Application Guide Electrical Measurement in Automation Industry · 2020. 2. 13. · versions. The split-core design makes installation a snap. Industrial Electrical Heaters Electric

Application GuideElectrical Measurementin Automation Industry

2

When your job is to controlmotors, heaters, lamps andother electrically powered loads,you need accurate, real-timestatus feedback. Until recently,the traditional approach to thismonitoring problem has been touse optical sensors, zero-speedswitches and pressure switches.But these devices can be bothexpensive and unreliable.

Now LEM offers you bettersolutions. Our current, voltageand power sensors give you thatcritical feedback with all thespeed, simplicity anddependability you want andneed. Based on the premisethat, “By measuring the powerinput to your load, you gain clearinsight into actual equipmentperformance,” these solutionsare:

Faster…because you seeload changes immediately. Withthis knowledge, you can preventequipment failure and avertprocess disruption.

Easier…because yousimply snap a sensor over awire. No need to bolt or weldcomplex brackets, valvemanifolds or pipe taps.

More reliable…becausesolid state sensors are tougherthan electromechanicaldevices.

Economical…becausecosts are reduced throughquick, easy installation and longterm dependability.

Please take a few minutes tolook at the control, protectionand monitoring applications inthis guide. They describe just afew of the ways our customershave used LEM tranducers.Take it as an "idea generator"which will suggest a solution tocome of your control problems.

Made to measure…

TABLE OF CONTENTS

Process Control and Product Quality 3 – 5Maintenance Operations 5 – 6Safety Operations 7 – 8Facilities / Infrastructure Monitoring 9 – 11

Crusher and Grinder Motors

You can optimize the performance ofyour size reduction equipment byautomating the feed mechanism.Controlling the feed rate to grinders,crushers and shredders

helps prevent jamming,improves the uniformity orstructure of ground product,andenhances the efficiency ofsubsequent processingoperations.

Process Control and Product Quality

For a precise indication of the load onthe crusher, simply install a currenttransducer on the motor lead (Fig.1).The output can be used for reliableclosed-loop control between thecrusher and the feeding mechanism.A drop in load will signal the conveyoror loader to increase the feed rate. Arise in load will initiate a decrease inthe feed rate.LEM current transducers are availablein both self-powered and loop poweredversions. The split-core design makesinstallation a snap.

Industrial Electrical Heaters

Electric heaters are used to supplyheat to manufactured products,storage systems and re-circulatingmaterial. If a heater fails, the batch orprocess may have to be scrapped. Areal time indication of heater statusimproves product quality and productionefficiency. Applying a current switch(Fig.2) to the heater lead andintegrating the signal with your DCSwill allow you to

monitor the heater’s on/offstatus,alarm a failure, orautomatically switch on abackup heater.

LEM current-operated switches offeryou solid-state reliability at a lowinstalled cost. The units are availablein both solid-core and split-coreconfigurations.

Fig 1.

Fig 2.

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Part Counting

Proximity sensors are frequently usedto count milled, forged and stampedparts coming off an automated tool.Because these devices require precisealignment, dimensional variations or achange in part position can inducecounting errors.

You can ensure more accurate countsby installing a current switch on themachine tool motor (Fig. 3). The switchwill output a change-of-state signalevery time the motor is loaded (thepart is being machined) and unloaded(the machining process is completed).This method is more exact, and also

Process Control and Product Quality

eliminates the need for manualre-setting or tuning of a position-sensitive sensor.

For maximum resolution, LEM current-operated switches offer user-adjustablesetpoints over three selectableranges. The integrated LED providesalso provides a visual indication ofmotor status.

Status Alarming

A common belief is that auxiliarycontacts attached to a motor starterwill indicate when a load comes on.However, auxiliary contacts only signalthe position of a contactor, not the

actual load status. If a downstreamdisconnect is opened for maintenanceor the contact sticks, there can beserious consequences.

