user manual
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1. XP or Windows 7 with a CD ROM drive 2 5V power supply 2 2 software installation Software has been provided with the module to allow immediate use of the product However if custom user programmes are required then section 4 programming defines the necessary interface protocol for users to follow Insert the counter timer software compact disc into the CD ROM drive of your computer The set up program will install the counter timer software on your PC together with a virtual COM port driver for the USB interface note installation set up starts automatically on most computers If it does not run the set up programme on the CD 2 3 interfaces see appendix A module interface characteristics 2 3 1 connect the module to a light tight housing or sample chamber 2 3 2 connect the USB lead to the computer 2 3 3 connect the power leads to the 5 V power supply red 5 V black 0 V 2 3 4 if used make the appropriate connections to the trigger Input grey and user ouput violet 5V Light tight enclosure Supply PxxUSB module USB lead 2 3 9 switch on the 5 V power supply note the photodetector module must be installed in a light tight housing or sample chamber before the selecting the lt HV on gt command failure to do so may damage it 2 3 6 Driver installation After installation of the software when the first module is connected to a USB port the PC will detect new hardware and install the two drivers Foll2. Select the module from the drop down list and click Open A results window will then open for that module showing an empty table and graph If it is not already present the control window will also open at this time P25USB Module SN 29113 Rate Counts Offset 0 Multiplier 1 00 Set If you wish to use multiple modules the above process must be repeated for each one The results window for each package is identified on the title bar by the package serial number P25USB P30USB user manual issue 2 September 2010 Sens Tech Limited 2010 page 4 of 21 e SENS TECH KS SENSOR TECHNOLOGIES 3 2 control window The control window opens automatically when a results window is opened It may also be opened by selecting Window and then Show control window Control Ext Trigger Off C Continuous C Fired Readings B 1 32000 Period 1000 ms 10 2500 High Voltage f Off C On C Fallow start Esen User Signal f Off C On C Follow start Delay Start Do m Note If multiple modules are used there will only be one control window and this will control all the modules in unison If you wish to control multiple modules individually you should open an instance of the program for each package In the Control window set up the following 3 2 1 external trigger Select the external trigger mode as either Off Fixed or Continuous These operate as follows Off When the start button
3. provide the optimum gain for photon counting At this operating point on the signal counts vs HV plateau characteristic the slope is less than 0 2 per volt and hence we have stable performance P25USB P30USB user manual issue 2 September 2010 Sens Tech Limited 2010 page 14 of 21 ej SENS TECH KS SENSOR TECHNOLOGIES 7 1 2 signal to noise The photoelectric effect is a quantum mechanical process subject to fluctuations described by Poisson statistics A steady light source generating m photoelectons per second for a period of t seconds will produce z gi 1 2 i ht an average of mt photoelectrons with a standard deviation of mt Hence signal to noise ratio is given by mt mt mt In photon counting there is negligible additional noise generated in the gain process or in the amplifier discriminator hence this expression is also valid for the complete Detector It should be noted that the signal to noise ratio depends on the number of counts hence for low count rates an increased measurement period will always be advantageous 7 1 3 responsivity The responsivity of the Detector is the output count rate less dark counts for a given light power incident on the photomultiplier window responsivity QE f h c where QE A is the quantum efficiency of the photocathode at wavelength h is the Planck Constant 6 626 x 10 Js c is the speed of light 3 x 10 ms and f is the collect
4. readings The SP Stopped message Carriage return R followed by Sets the Number of Readings to the byte value of the The VA Valid message a character character following R AQ is seen as 1 The default Number of Readings is 1 P followed by Sets the Periods setting P to the number following P The VA Valid message a character A 0 is changed to 1 This sets the counter gate interval in multiples of 10ms eg P 100 gives a one second gate time The default Periods setting is 10 P25USB P30USB user manual issue 2 September 2010 Sens Tech Limited 2010 page 10 of 21 ej SENS TECH KS SENSOR TECHNOLOGIES O followed by a Turns on the Output Signal 1 5V out when the character The VA Valid message character following the O has a byte value of 1 or turns off OV out the Output Signal 1 when it has a byte value of 0 Byte values greater than 1 cause a BC message to be sent to the PC The default value is off V followed by Turns off the Voltage when both of the characters following the The VA Valid message two characters V have byte values of zero or turns on the Voltage if either one of the characters has a byte value that is not zero port 3 7 is 0 The default value is off Do Turns on the high voltage The VA Valid message example To initialise and take 20 readings in fixed count mode using a 100ms gating period Apply power to counter Replies ST After a power on reset two AS
