Myth or Reality: The Facts about Radar, and the Right option for Level in Solids Applications
With so many level technologies on the market today, the option of technology is much more difficult and can be confusing. Process determination and controls are an vital component for any commercial plant attempting to conform and abide by the definite security and environmental regulations set forth by state agencies. Not only is it foremost to know what is contained within any silo or vessel, but it is vital to know whether a silo or flow area has material blocked. whether that material is too high or low in the containment is also vital as it can cause great security hazards to plant personnel as well as clean-up costs and agency fines. Additionally, installing point detection devices in exchange chutes for blockage detection is also foremost as it is an inexpensive way of preempting a nasty chute blockage. These exchange chutes are all over the place throughout a mining site, and one plugged chute can stop production, which incurs hundreds of thousands of dollars in downtime output costs. So with that stated, dependable continuous level determination and redundant point level detection are an foremost part of any process plant, particularly at a time when enhancing energy efficiency and reducing operating and maintenance costs are foremost considerations. Plant security and meeting stricter environmental regulations become a challenge in this tough competing marketplace.
Many level applications pose extra problems for process level equipment and technologies. whether the commercial site is a mine, power generation facility, or cement plant, these sites all require technologies that will withstand the tough environmental conditions as well as the harsh nature of the solids applications. These include heavy dust in the airspace, steep angles of repose, high temperatures, changing process conditions, corrosive media, grinder solids materials, and more. In addition, so many different sizes and shapes of containment mean that many installations have to deal with obstructions like mechanical bracing for structural support.
Plant personnel like reliability engineers, operations managers, facilities engineers, maintenance, and more are all the time seeing for ways to increase throughput, sacrifice downtime, and heighten process efficiencies. With technology on the constant cutting edge, companies are designing process instrumentation that offers many different types of techniques for providing dependable level and point level detection solutions for tough applications. In order to be victorious in this instrumentation market, a firm must be gift solutions that are value added to customers, and offer user cordial configuration with high accuracy and reliability in mind. With technology like it is today, upgrading of level instrumentation at a plant location from older determination techniques to newer designs will by all means; of course lower maintenance costs, heighten process efficiency and supply higher accuracy devices, which will supply many benefits. With security being most commercial company's amount one goal, any basic level determination must be reliable, robust and definite and there must also be robust systems to guard against spillages from overfilling vessels.
Unfortunately, even with today's advancement in process instrumentation, there is not one technology that will supply undaunted determination results in every application. Although, it is the technology of microwave radar that has been promoted over the last any years as the panacea for all liquid or solid level materials. Is this truly the case? What has happened in this instrumentation market to the idea of providing the right engineered explication for the customer's application? Let's truly look at the technologies out there for liquids and solids level determination like through air radar, guided wave radar, ultrasonic, and what's being referred to by Hawk as acoustic wave. In applications, there are mechanical installation constraints, the conditions within the containment, and the capabilities of the level device will all influence the option of measuring device. In the level instrumentation spectrum, there are many different technologies, but the major technology contenders are ultrasonic or acoustic wave, Tdr (guided wave radar), and non-contact microwave radar. It is entertaining to note too that the technology of ultrasonic or sometimes promoted as acoustic wave technology has flat lined or hit a road block in growth. The technology of microwave radar has been growing at the "speed of light" and being regarded, or at least touted as the end all beat all technology for measuring level in liquids and solids. Well, selecting the allowable technology from one of these three can be a challenge, but if you're seeing for high reliability, low maintenance, and repeatable performance, then look below for some guidelines on each technology.
So, when one looks at level applications, the split is whether liquids or solids. With liquids, many technologies can be applied depending upon the conditions in the application (temperature, pressure, air space conditions above the liquid surface, mounting, mechanical obstructions, and more. Liquids though are not nearly as difficult to solve with level technologies as the solids materials, which can range from fine powders to chunked mixture materials, to the worst conditions of wet, moist fine powdery material that adheres to approximately anything. When it comes to the technologies of through air radar, guided wave radar, or ultrasonic or acoustic, the option of the technology is relatively level transmit with a few exceptions. If the liquid material is water based, with virtually conditions of a non-vaporous atmosphere, and temperatures/pressures in the ambient/atmospheric range, then ultrasonic or acoustic is suitable. With microwave radar applied, the liquids are probably going to be of a chemical or hydrocarbon formulation, probably have some inordinate temperatures or pressures, and have heavy vapor conditions in the airspace. Guided wave radar can be applied as well in the aforementioned conditions, with the irregularity maybe of the range being too lengthy for a rod or flexible cable antenna or if there is an agitator in the vessel.
