PLT unit - t Labo

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Pipette Leak Testing Unit (PLT unit)According to monitoring of measuring instruments,air-displacement pipettes must be checked at regularintervals and the results must be compared with theISO 8655-2 error limits.However, a calibration certificate only reflects the resultsat the time of testing. The time between thesecalibrations is crucial, since leaks can occur at any time.Well over 80% of pipettes sent in for repair have leaksand are outside their volume tolerances, even if theydon’t drip.While the PLT unit cannot replace regular gravimetrictesting, daily pipette checks can provide a safeguardduring the periods between calibrations. Even the smallestleaks are detected! Process reliability for the pipettesis thus significantly improved.Leak rates and their detectionThe leak rate is a measure of the quantity of material that flowsthrough a leak per time unit. For air-displacement pipettes thePLT unit determines the rate through a differential pressure measurement,i.e., after creating a negative pressure, the pressurerise over a given time is measured.n Complex determinationsThe leak rate is determinedby considering complexphysical relationships.Calculation of the limit valuesresident in the PLT mustinclude factors such as thedead volume of the pipette/tip system, flow crosssectionof the pipette tip,pressure rise per time unit,pipette volume and type, etc.n The pV valueThe pV value is the productof the pressure and the volumeof a certain quantity ofa gas at the prevailing temperature.This is a measureof the quantity of material orthe mass of the gas.n The leak rate Q LThe leak rate Q L is the ratioof the pV value and theperiod of time during whichthe gas flows through a pathcross-section.DisplaySingle-channeladaptern The volume lossFor the pipette test,hPa ml/s is a suitable unitfor the leak rate. A leak rateof e.g., 1 hPa ml/s at anair pressure of 1000 hPameans a volume loss ofabout 1 μl/s."Start/Execute"button"Back" buttonSelect knobLED displayPLT unitSingle-channeladapter for pipetteswith tipSingle-channeladapter for pipetteswithout tipPE filter in singleandmultichanneladaptersMultichannel adapterfor pipettes with andwithout tipBack of the instrumentwith AC adapter socketand USB port
Main MenuA wide variety of submenuscan be selected from themain menu, e.g., pipette type,volume range, self-test, andsettings (language, shut-offtime, pressure units, etc.)Main MenuPipette TypeSelf TestSwitch OFFSettings...Auswahl selectzurück backTesting with and without tipTo check the overall pipette system,the test is conducted withmounted, unused tip.When a leak has been identified,the test can be repeated withouta tip to determine whether theleak arises from the tip cone/tipcoupling region.Dynamic or static test?The dynamic test can rapidlydetermine whether a defectivepiston (contamination,scratches, etc.) has caused aleak. The pipette button mustbe pushed down numeroustimes during the measurementperiod. The associated pistonmovement allows a defectivepiston to be recognized.In the static test, the pipettebutton is not pressed duringthe test procedure, i.e. the pistondoesn't move. This will onlydetermine a leak in a generalway, without attributing it to aparticular component.Limit valuesThe limit values referenced duringtesting represent a warninglimit, from which significantlylower volume values can alsobe determined gravimetrically.This is one quarter of the volumetolerances, according toISO 8655-2.The limit value for the leak volumeof a given pipette allowsthe leak rate to be calculated.These calculations, which arebased on over 35 years ofexperience in the developmentand production of pipettes, includethe dead volume and theintake characteristics, amongother things.If the pipette is mechanicallydefect-free, clean, and thetest is carried out properlywith the BRAND PLT unit,then the instrument is withinthe ISO 8655-2 tolerances.The marks in the verticalprogress bars in the displaystartstartPASSWith the correlation table inthe PLT operating manual,the pipette is leak-tight, andSC – 100 µlwhether itQ L: 0.04 hPa lies within thetolerance limits or leaks.* ml/srepresent the resident limitvalues for the leak rate Q L .PASSSC – 100 µlQ L: 0.04 hPa* ml/sthe missing volume can beapproximately determinedfrom the leak rate. The levelof the progress bar in thedisplay indicates whetherFAILSC – 100 µlQ L: 4.6 hPa* ml/sstart
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PLT unit - t Labo

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