5. typeA Ess Red male plug OV Black I O out Violet I O in Grey P25USB P30USB user manual issue 2 September 2010 Sens Tech Limited 2010 page 19 of 21 e SENS TECH KS SENSOR TECHNOLOGIES appendix D the activeX control This is the documentation for the ActiveX control It describes the function and parameters of the methods properties and events in the control Several examples are provided on the CD ROM to help in software development Specifically we provide examples for Visual Basic Labview Excel and Delphi The examples are intended as a guide to programming with the ActiveX control and not as complete solutions The following example describes the correct sequence for using the ActiveX control 1 first open the COM port object Open 1 2 then setup the device object Continuous false sets non continuous mode ie fixed number readings object Triggered false disable external trigger input object OutputSignal false sets the user output violet wire to O volts object OutputVoltage true turns on the photomultiplier HV supply object Period 100 sets gate period to one second object ReadingCount 100 sets number of readings to be taken as 100 3 call the Start method and handle the events generated object Start starts counting finish by turning off the HV and closing the COM port object OutputVoltage false turns off the photomultiplier HV supply object Close remarks it
6. CII characters are sent to PC to indicate startup initialisation is complete PC sends R x CR LF Four ASCII characters where x represents an ASCII character with the value in the range 1 to 255 setting the number of readings to be taken In this example we want the character with the decimal value 20 and should transmit a single byte with the value 14 hex replies VA Two ASCII characters acknowledging a valid command PC sends P y CR LF Four ASCII characters This sets the gating period y represents an ASCII character with a value in the range 1 to 255 and sets the gating period in multiples of 10ms In this example we want 100ms and so y would be the ASCII character with the decimal value of 10 10x10ms 100ms replies VA PC sends S CR LF Three ASCII characters This starts the measuring process NoVA reply is sent to PC replies b1 b2 b80 80 bytes The counter will transmit back a string of bytes containing the reading in binary Twenty readings will produce 80 bytes in total When the first reading is complete it will be transmitted as four binary bytes as detailed above Whilst this transmission proceeds the next reading begins P25USB P30USB user manual issue 2 September 2010 Sens Tech Limited 2010 page 11 of 21 w SENS TECH SENSOR TECHNOLOGIES troubleshooting no counts check all connections have been made correctly check the 5 V power supply is on and correctly set check the HV has been sel
7. age Select the HV voltage as Off or On or Follow start noting the precautions stated in section 1 The module will not count until the HV voltage has been activated When Follow start is selected the HV will switch on automatically when the start button is clicked See also Delay Start below 3 2 5 user signal Select the User Signal as Off or On or Follow start This will then control the external output line violet wire switching it between 0 volts off and 5 volts on to permit control of external apparatus such as a shutter mechanism see appendix A module interface characteristics When Follow start is selected the user output goes to 5V when the start button is clicked This is unaffected by the setting of the delay start 3 2 6 start stop Selecting Start Stop will either Start or Stop counting On selecting Start the software will function in accordance with the selection made in the Control Window 3 2 7 delay start Setting a value here allows the start of the counting to be delayed by up to 10 000ms from clicking the start button This can be used for example when using Follow start to allow the HV to settle before counting begins The HV takes approximately 600ms to settle however a warm up time of at least 2 seconds is recommended P25USB P30USB user manual issue 2 September 2010 Sens Tech Limited 2010 page 6 of 21 a Sens Tech Counter Timer Software Ele Edt Window Help D ce bed Ge P25U58 M
8. e greater than the one specified in the BufferSize property P25USB P30USB user manual issue 2 September 2010 Sens Tech Limited 2010 page 21 of 21
