Field Precision software tips

Coil force integrals in Magnum

shumphries — Tue, 24 Apr 2012 20:39:18 +0000

The magnetic force on a vector current element dl carrying current I in a magnetic field with flux density B is

dF = I dl × B (1)

In Magnum applied currents are represented by a collection of filamentary elements, so you might think that it would be straightforward to implement automatic routines to find forces on drive coils. The problem is one of accuracy when the drive coils are the primary source of the field. The field varies rapidly around the filamentary elements so a simple integral using Eq. 1 may give misleading values.

On the other hand, there are situations where such an integral would be very useful. I recently had a consulting project where a strong permanent-magnet assembly exerts a force on a current loop. The loop carries less than an ampere and makes only a small contribution to the field. Accordingly, I recently added a routine for automatic coil-force integrals to MagView. The new command Coil force is in the File operations menu. Here’s how it works:

Figure 1. Magnet assembly with diagnostic coil paths

1) Suppose you have a solution for a permanent-magnet assembly or an electromagnet and want to find the force on a coil inserted in the magnet volume. Load the solution into MagView with the File operations/Load solution file command.

2) Use Magwinder to define the sensor coil. It may be a simple rectangle (as in Fig. 1) or multi-turn shape of any complexity like a coil box. Assign a coil current of 1.0 A.

3) If you want to check the force at multiple positions, define multiple Coils in the CDF file with different values for the Shift and Rotate operations, as in Fig. 1.

4) Export an element file (WND).

5) Load the element file into MagView with the File operations/Load coils command.

6) Click on the Coil force command (note that the command functions only when both a solution and coil file have been loaded). The command shows a dialog with force components for each coil in the WND file and also write values to a data file if one is open. Here is an example listing:

--- Coil forces  ---
 NCoil         Fx          Fy         Fz
 ===========================================
 1   9.4794E-03   1.2813E-09  -3.9264E-06
 2   8.9958E-03  -2.5137E-04   9.6336E-07
 3   8.9808E-03   3.3423E-04  -2.9572E-06

If the diagnostic coils carry 1.0 A, the units of force are newtons/A.

Universal curves for high-frequency wire losses

shumphries — Sat, 31 Mar 2012 19:41:26 +0000

My original intent was to write an article to show when it is necessary to use an eddy-current code to find time-varying magnetic fields and when a static field code like Magnum is sufficient. As a preliminary, I thought it would be useful to review how eddy currents affect magnetic fields in single wires. This tutorial has two purposes:

Document useful general results on the effective resistance and ohmic losses in wires at high frequency.
Show how to set up calculations of magnetic field distributions in wires with the two-dimensional code Nelson.

To start, let’s review some basic equations for a long wire with cross-section area Aw (m2) and conductivity σ (S/m). At low frequency, the current density is uniformly distributed across the wire and the resistance per length given by Eq. 1. If the wire carries an alternating current I0 cos(2πf t) at frequency f, Eq. 2 gives the time-averaged power dissipation.At high values of f, the magnetic field associated with the current flow is inhibited from penetrating the metal wire, concentrating the current density near the wire surface. The effective effective cross-section area of the wire is therefore smaller than Aw, increasing the resistance per length and the ohmic power loss for a given current. The penetration distance for magnetic fields, called the skin depth, is given Eq. 3. The quantity μ is the magnetic permeability, given by μ = (1.257E-6) μr, where μr is the relative magnetic permeability. The relative permeability equals 1.0 for most wire metals.

The skin depth allows us to define the high and low-frequency regimes. For a circular wire of radius rw, Eq. 4 gives the condition for enhanced ohmic losses. In the following calculation, we’ll use the example of a circular copper wire 1.0 mm in radius. The conductivity of copper is σ = 5.814E7 S/m. Using Eq. 3, the frequency corresponding to δ = 0.5 mm is 17.4 kHz. For a wire area Aw = 3.142E-6 m2, Eq. 1 gives the steady-state resistance R = 5.474E-3 Ω/m. For a drive current amplitude I0 = 1.0 A, the low-frequency power loss is P = 2.738E-3 W/m.

