although the applications of both also are seeing straightforward applications. These two technologies are more often seen though on the difficult applications where a sign of fabric absence /presence is critical within the customer's process, and thus reliable detection is mandatory. The microwave detection technology is such the faces of the transmit and receive sensors are across from each other over a particularly short or long distance, but looking through a plastic window like Teflon. there's no contact with the fabric within the silo and no protrusion thus no wear and tear and reliable performance provided the fabric is dry. If the fabric has some moisture or it is often dry, then the applicability of the sound wave technology is often done. the sweetness of this technology is that the incontrovertible fact that it's also not protruding into the vessel and uses a really wear-resistant titanium face for long-lasting durability in abrasive applications. the prices for the microwave or sound wave design are quite a conventional point level technologies like capacitance or rotating paddle wheels, but the replacement of those devices doesn't occur once installed within the applications. It's found out with minimal configuration, then literally walks away with no problems then point.
