VacTran 3 Manual (779748), страница 11
Текст из файла (страница 11)
At this point, you can use the zoom slider (shown) toenlarge the image for more detail.Step 2: Specify log or linear axisCheck the graph image carefully to determine if the pump speed and pressure axes are log or linear. Check theappropriate settings.© 2011 Professional Engineering Computations72VacTran 3Step 3: Pressure scaleClick anywhere on the left most edge of the graph for the left scale point, and the right edge of the graph for the rightscale point as shown. The screen units value (in pixels) will change as you move the cursor.
Enter the values for thereal units. In this case, the left scale point is 1e-3 and the right scale point is 1e3.Step 4: Pump speed scaleClick anywhere on the bottom edge of the graph for the low scale point, and the top edge of the graph for the highscale point as shown. For the top edge, we used the “20” line because it is clearly marked. The screen units value(in pixels) will change as you move the cursor.
Enter the values for the real units. In this case, the low scale pointis 0 and the top scale point is 20.© 2011 Professional Engineering ComputationsPump models73Step 5: Select unitsSelect the appropriate units from the pull down menus.Step 6: Digitize the curveZoom in on the graph as necessary to get a better look at the curve, and start clicking todigitize each point. The digitizer tool will convert the screen units to real units based on thescale factors that were entered in previous steps. Use as many points as you like, andchange cursors mid-way if a different shape makes it easier to see what you are doing.
Usethe pull down menu as shown to change cursor shape. When done click on “Export data tonew pump model” to create a new pump model. You can always edit the data values oncethey are in a pump model if the curve needs to be tweaked.© 2011 Professional Engineering Computations746.9VacTran 3Additional data in the tabbed pagesWhen a graphic image is pasted into the Picture, Drawing, or Vendor’s curve tabs, these images are stored asseparate files from the pump model and loaded when the pump model is opened.
Therefore, if pump model ismoved to a new directory on your hard drive after it is created, be sure to move the graphics files with it.© 2011 Professional Engineering ComputationsPump models6.1075Example 1 Mechanical pumpThis example is included on the directory labeled “Examples”.The mechanical pump example shown is created by selecting the New... command from the File menu. Data isentered using the Add command for each entry. Simultaneously, with automatic graph updating enabled, the MainGraph Window updates the pump performance curve as each point is entered.© 2011 Professional Engineering Computations76VacTran 3The mechanical pump example is shown plotted below on a log-log axis. Units can be changed using pull downmenus.© 2011 Professional Engineering ComputationsPump models6.1177Example 2 Roots pumpThe Roots pump, is often used for mid range pumping between 10 torr and 10-3 torr.
Roots blowers are usuallyused in stages or in combination with mechanical pumps, because they cannot pump alone at higher pressures.The details of roots blower operation are only superficially mentioned here, and are covered in far greater detail intextbooks and vendor literature.© 2011 Professional Engineering Computations78VacTran 3Notice the small number of data points used to describe this pump. Many more could be used to create asmoother curve, but these six points are probably adequate for example purposes.Common units for roots pumps are cubic ft/minute, liters/second, cm3/minute, and m3/hour.© 2011 Professional Engineering ComputationsPump models6.1279Example 3 Combining two or more pumpsThe combination of a roots blower backed by a mechanical pump is often characterized on a single curve by pumpmanufacturers.
Two pumps can be combined into a single model, using the Add from file… command on thepump dialog.Caution:Pumps in series have combined speeds that are not necessarily simply the sum of the individual pumps. The Addfrom file… command is good for parallel pump combinations. For information on combining pumps in series, callthe manufacturer.When combining two pumps, VacTran uses the boundary pressure values of each as the range for the final data.The resulting data will range from the highest to lowest pressures of the two pumps. Data from each pump isinterpolated over the total pressure range divided into the number of points in the larger pump file. If one pumpcontaining 10 points is combined with another containing 20 points, the final summed pump will contain 20 points.© 2011 Professional Engineering Computations806.13VacTran 3Importing DOS pump filesPump files created on DOS version 2.0 or later of VacTran can be imported into VacTran for Windows.Step 1 Create a text file on the DOS versionStart the VacTran DOS program, and open the pump file.