9. ected to on count overflow or very high count rates check for light leaks software will not install check that the computer is running Windows XP or Windows 7 no readings can be taken check count mode not selected to external trigger or trigger not available communication timeout check the module is powered up and connected to the USB port If a module is momentarily powered down or disconnected when in use it will be necessary to restart the software before it can be re selected P25USB P30USB user manual issue 2 September 2010 Sens Tech Limited 2010 page 12 of 21 e SENS TECH KxS SENSOR TECHNOLOGIES 6 module design P25USB photodetector modules include a 25 mm diameter photomultiplier tube with a 22mm active photocathode diameter The P30USB photodetector modules includes of a 30 mm photomultiplier tube with a 25 mm active photocathode diameter The photomultiplier is powered by a very efficient HV Cockroft Walton power supply Low power dissipation ensures negligible heat generation within the module The high voltage is factory set at the optimum operating voltage to ensure stability of operation and stable photon counting performance The signal from the photomultiplier is connected to a high performance amplifier discriminator combination which is factory preset to accept signal but to reject electrical noise This is described in section 7 photon counting techniques Pulses from the outpu
10. f the J O dynamic range by 10 subtracting dark 3 counts gt 10 Bialkali 10 ___ With dark count 40 subtraction 10 10 40 10 incident light power W at 400 nm and 20 C Over the majority of their useful operating range the responsivity of Photon Counting Detectors is linear and will produce an output count rate which is proportional to input light power as shown in figure 4 At low count rates the effect of dark counts becomes significant causing the curves of figure 4 to flatten Some improvement can be achieved by cooling or at least preventing the module from being heated by other apparatus Dark count subtraction can be used down to the point at which signal is less than about 1 10 of background At lower signal rates the statistical uncertainty associated with the subtraction process becomes excessive In background subtraction the signal count rate S is deduced as the difference between the measured rates of S B for signal and background and B for background alone It should therefore be noted that the signal to noise ratio for the deduced signal rate will be S S 2B At high count rates the dynamic range is limited by electronic dead time effects caused by pulse pile up Pulses that arrive whilst the discriminator is busy are not counted Correction for dead time is automatically applied in the software in the form N n 1 nt where N is the corrected count rate n is the measured count ra
11. ical support this takes you to the Sens Tech web site where a list of technical support contacts are available about this states the software version being used P25USB P30USB user manual issue 2 September 2010 Sens Tech Limited 2010 page 8 of 21 e SENS TECH KS SENSOR TECHNOLOGIES 4 programming The tables on the following pages list the commands available to operate the module This information is helpful when writing your own software In addition an ActiveX control driver is provided on the installation CD together with example programmes for use with Excel Lab View Visual Basic and Delphi Details of this module are shown in appendix D the ActiveX control 4 1 command description All commands sent from the PC must consist of strings of ASCII characters terminated with CR and LF except the stop command which is just a CR As shown by the following table commands consist of a single upper case letter which will in some cases be followed by a value The value is sent as a single ASCII character except for command V which uses two For example a decimal value of 21 would be transmitted as a single byte with the value 14 hex Values are limited to the range 0 to 255 Commands will either be acknowledged with a pair of ASCII characters as shown in the table or will initiate a flow of data back to the PC Where the command is not recognized there will be no reply If the characters following a valid co
12. ion efficiency of the first dynode typically 0 95 for the standard range of photomultipliers used in photon counting Hence when responding to light of 400 nm wavelength a module with a bialkali photocathode with typical QE of 0 25 has a responsivity of 4 78 x 10 counts WwW so 1 fW of 400 nm light incident on the photomultiplier window will produce a mean output count rate of 478 s excluding dark counts The temperature coefficient of quantum efficiency and hence of responsivity is shown in figure 2 Bialkali figure 2 temperature coefficient of various photocathodes used for photon counting temperature coefficient C 300 400 500 600 700 800 900 wavelength nm P25USB P30USB user manual issue 2 September 2010 Sens Tech Limited 2010 page 15 of 21 e SENS TECH KS SENSOR TECHNOLOGIES 7 1 4 background Background or dark count is the unwanted signal produced by the photomultiplier tube in the absence of light stimulation Dark counts in photon counting detectors are a function of photocathode type and temperature as shown in figure 3 5 10 4 10 figure 3 2 10 The beneficial effect 5 5 of cooling a lt 40 Bialkali photomultiplier 3 10 0 10 60 40 20 0 20 40 60 temperature C Typical dynamic range is shown in figure 4 10 10 10 figure 4 A c 10 extension o
