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Control Web Examples

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First application

We will start work on the development environment by creating the simplest application and will gradually use the functions and show the properties of the basic components of the system. This Chapter cannot introduce all virtual instruments and all manners of their use. Rather, it shows the basic procedures and the number of individual complicated instruments will increase in subsequent chapters.

Step 1 — the simplest application

The typical first application described in various textbooks about programming is as a rule writing the sentence “hello world”. The Control Web is a tool of another level than a programming language compiler — several series of components are available with already built-in rich functionality, so we can start considerably complicated applications. Our objective will be to display analogue (continuous) value.

The Control Web IDE allows working in several editors, which can be switched between using toolbar, always located right under the window title.

Hint:

The toolbar is the only firmly placed part of the GUI of the Control Web system. All other commands and instruments are located in palettes, which can be organized at your will.

Since the application in source text is always stored in text form, the first editor offered by the development environment is the Text editor. Theoretically, any application in the Control Web system can be created using only text editor, provided the user knew all parameters of all required components, data sections etc. Given the extent it is apparently difficult and also uneconomic and that is why the Control Web offers other editors that make the creation of applications simpler and faster. We will continue to work in the mode of graphics editor and its supporting command and tool palettes. Let's just make sure that Graphics editor is selected in the toolbar (button is highlighted).

If you start the Control Web in default configuration, a palette called Applications is on the upper left (under the line enabling editor switching).

If the Applications palette is not visible (is covered with other palette), all you need to do is click the tab with the name and the palette immediately pops up). Command buttons in this palette allow, among other things, saving, starting and stopping the application.

After you click on the button, the introductory window will open, making it possible to create a new application or select an existing application for further editing. The opening of a demo example is also offered. However, we want to start working on a new application.

New application creation window

New application creation window

After pressing the OK button, the first page New Application Wizard is opened, which requires the typing of the name of the file in which the application will be stored. Let’s name the application 'first', the file 'first.cw' is created. Although New Application Wizard offers the creation of an easy structure of application and, of course, in real implementation it is preferable to use the wizard, now, for didactic reasons, we reject its further services and are satisfied with the creation of an empty application file by clicking on the Finish.

Hint:

New Application Wizard offers on the first page not only the name, but also the folder where the file should be stored. The folder 'Control Web Projects' is offered as the default setting in the document folder ('My Documents' in the English versions of Windows) of just the logged-in user. It is possible to store in another folder in which the user must have the right to create files and store them.

Make sure the development environment is in the graphic mode (the tab Graphic editor) is selected. Using the tool open the window Instrument Palette. Make sure that in the list of options above the tree structure in the left part of the palette window the option Instrument categories is selected (not Instrument libraries). If you want to display a continuous value, gradually expand the sub-tree Flat instruments, Display and Continuous. The palette window will appear like this:

Instruments palette displaying flat instruments to display continuous values

Instruments palette displaying flat instruments to display continuous values

Drag by mouse the instrument meter on the desktop of the graphic editor. In the application there is one instrument making it possible to display continuous value. To see that the instrument works, we need to change this value somehow (to set). Return to the window Instrument Palette and gradually expand the tree structure Flat instruments, Control and Continuous. Among these instruments there is the control instrument which carries out exactly what we want — sets continuous values. Drag it by mouse to the application beside the instrument meter. In the graphic editor we can see both instruments:

Instrumentsmeter and control in the graphic editor

Instrumentsmeter and control in the graphic editor

Now we have in the application two instruments, one can measure the set value and the second can display it. However, there is no place where this value can be stored. To store the value, it is necessary to define the data element.

Select in the development environment the tab Data Inspectors. In the application there is not yet any data section within which it would be possible to edit the data element. For our purposes we need a simple variable capable of storing continuous values. Select var from the predefined sections of the subtree in the left part of data inspectors space, which is a type of section storing variables. If the var section in the subtree does not exist yet, click item <add section> and select var. Within the section there can be several types of variables — scalar variables, variable arrays and buffer type variables. Select the simple (Scalar) variables and write into the table in the right part the name of the variable (e.g. value). It is also necessary to select the type. Continuous values are represented by the type real (real number).

