Floating Palettes in LabVIEW

LabVIEW has three often-used floating palettes that you can place in a convenient spot on your screen: the Tools palette, the Controls palette, and the Functions palette. You can move them around by clicking on their title bar and dragging. Close them just like you would close any window in your operating system. If you decide you want them back, select the palette you want from the View menufor example, View>>Tools Palette opens the Tools palette.

Controls and Functions Palettes

You will be using the Controls palette a lot, because that's where you select the controls and indicators that you want on your front panel. You will probably use the Functions palette even more often, because it contains the functions and structures used to build a VI.

The Controls and Functions palettes are unique in several ways. Most importantly, the Controls palette is only visible when the front panel window is active, and the Functions palette is only visible when the block diagram window is active. Both palettes have subpalettes containing the objects you need to access. As you pass the cursor over each subpalette button in the Controls and Functions palettes, you will notice that the subpalette's name appears in a tip strip beneath the mouse pointer (see Figure 40).

Figure 40. Controls palette

To select an object in the subpalette, click the mouse button over the object, and then click on the front panel or block diagram to place it where you want it.

Palette Item Categories

At the top level of the palettes are several "Categories," such as Modern, System, Classic, Express, Addons, Favorites, and others. You can expand and close these categories, by clicking on them, to navigate the tree of items and subcategories that are available within the palette.

One great category is Favorites (this is only present on the Functions palette, not the Controls palette). You can use this to group together items that you access frequently. When you find a function, structure, VI, or subpalette that you really like, right-click on the object and select Add Item to Favorites from the shortcut menu. This will add the object to the Favorites category, for quick and easy access.

Showing and Hiding Palette Categories

You can choose which categories you want to appear on the Controls or Functions palettes by pressing the View button and then selecting categories from the Always Visible Categories submenu. If you want all of the categories to be visible, select the Show All Categories option from the Always Visible Categories submenu (see Figure 41).

Figure 41. The Always Visible Categories

submenu of the palette View button

If a category is not selected in the Always Visible Categories, then you will not normally see it in the palette. However, you can temporarily display all of the categories by clicking on the double "down" arrows at the very bottom of the palette, as shown in Figure 42. You can hide those categories again by clicking on the double "up" arrows at the very bottom of the palette, as shown in Figure 43.

Figure 42. Functions palette with only

the "always visible" categories visible

Figure 43. Functions palette with all categories visible

Reordering Palette Categories

You can reorder the palette categories by right-clicking on them and choosing Move this Category Up, Move this Category Down, or Move to Top (Expand by Default). Additionally, you can drag and drop the categories within the list by clicking on the two vertical grab-bars (||) to the left of the category text.

Palette View Formats

The way that you navigate the palettes can be changed by choosing a different palette View Format. Pressing the View button at the top of a palette will open a menu. In the View This Palette As submenu, you can choose from six different View Formats, as shown in Figure 44.

Figure 44. The View This Palette As submenu

of the palette View button menu showing the

currently selected checked palette view format

Category (Standard) is the default View Format, and the one shown throughout this tutorial.

Category (Icons and Text), shown in Figure 45, is similar to Category (Standard), except that each item's name appears directly beneath its icon.

Figure 45. "Category (Icons and Text)" palette view format

Icons, shown in Figure 46, is the format that most are familiar with from previous versions of LabVIEW. Each subpalette and item is represented by an icon. When you mouse-over an item, its name appears at the top of the palette.

Figure 46. "Icons" palette view format

Icons and Text, shown in Figure 47, is similar to Icons, except that each item's name appears directly beneath its icon.

Figure 47. "Icons and Text" palette view format

Text, shown in Figure 48, is minimal. It behaves like the Icons and Icons and Text formats, where clicking on a subpalette navigates down into that subpalette. Subpalettes are represented by folders with names, and items are represented by their name.

Figure 48. "Text" palette view format

Tree, shown in Figure 49, is also minimal, having only folder icons and item names. However, it behaves more like the Category formats, having a tree hierarchy.

Figure 49. "Tree" palette view format

The "Icons," "Icons and Text," and "Text" palette view formats all have an "up" button (see Figure 50), which, when pressed, returns you to the previous ("owning") palettesince these view formats are not a tree view. You can search for a specific item in a palette by clicking on the spyglass icon (see Figure 50).