At a large fish farm, failed aeratorpumps resulted in massive stocklosses. Because the auxiliary contactsremained closed when a pump failed,the alarm was never activated, theback-up pumps were not switched on,and the fish suffocated. Now LEMcurrent switches have been installedto alarm the operator and automaticallyswitch on the back-up aerator pumps(Fig. 4).

Fig 3.

Fig 4.

4

Generator Startup

If power failure can stop your businessin its tracks, you must have emergencygenerator power available. Switchingto back-up power can be as simple asinstalling a current switch on theincoming utility line (Fig. 5) andintegrating the signal with yourgenerator control system. If primepower fails, your controller willautomatically start up the standbygenerator.

LEM current-operated switches featureinherent electrical isolation, and providea safe and reliable solution for thisapplication. The compact units aretotally powered by induction from themonitored line, and are UL and CEapproved.

Process Control and Product Quality

Maintenance Operations

Dull Tool Indication

Replacing or sharpening cutting toolsbefore you need to is a waste ofmoney. However, delaying thisoperation for too long can result in aquantity of rejected material. A goodindicator of a tool’s effectiveness is themotor’s current draw.By installing a current transducer(Fig .6) on the cutting tool, you candetermine when the motor is drawingtoo much current. This is an indicationthat the tool is dull and should besharpened or replaced. The single-piece design of LEM currenttransducers eliminates the need forpanel wiring.

5

Fig 5.

Fig 6.

Pump Jam & Suction LossProtection

Wastewater pumps can becomejammed with organic matter and causedamage to both the motor and pumpbefore thermal overloads are tripped.Alternately, a blockage in the pumpsuction line can cause the pump to rundry, overheat and break a seal. Byinstalling a motor monitor on one leg ofthe motor leads you can monitoroverloads (jammed pump) orunderloads (loss of suction) (Fig. 7).

Used LEMs' current tranducers whichgive a real time motor's currentfeedback associated to a PLC makesa cheap an evolutive solution. Indeed,the PLC can be programmed liketimers to compensate short durationabnormalities and motor startup inrush.

Motor Start Counting

Large industrial electric motors needto be overhauled or rebuilt periodically.A predictive maintenance schedule,based on the number of motor starts,ensures proper operation and reducesthe risk of motor failure.

By installing a current switch (Fig. 8)on the motor lead, and using the signalto run a counter, or feed into anautomation system, you can obtainan accurate count of motor starts.This allows you to schedule motormaintenance and avoid costlyemergency repairs. The top mountedterminals on LEM current switchessimplify installation. And because theyare selfpowered devices, there is noneed for power supplies or power wiring.

Maintenance Operations

6

Fig 7.

Fig 8.

Safety Operations

Safety Light Monitoring

Safety lights on smokestacks, towersand airport runways are frequentlymonitored with a photocell. Thismethod works fine if there is nocontamination from other light sources.This method also requires a sensor atthe lamp, which translates to longwiring runs and high installation costs.

A simpler and more cost-effectivemethod is to monitor lamps directlyfrom the lamp control panel. To monitora single lamp, install a current switchon the lamp lead (Fig. 9). Alternately,you can install a current transducer atthe control panel to read current changeand detect failure of any lamp in thecircuit.Because LEM current sensorsmeasure power rather than light, thereis no risk of light contamination. Thisensures a reliable reading of lampstatus.

Ground Fault Protection

Undetected ground faults can exposepersonnel to lethal current. Nationaland international standards now requirethat all electrical installations providea means to protect equipmentoperators from ground faults.An effective solution to this problem isto install a ground fault sensor on thepower lead (Fig. 10). The device’s outputsignal can then be integrated with yourcontrol system or power-interruptingdevice. This protects personnel workingwith electric loads, such as:

Electric heat tape Immersion heaters Production tools and equipment

LEM ground fault sensors provide anisolated solid state contact and offerexceptional sensitivity - down to 5 mAleakage. The same sensor can beapplied to a single-phase 50 ampcircuit or a 10,000 amp three-phasecircuit.

7

Fig 10.

Fig 9.

Safety Operations

Safety Interlocks

Personnel protection is frequentlyaccomplished by interlocking two ormore motors. The objective is to startthe second motor only when the first isrunning and driving its load.