Newly defined variable value of the type real

Newly defined variable value of the type real

Now we can return to the graphic environment — select the tab Graphic editor. The next step during the creation of the application will be “connection” of instruments to the data element — Instrument control must write the value of the data element value and the instrument meter must display it. These abilities (writing of the value and its display) are characteristic of the selected instruments (control and meter) but it is necessary to specify for each instrument which data element it is necessary to work with. Since it concerns properties of instruments, it is necessary to specify them in the Instrument Inspector window opened for the instrument in question. You can open this window from the context menu of the respective instrument (it is opened after right-clicking with the mouse on the desktop of the instrument in the development environment).

Hint:

The development environment makes it possible to select whether the right mouse button opens on particular instrument’s context menu, from which it is possible to open Instrument Inspector or directly the Inspector Window. Operations mentioned in the context menu can be executed only by keys, so quick opening of the inspector may save time for more experienced users.

Instrument Inspector has several tabs in which it is possible to define different parts of the instrument in question. Lets start with the first tab Properties. This tab displays all parameters which can be set for the respective instrument. Open the inspector over the instrument control and select the parameter output.

Instrument Inspector of the control instrument with the selected parameter output.

Instrument Inspector of the control instrument with the selected parameter output.

Hint:

As well as all command and tool palettes in the Control Web development environment, even Inspector can be configured according to user's preferences. Standardly, the inspector is displayed as a palette on the right side of the development environment window, as shown in the previous picture. All you need to do is grab the Inspector tab with your mouse and drag it outside the development environment window and the Inspector will be placed in a separate window as in the previous version of the Control Web.

The third option is to keep the palette in the main window, but roll it up. Only the tab with the name will remain visible from the palette. If the palette is needed, it rolls out into full size. When it is no longer needed, it roll back up. The palette then takes only a minimum of space and the display space if available for the application itself.

All these options of customization involve all palettes of the Control Web system. More about the Control Web

The parameter output specifies the data element where the value will be recorded. How do we know that for the instrument control it is necessary to set the parameter output? The Inspector displays the description for all parameters, which may help for the first orientation. After some time you will use the basic parameters without problems, just like pressing the clutch and engaging a speed when driving.

Write into the field the name of the previously defined variable value. If you are not sure which data element it is necessary to use, use the auxiliary inspector panel, which offers all the defined data elements of the suitable type:

Auxiliary pop-up window offers defined data elements

Auxiliary pop-up window offers defined data elements

Changes in values of parameters carried out in the inspectors are not reflected in the application as long as you decide to confirm them. Of course, you may think it over and cancel the performed changes before confirmation. The first three tools in the Inspector window have the following meaning:

Confirmation of changes. The existing changes in the inspector are reflected in the application but the inspector remains open.

Confirmation of changes and closing the inspector. The existing changes in the inspector are reflected in the application and the inspector is closed.

Cancellation of changes. The existing changes in the inspector are forgotten and the inspector is closed.

If in the parameter output contains the name value, confirm the changes and open the inspector above the instrument meter. Here, select the parameter expression and write into it the name of the data element value.

Remark:

In both cases you wrote the value of the parameter into the data element value:

  control control_1;
    ...
    output = value;
  end_control;

  meter meter_2;
    ...
    expression = value;
  end_meter;

There is a principal difference between the parameter output and expression. Whereas output of the instrument control must be just one data element, after expression there can be any numeric expression. Instead of a simple entry of value it would be possible to type, e.g. 100 - value.

Of course, this difference is reflected if you open the auxiliary window of the parameter expression for the instrument meter. The inspector does not offer you a simple list of data elements but the whole editor of expressions:

Expression editor window

Expression editor window

Creating of our simplest application is nearly finished, but the application in existing form will not work according to our expectations. The instrument control will write the respective value during each user action into the variable value but no manner of activation of the instrument meter is defined. Instruments, which do not work on the basis of some action of the user (e.g.control), perform their activities at the moment of activation and, therefore, it is necessary for the instrument meter to ensure activation. The simplest manner is to specify timing for the meter instrument. Set the period parameter value to 0.1 in the inspector. This will ensure that the instrument meter will be activated ten times per second, i.e. the expression mentioned in the parameter-times per second, that means the expression defined in the expression parameter will be evaluated and the result will be displayed (the pointer will turn).

