Charge Sensor - Data Harvest
Contents
1. if whilst conducting the investigation the user ANA is connected to a good ground or earth point The electrostatic discharge apparatus e g wrist band grounding cord and earth bonding plug used by circuit board assemblers will provide a good link to earth Be careful not to touch any voltage sources while you are grounded If it isn t possible for the user to connect to an earth point then they should keep as still as possible with their feet on the floor Movement from people or equipment in the locality can produce static which will disrupt readings When conducting investigations where the quantity of charge needs to be measured accurately and not comparatively mount the Charge Sensor so it won t be moved during an investigation e g in a retort stand and clamp It is best to use the shorter sensor lead 150 mm long Product No 3004 to connect the Charge Sensor to an EASYSENSE unit The Charge Sensor is sufficiently sensitive to detect charge accumulation on the leads if left connected to the EASYSENSE unit between taking readings Leave the crocodile clips at the end of the lead set connected 3 Smart Charge Sensor together so they are shorted out or press the reset button before collecting data 7 In some circumstances wrapping the Sensor in aluminium foil may help stabilise readings 8 Weather conditions can have an effect on readings In dry weather keep body movement to a minimum to reduce the effect of2. in the breath will be enough to neutralise any residual charge Charge 100nC nC 60 0 5 C Discharged conductor reintroduced into pail no effect D Pail grounded then discharged conductor lowered in no effect 0 0 r 00 0 02 5 3 07 5 10 0 10 0 18 April 2005 14 52 06 The results should show that A A charged conductor when inserted into a hollow conductor induces the same sign of charge on the outside of the hollow conductor B The whole of the charge is transferred to the hollow conductor when the inserted charge touches the side C Confirms that all the charge has been transferred and that no charge resides on the inside surface of the charged hollow conductor D Further confirmation that all the charge has been transferred Information Charging a disc conductor by induction What you need 1 Mounted disc conductor 2 Insulator sheet 3 Duster or cloth or fur 4 Earth connection What you need to do Charge insulator sheet by rubbing with the duster or cloth Smart Charge Sensor Place the conductor on the charged sheet and Earth it with the earthed wire Remove the Earth and lift the conductor off the charged sheet using the insulating handle The conductor is now charged with the opposite charge to the sheet E g if the sheet is polythene the conductor will now have a positive charge Warranty All Data Harvest Sensors are warranted to be free
3. stray static charge In humid weather the charge may leak too rapidly to get reasonable results from some investigations e Equipment used for static investigations must be clean and dry It must be kept dry even whilst working under humid conditions Putting the cloths rods and other equipment on a metal plate above a radiator works well A warm air blower e g a hairdryer can be very useful e If the equipment being used proves difficult to discharge breathe gently over it The moisture and heat in the breath will be enough to carry any remaining charge away A yellow Bunsen flame will discharge insulators very effectively when used with care The hot gases rising from the flame are ionised and will neutralise surface charge on insulators e The Charge Sensor will be affected by devices that use electromagnetic fields The equipment that can produce interference includes computer monitors mobile phones televisions switching power supplies electric motors etc e Even after shorting out the terminals or pressing the reset button there can be a small offset voltage recorded the reading may not be exactly at zero This offset can be subtracted using a pre or post log function see page 5 e The Sensor has over voltage protection of 40 V but this would be insufficient to protect the device from the extremely high voltages in the thousands created by a Van de Graaff or similar high voltage generator e High frequency fluctuating fiel