13. is clicked counting beings immediately Counting will then continue until the set number of readings have been taken or the STOP button is clicked Fixed When the start button is clicked counting will not begin until the first falling edge on the external trigger input grey wire Counting will then continue until the set number of readings have been taken or the STOP button is clicked Continuous When the start button is clicked readings will only be taken whilst the trigger input is at logic high Readings begin within 50us after the trigger input is taken high When the trigger input is taken low the current reading period will complete before the gate is closed Counting will continue until the set number of readings have been taken or the STOP button is clicked 3 2 2 readings Select the total number of readings you wish to take 32000 max 3 2 3 period Select the gating period of the reading 10 ms to 300 s By clicking on the box that states the units of the period setting the user can toggle between ms 10 2500 and s 1 300 When ms 10 2500 is used the software reads counts from the hardware dependent on the period set When s 1 300 is used the software reads counts from the hardware every 1 s and then accumulates the results until the desired period is achieved P25USB P30USB user manual issue 2 September 2010 Sens Tech Limited 2010 page 5 of 21 e SENS TECH KS SENSOR TECHNOLOGIES 3 2 4 high volt
14. is not unusual for the com port to be open for the entire duration of the program P25USB P30USB user manual issue 2 September 2010 Sens Tech Limited 2010 page 20 of 21 SENS TECH SENSOR TECHNOLOGIES oe Gets the number of readings currently in the buffer that are awaiting processing Gets or sets the number of slots available to the software FIFO buffer Gets or sets the continuous mode of data acquisition Setting this property to TRUE causes data acquisition to be continuous Setting this value to false causes data acquisition to stop after the number of readings specified in the properties Reading Count property Gets or sets the state of the output signal Setting this property to TRUE causes the output signal set to 5 volts Gets or sets the state of the photomultiplier high voltage supply Setting this property to TRUE causes the high voltage to be switched on caution see precautions in section 1 1 Gets or sets the counter gate period in multiples of 10ms Gets or sets the number of readings to be taken in non continuous acquisition mode Gets or sets the triggered mode of data acquisition Setting this property to TRUE enables Closes the COM port used by the ActiveX control Opens a COM port for use by the ActiveX control Begins counting Ends counting methods events Occurs when a new reading is available for processing Occurs when the FIFO buffer attempts to grow to a siz
15. missions The photocathode has a wavelength dependent probability of releasing a photoelectron for each incident photon This probability is known as the quantum efficiency QE and is normally expressed as a percentage Typical spectral response characteristics for the photocathodes used in photon counting detectors are shown in figure 1 30 Bialkali D figure 1 20 oe KE photomultiplier light 2 4 RbCs sensitivity as a function 7 l of wavelength described z l as quantum efficiency QE I S20 o l 0 100 300 500 700 900 wavelength nm Photoelectrons emitted by the photocathode are accelerated and focussed onto the first dynode of the electron multiplier section of the photomultiplier On impact each photoelectron liberates a number of secondary electrons which are in turn accelerated and focussed onto the second dynode The process is repeated at each subsequent dynode and the secondary electrons from the last dynode are collected at the anode Individual charge pulses from the photomultiplier vary in magnitude because of the statistical nature of the gain process but so long as they exceed the preset threshold of the discriminator each will be counted as one pulse Only small pulses resulting from single electrons originating from intermediate dynodes will fall below the threshold and thus rejected The voltage applied to the photomultiplier in the detector is factory set to
16. mmand are not as expected the reply BC bad command will be sent to the PC Replies to the PC are not terminated with CR and LF The commands S C B Land E cause the module to transmit readings back to the PC The readings consist of blocks of four bytes which hold the binary value of each reading The first byte transmitted is the most significant byte If the most significant bit of the first byte is a 1 an overflow has occurred in the counter The maximum possible uncorrected count for each reading is 67 108 863 All commands will stop any reading in progress or stop any EEPROM memory transmission to the PC and then perform the specified action An ST Start Message is sent to the PC at power up and whenever a Reset occurs P25USB P30USB user manual issue 2 September 2010 Sens Tech Limited 2010 page 9 of 21 e SENS TECH Os SENSOR TECHNOLOGIES Sil cic Bs Poer o or reset The ST start message Starts R readings where each reading is timed over P 10ms At the end of each reading the reading is sent to the PC in binary form as 4 bytes with the most significant byte sent first If the count exceeds 67 108 863 during a reading that reading is terminated immediately and an error reading is sentto the PC The software then continues with the next reading An error reading is distinguished by having the most significant bit of the first byte as a 1 otherwise it is 0 Thus a valid reading has a maximum of 31 bi