Warning:

Decimal places in the Control Web system are separated by dots regardless of the regional settings.

Hint:

If you open the inspector above the instrument meter, you will not find the parameter period in the list of parameters at the first level. To increase the lucidity, the inspector does not display all parameters in one list, but some logically linked groups of parameters are displayed in independent sub-tables, which can be unrolled and collapsed. An example of such groups is activity group, which contains parameters for condition settings of instrument activation. In the rolled form it is hidden in one line:

Rolled form of standard parameters

Rolled form of standard parameters

When you click on the symbol + you will unroll the table with the standard parameters:

Unrolled standard parameters

Unrolled standard parameters

Run the application by clicking on the tool in the development environment. As soon as the application runs, try to set the value using the instrument control and observe how the instrument meter displays the value.

Stop the application using the tool in the development environment or by means of the menu, which can be opened by clicking the mouse on the Control Web running application icon in the icon tray (on the right side of the Windows task bar):

Menu of the of the Control Web running application

Menu of the of the Control Web running application

Step 2 — Instrument parameters

If the first application works, you may start to modify it. Let’s consider that you are not satisfied with the setting of the value — instead of the rotating control knob we want the vertical slider. The function of the instrument remains the same, we only want to change its look. It is not necessary to use another instrument, control offers a series of possible looks.

Looks may be changed by means of the parameter mode. If the parameter mode is selected in the inspector you will get the offer of all possible modes of the instrument. Select the value vertical_slider. After confirmation of changes in the inspector the visual form of the instrument control is changed, however, its dimensions remain unchanged. The square is not a suitable form for the vertical slider, so select the instrument in the development environment and change its dimensions according to requirements using the dragging points. The graphical form of the application is as follows:

Application after the change of mode of the control instrument

Application after the change of mode of the control instrument

Similarly, you can modify the form of the instrument meter. For example, you want to see the graph of values displayed by the instrument for the last 10 seconds. Because the instrument meter is timed 10× per second, it will be activated 100× within 10 seconds. So, change two parameters of the instrument meter: First of all, set the parameter mode for the value flow_graph (even though the parameter mode is similar to the parameter of the instrument control with the same name, it is necessary to take into consideration that this similarity only simplifies remembering the names of parameters, otherwise they are quite different parameters of two different instruments). Then set the value of the parameter history for 100 (so that the instrument displays the 100 last values). It is possible to change on the instrument meter the parameter content for the value med. This parameter specifies the richness of display and the medium value causes displaying of the actual value of the expression expression outside the simple graph. After these changes the application looks as follows:

Application after the change of the mode and the content of the instrument meter

Application after the change of the mode and the content of the instrument meter

Hint:

Because the form of many instruments can be considerably changed by its parameters, these forms of one instrument are offered directly by Instruments Palette. If you click in the tree in the left part of the palette directly on the particular instrument, possible forms of the respective instrument will appear in the right part (if the instrument supports more forms). For example, the instrument meter can be simply dragged in the form of a graph directly from the palette:

Palette of instruments with various forms of the instrument meter

Palette of instruments with various forms of the instrument meter

The running application looks like this:

Running application with modified form of instruments meter and control

Running application with modified form of instruments meter and control

Step 3 — panels and windows

The currently created application creates virtual instruments directly on the Windows desktop, where instruments can be overlapped, for example, by windows of other applications. The Control Web system brings absolute freedom into the creation of the visual form of the application. It is evident from previous applications that it is possible to build an application quite freely and that the Control Web does not enforce any “main application window” with the title, etc. If you want to place the application into the window, there are no obstacles to doing so.

First of all, we mention the organization of elements of the graphic user interface (GUI), because visible virtual instruments represent the graphic user interface of the application. From the first GUI systems its individual elements (windows, buttons, menu, etc.) have been organized into a hierarchic structure. Some GUI elements are superior to other elements. We say that superior elements “own” subordinate elements. For example, the dialog window owns edit boxes, check boxes or command buttons. This structure is not only single-level, one element may be owned by a higher element and, at the same time, own lower elements.

For organization of GUI elements it is valid that:

  • Individual GUI components represents a hierarchical (tree) structure. The root of this tree is the desktop.