The program Nelson finds field magnetic distributions in the frequency domain — all quantities (including drive currents) vary harmonically at the same frequency. The input files to define the mesh and to control the calculation are circular.min and circular.nin. Figure 1 shows the mesh with dimensions in millimeters. The wire extends an infinite distance out of the page. The large air region was included so that the calculation could easily be modified for non-circular wires — the distant boundary has little effect on the magnetic fields inside a wire.

Figure 1. Mesh for the Nelson circular wire calculation.

In the Nelson control script circular.nin, the boundary is a surface of fixed vector potential (flux conserving boundary) and the air region has μr = 1.0 and σ = 0.0 S/m. The copper wire has μr = 1.0, σ = 5.814E7 S/m and a drive current I0 = 1.0 A at a phase of 0.0°. The calculation of eddy currents in the wire uses the multistage, self-consistent method described in Chap. 4 of the Nelson manual. Figure 2 shows lines of B. At low frequency, |B| inside the wire increases linearly with distance from the axis, consistent with uniform current density. At high frequency, the magnetic flux density is concentrated on the surface.

Figure 2. Lines of magnetic flux density in and around a circular copper wire at low and high frequency.

To make a quantitative comparison, we can use the automatic volume integral in the Nelson Analysis menu to find the total power dissipation per length along z. Results of calculations at several frequencies are plotted in Fig. 3. The theoretical steady-state value is shown as a dashed line. As expected, power losses increase significantly in the range 10-20 kHz. At high frequency, the current is confined to a thin layer on the wire surface. In this case. the power loss increases approximately as √f, proportional to 1/δ.

Figure 3. Power dissipation per meter in a copper wire of radius 1.0 mm as a function of frequency with a drive current amplitude of 1.0 A.

It is important to recognize that the numerical results for the 1.0 mm copper wire may be applied to circular wires of any diameter or composition. It is not necessary to repeat the calculation for each special case. The strategy is to recognize scaling laws and to incorporate them into a universal curve. As an example, the green line of Fig. 4 plots the power level relative to the steady-state value as a function of the ratio of the wire dimension to the skin depth. There are two advantages to applying scaling laws:

Generality – the graphed data may used to determine the effective resistance of any circular wire.
Identification of trends – it’s evident that the power loss is proportional to 1/δ at high frequency.

Figure 4. Universal curve for high-frequency wire resistance, power relative to the steady-state value plotted as a function of the wire dimension normalized by the skin depth. Circular and square wire cross sections.

As an example, suppose we have a 1/8″‘ diameter stainless steel rod and we want to find the frequency limit such that the power loss is no more than 50% of the low-frequency value. An inspection of Fig. 4 shows that δ must be greater than rw/2.5. With σ = 1.240E6 S/m and rw = 1.59 mm, the frequency corresponding to δ = 0.636 mm is f = 503.7 kHz. To check the result, I set up another Nelson calculation with modified wire radius and conductivity. For I0 = 1.0 A, the predicted steady-state power dissipation is 50.77 mW/m. The Nelson calculation gives 50.77 mW/m at f = 1.0 Hz and 76.28 mW/m at 503.7 kHz. The ratio of the two power levels is 1.50.

The results for circular wires could have been derived analytically with some effort. The true advantage of a numerical approach is that complex shapes are no more difficult to handle than simple shapes. To illustrate, I set up a run for square copper wires by changing the shape of the wire region in the Mesh input file. I used a wire with side lengths D = 2.0 mm. Figure 5 shows lines of B at high frequency. The universal power dissipation curve for square wires is plotted as the blue line in Fig. 4.

Figure 5. Lines of magnetic flux density in and around a square copper wire at 40 kHz.

Sharing dimensions of Mesh setups

shumphries — Fri, 30 Mar 2012 16:38:31 +0000

My consulting projects involve beam optics studies for a variety of devices: electron guns, transport solenoids, beam collectors,….. Typically, I develop optimal shapes for cathodes and internal electrodes and then send the information to the customer’s engineers who worry about external matters (power supplies, vacuum seals, high-voltage insulation, cooling,…). This process involves communicating dimensions.

In principle, all dimensions for calculations with EStat, PerMag and Trak are contained in the Mesh input script (MIN). On the other hand, it’s an imposition to expect the engineers to figure out the format. You could create a mechanical drawing, but there’s a quicker way to send full dimensional information: the DXF export function in the Mesh Drawing Editor. It’s documented in the Mesh manual, but people (including myself) tend to forget about it.

