Mobrey ultrasonic liquid level detection systems ATEX

Interface detection and sludge measurementUltrasonic technology can be usedto discriminate between immiscibleliquids, to indicate the interface andto detect and monitor suspendedsolids.Interface detectionFor interface detection betweenimmiscible liquids, two techniques areavailable: ultrasonic attenuation andultrasonic reflection.Both techniques use standardMobrey liquid level control electronicsystems. Suitable sensors for interfacemonitoring, are typically the largergap types, that is 150mm upwards.Interface detection by attenuationSensor in oilThe ultrasonic beam is attenuated and will not reachthe receiver crystalAirOilSensor in waterThe ultrasonic beam reaches the receiver crystalOilWaterReceivercrystalTransmittercrystalHeadelectronicsHeadelectronicsUltrasonic attenuation is thereduction in energy of the beam asit is transmitted through the liquid.Viscous liquids, emulsions and liquidswith entrained solids generally have ahigher ultrasonic attenuation than lowviscosity clear liquids such as water.When the attenuation difference issufficient, the amplifier gain can beadjusted so that the ultrasound beampasses through the less attenuativeliquid but is stopped by the moreattenuative liquid. The output relaycan then be set to monitor whichMultipoint & special combination sensorsSpecial sensorsSpecial combinations of sensors areproduced for specific applications- e.g. combined sludge blanketdetectors, pump controls and veryhigh level alarms. Such combinationsare designed and engineered for eachindividual application, whether forshipboard high level alarms, wasteprocessing plants or reservoir controlsystems. Contact the sales office forfurther information.Multipoint sensorsUltrasonic sensors are easily combinedinto multi-point transducers for twolevel pump control or combined highand low level alarms.liquid is in the gap.The ultrasonic attenuation of a liquiddepends on many factors, the mainones being the complexity of themolecule, followed by the viscosity,assuming there is no aeration. Manyliquids can be distinguished by thistechnique and for further informationon previously tested liquid systemsconsult our technical sales. If samplesof the liquids are available then asimple site test can often be done.Interface detection by reflectionAirOilWaterAirOilWaterReceivercrystalTransmittercrystalHeadelectronicsHeadelectronicsWhen two immiscible liquids havesimilar attenuations the above methodcannot be used, however it is likelythat the velocity of ultrasound willbe different. In this case a beamof ultrasound passing through theinterface will be reflected andrefracted and if the sensor is arrangedat a shallow angle the effect is thatthe transmitted beam tends to missthe receiver and is thus effectivelyattenuated. An angle of 10 degrees ischosen and often this results in totalinternal reflection of the transmittedbeam. Thus when the interface iswithin the gap of the angled sensor,Typical standard sensors are:Model HD - A two point dual high levelsensor using two Hi-sens HL sensors.This is typically used for 95% and98% high level alarm on marine cargotankers, for outline dimensions seepage 9.Model 373 - A multipoint versionof the 393 sensors, with up to 6switching levels.Fitting: ¾" BSPT from inside thevessel. Option: flanged to customerspecificationModel 352 - Two point version of the302 type sensor, fitted from inside oroutside of vesselvery little ultrasound reaches thereceiver, but when the interface isabove or below the sensor (ie in eitherliquid) then there is a large signalpresent. The control unit gain is set toactuate the relay when the interfaceis in the gap. Note this condition willalso occur if the upper liquid drainsaway and air (gas) is in the gap. Notefor further information on suitability ofthis application consult our technicalsales.Suspended solids measurementSolids suspended in a liquid willscatter ultrasonic beams, causingattenuation. This attenuation dependson the size and nature of the particlesand for typical sewage sludges it ispossible to use Mobrey ultrasonicsystems to detect 1% to 15% w/w.Industrial slurries such as fine potteryslips can often be measured to 65%,but coarse granular material is oftenvery attenuative. Leaflet IP250 givesdetails of Mobrey sludge measurementsystems.Interface and sludge monitoringTypically sensors with gaps of 150mmor larger are used for interface andsludge measurement. These sensorsare standard types 402, 433 and the442 (a pair of sensors for mountingacross or along a pipe section). Specialflanged sensors with the 10 degree tiltbuilt in are also available. Generallythese sensors work at 3.7MHz andare compatible with Electropulse andElectrosensor electronics or plantmounted MCU200 electronics.D C B AMin 27Min 13Max3000BMin 3513¾" BSPTClearance dia. min. 75AMin 37Min 71Max 4553722