  • Each GUI element has an owner (with the exception of the desktop). Some elements (e.g. windows) may own other subordinate elements.

  • In addition to relations “to own” and “to be owned” for each GUI element occupies a rectangle, which defines its area. The position of each element is always determined in relation to the owner.

  • The area (rectangle) of any element cannot exceed the area of its owner. If the area of the element is larger than the area of the owner, the parts exceeding the area of the owner will not be displayed (the element will be “slipped” by the rectangle of the owner).

  • If two elements are at the same level (they have the same owner) and their areas overlap, the so-called z-coordinate decides their display. So, the element will be drawn which in the z-coordinate is above the other element and will cover it.

Remark:

The above-described structure concerns only flat (two-dimensional, 2D) instruments. Three-dimensional (3D) virtual instruments define mutual position by general spatial coordinates. If we speak about visible virtual instruments in this chapter, we will always consider only flat (2D) instruments.

All the above-mentioned rules concern all visible virtual instruments of the Control Web:

  • All visible 2D virtual instruments represent elements of the GUI application. They have their rectangle and may be part of the hierarchical structure. The rectangle of the instrument is defined by keyword position (for instruments with fixed dimensions the position contains only the x and y coordinates, otherwise they contain four numbers defining gradually the x and y coordinate, width and height of the rectangle of the instrument), the owner of the instrument is defined by keyword owner.

  • The only instrument panel may not only be owned by another panel, but it may also own other instruments. The parameter owner of instruments may define the name of the other panel or keyword background, which says that the instrument will be directly on the desktop.

The parameters position and owner define the position of visible instruments in the tree of the application GUI structure and as the only parameters they cannot have any standard (default) values — there is no standard position or standard owner. Therefore, if you drag by mouse some instrument to the application, at last these two parameters will always be defined:

  meter meter_1;
    gui
      owner = background;
      position = 10, 10, 180, 120;
    end_gui;
  end_meter;

Remark:

Parameters position and owner are not defined on the first level in the inspector, but are placed in group gui, which contains parameters affecting appearance and location of the instrument.

Our first application contains only two instruments meter and control located directly on the desktop. The development environment also displays, in addition to preview of the application, visual representation of the tree structure of the application. On the left from the desktop there is a panel with four areas named Template, Visibility tree, Timing tree and Selected Instrument (the ratios of the size of these areas can be changed by dragging of the title by mouse). The display of hierarchical dependence of instruments of the application is in the area Visibility tree:

Display of the structure of visible instruments

Display of the structure of visible instruments

If you insert the instrument panel into the application (by dragging it from the palette), it will appear at the same level (its owner will be background) like other instruments. However, it was last inserted into the application, it is at the highest level of the z-axis and will cover other instruments. We need to place it under the meter and control. There are several possibilities how to do it:

  • Select the panel in the graphic editor and open the context menu above it (by clicking the right mouse button). In the menu there are the items To front, To back, One up and One down, which makes it possible to move the instrument in the z-coordinate. Select the command To back and the panel is submerged under the other instruments.

  • The menu also offers keyboard shortcuts Keys <Ctrl>+<PgUp> to move the panel on the bottom as the command from the menu. Or it is possible to press <PgDn> twice and gradually submerge the panel under the other instruments.

  • The last possibility is to drag the instruments by mouse in the visual presentation of the instrument trees (in the area Visibility tree).

Application with panel

Application with panel

We have the panel in this application, but the instruments and the panel are still at one level, the owner of all instruments (the panel is also a virtual instrument) is the desktop (background). It is easy to change ownership relations:

  • Select the respective instrument (meter or control) and press the key <Ins>. The development environment finds whether the left upper corner of the selected instrument is located on the area of some panel and if so it inserts the instrument into the respective panel.

  • It is possible to drag by mouse in the area Visibility tree and paste it above the panel.

This will change the owner of both instruments, the parameter owner contains the name of the panel:

  ...
  owner = panel_1;
  ...

The graphic editor shows the rectangle of the owner by a dashed line. If you select meter or control, the rectangle of the panel is bordered by a dashed line.