To create a DXF file, first load your MIN file into Mesh. Next, choose the Edit script (graphics) command to open the Drawing Editor. Then use the Export DXF command. It produces a standard DXF file that can be opened with the engineer’s favorite CAD program (AutoCAD, DraftSight,…). In a familiar environment, it’s easy to find dimensions.

The vectors for mesh regions are organized in layers with the names “0″, “1″, “2″,…. The “0″ layer is for reference lines. You can omit writing information from the region (or any other region) to the DXF file. Before exporting the file, click on Settings/Region properties and turn off the visibility of the regions to be excluded.

GamBet computing power unleashed

shumphries — Fri, 09 Mar 2012 21:15:18 +0000

GamBet, our Monte Carlo code for X-ray science and technology, has always been ahead of competitors with regard to special features (I’ll mention some later). In the past other packages may have had more raw computing power. We advanced the number-crunching capability of GamBet last year when we introduced parallel processing (http://fieldp.com/myblog/2011/multicore-gambet/). With this feature, GamBet runs could utilize the full power of a single, multi-core machine.

We’ve taken another step forward to make GamBet the best program for power users. We now support distributed computing. Runs may be divided between an unlimited number of machines. Here’s how it works:

The new GamBet Distributed-computing Extension (GDE) is an add-on package for GamBet or Xenos Pro. The package includes two programs, GB_SOW and GB_REAP.
GB_SOW includes all technical features of GamBet. The program may be installed on any number of computers without a license requirement. GB_REAP is installed on a master computer with a GamBet license.
The user sets up and tests a GamBet run using the standard programs. Then, the required input files (GamBet control script, mesh definition, electric or magnetic field files,…) are sent to the worker computers.
GB_SOW is launched on each worker computer, either from a window or from the command line. Multiple instances of GB_SOW may run on multiprocessor machines.
The GB_SOW run produces a single binary file with a unique identifying name that contains all information from the GamBet calculation (escape particles, dose, statistics,…). The user moves output files from the worker computers to a data folder on the master computer.
GB_REAP identifies all binary input files in the specified directory and combines them to produce GamBet output files in standard format. These files may be analyzed with GBView2, GBView3 or GenDist. Escape particles are combined in a single escape file with appropriate weightings. Statistical and dose information is averaged.

In the procedure, the user’s only role is to transfer files to and from the worker computers. This leaves complete flexibility for configuring the distributed network and automating file transfers. Despite its simplicity, the GDE concept has several advantages:

Calculations are independent and need not be synchronized.
There is no overhead for parallel processing. Five quad-core computers can reduce the time to generate a required number of showers by a factor of 20.
If one machine fails during the computation, data from the other computers is still valid and useful.
It is easy to improve the accuracy of a calculation by adding more showers without starting from scratch. The user simply creates more worker-computer files. They are added to the master folder and the total collection is recombined with GB_REAP.
Communication between computers is solely through file transfers. Therefore, it is easy to carry out extended calculations at any locations via a company network or the Internet.

While we’re on the topic of GamBet, it’s useful to review some other features that differentiate it from other Monte Carlo codes:

2D and 3D geometries are defined with powerful finite-element mesh generators rather than idiosyncratic solid-modeling algorithms. Advantages include the direct input of complex shapes from SolidWorks, ProE and other packages as well as extensive visualization options. The conformal meshes provide close fits to material surfaces.
2D or 3D calculated electric and magnetic field solutions may be imported for detailed electron dynamics.
GamBet incorporates the Penelope 2006 physics engine for high-accuracy interaction calculations, from GeV energies down to less than 100 eV.
Calculations of fields, electron beam dynamics and target heating are integrated with Monte Carlo simulations in Xenos, a comprehensive software suite for X-ray source development.
GamBet features extensive graphical and quantitative post-processing capabilities for dose distributions and particle statistics.

The GDE package will listed in our catalog and available for purchase on March 30, 2012.