Change the units of measure so that pressure is in Torr,and pump speed is in liters/second. Select the "Write to ASCII file" command from the pump menu in the DOSVacTran program. You will be prompted for a new file name. Close the pump file, and repeat this process for anyother pump files you wish to transfer to Windows. When finished, quit the VacTran DOS program.Step 2 Change the file extension to ".PMP" for all translated pump filesStep 3 You may wish to move all the new pump files to a directory within the VacTran for Windows directory.Step 4 Read the text fileAfter the transfer files have been translated, start the Windows VacTran program. Select the Open... commandfrom the File menu, and open the pump file.6.14Importing VacTran 2 pump filesPump files created on VacTran for Windows version 2.0 or later of VacTran can be opened into VacTran 3 forWindows. VacTran version 2 cannot read VacTran version 3 pump files.© 2011 Professional Engineering ComputationsPump models6.1581Importing pumps from ExcelImport pump model data directly from a native Microsoft Excel .xls file.Please note the following constraints:The pump data will be expected in the first two columns of the Excel file, on the first tab sheet.
VacTran will notfind the data anywhere else in the Excel file.The pressure data is read from column A, and pump speed is read from column B.Only .xls files are supported in this version. If you are using Excel 2007 (.xlsx) or later, save your Excel file as a .xls file before importing the pump data. A future update will address .xlsx files.Import Procedure:1) Use File|Open...
from the main menu or clickspreadsheet)"© 2011 Professional Engineering Computationsand select "Excel (.xls82VacTran 32) Select the Excel file to open:3)Tell VacTran the units to use when reading the data from the Excel file:© 2011 Professional Engineering ComputationsPump models833)The pump data will be read using the selected units.
It can now be saved as a pump file using the Pump Units, orit can be saved as another Excel file using the Excel units. You can view the data in either set of units by clickingon the "Show data using " radio buttons.© 2011 Professional Engineering Computations846.16VacTran 3Exporting pumps to ExcelExport pump model data directly to a native Microsoft Excel .xls file.Please note the following constraints:The pump data will be exported to the first two columns of the Excel file, on the first tab sheet.The pressure data is written to the Excel column A, and pump speed is written to column B.Only .xls files are supported in this version. All versions of Excel (97 or later) can read the .xls file.
A futureupdate will address .xlsx files.Export Procedure:1) Open a pump model in VacTran. An example is shown below.© 2011 Professional Engineering ComputationsPump models2) Use the right mouse button to open up the pop up menu:3) The pump data will be written to the XLS Viewer:© 2011 Professional Engineering Computations8586VacTran 34) Change the Excel units so that the pump data is written to the Excel file as desired. Click on "Excel units" todisplay the data as it will be saved to the file. An example of this data converted to Cubic feet/minute is shownbelow.5) Click on "Save as Excel File" to create the new file.© 2011 Professional Engineering ComputationsPump models6.17Exporting pumps to Excel via text exportSending pump data to Microsoft Excel is relatively straightforward using the following procedures:step 1) Set the text window options as follows:Do HeaderTab delimitedNo item numbers© 2011 Professional Engineering Computations8788VacTran 3step 2) In the Main Text Window, highlight the pump data:3) Right click over the Main Text Window, and select "copy":© 2011 Professional Engineering ComputationsPump models894) In an open Excel file, select a single cell and select "Paste" from the Edit menu.
The result is shown below:© 2011 Professional Engineering Computations906.18VacTran 3Tips on modeling pumpsPumps are defined in units of volume/time. Common units for pump speed are liters/second, and cubic feet/minute (CFM).A pump model is an independent text file, which can be referenced by any number of system models. Anychanges to a particular pump model will be reflected in all newly opened system models that use it.
An opensystem model will be updated by a change to a pump model.We recommend that the entire pressure range of the pump be modeled, so that many system models in differentsituations may use it. Data outside the used pressure range will simply be ignored, so having extra rangemodeled in a pump will not affect calculations.Pump data can be entered in any order, and sorted based on either speed or pressure.
Because VacTran usesinterpolation to determine pump speed from the curve, a minimum of two data points is needed for a valid model.In the real world, numerous factors can affect the reliability of catalog pump speed data. Regeneration cycles,contamination, preventative maintenance, and a host of other factors will affect the real performance of differenttypes of pumps. Be sure that you are familiar with the pump technology that you are modeling to account forperformance variations that are not considered in the classic vacuum formulas. Contact a reliable vendor forinformation on applicability of a given type of pump to a specific application.In VacTran, a vacuum pump is modeled as a data set of pump speed vs.
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