Instruments meter and control registered in the instrument panel

Instruments meter and control registered in the instrument panel

Let’s notice that now the area of the panel “clips” owner instruments. If you try to drag meter outside the panel, you will not manage to do so:

The area of the panel clips the areas of inserted instruments

The area of the panel clips the areas of inserted instruments

But it is still not possible to handle such panel as a common Windows application (e.g. drag it with a mouse). Sometimes it is an intention (the panels over the whole screen represent the base of the application and any handling on the part of the user is undesired). However, if we wish the panel had the same frame as other application windows, simply set the parameter type in section window, which is a part of section gui . This parameter can have the value normal (the instrument will have its window which corresponds in its appearance to Windows application windows), tool (the window will be created used, e.g., for palettes with tools — it is not possible to minimize this window, it has a thinner title and does not have an icon in the title) or none (the instrument in the application will be without a window).

The other parameters make it possible to set the title of the window (title) or disable handling of the window (disable) — in our case it will evidently be good to disable change in the size of the window and its maximizing. The running application then looks like a common window in the Windows environment:

Running application with the instrument in the window

Running application with the instrument in the window

Hint:

The frame of the window is not the exclusive property of the instrument panel. In fact, each visible instrument can be located in the window. However, similarly as in the case of other applications, it is not useful to locate in the window, e.g. an independent edit box, also in the case of application of the Control Web system only panels are located in windows as a rule.

Step 4 — timing and activation

We set in the first step the timing (parameter period) of the instrument meter for the value 0.1, which ensured activation of the instrument ten times per second. Periodical timing of the virtual instrument by means of the parameter period is so far only manner used for the activation of the instrument. In many cases it is not the best solution.

Let’s start with the change of mode of the instrument meter in our first application to display current value without history. Open the inspector over the instrument meter and set the parameter mode to the value digital and you may return the parameter history to the value 2 (the history in this mode is not necessary). Due to the changed mode of the instrument you may slightly modify the visual form of the application — it is for instance possible to change the mode of the instrument control from the vertical to the horizontal slider:

First application in changed form

First application in changed form

Let’s return to the activation of the instrument meter. The value of the variable value is changed only if the user moves the slider. If you do it say once in an hour, the instrument meter performs a thousand activations quite unnecessarily. Therefore, in the Control Web system there is another possibility of activation — each instrument can activate another instrument only if it is necessary.

To be able to test this possibility, first of all cancel the timing of the instrument meter. Simply delete the parameter period in the inspector or in the Timing tree pane (it is located on the left from the working area of the development environment, under the Visibility tree pane, where we modified the visual structure of the application) drag the instrument meter among non-timed instruments.

Now open the inspector above the instrument control and set the parameter receivers. This parameter contains the list of the names of instruments, which the instrument control will activate always in the case of change of its value. Type the name of the instrument, which you want to activate (meter_2), as the parameter value or open the auxiliary window in the inspector making possible selection of the respective instrument from the menu. Selection from the menu may be difficult due to the possibly high number of instruments in the application. Therefore, the inspector reduces the listed instruments only to one class. From the combo-box Instruments classes in the left part, select the required class of instruments (in our case meter) and from the lists of all instances (Instruments names) of the meter instruments select the only one we want to activate. The instrument meter_2 appears in the list on the right side:

Auxiliary pop-up window of the inspector for editing of the parameter receivers

Auxiliary pop-up window of the inspector for editing of the parameter receivers

Hint:

The parameter receivers may contain the list of instruments, not only one instrument. It is also possible to mix classes of individual instruments — it is possible to activate, e.g. meter and panel.

In the text form of the application the value of the parameter receivers is the simple list of names separated by commas. The part of our first application will appear as follows:

  control control_1;
    ...
    receivers = meter_2;
  end_control;

  meter meter_2;
    ...
  end_meter;

Remark:

It is good to take into consideration that all instruments with the respective name will be activated. If there are more instruments with the same name in the application, the mentioning of this name in the list receivers will cause activation of all these instruments.

Our first application will operate at first sight identically as before modification. Despite this fact there are two very important differences in its running:

  • The instrument meter does not consume any time if the user does not manipulate with the instrument control.