Creating a coil box with MagWinder

shumphries — Sat, 25 Feb 2012 17:09:56 +0000

Many designs for electromagnets include a coil of the shape shown in Figure 1 wrapped around an iron mandrel with a rectangular cross section. The utility program Magwinder is used to define drive current elements for three dimension magnetic field calculations with the Field Precision Magnum program. In Magwinder, a coil box like Fig. 1 is constructed of four BAR type parts connected by four ELBOWR (elbow with a rectangular cross section) parts. The boxes must be rotated and translated from the their standard configurations to generate current in the correct position and direction, and the elbows must be shifted to the connecting positions. This involves some concentration and much busy work. Furthermore, the chances of error increase when there are multiple operations. In this article, I’ll describe resources that I created to automate the process and review the plotting capabilities in Magwinder to check the results.

Figure 1. Definition of coil box parameters

Figure 1 defines the geometric parameters of the coil box:

The coil cross section has width W1 in the x-y plane and W2 in z.
The coil is approximated by N1 current filaments in the x-y plane and N2 filaments in z.
The BAR models have length D1 in x and D2 in y.
The ELBOWR models have inner radius R1 and outer radius R2 and extend 90°.
I is the total current carried by the filaments.

In the standard position, the current flows in the x-y plane in the direction of positive θ (counterclockwise) when view from the +z direction. You can download the Magwinder sample input file coilbox_example.cdf which creates the structure for a specific set of parameters. The equations for the model parameters are listed as comment lines.

Figure 2. Spreadsheet for automatic calculation of coil box parameters

I have also set up the spreadsheet shown in Fig. 2. To use it, fill in the parameter values and then copy and paste the cells starting at GLOBAL as text into a MagWinder script (CDF). Here is a link for a file for the OpenOffice spreadhsheet (coil_box.ods). If you enjoy purchasing office software, here is a link to an Excel file (coil_box.xls).

Figure 3. Resulting current elements with polarity indicators projected to the x-y plane (N1 = 3)

Figure 3 shows the resulting assembly projected in the x-y plane. The plot illustrates the new Magwinder capability to display the polarity of current elements. They are represented as sperm cells swimming in the direction of the head. There are two ways to reverse the current direction.

Use a negative coil current, I → -I.
Rotate the COIL 90° about the x or y axis.

Figure 4. Quadrupole assembly with four coil boxes

You can use the basic assembly multiple times in a Magwinder script. For example, Fig. 4 shows a quadrupole magnet. The standard text from the spreadsheet was pasted into four COIL sections, and then each coil was assigned a specific rotation and translation.

Multitasking made easy

shumphries — Tue, 03 Jan 2012 16:29:09 +0000

Field Precision programs are optimized for the latest generation of multi-core or multi-processor PCs. The 64-bit major solution programs (HiPhi, Magnum, GamBet,…) feature true parallel operation. The time-intensive subroutines have been coded in OpenMP, giving significant improvements in speed (see magnum-in-parallel or multicore-gambet). A second feature is the capability to run multiple independent calculations simultaneously. All the solution programs can run in the background if launched from a Windows batch file. Background operation is automatic and faster than running in a window. Unfortunately, this capability is often overlooked because of the effort required to create batch files and to keep track of what tasks are running. The problem was brought home to me during a recent consulting project where I needed to make an extended sequence of Trak calculations with small changes in geometry. Each step involved re-running three programs. Even though I was well aware of the batch file capability, laziness prevailed and I ran each calculation interactively. My irritation level was not quite high enough to overcome my inertia. We recently added a new feature to our program launchers (TC, AMaze, GBLaunch and Xenos) that should tip the balance — the ability to create and to run Tasks. A Task is any sequence of installed programs and input files for a background run. With the feature you can 1) quickly define Tasks in an interactive dialog, 2) launch simultaneous Tasks in the background and 3) find out which tasks are running. I’ll discuss how it works in this article.

Figure 1. Task control group in the TC program launcher.

Figure 1 shows the new Task control group in the TC program launcher. The CREATE TASK button calls up the dialog of Figure 2. The user supplies a file prefix FPREFIX that indicates the function of the Task. The Task information will be stored in a DOS batch file FPREFIX.BAT created in the current TC data directory. Commands in the file are compatible with all recent Windows versions including Windows 7.

