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By Rich Merritt, Senior Technical Editor
IN A RECENT CONTROL reader poll, we asked “Which level devices give you the most problems?” Radar sensors scored the best, with only 4.88% reporting problems. Differential pressure sensors were the most troublesome at 25%, but ultrasonic sensors were right behind them with 18% reporting problems. There is an almost 1:1 correlation with the number of new level products we found in our annual roundup vs. the number of problems reported. It’s almost as if level vendors are avoiding introducing troublesome products.
Only one new DP sensor was announced, and DP sensors were the most troublesome in our survey. Although DP sensors are one of the most popular level sensors being used today, it looks like they may be going out of style.
Second most troublesome were ultrasonic sensors. Only two new ultrasonic products were announced (the other two in the roundup are older products). We have more new capacitance level sensors than ultrasonics.
Radar sensors, the least troublesome of all, won the new product sweepstakes: We have eight new radar level sensors in this year’s roundup, four times as many as ultrasonics, and the most in any category.
One can argue that traditional DP and float sensors are the most popular systems, with hundreds of thousands of sensors installed worldwide, so it’s to be expected that a large number of people would report problems. On the other hand, ultrasonics and radar are relatively new sensors (compared to floats), so one would expect teething problems to boost their problem numbers. It didn’t happen with radar.
We don’t know for sure if there is a relationship between problems and new product announcements. It all may be purely anecdotal. On the other hand, it’s probably as scientific a guess as the market researchers use.
We reported last year in this space that market researchers predicted radar sensors would be the fastest-growing sensor, and it would be at the expense of more traditional level sensing technologies. We hate to admit that the market researchers can be right every once in a while, but it looks like they nailed it this time. On the other hand, here in Iowa we say, “Even a blind squirrel finds a chestnut once in a while."
Sensor Bulks Up
Vibracon point level sensors perform level monitoring for liquids or bulk goods in temperatures up to 300º F. They are immune to foam, turbulence, media changes and build-up, and can be tested inside an empty tank for reduced maintenance requirements. Models are available in intrinsically-safe, explosion-proof, terminal housing and quick-disconnect versions. Options include process connections and the length and material of the sensing fork. Pepperl+Fuchs; 330/486-0002; www.am.pepperl-fuchs.com
Ultrasonic Sensor Sees All
The Type 8175 ultrasonic level transmitter can display a measured value as a level, distance, volume or open channel flow. It has 0.25 % full-scale accuracy over a 1–32-ft. range, with resolution of 1/8 in. It includes an ultrasonic sensor, transducer, and eight-digit multi-language display protected by a splash-proof plastic NEMA 4 enclosure. Burkert; 800/325-1405; www.burkert-usa.com
Laser Looks Good
The LM200 laser transmitter measures level, distance, and position of dry bulk solids, opaque liquids, and slurries at distances of up to 200 ft., in the presence of dust, vapors, or turbulence. It has a powder-coated aluminum enclosure rated for IP65 or NEMA 4X, and CL II and III, Div 1 and 2, Groups E, F, G dust ignition-proof ratings to FM and CSA. Stainless steel dust tubes prevent dust build-up and protect the optical lens from being coated. K-Tek; 225/673-6100; www.ktekcorp.com
Solid Radar Sensor
The Vegapuls 68 measures level of solid materials, such as flour, sugar, cement, grain, plastic pellets, and aggregates, at ranges up to 230 ft. It is able to see and evaluate echoes in low dielectric conditions, is unaffected by product characteristics such as dust or buildup, and its swivel antenna allows for mounting to match the angle of repose created by fill or empty conditions. Ohmart Vega; www.ohmartvega.com
Ultrasonic Sensor Has a HART
The USonic Series Ultrasonic transmitter measures liquid levels at ranges up to 30 ft. and provides a two-wire 4–20mA, HART output signal. Made of CPVC, it is suitable for use in environments that are classified hazardous (Class I, Div. 1) or require intrinsically safe or explosion proof installation. The sensor works in temperatures from –40–158° F and in process pressures up to 50 psig. Ametek Drexelbrook; 215/674-1234; www.drexelbrook.com
Pulsar pulse burst radar transmitters measure liquid level. The lightweight device is loop-powered with HART digital communications. It has horn and rod antennas, a quick connect coupling to remove or install the transmitter without removing the antenna from the process, and full international safety and telecommunications approvals. Magnetrol; 630/969-4000 x343; www.magnetrol.com
Strick It to Me
The 7330 Series Magnetostrictive Level System measures liquid level and diagnoses problems. The normal 4–20mA output indicates the position of the float within the span. If the level is outside the set span, the output is either 3.9 mA or 20.1 mA. If the float moves into the null or dead zones or there is a sensing failure, then the output is 3.8 mA. Ametek A&PT; 248/435-7540; www.ametek.com
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