  • The instrument meter reacts to the change of the value value in the nearest possible moment. For periodical timing, the meter was activated exactly (and the only!) ten times per second and if, for example, the value value changed twenty times per second, the meter displayed only every second change. In the case of activation by the instrument control the activation of the instrument meter will always be carried out as soon as possible.

    Let’s mention that it does not exclude the possibility that the value of the variable value will be changed several times between the activation of the instrument meter. This can happen if the system is very loaded and the computer does not manage to activate meter more frequently than the user changes the value value.

There are situations when periodical timing is necessary. For example, in the previous version of our first application the meter was in the graph mode and it was purposeful to show the respective time history, not the history of the last 100 changes of value value regardless of the time. It is possible to try to change the mode of the instrument meter to flow_graph and history to 100 and look at the application response.

Step 5 — communication with outside world

The ability to read and write data from and into peripherals for industrial automation is certainly one of the basic functions of the Control Web system. A very important feature is its consistently kept independence of concrete types of hardware with which it communicates. It does not matter whether the application reads and/or writes technological data through the plug-in card directly in the computer, an independent unit connected through some standard interface (RS-232C or RS-485, USB, etc.), or an independent programmable logical controller.

This independence is achieved by the use of drivers of industrial devices. The driver is an independent software unit which on the one side implements the program interface required by the Control Web system and, on the other, implements all features of communication with the device for which the driver is used. It hides device-specific features of devices used. In terms of the remaining part of the system, all equipment behaves the same.

Warning:

Due to the different nature of various devices, the behavior of various drivers differs. The basic differences are in the time period during which the driver is able to return the required data and in the reliability of the transfer. The driver, which reads data directly from the measuring card inserted in the slot of the computer, is able to return the data practically immediately and quite reliably, whereas the driver, which reads data through a slow (and possibly disturbed) serial line, will have a response time considerably longer.

So, it is possible to say that during the design of the application we should rather be interested in the speed and the volume of data which the peripheral is able to provide depending on the requirements of the application irrespective of the actual producer of the respective hardware.

On the part of the application the driver is accessible through so-called channels. It is possible to consider channels as being similar to variables with several differences:

  • Reading of the channel causes communication of the driver with the peripheral and reading of its value.

  • Writing into the channel causes recording of the value through the driver into the peripheral.

Unlike simple variables, which change the value only on the basis of writing in the application, values of channels are changed on the basis of data read from peripherals.

Because it is not possible to suppose which hardware is used by users and which drivers are available, we will show the work with drivers on virtual driver, which is delivered with each installation of the Control Web system. Why virtual? Despite the fact that this driver offers channels on which various courses appear, in fact it does not communicate with any peripherals — the values of channels are calculated inside the driver.

Insert the driver into the application in the tab Data Inspectors of the development environment. Make sure that in the list of options in the left upper part there is either All or Drivers. Then, you may click on the item <add driver> and write its name; in our case name the driver, e.g. drv:

Adding a new driver

Adding a new driver

After adding a new driver its definition appears in the graphic development environment. However, the definition of the driver must also contain other parameters in addition to the name. These obligatory parameters are indicated in the development environment in red text <expected data>.

Obligatory parameters of the definition of the driver:

ParameterMeaning
Driver

List of options with all drivers installed in the system. Select the driver Virtual Device Driver.

Map file

File with definition of channels of the driver. Open the auxiliary window Driver Map File, switch to the folder 'dmf' and select the file 'vsource.dmf':

Window of selection of the map file

Window of selection of the map file

Parameter file

File with configuration parameters of the respective driver. Again using the window Driver Parameter File select the file 'vsource.par' from the folder 'par':

Parameter file selection window

Parameter file selection window

The such defined driver appears in the source text of the application in the form of one line in the section driver:

driver
  drv : 'vsource.dll', 'vsource.dmf', 'vsource.par';
end_driver;

When the driver is established in the application you may define channels. Similarly as in the first step when we defined the variable (first of all, it was necessary to declare the section of variables and then to declare the variable in this section), we declare the section of channels channel and create in this section the channel sinus:

Channel sinus defined as the first channel of the driver drv

Channel sinus defined as the first channel of the driver drv

Then, it is enough to create the instrument meter in the mode flow_graph whose parameter expression will have the expression with one channel sinus and with the timer (parameter period) 0.1 s (do not forget to set history for the value of 100). The running application will read ten times per second the value of the channel sinus and display it in the form of the graph:

The instrument meter displays the value of the channel sinus of the virtual driver

The instrument meter displays the value of the channel sinus of the virtual driver

Configuration of drivers (creation of the parameter and map file) by means of tools of the integrated development environment is described in Chapter Communication with Peripherals — Drivers.

