Magnetic Field Sensor - Serrata Science Equipment

SmartTECHNOLOGYQMagnetic Field SensorIntroductionThe Smart Q Magnetic FieldMagnetic FieldSensor is a Hall Effect device.The sensing area consists ofa small piece of semiconductormaterial. A current is supplied+(by the EasySense unit) to thesemiconductor. When amagnetic field passes throughSemiconductorthe semiconductor a potentialdifference is generated at rightangles to the magnetic field.The magnitude of this potential _difference (called the HallVoltage) is used to calculate thestrength of the field.Hall VoltageElectric CurrentThere are two Hall Effect devices in the Sensor, placed at right angles to eachother. This enables fields along the axis of the Magnetic Field Sensor (the axialfield) or at right angles to it (the radial field) to be measured.The EasySense unit can detect that the Smart Q Magnetic Field Sensor isconnected and the range it is set to.ConnectingSmart Q label on topSensor cablewith locating arrowfacing upwards Hold the sensor housing with the Smart Q label showing on the top. Push one end of the sensor cable (supplied with the EasySense unit) intothe socket on the Sensor with the locating arrow on the cable facing upwards. Connect the other end of the sensor cable to the Input socket on theEasySense unit (with the locating arrow facing upwards). The EasySense unit will detect that the Magnetic Field Sensor is connected.1

SmartTECHNOLOGYQMagnetic Field SensorTo set the rangeThe methods available to alter the selected range of the Sensor will depend on thetype of EasySense unit used.EasySense Advanced and Logger Users can set the required range from the unit:-Use the scroll buttons () on the unit to select the System Menu, ENTER.Use the scroll buttons to select ‘Set Sensor range‘, ENTER.Select the number of the input that the Magnetic Field Sensor is attached toe.g. Input 1 ENTER.Use the scroll buttons to view the ranges available i.e. Axial or Radial. PressENTER to select the required range.An asterisk* will indicate the range selected.Press STOP twice to return to the main menu.EasySense Advanced, Flash Logger, Fast, and Real-time Users can set therequired range using the Sensor Configuration application in the SensingScience Laboratory program: -Connect the Magnetic Field Sensor to theEasySense unit and run the Sensor Configurationprogram.Select the number of the input that the Sensor isconnected to from the list.Click on the Set Range button. The current rangewill be highlighted.Select the required range, Radial or Axial, andclick on OK.Exit the program. The sensor range setting will beretained until reselected.Practical InformationSide face of the Sensor housingEnd of the Sensor housingCentre LineRadialSensorAxialSensorThe two Hall Effect devices are located immediately behind the moulded circles onthe Sensor housing. The axial device is 2.35mm behind the circle on the end face,and the radial device is 2.85 mm behind the circle on the side face. Each device isapproximately the same size as the circle.2

SmartTECHNOLOGYQMagnetic Field SensorThe Sensor will measure onlythe component of magnetic fieldthat is acting at 90 degrees to thecircle on the sensor housing.Direction ofmagnetic fieldUse the centre line markings on the sensorhousing to line up the correct position.AxialdeviceDirection ofmagnetic fieldRadialdeviceTIP: As the values obtained will be sensitive to the position in the field, and theorientation of the Sensor to the field direction, it can be useful to: -a. Fix either or both the source and the Sensor in one position.b. Use a non-metallic ruler or metre rule as a guide to move either or both thesource and the Sensor.c. Use a non-metallic clamp and stand to secure the Sensor so it is keptfacing at the same angle and in the same direction during the investigation.Note: A false low value could be achieved if the direction of magnetic field is not at 90° to the plane ofthe Sensor i.e. perpendicular to the relevant circle.Select the range most suitable for the direction of the magnetic field or theposition of the Magnetic Field Sensor during an investigation.Examples: -Direction ofmagneticfieldSelect the Axial range when themagnetic field direction is parallelto the axis of the circle on the endface of the Sensor e.g. inside coilsor solenoids.The Sensor can be positioned in either ahorizontal or vertical position when usingthe Radial range to detect the field froma magnet.The Sensor can be positioned end-facingwhen the Axial range is used to detectthe field from a magnet.3