Figure 2. Create task dialog

Each row represents an operation (batch file command). The first column defines the action. Clicking on a cell brings up a menu that includes all TriComp programs capable of background operation that are installed on the user’s computer. In addition, several relatively safe DOS commands are included (ERASE, COPY, MOVE, RENAME and REM). All commands operate on a file (FILEIN). The DOS commands COPY, MOVE and RENAME require a second file name (FILEOUT). You can type file names in the cells. By default, the files are in the TC working directory, but you can include path information if the files are in other directories. Alternatively, you can click in a cell and pick the SELECT FILE command to raise the standard Windows dialog for choosing files anywhere on the computer. There is a nice feature for the TriComp programs — only files with appropriate suffixes are displayed (e.g., *.EIN or *.SCR for EStat).

Click the OK button when the sequence is complete to create the batch file. Here is an example:

REM TriComp batch file, Field Precision
START /B /WAIT C:\fieldp\tricomp\mesh64.exe C:\Temp\convergegun
START /B /WAIT C:\fieldp\tricomp\estat64.exe C:\Temp\convergegun
START /B /WAIT C:\fieldp\tricomp\trak64.exe C:\Temp\convergegun
ERASE *.?ls
START /B /WAIT C:\fieldp\tricomp\notify.exe
IF EXIST Electrode01.ACTIVE ERASE Electrode01.ACTIVE

The operations listed perform a complete Trak calculation in the background and then erase all listing files. Here are some notable features:

The operations are performed sequentially because data from one operation may be used in the next. To run calculations in parallel, define and run multiple Tasks.
You can modify the file with an editor if you are familiar with DOS commands.
The DOS commands recognize the standard wildcard conventions (* for any character grouping, ? for any character).
The programs adds the command notify.exe to the task sequence if AUDIO ALARM is checked. In this case, the computer beeps when a task is completed.
The final command to erase a file FPREFIX.ACTIVE is added to all batch files. The presence of an activate file indicates that the task is running.

Figure 3. Run task dialog

Click the RUN TASK button when you have created Tasks or moved predefined task files to the data directory. The dialog (Figure 3) organizes tasks into two groups: ones that are available to run and ones that are currently running (i.e., FPREFIX.ACTIVE has been detected). To launch a task, choose one from the top list and click OK. The program creates a file FPREFIX.ACTIVE and runs the batch file. The program sequence runs silently in the background and the results appear almost magically. In the meantime, you can prepare other inputs or run other tasks.

This year, we’re concentrating on program features to improve the user experience. We have two goals: 1) increase the computation speed and efficiency and 2) reduce the setup times. Clearly, users should worry less about program details so they can concentrate on physic issues. Our next job is to add macro capabilities to the 2D and 3D postprocessors. With this feature, the programs will remember the steps in a session to create an analysis script.

Popup menus in RealBasic

shumphries — Sat, 03 Dec 2011 13:58:10 +0000

Popup (or contextual) menus appear when you right-click the mouse. They are a part of almost every Windows program. Nonetheless, it took me some effort to find out how to create popup menus in RealBasic with all the features that I needed. The examples supplied by Real Studio were either out-of-date or simplistic. The only other alternative was the user forum. I find it difficult to get useful information from forum threads, and I wish search engines didn’t include them. Many of the answers are off-the-point or even totally wrong. Spelling is iffy and grammar is almost non-existent. The layout is often confusing (i.e., each answer often shows all the previous correspondence), so it’s difficult to gauge where you are on the path to a solution. Finally, the worst case is when you have to register to see the answer. Registering gets old after the first 1500 sites.

Example of a popup menu in RealBasic

This article shows how to set up a popup menu using the current routines of RealBasic. An important feature is setting the enable status of menu entries. Except in the simplest programs, entries must be disabled depending on the program context to avoid illegal operations (i.e., save a entity that hasn’t yet been created).

The example produces the popup menu shown in Fig. 1. Notice that some entries are grayed because rulers do not exist when the program opens. The code listed below is included in the MouseDown event of the associated window. Note the comment numbers added to the Append statement documenting the order of entries (separators don’t count). These indices are used in the code lines that set the enable status. It’s important to include the test

if (HitItem <> nil) then
end if

to avoid an error if the user clicks on a disabled menu entry.

