Back in the day, Egyptians measured water levels with gauges called nilometers. Rising water levels were observed at the nilometers, and runners carried the information from station to station to predict inundated fields, and thus a year’s harvest, and also establish water level as a tax basis.
The automation age has changed the way we measure level — but some of the old principles still apply, especially in the solids industry.
Analysts at Frost & Sullivan (www.researchandemarkets.com) report that, “As process industries seek to integrate their systems onto a common plant network, there is an increased need for remote monitoring of process parameters. To this effect, level sensors and transmitters have evolved to offer better intelligence in the form of transmitting greater information and controlling processes. In addition, online monitoring systems are finding greater acceptance because of the ease of data acquisition.”
The level measurement of solids consists of two technologies: point level and continuous level measurement. Unfortunately, no single technology applies to all solids level measurement applications. Be prepared to answer many questions when choosing from a variety of bulk level measurement technologies, such as ultrasonic, load cell, radar, guided wave radar, weight and cable, capacitance, nuclear or laser. Consider storage container configuration, material properties, such as density, temperature, and abrasiveness, filling method, accuracy requirements, device costs, installation and operational and maintenance costs and other factors.
The 30-mm Superprox Model SM902-A Series long-range ultrasonic dual-level sensors have a 203-mm (8-inch) dead band that eliminates the need to mount the sensor at greater distances from the object being detected. The sensing range stretches up to 8 m (26 ft) and the 116-mm (4.58-inch) long housing can be installed without positioning limitations. The 12 VDC to 24 VDC sensors can be factory- or field-configurable for various NPN and PNP, NO, NC or complementary output modes.
Digital E3 Modulevel liquid level displacer transmitter is an intrinsically safe, two-wire instrument for level, interface or density measurement. It has microprocessor-based electronics with 4-20 mA/Hart or Foundation fieldbus output. E3 supports the FDT/DTM standard, and a PACTware PC software package allows for additional configuration and trending possibilities.
AccuTrak AT100 and AT200 magnetostrictive level transmitters are certified for IEC 61508 SIL 2 environments. AccuTrak AT100 can be directly inserted into the medium to be measured, while the AccuTRAK AT200 is an externally mounted, non-contact transmitter that can be attached to the KM26 magnetic level gauge or other magnetic gauges to complete a level measuring system.
BCC capacitive sensor series offers EMC and ESD immunity and detects the level of plastic pellets in a hopper while withstanding environmental interference. The sensors are mounted on a plastic sight glass or in the hopper containing plastic pellets for point level detection.
AMETEK US M&CT/PMT Products
Model 675 submersible level transmitter is designed for slurries and highly viscous environments where clogging of the sensor is possible. It uses a 3.5-inch flush diaphragm within a stainless steel shark cage to prevent unwanted clogging. The device performs in depths up to 138 ft of water and is approved for intrinsically safe operation in hazardous locations as designated by Class 1, Div. 1, Groups A, B, C and D, and Class 11, Groups E, F and G when used with an approved barrier.
Fisher (Emerson Process Management)
L2 pneumatic liquid level controller uses low-temperature materials and a NACE construction for oil and gas patch control. It offers two control modes: snap-acting or throttling control. Other features include a two-inch NPT vessel connection; ASME Class 1500 pressure rating; interface capability; low-bleed environmentally friendly relay; field-configurable vertical or horizontal displacer and a vent-away case.
Optiwave 6300 C radar level instrument measures powder, granulates and bulk solids in uneven silos, hoppers, bulk storage containers and on conveyor belts in the mineral and mining, food, chemicals, pulp and paper, and power industries. The drop form of the plastic antenna generates a smaller beam angle to eliminate amplifying the reflected signal.
LVL-B Series vibration limit switch is insensitive to material build-up and can be used to measure the level of bulk solids, such as fine or coarse-grained material, sugar, animal feed, beans, gypsum, sand, plastic granules, chalk, cereals and cement. It is FM- and CSA-certified as Dust Ignition Proof (DIP) for Class 11 and Class 111, Div. 1 and 2, Groups E-G.
Emerson Process Management
Rosemount 5300 Series radar level sensors now come with a cryogenic seal that enables level measurement of condensed and liquefied gasses at very low temperatures (0 ºC-196 ºC). It is suited for use in process tanks, side chambers, storage tanks and transportation vessels.
Burkert Fluid Control Systems
Type 8185 guided microwave level transmitter has a choice of either cable or rod probe of 316L stainless steel and performs continuous level measurement for liquids and solids. Measuring range is up to 13 ft (rod) or 150 ft (cable). Output is 4-20 mA/HART.
The Ronan FlexDetector offers the newest design of flexible detectors. In comparative testing of fill-fluid and fiber bundle designs, the FlexDetector measured 2.4 times greater output at low-level exposure rates from 0.05 mR/hr to 0.9 mR/hr, making this the safest and most reliable solution for your radiometric level measurement applications. The FlexDetector uses a non-hazardous, non-flammable, scintillating fill-fluid, which is doubly encapsulated and protected by an outer sheath of armored conduit. The FlexDetector is available in lengths up to 23 ft. Up to six detectors can be summed, giving an overall continuous level measurement of 138 ft.
Automation Products Group
LPU-2428 loop-powered, ultrasonic level sensors are cCSAus-certified for use in Class 1, Div. 1, Groups C and D, and Class 1, Zone 0, Group 11B hazardous locations. Class 1, Div. 1, Group C, and Class 1, Zone 0, Group 11B atmospheres contain ethyl-ether vapors, ethylene or cyclopropane. Class 1, Div. 1, Groups C and D atmospheres contain gasoline, hexane, naptha, benzene, butane, propane, alcohol, acetone, benzol, laquer solvent vapors or natural gas. The microprocessor-controlled sensor internally performs volume, flow and totalization.
KING-GAGE ES2R loop-powered pressure transmitter features environmental isolation for sanitary washdown applications. It has thermal recovery, small diaphragm profile and polished stainless construction. The IP68-rated, hermetically sealed M12 connector and molded cable assembly enhance resistance to condensation, aggressive surfactants and other agents that typically attack seals and other egress points.
MTS Systems, Sensors Div.
M-Series Level-Plus liquid-level transmitters are designed for continuous or batch processes, providing product level, interface level and temperature data all from one sensor, so there is no need for multiple openings at the top of the tank. The transmitter can be used for removal and transportation of waste only when the tank is full by detecting the liquid level instead of the foam level.