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Creating a graphic HMI for Mervis SCADA
Prerequisites
- Existing Mervis IDE project created according to the Creating a Mervis SCADA project tutorial
- All prerequisites from the mentioned tutorial
Graphic HMI variant for Mervis SCADA is available only via a web interface, as the Mervis mobile app currently does not support it. It is thus necessary to connect all data points used in this tutorial to the data point table as well.
Creating a template
You can create a HMI template by right-clicking on HMI project and selecting Add New HMI Template
A dialogue window will appear. Enter the name of the template and set other properties as needed.
- Name should be considered carefully, we also recommend to use a prefix separated by underscore, ie. SCADA_schema.
- Display Type determines the template type → select Graphic
- Template Type - choose a Terminal
- Terminal - choose terminal the template is created for
You now need to assign the template to the terminal. Click on the terminal and look for Schemes in its properties in the right column. Here you need to insert the template you created in the previous steps.
Creating a HMI
All data points (variables) used in the graphic HMI also need to be connected to a data point table and, by extension, to the Mervis DB as well.
In the left panel, double-click on the created HMI template. On the bottomn of this panel, switch to HMI Objects tab - your screen should look like this afterwards:
In the HMI objects window you can see a wide collection of graphic gadgets that can be added to the template. In this tutorial, we will start with the Value Indicator element designed for displaying numeric values. This makes it ideal for displaying the current temperature in an office, for example. Click on the element in the left panel and drag it onto the main panel.
The element will appear on the main panel and will stay highlighted. In the Properties menu, you can now see all available configurations for it. Right now, the most important attribute is Variable placed in the HMI section. Using this setting we will tell the element which variable will be used as a data source. Click on Variable and then click on the button. 
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A well-known Select variable dialogue will appear, in which you can search for the needed variable. In this tutorial, we are looking for an already existing office_temperature variable. Look it up, select it from the list and confirm by clicking on OK.
Go back to Properties. Change the Unit setting determining the displayed value's unit. In the HMI, this unit will be automatically added behind the displayed values. As we are talking about a temperature value, set the Unit attribute to °C.
It may be also handy to give the value a suitable name. In the HMI objects menu choose the Text element and place it into the template. In the Properties panel, change the Text attribute to Current temperature.
As the new name is much longer than the default one, you can enlarge the text field by dragging one of the yellow squares around the element to make the whole text visible.
Right now, the element is not legible enough, and its current design makes it look more like a button than a nametag. Let's improve it by changing the text's colour to blue using the Foreground attribute in the Text property section.
Now change the Background colour to white, and Text Horizontal Alignment to Right.
The next step is to add an element that would allow us to display and configure the values of an analogue variable. Theoretically, we could again use the Value Indicator. However, this element can only display values, not change them. A more suitable choice is the Analog Setter. Select it and place it onto the canvas. In the HMI properties, configure it as follows:
- Variable: choose a suitable variable representing temperature. In our case, we will select threshold_temperature variable
- Unit should be set to °C as the variable is expressed in degrees Celsius.
- Min Value will be 18, which will prevent users to set a temperature lower than 18 °C
- Max Value is 30 to prevent users to set a temperature higher than 30 °C
- Step Value, or the increment by which the temperature can be adjusted. Set it to 0.5
We will also create a text label for the element in the same way as with Current temperature. You can simply copy and paste the text fields and edit the text afterwards.
The last element we will need is an indication of heating status, eg. if the heating is ON or OFF. Again, we could simply use the Value Indicator, but we won't since this element can display only binary values (0 or 1). A better choice is the Digital Indicator. Select it and place it onto the canvas. Here, you need only to select the correct variable, ie. DI_1.02.
We recommend giving inputs/outputs descriptive names such as light_kitchen, door_bell etc. There are two main reasons:
- Such names will make the project much clearer and easier to read
- If you decide to plug a sensor to a different input, all you need to do is to rename the input variable with the rest of the program still using the same name
At this point, only a couple of finishing touches is needed. Give the heating status indicator a name and then create another, a larger text field for the name of the entire HMI project. The result can look like this:
Uploading Mervis SCADA project definition
With all things in place, click on Build Solution. In the build dialogue, make sure to check the SCADA box next to the terminal. By building the solution an export subfolder will be created in the folder containing all project files. Another subfolder will be then created in the export subfolder containing a ZIP archive with a SCADA project definition. This archive is the last important component needed to get the Mervis SCADA running.
In the Unipi customer portal, open the project created in the first chapter. The Options tab in the upper right corner is used, among others, to upload SCADA terminal definitions into Mervis SCADA projects. The SCADA definition is represented by the above-mentioned SCADA project archive, all you need to do is to click on Upload SCADA definition:
Here, select the right archive from the export folder placed in the project's folder.
You can now return back to the main Mervis SCADA tutorial.