Step 6 — Boolean values

All currently used data elements were of numeric type (real). Of course, the Control Web system is not restricted to work only with numbers. In most cases, it is necessary to work with conditions whose values have only two statuses — true and false (represented by keywords true and false in the Control Web). For these logical values there is a special data type boolean (this type was named after the famous English mathematician George Bool). In addition to “truth values” the denomination “binary values” is used.

You meet logical values very often even if you do not define any logical data element. For the instrument meter we typed the value of the parameter expression numeric expression, for example:

expression = 100 - value;

The instrument indicator is used to display logical values. Although it also has the parameter expression, the value of this parameter must have the expression of the type boolean, whose evaluation results in either true or false.

The fact that the expression must be of the type boolean does not mean that it consists of only data elements of the type boolean. Many operators and functions return a logical value even if their arguments are numeric. The typical example are relational (comparative) operators. The parameter expression for the instrument indicator may have the form:

expression = value > 50;

This expression will have the value true if the number in the variable value is greater than 50, otherwise it will have the value false.

We will expand our second application so that in addition to the instrument meter, which displays the course of the channel sinus, it will also contains the instrument indicator, which will signal that the value of the channel sinus exceeds 50. The instrument indicator can be found in the category Flat instruments, Display, Logical. Drag it into the panel beside the instrument meter. Now, it suffices to set the parameters expression to the sinus > 50 and period to 0.1. The running application looks like this:

The instrument indicator signals that the value of the channel sinus exceeds 50

The instrument indicator can be used more times and using the parameters true_icon and false_icon it is possible to modify its appearance. Then, it is possible to create for the instrument the meter bar indicator:

Series of instruments indicator

Series of instruments indicator

Remark:

Similarly as in the first application we used the instrument control, which set the value displayed by the instrument meter, in the case of binary values it is possible to use the instrument switch to set the logical value which can be displayed in the instrument indicator.

Similarly, the instruments string_control and string_display set and display string (text) data elements and expressions.

Step 7 to n — anything you can think of

Perhaps it is not possible to estimate the number of steps which are necessary for detailed description of all features of all instruments in the Control Web system and related topics, for example, access to databases, HTTP protocol used for transfer of HTML documents, Active X components, animated drawings, visualization in 3D, etc. It is important to know the basic general principles (and this Chapter serves for it) and then to select the components and use the correct properties which suit the respective application.

Mainly, take into consideration that for successful work with the system it is not necessary to know detailed use of its components. If the application does not have a WWW interface, it is not necessary to understand the httpd instrument, TCP/IP and HTTP protocols or the format of HTML documents and you will create applications quickly and efficiently for visualization and control of technologies. Similarly, it is not necessary to deal with programming, control constructions of algorithms, etc. Let’s concentrate on what you actually need. And if the demands of the application change, you can return to those components which are suitable for the solution.

Summary

  • Applications consist of virtual instruments and data elements.

  • Virtual instruments are inserted into the application by dragging from the instrument palette in the Graphic editor tab, data elements are added to the data sections in the tab Data Inspectors.

  • The properties of virtual instruments (e.g. with which data elements they should work) are typed in the window of the instrument inspector.

  • Virtual instruments can be sorted into the tree structure of visibility. The nodes of this tree are instruments of the type panel.

  • For real-time applications, instruments perform their activities if they are activated. The exception are instruments working on the initiation of the user (e.g. control). Periodical timing is not the only way of activating instruments. Another possibility is, e.g. activation by another instrument.

  • If you want to communicate with the outside world, you have to use a driver for the peripheral in question. The Control Web is consistently independent of the hardware cooperating with it and it may cooperate with the respective driver with any hardware or software system.

  • In addition to numeric values, there may exist binary or string values. Different instruments operate with various types of value.

 
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