if IsContextualClick then
// ===============================
// Define menu extries
// ===============================
dim base as new MenuItem
base.Append( new MenuItem( "Create ruler" ) )  '1
base.Append( new MenuItem( "Analyze graph" ) )  '2
base.Append( new MenuItem( "Analyze drawing" ) )  '3
base.Append( new MenuItem( MenuItem.TextSeparator ) )
base.Append( new MenuItem( "Flip ruler" ) )  '4
base.Append( new MenuItem( "Hide/show rulers" ) )  '5
base.Append( new MenuItem( "Close ruler" ) )  '6
base.Append( new MenuItem( "Save ruler" ) )  '7
base.Append( new MenuItem( "Load ruler" ) )  '8
base.Append( new MenuItem( MenuItem.TextSeparator ) )
base.Append( new MenuItem( "Instruction manual" ) )  '9
base.Append( new MenuItem( "About FP UniScale" ) )  '10
base.Append( new MenuItem( MenuItem.TextSeparator ) )
base.Append( new MenuItem( "Exit program" ) )  '11

// ===============================
// Set the enabled status
// ===============================
if (RulersHidden) then
base.item(4).enabled = False   'Flip ruler
base.item(5).enabled = True    'Hide/show rulers
base.item(6).enabled = False   'Close ruler
base.item(7).enabled = False   'Save ruler
base.item(8).enabled = False   'Load ruler
else
// Ruler1 closed, Ruler2 closed
if ((not RulerOpen1) and (not RulerOpen2)) then
base.item(4).enabled = False  'Flip ruler
base.item(5).enabled = False  'Hide/show rulers
base.item(6).enabled = False  'Close ruler
base.item(7).enabled = False  'Save ruler
base.item(8).enabled = True   'Load ruler
// Ruler1 open, Ruler2 closed
elseif (RulerOpen1 and (not RulerOpen2)) then
base.item(4).enabled = True   'Flip ruler
base.item(5).enabled = True   'Hide/show rulers
base.item(6).enabled = True   'Close ruler
base.item(7).enabled = True   'Save ruler
base.item(8).enabled = True   'Load ruler

// Ruler1 closed, Ruler2 open
elseif ((not RulerOpen1) and RulerOpen2) then
base.item(4).enabled = True   'Flip ruler
base.item(5).enabled = True   'Hide/show rulers
base.item(6).enabled = True   'Close ruler
base.item(7).enabled = True   'Save ruler
base.item(8).enabled = True   'Load ruler
// Ruler1 open, Ruler2 open
else
base.item(4).enabled = True   'Flip ruler
base.item(5).enabled = True   'Hide/show rulers
base.item(6).enabled = True   'Close ruler
base.item(7).enabled = True   'Save ruler
base.item(8).enabled = False  'Load ruler
end if
end if

// ===============================
// Carry out actions
// ===============================
dim hitItem as MenuItem
hitItem = base.PopUp
if (HitItem <> nil) then
select case (HitItem.Text)
case("Analyze graph")
// Action code
case("Analyze drawing")
// Action code
case("Create ruler")
// Action code
case ("Flip ruler")
// Action code
case ("Load ruler")
// Action code
case ("Save ruler")
// Action code
case ("Close ruler")
// Action code
case("Instruction manual")
// Action code
case("About FP UniScale")
// Action code
case("Exit program")
// Action code
end select
end if
return true
end if

Measure anything on your computer screen

shumphries — Fri, 25 Nov 2011 17:30:37 +0000

One of my all-time treasured possessions is a Gerber Variable Scale [1] (Fig. 1). It was an absolute must-have if you were doing science in the 60s and 70s. The idea was straightforward — the device was a ruler consisting of a precision spring that you could adjust to any length to match graphs or oscillographs [2]. Simple but remarkably useful!

Figure 1. The Gerber Variable Scale (circa 1970)

Nowadays, practically everything I measure is on a computer screen. For this application, it’s almost impossible to use my old Gerber scale, although I have tried many times. For a couple decades, my dream has been to make something I could use on the computer that would be as useful and (hopefully) as simple. I tried several freeware screen rulers, but the results were disappointing. They were designed to measure literal distances on the computer screen (in pixels, mm, …) rather than the lengths of objects displayed on the screen. The situation was analogous to having a ruler that could measure the size of a sheet of paper, but not the dimensions of data printed on the paper.

I am happy to announce that I have just completed my vision of the ideal screen measurement system, the Field Precision Universal Scale. With it, you can create custom rulers calibrated to graphical objects displayed on your computer screen by any program. The Universal Scale has other analysis features that extend well beyond simple rulers. The program is available for free download as a service of Field Precision to the science and engineering communities. The official release date is January 1, 2012. You can get a beta copy now at http://www.fieldp.com/fpuniscale.html.

