DSO54-No2 Light Gate.qxp - Serrata Science Equipment

TECHNOLOGYQ SmartLight Gate(Product No. 3250)DATA HARVESTData Harvest Group Ltd1 Eden Court, Leighton Buzzard,Beds, LU7 4FYTel: 01525 373666Fax: 01525 851638e-mail: sales@data-harvest.co.ukwww.data-harvest.co.ukDS 054 No 2© Data Harvest. Freely photocopiable for use within the purchasers establishment.

SmartTECHNOLOGYQLight GateIntroductionThe Smart Q Light Gate is a digital switch-type sensor that has two states low (ONcondition) and high (OFF condition). The Light Gate comprises an infraredtransmitter and a receiver mounted and aligned in a plastic frame.A Light Gate can be used singly or in pairs to provide timing and event monitoring.Solid bodies breaking the beam between the transmitter and receiver allowEasySense to detect the elapsed time for individual events or a series of events.The Light Gate is supplied with a steel support rod (80mm long x 10mm diameterwith a M6 thread). This support rod can be screwed into the mounting threads,which are found at the base and sides of the Light Gate. The rod can be used forclamping into a suitable holding device.LED On/OffindicatorInfrared ReceiverInfrared TransmitterDetection LineMounting threadfor support rodSensor leadsocketMounting threadfor support rodSlot and mounting thread forthe Spoked Pulley Accessory(Product No. 3177)InvestigationsDynamics experiments involving calculating time, speed, velocity, accelerationusing inclined planes and air track.Acceleration due to gravity investigations.Pendulum investigations.Measure the time period of an oscillating body.In the Additional Physics worksheets the Light Gate is used with the ForceSensor to investigate: Impulse and change in momentum and Centripetalforce in a pendulum.1Internal width56mm wideMounting threadfor support rod

SmartTECHNOLOGYQLight GateConnectingIf Smart Q Light Gates are used for Timing operations and only one Light Gate isused, it must be connected to the input labelled A. If two Light Gates are usedthey should be connected to Input A and B.If used to record non-Timing data e.g. when used to record with the Graphprogram, a Light Gate can be connected to any available input.Connect the end of the long sensor cable (supplied with the EasySense unit)to the Input socket on EasySense with the locating arrow facing upwards.EasySense Flash Users: A mini-din sensor extension lead (Product No. 3017) could be used toextend the length of the Flash sensor lead.Connect the other end of the sensor cable to the mini-din socket on the LightGate.The EasySense unit will detect that the Light Gate is connected and will eithershow as On/Off or as a percentage value, depending on the application used.DATA HARVESTProduct code 3250Light GateSensor cablewith locating arrowfacing upwards.Once powered by the EasySense unit, the On/Off indicator on the body of theLight Gate can be used to show its signal status. The red LED will light when theinfrared beam is blocked.LED OFFLED ONReceiverTransmitterReceiverTransmitterWhile unblocked the Light Gatewill be high - in the OFF position.When blocked the Light Gatewill be low - in the ON position.Note for EasySense Advanced and Logger users: If the EasySense unit is in ‘sleep’ mode, the LightGate will not be powered and the On/Off indicator will not light. Press the ENTER or STOP button to‘wake up’ the unit and power the Light Gate.2

Product code 3250Light GateSmartTECHNOLOGYQLight GateMeasurement procedureScrew the support rod into the appropriate mounting thread and clamp to a stand.Product code 3250Light GatePosition 1Position 2Position 3Position the Light Gate so the object will block the infrared beam when it passesthrough the Light Gate.Timing investigationsProbably the most common use of Light Gates is in timing experiments.Measurements can be taken from either a single Light Gate connected to Input Aor from two Light Gates connected to both Input A and B.Timing is started when the infrared beam at Input A is blocked T 0 (which changesthe logic level from 0 to 1). When the infrared beam is unblocked its logic statechanges back to 0 and the time interval is stored as T 1 . If another Light Gate isconnected to Input B then the time its infrared beam is blocked is stored as (T 2 )and when it’s unblocked T 3.INPUTABlocked: logic 1INPUTBSTARTUnblocked: logic 0T 0T 1T 2T 33

SmartTECHNOLOGYQLight GateParametersCertain parameters used in an investigation will need to be entered in the Timingprogram to enable calculations to be made from these time intervals.Normally an interrupt card is attachedto the moving object and theinvestigation is set so the card passesthrough the Light Gate.Light GateThe length of the card used to interruptthe beam or the distance between LightGates should be measured accuratelyand this value entered in the Wizard ofthe Timing program. Errors caused byinaccurate measurements are far moresignificant than timing errors.10cmA singleinterrupt cardA ‘single’ interrupt card is used when calculating Time and Speed at A, Velocityat A, Velocity at A then at B, Velocity at A or B and Acceleration from A to B.A ‘double’ interrupt card is used when calculating Acceleration through A. Thecard is made up so that two segments pass through the Light Gate. This allowsthe times T 0 , T 1 , T 2 , and T 3 to all be recorded at Input A. These segmentsmust be equal in size and measured accurately.Light Gate3cm3cmA double interruptcard with equallength segmentsA squaredoubleinterruptcardLength ofboth segmentsis 4cm4