4. ETS D e A E PEE E E IET A T AEO E A ODWMAAAWWHN Introduction The Smart Q Charge Sensor can measure the amount of charge on a source where the charge available is very small e g as in many electrostatic experiments It can replace a traditional gold leaf electroscope by showing not only the polarity of the charge but also performing quantitative measurements It can also measure the potential difference between two points The Charge Sensor has an input capacitor connected in parallel across the input terminals to a voltage amplifier An applied charge will charge the input capacitor resulting in a rise in the magnitude of the voltage across the capacitor The Sensor will use the value of the potential difference across the capacitor to calculate the charge nC or voltage V The Charge Sensor is a very high impedance voltage sensor at least 10 tera ohms 101 ohms which will draw practically no current whilst measuring the potential difference between the ends of an electrical component Power on LED Reset Ground button BNC crocodile lead The Sensor is supplied with a shielded BNC crocodile lead This lead should not be substituted by another manufacturer s lead which could give false results The lead ends with a red and black earth crocodile clip The Sensor has an LED to indicate it is powered and a reset ground button which can be used to discharge the Sensor s input capacitor so there is no need to s
5. Smart Q TECHNOLOGY Fone Charge Sensor Product No 3268 narge Ranges 10 nCoulomb nC Resolution 0 01 nC e 100 nCoulomb nC Resolution 0 1 nC J e 220 nCoulomb nC Resolution 1 nC voltage Ranges 0 5 V 500 mV Resolution 0 001 V e 2V Resolution 0 01 V e 10V Resolution 0 01 V DATA HARVEST Data Harvest Group Ltd 1 Eden Court Leighton Buzzard Beds LU7 4FY Tel 01525 373666 Fax 01525 851638 e mail sales data harvest co uk www data harvest co uk Data Harvest Freely photocopiable for use within the purchasers establishment DS 059 No 2 Smart Charge Sensor Contents gilgele le 11019 PAT meer eer one rer cnr E T E A nn arr anne ne neh rere CONOC CUN eee eee ener ane nee eee nee en ere ance en ene errr ener TO set the VAN GG ies sxccussassasaecdceenteneseseesaupevesceseesaeenesanersdenanebucaseasiectansataaecdes Practical iN ma O sceniniai ei p iaaiiai SDE CIC AMON Secs eencures soem teeta thas hare d pereira pinap aves daei sirenas reri ieies SE EF AC WING an OU SS clr attests aseeclame ater a rE n oisin Airi ire on aE NEY SCI NIOINS crave neeee cern ccacacsans ocatecnn sasexeecseesnwsesaces mnie seraeveateciscotuasccaunecsass Determine the Sign Of Charges cccssssccccscseeececeeeseescessesessenseeeseas Faraday esd acl Merrett tr terra marten Tren iiaiai terre res Information Charging a disc conductor by induction 0 cc00 A
6. cond Specifications Input impedance 101 ohms minimum Input capacitance 22 nF 1 0 022 uF Input voltage Range 10 V Input over voltage protection up to 40 V Subtracting an offset A Pre or Post log function can be used to subtract an offset from the Sensors readings Use the Pre log function for the tare to be applied to the data as logging progresses or the Post log function to apply the tare to data that has already been recorded e Select Test Mode from the Tools menu to find the tare value and then click on Stop Ea e Select Pre or Post log function from the Tools menu e Select a Preset function with General from the drop down list and then Tare from the second list Next Select the Charge Sensor as the Channel Next Enter a name for the corrected data set e g Charge adj Uso Pis rolon 0 auat on afee fon o Sereda and enter the tare value Click on Finish Gxt O Expand to fit Manual jake the value negative or positive as appropriate e g 2 2 0 2 2 0 Investigations Magnitude and sign of the charge on different objects Electrostatic phenomena Simple demonstrations of sign of charge Charge sharing between conductors Faraday s ice pail investigations Electrostatic shielding Induced charge Charging by induction Density of charge on the surface of a conductor Investigating the relationship Voltage is proporti
7. ds such as 50 Hz or above will usually not be detectable The Sensor has a low pass filter to ensure that any 50 60 Hz mains signal is attenuated Input signals with a rise fall time quicker than approximately 80 ms will be significantly reduced in value e When used to measure the potential difference between the ends of an electrical component the Charge Sensor should be connected in parallel i e across the component e For reasons of accuracy if the Charge Sensor is used with another Charge or Voltage Sensor in a circuit ensure they share a common earth the same black lead e The Charge Sensor can be used to measure DC circuits SAFETY Never use with high voltages e The Charge Sensor can be used to look at low voltage AC signals if the following is followed 1 The maximum voltage is 20 Vpp peak to peak i e low voltage low frequency AC signals It is not suitable for looking at mains supply voltages 2 The maximum frequency is limited to 12 Hz 4 Smart Charge Sensor e When measuring the charge on a capacitor it is necessary to use capacitor values significantly less than 22 nF For good results use low current leakage capacitors below 1 nF The error in this case will be less than 4 6 The lower the value capacitor the more accurate the results The SI unit of electric charge is the Coulomb It is equal to the amount of charge which passes a point in a conductor if one ampere flows through the conductor for one se
