One of my U.K.-based colleagues pointed a great article my way, Defining and refining process radar level, in the November Control Engineering Europe magazine. Unfortunately, the article is not viewable online unless you subscribe to site–so I don’t have a link for it. The article shares the history of the development of the use of radar for tank level measurement. Emerson’s Olle Edvardsson, a senior technologist for the Rosemount Tank Gauging family of products is the inventor and brains behind this innovation. Here are a few highlights from his article.
Like many great inventions, it began with looking at something that worked in an unrelated application and asking the question, “What if?” In this case, Olle was working on radars for a division of Saab Aerospace in Sweden in the late 1960s. One of the applications on which he was working was the use of radar to measure the altitude of a plane in flight.
Around this same time, tanker ship owners were having problems with their mechanical tank level gauging systems. The problem was that these level measurements required frequent maintenance–and this maintenance process was dangerous. Washing the tanks created static electricity, which could lead to sparks and explosions in the tanks containing flammable materials, such as fuel. In the article, Olle wrote:
Tanker ships increased in size to 250,000-400,000 tonnes in this period, and because the resulting larger tank sizes were more susceptible to static, they were directly responsible for a number of accidents. There was therefore a real need for in-tank, maintenance free, reliable level measurement.
Olle described the “what if” moment:
However, when I heard about the marine requirements, I thought that maybe we could apply this same radar technology. Thus the idea of using radar technology for tank gauging was born!
There were lots of issues to work through. Level measurement required few hundredths of a percent accuracy versus a few percent in the aerospace application. The environment was harsh and hazardous. Olle and the team worked through these issues and installed the first radar level system on a commercial oil tanker in 1976.
Over the next two decades, advances were made in accuracy and reliability. Applications expanded to refinery tank farms, and:
…to some niche applications in the steel industry and even for wave height measurement for marine and offshore platform safety and statistical applications.
Emerson acquired Saab Marine Electronics in 2001. During the subsequent period, the technology advanced from four-wire connections to the standard, two-wire connections. The first products to come out after the acquisition included the Rosemount 3300 series–the first two-wire level and interface guided wave radar (GWR), followed by the Rosemount 5300 (GWR) and 5400 (non-contacting) series.
Olle described the two technologies:
…a top down ‘through-air’ non-contacting transmitter and a contacting guided wave radar (GWR) transmitter, which uses a guide wire or rod. Both are capable of measuring almost any liquid. Non-contacting radar is ideal for aggressive and corrosive liquids, while GWR is particularly suitable for low dielectric, high temperature and pressure liquids such as hydrocarbons, or solids such as plastic pellets.
For non-contacting radar, Olle cited some common applications including flare knockout vessels, storage tanks, blending vessels, and reactors. Radar is a direct measurement so the accuracy is not impacted by fluid density change. For GWR applications, Olle highlighted several, including:
…separators, free water knock-out vessels, water and skim tanks, natural gas liquids storage, accumulators and ammonia storage.
As digital signal processing continues to improve, so do the number of applications and the extreme environments in which radar level measurement can be applied. And, IEC 62591 WirelessHART tank gauging transmitters open more applications where the installation is physically or economically not feasible with the existing wiring infrastructure.
Ever the forward-looking innovator, Olle envisions:
…radar devices becoming easier and easier to commission and use, eventually reaching a point where they offer pushbutton set-up capability. Users can look forward to increasing signal sensitivity as well as the ability to automatically compensate for more changing process conditions. Expect to see radar devices that have sensors capable of detecting the dielectric change of the upper medium in interface applications and automatically compensating to ensure the accuracy of measurement. We can expect higher frequencies such as 60 and 80 GHz to be used by non-contacting radar, as well as having double frequency in the same radar device. We will probably see more innovative probe and antenna designs and certified SIS radars. Without doubt, we will also see further developments in enhanced instrument diagnostics that will enable remote interrogation of instrument condition and advance warning of potential problems.