SmartTECHNOLOGYQLight GateEnter the distance between the two Light Gates when calculating Speed from Ato B. This is best done using the detection line on each Light Gate as a marker.Distance betweenthe two Light GatesStartto Input Bto Input ASensing InvestigationsWhen a Light Gate is used in the Graph or Meter program it will show a value ofapproximately 0 – 5% when the infrared beam is unblocked and 100% whenblocked.The Smart Q Light Gate can be connected to any input and used with the SensingScience Laboratory Graph program to:1. Time the length of an eventThe Light Gate can be used to calculatevelocity during an investigation by usingthe interval option to determine the lengthof time the Light Gate was interrupted.t 1t 2Velocity V =lt 2 - t 1Where l = length of the interrupt card.t 2 – t 1 = the interval time5

SmartTECHNOLOGYQLight Gate2. Mark an event on a graphA digital sensor, such as a Light Gate, can be used to mark an event on a Graph.An example would be measuring the heat of neutralisation in a reaction between astrong base and a strong acid. Logging can be started before the acid is added sothe initial temperature of the base is shown on the graph. The Light Gate can beused to mark the point at which the acid is added. If an indicator, such asphenolphthalein, is used then the Light Gate can mark when the indicator changedfrom pink to colourless.3. To start or trigger a recordingA Light Gate can be used to triggerthe start of a recording when inRemote or Fast recording modein the Graph program or on theEasySense Advanced unit. Remote(EasySense Advanced & Logger),Fast (EasySense Advanced & Fast).If Digital Falling or Fallingedge is selected, logging willstart when the object haspassed through the infraredbeam.If Digital Rising or Risingedge is selected, logging willstart when the first part of theobject breaks the infraredbeam.6

SmartTECHNOLOGYQLight GatePractical InformationMeasure the length of the object or interrupt card that passes through theinfrared beam or the distance between two Light Gates as accurately aspossible. If measurements are not accurate all the calculated data will besystematically high or low. This measurement can be the most critical part ofthe investigation.Note: A value of one decimal place can be entered in the Recording wizard in the Timer program. If avalue with two decimal places is entered it will automatically be ‘rounded up’ to one decimal place.e.g. If 3.36 is entered then this value will be rounded up to 3.4. If measurements taken areconsistently high then reduce this value to 3.3.The segment length of a double interrupt card is used twice when calculating‘Acceleration at A’ so any measurement error will be doubled. If two LightGates are used to calculate acceleration - ‘Acceleration from A to B’ – theinterrupt card’s length is only used once to calculate the final velocity so theresults should be more accurate.When measuring the distance from oneLight Gate to another either measure:a. From the detection line of one LightGate to the detection line of the otherorb. The leading edge of one Light Gateto the leading edge of the other.baDetection lineUsing a long interrupt card e.g. 10cm,will improve the accuracy of results.Light Gate ALight Gate BIf you are measuring the diameter of an object thatis going to be dropped through a Light Gate makesure you measure the part that will actually passthrough the beam.If two Light Gates are used make sure they arealigned to each other (positioned in parallel, withback edges lined up so the void of one Light Gateis in line with the void of the other Gate). This iseasier to achieve if the same size bosshead isused to secure each Gate.Hint: We found it useful to mount the two Light Gates on a flatstrip of metal or wood, 23mm wide, slotted between the tworidges located in the centre portion of the Light Gate and screwedin place using two M6 x 12mm Pozidriv pan-headed screws.7

SmartTECHNOLOGYQLight GateTry to arrange the set-up so the object passes as close to the receiver (theslot) as possible. This reduces any possibility of a shadow changing theeffective length of the object e.g. an interrupt card.The best material for interrupt/timing cards would be rigid, coloured black andhave tidy parallel edges. Some users find that equal amounts of plasticine orBlutack used on each of the lower corners of the interrupt card will lower thecentre of gravity and make the card more stable and less likely to wobble whendropped.Ensure that the object/interrupt card cuts cleanly through the Light Gate’sinfrared beam. If it twists at all discard the result.Ensure that the bottom of an object(e.g. an interrupt card) does notinterrupt the Light Gates beambefore the object is released.Hold the card centrallyUse the support rod to clamp theLight Gate in position. Holding aLight Gate in your hand will giveinaccurate results.If you are dropping an interruptcard through the Light Gate, holdthe card centrally from the samestart position just above the Gate.ReceiverTransmitterIf masses or plasticine areattached to the interrupt card makesure they do not protrude beyondthe edges of the card. Massesshould be balanced to prevent thecard from twisting as it travels.Example: To apply a weight of 20g, use 2 x 10g weights positioned at each side of the interrupt card.2 x 10gweights8

SmartTECHNOLOGYQLight GateThe receiver can be sensitive to high levels of ambient infrared light or heat,shield from bright light, which can produce a false OFF result.Transmitter Receiver Transmitter ReceiverTransmitterReceiverOFFONOFFIf the Light Gate is giving false OFF results try rotating through 180° (so anyexternal light source is directed towards the transmitter) or close anappropriate blind in the room.The infrared LED transmitter in the Light Gates has quite high powerconsumption. If possible connect the EasySense unit to a mains power supplyor ensure batteries are fully charged.SpecificationsInfrared source: Peak at 880nmResponse time: Less than 5 microseconds.Timing Resolution: 10µs9

SmartTECHNOLOGYQLight GateWarrantyAll 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.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.10