8. from defects in materials and workmanship for a period of 12 months from the date of purchase provided they have been used in accordance with any instructions under normal laboratory conditions This warranty does not apply if the Sensor has been damaged by accident or misuse In the event of a fault developing within the 12 month period the Sensor must be returned to Data Harvest for repair or replacement at no expense to the user other than postal charges Note Data Harvest products are designed for educational use and are not intended for use in industrial medical or commercial applications WEEE Waste Electrical and Electronic Equipment Legislation Data Harvest Group Ltd are fully compliant with WEEE legislation and are pleased to provide a disposal service for any of our products when their life expires Simply return them to us clearly identified as life expired and we will dispose of them for you 10
9. ge Sensor will tend to pick up stray charges from its surroundings if left with nothing driving its inputs If so press the reset button to discharge before starting to record data After a recording short the object that is charged to earth and press the reset ground button on the Sensor to discharge the internal capacitor Smart Charge Sensor To set the range Set Sensor Range x e Connect the Charge Sensor to the EASYSENSE unit e Start the EASYSENSE program and select one of the cae logging modes from the Home page e g EasyLog Select Flange Select Sensor Config from the Settings menu TEETE e Select the Charge Sensor from the list it will be listed using its current range and click on the Change Range button Charge 220nC e The current range will be highlighted Select the Voltage 2 required range and click on OK Close Sensor Config Voltage 500m Voltage 10V Click on New and then Finish for the change in range to be detected by the logging mode The range setting will be retained until changed by the user With some EASYSENSE units it is possible to change the range from the unit Please refer to the EASYSENSE unit s user manual Practical information e The extremely high input resistance of this Sensor also makes it sensitive to stray electrostatic fields in its immediate vicinity To minimize the influence of static fields follow these guidelines le Better results are obtained
10. hort the crocodile clips together Smart Charge Sensor Connecting Sensor cable with locating arrow facing upwards Align marks push in and we rotate the BNC connector e Hold the Charge Sensor housing with the Smart Q label showing on the top e Push one end of a 150 mm short sensor lead Product No 3004 as supplied with the EASYSENSE unit into the shaped socket on the adapter with the locating arrow on the lead facing upwards e Connect the other end of the sensor lead to the input socket on the EASYSENSE unit with the locating arrow facing upwards e The EASYSENSE unit will detect that the Charge Sensor is connected Select the range required see page 3 e Connect the BNC crocodile lead Supplied to the BNC socket on the sensor housing by lining up the BNC connector with the pins on the socket push in and then turn clockwise to lock into place e Discharge the Sensor s internal capacitor by pressing the reset button on the adapter for about 2 seconds e When measuring charge connect the black lead to a good earth connecting point and the red lead to the object that is going to hold is holding the charge e Start the application you need for the investigation e g Graph and verify the Sensor is reading about zero Notes There maybe a small residual voltage which can be subtracted from the final measurement to give a more accurate reading see page 5 e Due to the extremely high input impedance the Char
11. l which is used for the investigation It is preferable for the person performing the experiment to be continually grounded to prevent stray charges e g by continuously touching the outer shield with one hand A piece of wire secured to the mesh shield can be used to ground the ice pail the wire needs to be long enough to touch the lip of the ice pail It can also be used to ground or discharge conductors as needed You will also need either e Aconductor mounted on an insulating handle e g the disc from a small electrophorus which can be charged by induction see page 9 e Or mounted conducting Charge producers which are charged by rubbing them together Smart aan Charge Sensor Setup the experiment as shown in the diagram The range of the Smart Q Charge Sensor should be set to 100 or 220 nC Connect the red lead from the Charge Sensor to the ice pail Connect the black lead ground to the outer mesh shield Grounding wire 5 Ground the ice pail by touching with the wire attached to the wire shield Any charge built up on the ice pail will travel across the wire to the outer shield then out to ground Lift the gro