Figure 50. The buttons at the top of each palette are used for navigation and configuration options.

There is another way to navigate palettes that some people find a little easier. Instead of each subpalette replacing the current palette, you can pass through subpalettes in a hierarchical manner without them replacing their parent palettes. You can do this by right-clicking (Windows) or control-clicking (Mac OS X) the subpalette icons (see Figure 51).

Figure 51. A floating subpalette created by right-clicking on a subpalette icon

Note that some subpalettes have subpalettes containing more objects; these are denoted by a little triangle in the upper-right corner of the icon and a raised appearance (see Figure 52). We'll discuss specific subpalettes and their objects in the next chapter.

Figure 52. Functions palette with two levels of floating subpalettes visible

Comparison of the terms SCADA, DCS, PLC and smart instrument

A. Scada System

A SCADA (or supervisory control and data acquisition) system means a system consisting of a number of remote terminal units (or RTUs) collecting field data connected back to a master station via a communications system. The master station displays the acquired data and also allows the operator to perform remote control tasks. The accurate and timely data (normally real-time) allows for optimization of the operation of the plant and process. A further benefit is more efficient, reliable and most importantly, safer operations. This all results in a lower cost of operation compared to earlier non-automated systems.

There is a fair degree of confusion between the definition of SCADA systems and process control system. SCADA has the connotation of remote or distant operation. The inevitable question is how far ‘remote’ is – typically this means over a distance such that the distance between the controlling location and the controlled location is such that direct-wire control is impractical (i.e. a communication link is a critical component of the system).

A successful SCADA installation depends on utilizing proven and reliable technology, with adequate and comprehensive training of all personnel in the operation of the system. There is a history of unsuccessful SCADA systems – contributing factors to these systems includes inadequate integration of the various components of the system, unnecessary complexity in the system, unreliable hardware and unproven software. Today hardware reliability is less of a problem, but the increasing software complexity is producing new challenges. It should be noted in passing that many operators judge a SCADA system not only by the smooth performance of the RTUs, communication links and the master station (all falling under the umbrella of SCADA system) but also the field devices (both transducers and control devices). The field devices however fall outside the scope of SCADA in this manual and will not be discussed further. A diagram of a typical SCADA system is given opposite.




On a more complex SCADA system there are essentially five levels or hierarchies:
• Field level instrumentation and control devices
• Marshalling terminals and RTUs
• Communications system
• The master station(s)
• The commercial data processing department computer system
The RTU provides an interface to the field analog and digital signals situated at each
remote site.
The communications system provides the pathway for communications between the
master station and the remote sites. This communication system can be radio, telephone line, microwave and possibly even satellite. Specific protocols and error detection philosophies are used for efficient and optimum transfer of data. The master station (and submasters) gather data from the various RTUs and generally provide an operator interface for display of information and control of the remote sites. In large telemetry systems, submaster sites gather information from remote sites and act as a relay back to the control master station.

SCADA technology has existed since the early sixties and there are now two other competing approaches possible – distributed control system (DCS) and programmable logic controller (PLC). In addition there has been a growing trend to use smart instruments as a key component in all these systems. Of course, in the real world, the designer will mix and match the four approaches to produce an effective system matching his/her application.



B. Distributed control system (DCS)

In a DCS, the data acquisition and control functions are performed by a number of distributed microprocessor-based units situated near to the devices being controlled or the instrument from which data is being gathered. DCS systems have evolved into systems providing very sophisticated analog (e.g. loop) control capability. A closely integrated set of operator interfaces (or man machine interfaces) is provided to allow for easy system configurations and operator control. The data highway is normally capable of fairly high speeds (typically 1 Mbps up to 10 Mbps).



C. Programmable logic controller (PLC)

Since the late 1970s, PLCs have replaced hardwired relays with a combination of ladder–logic software and solid state electronic input and output modules. They are often used in the implementation of a SCADA RTU as they offer a standard hardware solution, which is very economically priced.



Another device that should be mentioned for completeness is the smart instrument which both PLCs and DCS systems can interface to.

D. Smart instrument

Although this term is sometimes misused, it typically means an intelligent (microprocessor based) digital measuring sensor (such as a flow meter) with digital data communications provided to some diagnostic panel or computer based system.



This tutorial will henceforth consider DCS, PLC and smart instruments as variations or components of the basic SCADA concept.

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