But, make no mistake about the fact that when dealing with solids materials in an commercial environment like a metal or coal mine, or fly ash in a load out silo at a power generation facility, the conditions for determination are ordinarily much more difficult. It requires a technology that can endure the climate 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 in the application. If the height of the material containment for level determination is more than 30 to 40 feet, then it is more standard and practical to pick a non-contact level determination technology like ultrasonic, acoustic, or microwave radar. Tdr or guided wave radar can supply continuous level measurements up to 80 feet; however, in solids materials, the tensile military and loading on the cable become extreme, and thus will potentially cause breakage and shearing. It is just not practical to outfit any solids determination application with something of a contacting originate like guided wave radar when there is any sort of build-up potential, or lengths beyond 30 feet (10 meters). Also, as material shifts from one point to someone else in the solids, the cable follows that line of movement. Cost also becomes a factor too for guided wave radar in long measurements as cable lengths increase, so does pricing. With level determination in solids beyond 30 to 40 feet, it is a wiser option to go with a non-contact technology.
So let's get down to the facts about non-contact technologies, both new and older in the market place today. The technology known as ultrasonic has been nearby for many years, and it is as the name implies, sub sound technology in the kilohertz frequency band. The designers of ultrasonic technology have made valiant attempts to solve the difficult solids applications with frequencies down to as low as 8 to 12 kHz and assorted transducer designs in size and shape, but the allinclusive determination success has been inconsistent at best. Then along comes non-contact microwave technology with the claims that it is the new "sexy" technology to quantum the long range, dusty solids measurements. Great claims for something that performs well in dry materials, but induce moisture into the solids materials along with heavy dust, water sprayers for dust abatement, and that's a formula for disaster. This new technology is not the panacea for all level applications as many companies tout, and it by all means; of course does not have carte blanche carrying out in the industries like coal, metal mining, minerals, and other solids industries. With the less than desirable results on solids using "ultrasonic" and the through air radar not capitalizing in the mining industries, what technology is out there to solve these applications? Well the overlooked technology, which is a disagreement on a technology theme of ultrasonic, but designed in a way to offer vital application benefits, is acoustic wave technology. The magic behind this technology is the fact that it utilizes audible frequencies (5 to 30 Khz) in a transducer originate that is harnessed as a balanced resonant mass. The mixture of low frequency, high applied power, and variable adaptive gain control makes this acoustic wave technology a real solids explication that can't be beat and is truly underestimated. On the transducer, the low frequency with high applied pulsing power to the face creates a pressure wave that truly offers consistent and proven self-cleaning properties. Effectively, there are no materials that will bind to this transducer face regardless of 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 in the area, the acoustic wave technology can reliably supply level determination under those conditions. Microwave radar Can Not function under these moist solids conditions as it would be disastrous with material build-up adhering to the emitter on the inside of the horn antenna. Or worse yet, adherence of moist, powdered ore fines on the face of a "dust" cover that is designed to keep material from entering the horn antenna, but does not forestall adherence on the dust cover face. Many suppliers of non-contact radar designs today will advise the use of antenna purging with whether water or air within the plant site. This purging option sounds great in design, but in reality, the air purge causes more problems than it's worth because most instrument air supplies have moisture, and this moist air will increase the chances of dust build-up on the emitter within the horn. Additionally, the instrument air is not inexpensive to supply on a quarterly basis.
The key to measuring solids materials in conditions where moist, wet, powders, ores, mixture exist, then there needs to be a technology used where there are self-cleaning properties available. With acoustic wave technology, the power to the transducer with low frequency is one key originate criteria, however, it takes a lot more than just that, and that's where an Australian firm has led the solids determination fee within the level industry. The long wavelength of the low frequency designs also makes them standard for the tough stuff. Guaranteed for high carrying out without fail in the worst conditions known to man, the acoustic wave technology will truly amaze the doubting customer, until they see in action, and "how it take a beating, yet keeps on repeating" in the measurement.