17. oduct 1 2 supply voltage Ensure the 5 V supply voltage does not exceed 5 25 V Exceeding 6 0 V on the module or reversing the supply may result in permanent damage see appendix A module interface characteristics 1 3 maintenance Photodetector modules contain no user maintainable components Because of the High Voltages present inside the package dis assembly must not be attempted by the user Photodetector modules must be returned to Sens Tech for repair 1 4 cleaning The window of the photodetector module may be cleaned using lens tissue and alcohol but only while it is disconnected from its power supply The window should be treated as a normal optical component The housing may also be cleaned with alcohol and lens tissue The use of other cleaning agents is not recommended When cleaning observe the precautions stated under light exposure 1 5 environment The photodetector module must not be exposed to levels outside those specified in appendix B environmental conditions 1 6 magnetic fields The module housing is made of mu metal providing good shielding from transverse magnetic fields For applications involving strong axial magnetic fields please ask for assistance from our technical sales staff P25USB P30USB user manual issue 2 September 2010 Sens Tech Limited 2010 page 2 of 21 ej SENS TECH KS SENSOR TECHNOLOGIES 2 installation 2 1 system requirements 1 PC operating under Microsoft Windows
18. odule SH 29113 w SENS TECH SENSOR TECHNOLOGIES Control Off Continuous C Fied Readings 5 1 32000 Period 7000 _mst10 2500 High Voltage eon an f On 0 User Signal f Off f On f Follow start 3 3 counter timer software window The following facilities are available from the Main Window both as drop down menus and as items on the toolbar file Connect Open Save Save as Exit edit copy select all window math statistics show control window selects the module to be used as stated in section 3 1 allows the user to select a previously saved set of results for analysis allows the user to save a set of results note If there are multiple results windows open the relevant window must be selected by clicking on it allows the user to change the save file name exits the program copies highlighted data to the clipboard to enable it to be pasted into other software applications such as a spreadsheet or word processor selects and highlights all of the data in the table plots two existing sets of data as a ratio on a point by point basis allows previously recorded data to be analysed to find min max mean and standard deviation displays the counter control window P25USB P30USB user manual issue 2 September 2010 Sens Tech Limited 2010 page 7 of 21 e SENS TECH KS SENSOR TECHNOLOGIES help techn
19. ow the on screen instructions to carry out this process This process will repeat the first time a module is plugged into each of the PC s remaining USB ports P25USB P30USB user manual issue 2 September 2010 Sens Tech Limited 2010 page 3 of 21 w SENS TECH SENSOR TECHNOLOGIES 2 4 light collection When measuring low light levels always try to collect as much light as possible onto the window of the photomultiplier For example assuming a point source of emission at a distance of 22 mm from say a 22 mm diameter active area photocathode then straightforward solid angle considerations indicate that only 12 of emitted light reaches the photomultiplier Some enhancement may be achieved by the use of reflective surfaces or a light guide or by simply moving the window closer to the source 3 start up software 3 1 selecting module If not already done power up the module to be used and connect the USB lead to the PC Note If this is the first time any PxxUSB module has been connected to the USB port a new hardware message will appear Follow the on screen instructions to install the two drivers The module to be used with the software must now be selected from a list of the devices connected to the PC serial ports To do this select File then Connect from the menu at the top of the Main Window A window called New will appear Select device serial port Device P25USB Module SN 29113 X Cancel
