Reliable Level in Solids Using High Power Small Package Design
It seems to be an unending barrage of advertisements with statements of performance, high success, breakthroughs, reliability, and on and on, but are these level technologies really fact or fiction in their claims? With all of the level technologies at the availability of end users, it is becoming really difficult for people to make a wise selection of what technology will provide them with the best results for their application. There are many factors involved in deciding which technology is best suited for a level application, not to mention the thoughts of the technologies cost, the installation time, and the learning curve, if any, on the technology chosen. In the market for level measurement, there are technologies that are being pushed as the end all, beat all solution for liquids and solids level, but let me tell that there is no universal technology. There are some technologies that will have a broader application base for solving level, but never, ever rely on just one for your measurements. Focusing on continuous level will be the direction of this article and a detailed discussion on the mystique of microwave radar as the “chosen” technology.
Is it the panacea for all level applications? The answer is absolutely not, as overshadowed in the background of this highly promoted technology is the technology of acoustic wave. Not to be mistaken with ultrasonic wave, but this acoustic wave technology uses low frequency design harnessed within a short cylindrical, but narrow diameter transducer package. Different than anyone else on the market today, but this unique design drives the low frequency resonating mass to produce a pressure wave at the face of the transducer. With this pulsing to the face of the sensor, there is a self-cleaning effect that eliminates any type of build-up. So, low frequency (5 KHz to 30 KHz) combined with high power provides measurement capability in the toughest of applications. Now, I am not saying that acoustic wave technology is the chosen “ultimate” technique for measuring level. There are technologies and there are application conditions, and the two items have to be considered together and not separately. Many companies make the mistake of trying to shoe horn fit one technology into a plethora of applications, and this does not work well at all. Understand the application, and what the parameters are, as well as the customers’ requirements, and then discuss the technology for the measurement.
So, if there isn’t a universal technology for measuring level in liquids or solids, why is microwave radar being sold into a large majority of level applications? It is being falsely promoted as the solution to almost every application, and has claims that it can perform under all conditions of duress. Conditions of duress would be heavy dust in the airspace, heavy build-up on the antenna emitter, wet and moist conditions, the ability to read through foam, high temperatures, and just plain every other condition that other technologies fail at. Many, many times over, one can visit a plant site and see microwave radar designs installed in applications where they should not have been used, and yet they were embellished to be the solution. With microwave radar technology, like any other technology in the marketplace, there are advantages and limitations for its applicability and performance success. These things need to be understood by the end users.
Microwave radar is not the ultimate solution for all level applications, and that’s what this article will further point out. For this technology, difficult application conditions for liquids such as heavy vapors above the liquid surface, high temperatures beyond 300 F, pressures in excess of 50 psig, and turbulent conditions on the material surface would deem this technology as the most suited. It does not mean though that another technology could not be considered such as guided wave radar, capacitance, or differential pressure, but when presented with conditions, it makes sense to evaluate each technology and perform a process of elimination. With these conditions stated, would traditional ultrasonic be applicable? The answer is no and the reason being is that the vapors from the hydrocarbon will stratify with the changes in temperature in the vessel. The speed of sound depends on the temperature of air and it highly affected by the vapor density in the airspace. Errors in the measurement will occur if the air medium is different than pure air as the sound wave will be somewhat attenuated and travel will change. Additionally, the ultrasonic technology will be affected by the condensation in the vessel caused by the changing temperatures, as traditional ultrasonic is usually transducer frequencies of 40 to 55 KHz. With this higher frequency band, there are no self-cleaning properties because there is not enough power to create a pressure wave on the transducer face. So microwave radar would be an ideal choice for this liquid application.
As seen from above in the liquids market, microwave radar has its place and can work quite well in applications, especially when there are some harsh conditions like heavy vapors, strong turbulence, and temperature/pressure extremes. But again, it is not the broad brush solution to every level application, and that’s what has to be understood. Level applications that have build-up as a possibility are a real question mark for any technology. Applying a contact technology in an application with build-up or coating is not the smart choice. In that case, the application of a non-contact technology should be the first thing on the mind and then the thought about the type of build-up. Regardless of the build-up on the sensor of microwave or acoustic wave, there has to be either maintenance schedule of cleaning performed on a periodic basis OR the use of a self-cleaning technique to keep the build-up or coating off of the transducer face. It’s not to say that acoustic wave is the solution with any build-up, as it does depend upon the dielectric of the build-up from a microwave radar standpoint, but in general, the high power pressure wave created does eliminate the coating from happening.
Now, when the application involves the measurement of solids materials, like powders, grains, metal ores like copper, iron, coal, and cement materials, then applying the right technology takes additional thought. From a microwave wave radar perspective, the technology was introduced into the solids level market in the 2003 timeframe, and was promoted as being the new technology for measurement in all solids applications. Think about it from a level standpoint, a technology that could be the solution to difficult solids applications with conditions like heavy dust, dealing with angles of repose, long range measurements beyond 200 feet, high temperatures, and more. Although the technology sounds admirable and stellar in thought, it doesn’t fit the bill from a universal applicability standpoint. It has hit the level market and portrayed as the technology that could provide reliable and accurate measurements under any conditions. The microwave technology absolutely took the level market by storm, and in many cases, cannibalized other technologies in the process, especially in the solids industry. The use of non-contact ultrasonic and acoustic wave has taken a direct hit from a loss of sales standpoint and it is a result of the over promotion of microwave radar.