Figure 2. Universal Scale main window and sample ruler.

Figure 2 shows the main window with a ruler displayed. Note that the program comes in a nice leather case. The push buttons on the left call up the three main functions:

Create custom rulers that may be moved around the screen over other applications.
Measure points and digitize curves of graphs in publications and reports.
Measure dimensions on drawings and diagrams in documents.

Figure 3 shows a screenshot of a drawing analysis. In the remainder of this article, I’ll describe some interesting features of the program.

Figure 3. Set up to analyze dimensions of a diagram in a publication.

My Gerber Variable Scale may lie in a drawer for months between uses. When I take it out, I never have doubts about how it works. I tried to maintain the same user-friendliness in the Universal Scale. The challenge is that the program does a lot more than slide back-and-forth. I limited the program to few well-defined functions with minimal bells-and-whistles. Contextual instructions are displayed at each step, so it’s not necessary for users to memorize procedures.
Measurements with physical devices used to be fun in the old days, so I gave the program a retro look.
Calibration sheets are the key to program operation. They are translucent windows that act like tracing paper that can be moved over any displayed graphical material on the computer screen. Mouse clicks in the measurement sheet are used to calibrate rulers, graphs and drawings and to measure points.
I applied my experience with normal coordinates in finite-element analysis to measurements on graphs. The program uses a generalized trapezoid coordinate system. This means that you can obtain good measurements from badly-scanned graphs (rotations, distortions,…).

Footnotes

[1] Unfortunately, it appears that the Gerber Variable Scale is no longer available for purchase. As a matter of historical interest, here is a link to the original manual: GerberVariableScale.pdf.

[2] Oscillographs were Polaroid photographs of oscilloscope traces, the only way to record fast transient data before digitizers.

Website introduction video

shumphries — Thu, 13 Oct 2011 15:32:03 +0000

We’ve added a lot of content to our website at www.fieldp.com in 13 years. In fact, there’s so much material that the site might intimidating to first-time visitors looking for software or educational resources. To help, we’ve added a short overview video on the home page. Here it is:

Particle flux plots in Gendist

shumphries — Sat, 24 Sep 2011 13:55:09 +0000

A recent consulting project involved Xenos simulations of an intense, non-circular electron beam striking a graphite beam stop. A phosphor plate on the downstream face of the target was used as a diagnostic. The researchers wanted to know how the shape of the phosphor response correlated with the shape of the beam. One option was to add the phosphor plate as a region in a GamBet simulation and then to plot dose distribution as a slice plot in GBView3.

For the design of other diagnostics, the researchers wanted the spatial distribution of the X-ray flux emitted from the target. Such plots could be created using the GenDist utility program from information in the GamBet escape file. The escape file is a record of parameters for all particles leaving the solution volume. GenDist is a general-purpose program to create and to analyze large distributions of particles (e.g., electrons, ions, photons, positrons). For the application, the procedure was to load the escape file into GenDist and then to add filters that admit only photons at the exit face (i.e., z coordinate great than or equal to the exit face position). Of the GenDist plot types, the 2D histogram was appropriate for the application. Here, particles are assigned to a 2D matrix of bins according to their position in the x-y plane. The probability function N(x,y) may be weighted by the model particle current, energy or combined current/energy. In this way, the program can generate spatial distributions of the following quantities:

Model particle density.
Particle flux (weighted by model-particle current or flux).
Power flux (weighted by model-particle current and kinetic energy).

The previous version of GenDist had only one available style for 2D histograms — a projected 3D view showing N(x,y) as height above the x-y plane. Although the style gave attractive plots for presentations, it was not useful for quantitative work. We added the three new styles shown in the figure for better display of spatial particle distributions:

The existing 3D bin height plot improved with color coding.
A 3D plot with bin height displayed as an interpolated shape.
A 2D contour line plot, showing surfaces of equal probability density.
A 2D filled contour plot.

Plot styles for the 2D histogram type in GenDist

b) 3D plot with bin height display as an interpolated shape.
3) 2D contour line plot, showing surfaces of equal probability density.
4) 2D filled contour plot.