SmartTECHNOLOGYQMagnetic Field SensorUsing the conventional direction of magnetic fields i.e. from North to South, thevalue from the Sensor will positive when the direction of the magnetic field istravelling into the circle on the Sensor housing.Magnetic FieldSensorThe magnetic field direction is pointing into the circleon the side of the Sensor so the value will be positive.NSMagnetic field directionIf the direction of the magnetic field is pointing intothe back of the Sensor and away from the circle,the value will be negative.The Sensor gives a negativevalue when the magnetic fielddirection is pointing away fromthe circle on the end of theSensorThe Sensor gives a positivevalue when the magnetic fielddirection is pointing into thecircle on the end of the SensorThe Magnetic Field Sensor readings may drift when first switched on. Thebiggest shift is within the first second – it can be up to 0.3mT for the ±10mTrange and 0.6mT for the ±100mT range. Between 1 second to 3 minutes itdrops to 0.1mT for the ±10mT range and 0.2mT for the ±100mT range. It istherefore preferable to connect the Magnetic Field Sensor to an EasySenseunit that is on for at least 3 minutes before readings are taken.Potential Drift of Sensor ReadingsRange In 1st second From 1 second to 3 minutes± 10mT

SmartTECHNOLOGYQMagnetic Field SensorThe effect of switch-on drift will be minimal except when data is recorded withina second of being switched on. This can happen if an EasySense Advancedunit is used in remote mode for one hour or more, or for more than six minutesin EasyLog mode at which point the unit goes to sleep between readings toconserve battery power (data will then be recorded on wake up after a settlingtime of 1 second).The Hall voltage and internal resistance have low temperature coefficients.The effect of temperature can therefore be ignored in the normal schoollaboratory situation.This Sensor is not suitable for investigating very small field strengths e.g. theeffect of the Earth’s magnetic field.Check how smooth low voltage units are before using them for electromagnetic field experiments. Many DC low voltage supplies are not very smoothand will therefore vary the field with the ripple voltage.There should be no ferrous metal in the vicinity of a magnetic fieldexperiments. Iron or steel will distort magnetic field. Use non-metallic benchesand equipment e.g. wooden or plastic rulers, and supports for the Sensor.The safest coils to use for solenoid experiments are commercially wound coilsthat have the current rating marked on them e.g. the coils from a demountabletransformer kit. If homemade coils are used take care to avoid overheating. Donot switch on except when taking measurements. It may be useful to add acontact switch (which is normally open) to the circuit. Insert an ammeter orCurrent Sensor in the circuit to monitor the current, to ensure that it is at a safelevel. Too high a current may cause damage through overheating, and willprobably cause the resistance to rise.Fields in excess of the Magnetic Field sensors range (i.e. ±10mT for ProductNo 3170 or ±100mT for Product no 3172) will not cause any damage.This Sensor is not waterproof.UnitsThe magnetic field strength (also known as the magnetic flux density) is ameasure of the force the magnetic field will exert on an electric current or anothermagnet.S.I. unitsThe strength of a magnetic field is expressed in teslas (T).5

SmartTECHNOLOGYQMagnetic Field SensorA field of strength 1 tesla containing a wire of length 1m carrying 1A at rightangles to the field will produce a force of 1N on the wire.The tesla is a very large unit. The Earth’s magnetic field strength is, typically,only 50 µT. The values we will be dealing with will be expressed in mT (milliTeslas).cgs unitsThe magnetic field strength (magnetic flux density) is expressed in Gauss(G).1 G = 1 x 10 -4 T1 G = 0.1 mT1mT = 10.0 GInvestigationsComparison of the field strength of different types of magnet.Investigating materials that a magnetic field will pass through.Change of magnetic field strength with distance.Change in magnetic field strength between magnets.Directly measuring the field due to a magnet or coil.Investigating magnetic field patterns around magnets and coils.Relationship between the field due to a coil and the current in the coil.Relationship between the field due to a coil and the number of turns in the coil.The variation of the field due to Helmholtz coils.Variation of the field of a solenoid along its axis.Variation of the field of an AC current.Change in Magnetic field strength between magnetsMagnetic FieldSensorMove the Sensoralong this lineMagnet 2Magnet 1150mm0mmRuler(non-metallic)6

SmartTECHNOLOGYQMagnetic Field SensorSelect the Magnetic Field Sensor Range as Radial.Use two magnets positioned on top of a ruler with North Pole facing North Pole.Place magnet 1 at the 0mm mark and magnet 2 at the 150mm mark and securein position.Hold the Magnetic Field Sensor vertically with a non-metallic clamp and stand,this needs to be moved into different positions along the ruler without disturbingthe magnets. Ensure the Radial circle on the Sensor faces magnet 1 at all timesduring the experiment.Place the Sensor so the centre line from the radial circle is at the first positionon the ruler (e.g. either 5mm or 10mm).Open the Graph application from the Sensing Science Laboratory program.Select the New Recording Wizard and the method of data collection asSnapshot mode.Click on START and then click in the graph area to record the first value.Note: If using the ±10mT Sensor (Product No 3170) and the value shown is ±10mT (the maximum ofits range), move the Sensor further away from the magnet to record the first value.Typical strengths of magnets are:-Magnadur Magnet Alnico Bar Magnet Thin Alnico Magnet Weak Magnet30mT 20mT 10mT 0mTMove the Sensor to the next position and click in the graph area to record thevalue. Continue along the ruler until the 140mm mark is reached.Save the data.These results were obtainedusing 2 x Alnico Bar Magnetsplaced with North pole facingNorth pole7