By installing a current switch on themotors you can eliminate complexrelay logic, proximity switches andcontrol panel configuration (Fig. 11).

LEM current switches are frequentlyused as safety interlocks, in a varietyof commercial and industrial facilities.

■ At a grain mill, an exhaust fan mustbe turned on before the silo is filledwith flour. Flour dust is very flammableand a static electric spark can causean explosion. Current switches areinstalled on all exhaust fans.

■ A milling operation uses currentswitches to ensure that the sawdustexhaust system is operating as soonas any of the saws, planers or otherwoodworking machines are turned on.

■ At a commercial laundry the exhaustbooster fan must be turned on whenthe dryers are running. Current switchesare used to interlock these operations.

■ An aggregate producer has ensuredthat both the infeed and outfeedconveyors are running before startingthe crusher by installing currentswitches on the motors.

8

Fig 11.

Facilities / Infrastructures Monitoring

DC Power Supply and Batteries

DC power is frequently used in manyindustrial applications including, petro-chemical, telecommunications metalsand computers. In these applicationsbatteries are frequently used to providepower back up to protect against powerfailure.

In TELECOM to keep the substation ingood working order, manufacturers usedevices (Energy ManagementSystem), (Fig.12) which watch thenetwork power supply and auxiliarybatteries and activate an alarm in caseof problem.

By offering several options like split

core busbar transducer, + 24 V DC to+ 48 V DC power supply, or few mA forleackage current. LEMs' transducerrange is well adapted for DCapplications.

Cathodic Protection

Concrete structures build with steelreinforced, bridges, parking garages,pipelines, high voltage electricity pylonare damaged by corrosion with nonnegligible consequences.

Cathodic protection is the only provenstandard procedure to reduce corrosionin the time. This method consist todecrease the potential of the reinrcedsteel of the structure below the

potential of its environment. A lowgenerated DC current flow betweenpipes and an anode which is buried inthe earth. This current prevent againstthe electro-chemical process ofcorrosion (Fig.13).

Up to now the measurement of this DCcurrent is done by a shunt whichrequire to cut the cable to insert it andadd a signal conditioning electroningto interface with the monitoringsystem.

LEMs' current transducer integratealready the signal conditionning andprovide an isolation which protect thesystem against overvoltage due to thelightning.

9

Fig 12.

Fig 13.

Facilities / Infrastructure Monitoring

Fan And Pump Monitoring

Good engineering practice dictatesthat every output must have acorresponding status input. On fansand pumps, a current switch can besnapped over one motor power leg andthe output wired to your automationsystem (Fig.14).

LEM self-powered switch will closewhen the load comes on, and openwhen the load is off. By adjusting thesetpoint, you can also determinewhether or not the pump coupling orfan belt is intact. This reliable, solid-state solution eliminates the need fortemperamental pressure switches,and reduces the cost of labor andconduit.

The universal solid-state output of LEMcurrent switches is compatible withmost automation systems.

Pump Backup

Critical loads require a backup pumpthat starts automatically in the case ofa failure. Installing a current switch onthe power lead of each pump gives youreal-time on/off status. The solid stateoutputs can be wired into a PLC or tiedinto relay logic circuits to automatethe back-up routines.LEM current switches providemillisecond response and ensure fast,reliable response to pump failure.

10

Fig 14.

Facilities / Infrastructure Monitoring

Site Energy Monitoring

Liberalisation of the electricitymarket, and new environementalconsiderations, have opened up anew area of cost reduction for facilitiesmanagers and introduces the notion ofenergy management to establish theexact energy consumption.

By considering when possible thevoltage and cost as a constant, asimple current measurement is enoughto calculate an estimation of theenergy consumption and follow theload profile.

Based on this analysis, engineers canfind alternative solutions to replaceequipments (e.g. motors, fans, lamps...)or to change people habit to increaseenergy efficiency and reduce waste.

The LEM's current and voltagetransducer range can cover a widediversity of needs for new and existinginstallations. Split core case is a keyadvantage for the second category.

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