20. t of the amplifier discriminator are passed to a counter which is gated on off by the microcontroller according to the gate period setting The count is latched through to a parallel to serial converter before continuing to the next counting period This ensures the dead time of the counter is kept to an absolute minimum 11 1us gap between gate periods The microcontroller has a maximum count rate capability of 100 MHz after linearity correction All counts are automatically corrected for dead time losses caused by pulse pile up This is particularly important at high count rates The module also incorporates a watchdog circuit such that in the event of internal software failure the module will automatically reset itself to its default settings The module housing is mumetal providing good shielding from transverse magnetic fields P25USB P30USB user manual issue 2 September 2010 Sens Tech Limited 2010 page 13 of 21 ej SENS TECH Kx SENSOR TECHNOLOGIES photon counting techniques 7 1 operating principles These photodetector modules use the photomultiplier in the photon counting mode The following paragraphs summarise the salient features of this technique and provide typical performance data for these modules 7 1 1 photon counting The following section provides information on photon counting the intended role for these modules Photon counting is the most sensitive method for measuring weak or short lived light e
21. te and t is the count rate correction factor P25USB P30USB user manual issue 2 September 2010 Sens Tech Limited 2010 page 16 of 21 SENS TECH SENSOR TECHNOLOGIES re appendix A module interface characteristics absolute maximum ratings output output sinking 20 mA output sinking 20 mA mA output sourcing 80 pA a 4 ouput sourcing 12 WA 4 5 P25USB P30USB user manual issue 2 September 2010 Sens Tech Limited 2010 page 17 of 21 w SENS TECH SENSOR TECHNOLOGIES appendix B environmental conditions 1 temperature operating 9 10 459 C sinusoidal vibration non operating 10 to 500 Hz for 10 cycles in each axis at a peak amplitude of 2 g 1 octave min random vibration non operating 20 Hz at 0 02 g Hz to 50 Hz at 0 02 g Hz falling to 500 Hz at 0 001 g Hz humidity non condensing 93 at 30 C pressure operating can withstand pressure reductions from 68 kPa 0 68 bar to 100 kPa 1 bar P25USB P30USB user manual issue 2 September 2010 Sens Tech Limited 2010 page 18 of 21 appendix C outline drawings mm P25USB P30USB 34 0 0 5 35 0 0 5 22 0 active diameter 25 0 active diameter CH Choo photomultiplier photomultiplier 120 1 p mumetal case mumetal case 181 5 1 screened cable 610 50 screened cable 1850 50 610 50 USB typeA Loew Red male plug OV Black 1850 50 I O out Violet I O in Grey USB
22. ts Starts continuous readings where each reading is timed over P 10ms The readings are terminated by sending the Stop command CR or other command Allows continuous readings Readings are initiated where each Following the VA Valid message CR reading is timed over P 10ms whenever the External Trigger the readings are sent to the PC as pin is 1 and readings are inhibited whenever the External Trigger forthe S and C commands above pin is O Sending the Stop command CR or other command terminates this mode of operation Allows R readings where each reading is timed over P 10ms Each reading is initiated at the falling edge of the external Trigger pin This may be repeated any number of times Sending the Stop command CR or other command terminates this mode of operation Starts R readings where each reading is timed over P 10ms No readings are sent to the PC The readings are sequentially stored in the non volatile but when all of the readings have EEPROM along with the number of readings taken overwriting been taken the MF message is the currently stored readings Overflowed readings are also sent to the PC stored If R is greater than 126 only 126 readings are taken and stored Sends the readings held in the non volatile memory to the PC The readings held in the non These readings remain in the non volatile memory until volatile memory overwritten by the consequences of an M command Cancels the current set of
23. w SENS TECH SENSOR TECHNOLOGIES SENS TECH KS SENSOR TECHNOLOGIES mn P25USB P30USB photodetector modules page 1 precautions 1 1 light exposure 2 1 2 supply voltage 2 1 3 maintenance 2 1 4 cleaning 2 1 5 environment 2 1 6 magnetic fields 2 2 installation 2 1 system requirement 3 2 2 software installation 3 2 3 interfaces 3 2 4 light collection 3 3 start up software 3 1 selecting module 4 3 2 control window 9 3 3 counter timer window T 4 programming 4 1 command description 9 5 troubleshooting 12 6 module design 13 7 photon counting techniques 7 1 operating principles 14 8 appendix appendix A interface characteristics 17 appendix B environmental conditions 18 appendix C outline drawings 19 appendix D the Activex control 20 P25USB P30USB user manual issue 2 September 2010 Sens Tech Limited 2010 page 1 of 21 e SENS TECH KS SENSOR TECHNOLOGIES 1 precautions 1 1 light exposure The photodetector module is extremely sensitive to light It is recommended that the module is stored in the dark Exposure to bright light such as fluorescent lighting or daylight should be minimised After exposure to bright light the dark current or dark count rate may take up to 24 hours to return to the expected low level note the photodetector module must not be switched on using the lt HV on gt command in bright light this may result in permanent damage to the pr
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