SmartTECHNOLOGYQMagnetic Field SensorTo alter the display from reading number to distanceCreate a column to enter the distance data:- Select Function Wizard from the Tools menu. Select the Function as ‘a’. Make a = 0. Type in the name as Distance andthe units as mm. Alter the maximum scale to 150. Click on Apply. Move the left-hand margin of the graph to show the distance column, whichwill be full of zeros. Double click on each cell and enter the appropriate distance value. Select Display Wizard from the Display menu. Select Sensor as the X-axis. If necessary alter the data channel displayed (click to left of the axis) so that‘Distance’ is displayed on the X-axis and ‘Radial Field’ on the Y-axis.Repeat the experimentusing the two magnetspositioned with theNorth pole facing theSouth pole.These results were obtainedusing 2 x Alnico Bar Magnetsplaced with North pole facingSouth poleThe variation of Magnetic field along the axis of a coilAmmeter orCurrent SensorASafety:The coil can get hot!Magnetic FieldSensorMetre Rule(non-metallic)Finish Point Centre Point Start Point8

SmartTECHNOLOGYQMagnetic Field SensorSelect the Magnetic Field Sensor Range as Axial.Arrange the apparatus as shown in the diagram (don’t connect the power untilyou are ready to start recording).Open the Graph application from the Sensing Science Laboratory Program.Select the New Recording Wizard and the method of data collection asSnapshot mode.Note the distance from the centre of the coil to the start point.Note: The former for the coil is often longer than the coil itself. Pupils should be reminded to measurethe length of the actual coil.Position the end of the Magnetic Field Sensor at the start point.Connect electrical power to the coil. A Current Sensor can be used to monitorthe current, which should be constant.Note: Make sure the current doesn’t change during the experiment; this may occur if the temperatureof the coil rises.Click on START and then click in the graph area to record the first value.Move the Magnetic Field Sensor 10mm towards the coil, click in the graph areato record the value of the field.Continue this process until the Sensor has moved through the coil and out theother side to an equal distance.These results were obtained usinga 200-turn ‘home made’ coil and4.5V d.c. from a power supplyResult using 2 Helmholtz coils(each 320-turn 2A) set-up with a35mm air gap between them9

SmartTECHNOLOGYQMagnetic Field SensorHow does the field due to a coil vary when an alternating currentflows through it?Magnetic FieldSensorA C SupplyCurrent SensorCoilSelect the Magnetic Field Sensor Range as Axial.Arrange the apparatus as shown in the diagram (don’t connect the power untilyou are ready to start recording). Place the Magnetic Field Sensor in themiddle of the coilConnect the Magnetic Field and Current Sensors to the EasySense unit.Open the Graph application from the Sensing Science Laboratory Program.Select the New Recording Wizard and the method of data collection as Fast,with 4000 samples, a 100 microsecond intersample time with a StartCondition of None.Switch on and adjust the alternating current to the desired level. Click onSTART and the software will retrieve and display the results.Use Zoom or Sensor Axis Limits or select and then Use Selection to obtainthe required display.These results were obtainedusing the 350-turn Helmholtzcoil and the 10mT sensor10

SmartTECHNOLOGYQMagnetic Field SensorTo alter the display to an X-Y graph showing Magnetic Flux vs. Current Select Display Wizardfrom the Display menu.Select Sensor as theX-axis. If necessary alter thedata channel displayed(click to left of the axis)so that ‘Current’ isdisplayed on the X-axisand Axial Field on theY-axis.These results were obtainedusing the 600-turn coil froma demountable transformer,and the 100mT sensorWarrantyAll Data Harvest sensors are warranted to be free from defects in materials andworkmanship for a period of 12 months from the date of purchase provided theyhave been used in accordance with any instructions, under normal laboratoryconditions. This warranty does not apply if the sensor has been damaged byaccident or misuse.In the event of a fault developing within the 12-month period, the sensor must bereturned to Data Harvest for repair or replacement at no expense to the user otherthan postal charges.Note: Data Harvest products are designed for educational use and are not intended for use inindustrial, medical or commercial applications. This Sensor may not be used for patient diagnosis.WEEE (Waste Electrical and Electronic Equipment) Legislation.Data Harvest Group Limited are fully compliant with WEEE legislation and arepleased to provide a disposal service for any of our products when their lifeexpires. Simply return them to us clearly identified as ‘life expired’ and we willdispose of them for you.11