VacTran 3 Manual (779748), страница 30
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For JPG, only pixels are applicable.See also:Graph controls dialogBackground colorsLine stylePointsExport GraphTitlesFontsBorderPreset StylesAxis typeGrid StyleLegendGalleryUpdatesLog ScalesShadows© 2011 Professional Engineering ComputationsDefault Settings17.2293Units of measure dialogWhat is it?The Units of Measure dialog is used to to change the displayed units throughout VacTran.How to open the dialog:To access this dialog, click on the Units of Measure speed button as shown below or select Units of Measure fromthe Defaults Menu.If the Graph Update option is active, the most recent calculation will be repeated after clicking on the OK button inthis dialog.© 2011 Professional Engineering Computations294VacTran 3Additional clarifications on some types of units are given below:Vessel pressurePressure unit for all calculations other than those relating to throughput.Throughput pressurePressure unit for all calculations relating to throughput, such as torr-liters/second.
All other calculations using apressure unit are done using vessel pressure units.VolumeVolume used for all vessel volume references.Speed volumeVolume unit for all calculations other than those relating to pump speed or conductance, as liters/second.AreaArea unit for any case where area is not combined with other units in gas loads, such as surface area.Gas Load AreaArea unit for combinations of gas load data, such as torr-liters/second/cm2, or m2/hour.Elapsed timeTime unit of measure for any calculation in which time will be the abscissa if plotted, such as gas load vs.
time orpressure vs. time.Rate timeTime unit of measure used for any combination of units in which time is the divisor, such as in liters/second.See also:Default Settings© 2011 Professional Engineering ComputationsDefault Settings17.3295Environment dialog - globalWhat is it?The Environment dialog is used to change significant vacuum system parameters that are used throughout theprogram.See also:Environment dialog - systemDefault SettingsHow to open the dialog:It can be activated by selecting any of the global vessel parameters under the Model menu, or by clicking on thevacuum vessel icon on the speed bar.or(click to expand)The Environment dialog displays the current global settings as shown below:© 2011 Professional Engineering Computations296VacTran 3Click to expandGlobal start pressure: This is defined as the pressure at which pump down analysis starts, measured at thevacuum chamber.
This can be any value greater than the target pressure. For pump down calculations, the startpressure must be within the pumping capacity of at least one pump station. For example, the start pressure cannotbe selected as 760 torr with the highest operating pressure in any pump station at 10-2 torr,.Global target pressure: The pressure at which the pump down analysis ends, measured at the vacuum chamber.This must be less than the start pressure and greater than zero. For pump down calculations, the target pressuremust be within the range of at least one of the system model pumping stations.Calculation increments: This is the number of steps to divide a calculation. For a sequential set of calculationssuch as pump down time, this is the number of increments of pressure between the start and target. Moreincrements mean a more accurate calculation, but also requires more time to perform.
Generally, no more than 500increments are required to get an adequately smooth curve.Gas load decay time: The classical out gas formula approaches infinite gas load as time approaches zero. Realworld systems do not behave this way. Use the decay time to ignore the theoretical gas load curve values at earlierstart times. For example, for a decay time of 10 seconds, the calculated gas load curve will be based on an initialtime of 10 seconds.
The curve will then be applied to the system model at the Gas load start time.Gas load start time: Start time delays the addition of gas loads to the system during pump down calculations. Forexample, if gas load start time is one hour, the calculated gas load curve will start being applied to the system afterone hour.Gas load stop time: The allotted time to which all gas load calculations will be made. This time limit should be© 2011 Professional Engineering ComputationsDefault Settings297set by the user to be greater than the maximum pump down time for the system.
If stop time is excessively high,the temporal resolution of the gas load calculations will be reduced. If the stop time is less than the pump downtime for the system, it will shut off the gas load before a complete pump down curve can be generated.Rate of rise start time: Specifies that starting value for calculating pressure rise in the vessel. The gas load valueswill be calculated based on this elapsed time. Most gas loads decrease with time, so a higher value for the starttime will result in a lower gas load in the calculation.Rate of rise stop time: Specifies the end point for the pressure rise calculation.Rate of initial vessel pressure: Specifies the pressure from which the pressure rise calculation will start.Vessel volume: Total volume of the chamber to be evacuated, not including the conductance elements connectingto the vacuum pumps.© 2011 Professional Engineering Computations29817.4VacTran 3Environment dialog - systemWhat is it?The Environment dialog is used to change significant vacuum system parameters that are used by the open systemmodel.See also:Environment dialog - globalDefault SettingsHow to open the dialog:It is activated by clicking on the vacuum vessel in the System Model dialog as shown below:To change all subsequent open system models, use this dialog from the model menu or speed bar.© 2011 Professional Engineering ComputationsDefault Settings299System start pressure: This is defined as the pressure at which pump down analysis starts, measured at thevacuum chamber.
This can be any value greater than the target pressure. For pump down calculations, the startpressure must be within the pumping capacity of at least one pump station. For example, the start pressure cannotbe selected as 760 torr with the highest operating pressure in any pump station at 10-2 torr.System target pressure: The pressure at which the pump down analysis ends, measured at the vacuum chamber.This must be less than the start pressure and greater than zero. For pump down calculations, the target pressuremust be within the range of at least one of the system model pumping stations.Pump Station start: This is defined as the pressure at which the first pump station is set to start.Pump Station stop: This is the pressure at which the last pump station (if there are more than one active) is set tostop.Calculation increments: This is the number of steps to divide a calculation.
For a sequential set of calculationssuch as pump down time, this is the number of increments of pressure between the start and target. Moreincrements mean a more accurate calculation, but also requires more time to perform. Generally, no more than 500increments are required to get an adequately smooth curve.© 2011 Professional Engineering Computations300VacTran 3Gas load decay time: The classical out gas formula approaches infinite gas load as time approaches zero. Realworld systems do not behave this way. Use the decay time to ignore the theoretical gas load curve values at earlierstart times. For example, for a decay time of 10 seconds, the calculated gas load curve will be based on an initialtime of 10 seconds.
The curve will then be applied to the system model at the Gas load start time.Gas load start time: Start time delays the addition of gas loads to the system during pump down calculations. Forexample, if gas load start time is one hour, the calculated gas load curve will start being applied to the system afterone hour.Gas load stop time: The allotted time to which all gas load calculations will be made. This time limit should beset by the user to be greater than the maximum pump down time for the system. If stop time is excessively high,the temporal resolution of the gas load calculations will be reduced. If the stop time is less than the pump downtime for the system, it will shut off the gas load before a complete pump down curve can be generated.Rate of rise start time: Specifies that starting value for calculating pressure rise in the vessel.
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