So again, selecting in the middle of non-contact acoustic wave and microwave radar for solids materials can be challenging, but there are some simple rules to keep in mind when inspecting the option for the application. Remember that solids materials come in many different sizes and shapes, and regardless of the particle size, the material will be very dusty in the airspace. The formula of fill and removal from the containment will also increase the dust in the airspace which can cause added deterioration of the determination technology's signal. While fill using a dense phase pneumatic conveying system, which essentially blows the material into the silo from the top, the airspace conditions are highly clouded, and difficult for most level technologies to achieve reliably. While these conditions, the transmitted signal must be strong in power, have the right wavelength, and have the potential to penetrate the dust in the airspace without being attenuated.
For these dusty airspace conditions, let's rate and correlate the two technologies of non-contact originate and see which one is the most applicable under the toughest conditions. With microwave radar, the frequency of the device used and the antenna originate is very foremost in how well it will achieve in these dusty conditions. Non-contact microwave radar designs typically control in the frequency band from 5.8 to 26 Ghz, and some even go higher than that, with use of whether pulse or Fmcw technique. The technique of pulse wave radar seems to be most often used these days, and a frequency band of 24+ Ghz. The definite size and type of antenna is vital when selecting this technology for solids level measurements. The antenna type should be a horn style and the size should be as large as possible, but most manufacturers offer 2 to 6 inch diameter, with some gift 10 inch parabolic dish type versions. Applying a 2 or 3 inch size horn antenna is not standard for solids applications, as there is not enough of a range source at the receive area for the microwave signal. So selecting a horn diameter of 4 inch or larger is best for penetrating the dust in the airspace, as well as allowing for a best accumulator on the returning signals. The technology works well on determination ranges up to 125 to 150 feet, but after that, the readings become somewhat unreliable, and ordinarily build-up of dust becomes a major preventative to the propagation of the microwave energy.
The application of a Teflon fabricated dust cover is applied onto the end of the horn antenna to forestall the dust from entering and build-up inside the horn. However, the dust then builds on the dust cover and over time will impede the signal regardless of its dielectric value and moisture content. Remember what was stated earlier in this article, and that is when suppliers advise the use of purging options like air or water. Well, this is not a practical explication to removing adherence of solids particles. Suffice it to say that there are no self-cleaning properties for a microwave originate and the use of these antenna purges do not work properly and they are not practical for most commercial applications. In dealing with long, dusty airspace determination on solids, the larger parabolic horn antenna is recommended, but this horn size requires an occasion of 10+ inches in diameter. Build-up though also is a realistic qoute with this large antenna as it is a large covering area and again has no self-cleaning properties.
When we speak about ultrasonic technology (also acoustic wave) for use in level applications, we are talking about operating frequencies in the 40 to 5 Khz band, and sizes of 2 to 9 inches in diameter. For liquid level applications, the use of 30 to 40 Khz frequencies are suitable as the airspace conditions are not containing dust particulate, so propagation of the acoustic wave is only then affected by the vapor space. Keep in mind too, that acoustic wave technology is different than ultrasonic technology in that the application of lower frequency designs with high pulse power will create this pressure wave follow that truly atomizes any type of condensation adhering to the bottom of the transduce face. Any other ultrasonic originate on the market today does not offer these cleaning values. When you are speaking about solids level applications with heavy dust in the airspace, then a low frequency of high power is truly essential. There are also other things to think for the allowable propagation of the acoustic wave signal in dusty conditions. The dust particles in the airspace will most truly attenuate or absorb the acoustic wave if not properly sized to the application. The length of the measurement, the airspace conditions, and the mounting availability are all factors to be thought about when applying the right transducer. In the case of ultrasonic technology and solids level applications, size does matter, which means that the lower frequency transducers will make the long length shots and penetrate the dust particulate with minimal attenuation. These 5 or 10 Khz frequency acoustic wave transducers are audible in sound and have a lot of power applied to them with a variant gain scheme. The key to the carrying out on these difficult applications is the application of the lower frequencies.
Oversizing the transducer based on frequency and knowing the conditions in the determination will prove to be successful. The lower frequency with power will deal with the harsh conditions of dust, build-up, and moisture in the airspace, and much more. With long range measurements beyond 50 feet and very dusty airspace conditions, the option of the transducer frequency is foremost and should be at minimum, 15 Khz or lower. Remember though, it is not only the frequency for succeeding in these applications, but the power applied, the transducer design, and the dynamic gain circuit. With the right transducer selection, the next thing to think is the build-up possible of the solids materials in the application. As we discussed in the previous paragraph with microwave radar, there are no self-cleaning properties linked with that technology, so build-up can be a factor in impeding the energy from sensor to material surface. The acoustic wave technology uses high energy applied to a crystal set which causes mechanical vibration on the transducer surface, thus resulting in a movement enough to keep solids particles of dust off of the transducer face.