12. onal to the charge on an object by adding charges e Discharge of a capacitor Smart Charge Sensor e Use as a high impedance voltmeter e g measuring the voltage of chemical half cells e Measuring the emf of cells Determine the sign of charges What you need e Duster cloth fur e Different objects and materials e g polythene acetate nylon and ebonite rods balloons pens etc e Metal disc coin or small ice pail Red lead Black lead gt Metal disc coin or small pail Earthed lead Charge Sensor 1 Attach the Charge Sensor to the EASYSENSE unit The range of the Smart Q Charge Sensor should be set to 100 nC 2 Connect the red lead from the Charge Sensor to a metal disc and hang from a clamp Connect the black lead to ground The earthed lead can be used in addition to or instead of the reset ground button to discharge the Charge Sensor 3 Open the EASYSENSE program and select Meters from the Home page A Numeric window will open click on maximise so the window fills the screen Discharge the Charge Sensor by pressing the reset ground button Bring up a charged object towards the metal disc Observe and record the sign and charge reading 6 Discharge the Sensor and repeat using a variety of objects Compare the sign of the charge from each object ia Faraday Ice Pail Faraday originally used his ice pail to show that 1 When a cha
13. rged object is enclosed in a hollow conductor it induces a charge on the inside of the conductor equal in size and opposite in sign to its own on the outside of the conductor a charge equal in size and of the same charge as the object is induced Smart Charge Sensor 2 The total charge inside a hollow conductor is always zero In addition to proving the above principles the Faraday ice pail is a useful device for sampling and comparing charge It operates on the principle that a charge placed inside a conducting surface will induce an equal charge on the outside of that surface Faraday s ice pail was a modest pail about 27 cm tall and not a bucket sized container Use a cylindrical container for the ice pail the length of the cylinder should be at least two if not three times the diameter It will work better if the cylinder has a closed base We used an outer shield made from a cylinder of 1 cm galvanised steel metal mesh without a bottom The metal ice pail is placed inside the shield with an even space separating them The ice pail should be placed on a non conductive platform a block of dry wood is ideal Even gap between ry il Black clip T mane Red clip connected and shield Charge Sensor connected Ned ae to ice pail to shield Grounding wire Ice pail Ki i Non conductive gt platform e g block of dry wood The outer mesh cylinder is connected to ground and shields the ice pai
14. und wire back up Open the EASYSENSE program and select EasyLog from the Home page Press the reset ground button to discharge the Sensor Test mode from the Tools menu can be used to check the value is zero Click on the Start icon to begin Charge one of the mounted conductors and then insert the conductor into the lower part of the ice pail without allowing it to touch the bottom or sides and then remove Do not discharge the conductor Result A Ground the ice pail and press the reset ground button on the Sensor Right click in the graph area and use Add Text to label the graph Select the Overlay icon Click on the Start icon and lower the conductor into the lower half of the ice pail but this time touch the inside of the ice pail so it makes a good contact remove the rod Result B Do not ground the ice pail or charge discharge to conductor Charge 100nC nC 60 0 B Charged conductor lin and touched side A Charged conductor in and out 18 April 2005 14 52 06 10 Click on the Start icon and lower the conductor into the ice pail touch the side and withdraw it Result C Smart Charge Sensor 11 Ground the ice pail and repeat 10 Result D 12 Press reset on the Sensor Ground the ice pail then repeat the investigation using a conductor with the opposite charge Note f the ice pail proves difficult to discharge zero breathe gently over it The ions in the moisture
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