This self-cleaning technique allows for allowable propagation of the low frequency signal even under the dustiest of airspace conditions as no build-up will bind to the transducer face. Also, the reliable, continuous carrying out of the acoustic wave principles is dependent upon the adjustability of the gain circuit. As the acoustic signal decreases in amplitude, the dynamic gain circuit automatically increases gain to the signal so that there is an increase in the amplitude and the level can be maintained. This potential to vary the gain dynamically throughout the determination proves to be a strong point when having the lower frequency and high power principles also. It takes every bit of technology savvy to achieve a dependable level determination on solids applications.
Level determination on liquids applications are thought about to be much easier with regards to a dependable acoustic signal as compared to solids determination on things like coal, lime, mined ores, cement, and gypsum. The option of the right technology for these difficult solids applications does not have to be a brain teaser. Most companies are astute at assisting in the applicability of their designs, but it is foremost for you as the user to understand the limitations of the technologies. Below is a overview chart for the technologies discussed in this article along with others and the assorted conditions under which there could be exposure. It serves as a guide for the option of technology for your application conditions.
Now for every continuous level application in your facility, you should be inspecting the application of a dependable point level technology. The custom of using an alternate technology point level device with a continuous level determination should be adopted with every company. And no, it's not because the suppliers want to make or sell more product, but because it only makes logical sense. Think about it, if you have a malfunction or an application upset with your continuous device, and there is no point level shut-off for high level, then you will have a spill and that spill requires clean-up, which results in unnecessary costs, and possible fines by governmental agencies like the Epa. Additionally, these spills could also follow in a security violation with harm caused to employees or the process. In increasing to the high level back-up, there should be precaution taken and applicability of a point level switch for a low level shut-off as well as point detection in a chute with solids material. Using point level technologies for back-up security supply a high degree of cost prevention to replacing damaged pump systems, screw conveyors, valves, and other process control devices. With the cost of point level switches being anywhere from 0 to 00 depending the severity of the application, these are relatively low cost and supply a low cost of ownership as they serve to forestall problems.
With the point of having a point level back-up to your continuous level technology, it is wise to pick an alternate technology from what your continuous device is in the application. So for instance, if you have an acoustic wave principles for measuring coal in your load out silos, then you could apply a point level technology of vibration, capacitance, rotating paddles, or microwave. With this point level in mind, there are many different technologies to pick from. The most common used for solids applications would be capacitance, vibratory forks, rotating paddles, acoustic wave, and microwave designs. With solids materials, the grinder and heavy loading of the material can be a factor in causing more problematic issues with a point level device, especially on low level or high flowing materials, so selecting the right one is important. Other factors like build-up on the probe elements or impact from falling material can also influence the carrying out and reliability of the product.
The technologies of microwave and acoustic wave lend themselves to the more difficult solids applications, although the applications of both are also seeing the easy applications. These two technologies are more often seen though on the difficult applications where an indication of material absence /presence is vital in the customer's process, and therefore dependable detection is mandatory. The microwave detection technology is such that the faces of the transmit and receive sensors are across from one someone else over a sure short or long distance, but seeing though a plastic window like Teflon. There is no touch with the material in the silo and no protrusion thus no wear and tear and dependable carrying out provided the material is dry. If the material has some moisture or it can be dry, then the applicability of the acoustic wave technology can be done. The charm of this technology is the fact that it is also not protruding into the vessel and uses a very wear defiant titanium face for long chronic durability in grinder applications. The costs for the microwave or acoustic wave originate are more than conventional point level technologies like capacitance or rotating paddle wheels, but the exchange of these devices does not occur once installed in the applications. It's set up with minimal configuration, and then truly walks away with no problems after that point.
So in overview what I wanted to share with every reader is the idea that there are many technologies for measuring continuous and point level within the solids industry, but development the right option for long term reliability, low maintenance, and high carrying out is where the rubber meets the road. If safety, enhancing process efficiency, or rescue costs are your concern, then take to heart this information, and touch your local level master or me if you'd like some guidance. And finally, let me say that the success and carrying out reliability of any technology is not chosen based upon its popularity, but on its capabilities to deal with adversities. Don't sell short the technologies that have been nearby for many years.
Jerry Boisvert ( jerry.boisvert@hawkmeasure.com, 978-5308588)
Hawk determination Systems
7 River Street
Middleton, Massachusetts 01949