17 - VBOX Tools Maths Channels

Maths Channel Basics  

Having selected the Maths Channel in Report Generator or ‘Generate New Channel’ in the Graph screen a new window appears in which the mathematical expressions are entered.   The main window shows a list of logged or live channels available.   The ‘Expression’ box is the area in which the mathematical expression is created.   A channel from the list is added to the expression by clicking on it. Basic maths functions are added to the expression box by typing them directly into the box. The symbols for the basic maths functions are: +   –  Addition. –   –  Subtraction. *   –  Multiplication. /   –  Division. ( )  – Open and close brackets.

More complex mathematical functions can also be typed into the expression box or selected from the ‘Maths Functions’ drop-down menu .

Creating a New Channel in the Graph Screen

The following example demonstrates the creation of a Gradient channel from logged VBOX data. Gradient is calculated by dividing Vertical Velocity (km/h) by Speed (km/h) then multiplying by 100.

Step 1: Loading the File  

Load the logged file by clicking the ‘Load All’ icon and browsing for the file. Click on the ‘Graph’ icon to open the Graph screen, which will then show the loaded file.

Step 4: Calculating the Maths Expression  

Now click on the ‘Generate Channel’ icon at the top of the window. A box will appear with an example of your calculation performed on the data at the first sample point. Then a Channel Name box will appear into which you should type a channel name, in this case Gradient.   After clicking ‘OK’ the Channel Units box will appear; for this example ’%’ is used. Click ‘OK’ again and the new channel will appear in the channel list.

Step 5: Viewing the New Channel Now that a new Maths channel has been created it will appear in the list of available channels and can be viewed in the Graph screen like any normal channel. Step 6: Saving the New Channel Click the ‘Save’ icon in the main toolbar to save the file with the new Maths channel to a new file. The new file will then include the Maths channel.

Creating a Maths Channel in the Report Generator

This example details the creation of a Maths channel to show wheel slip, by determining a difference value between a CAN Wheel Speed channel and the Speed channel of the vehicle. The live results will be shown in the Report Generator screen, along with the five Maths channels. The Maths channels can also be shown in live windows.
 

Step 1: Connecting the VBOX for Live Data Connect the VBOX to the computer and switch the power on. Then connect the VBOX to the test vehicle CAN bus and configure the VBOX CAN input channels to pick up wheel speeds from the test vehicle. See the section ‘Configuring the VBOX and Modules’ for more information about how to enable CAN channels. Step 2: Running the Maths Channel Click on the ‘Report Generator’ icon to open the Report Generator screen and then start the Maths Channel feature by selecting ‘Maths Channel’ from the Report Generator toolbar. A new window will appear, containing a list of available channels enabled in the serial data stream of the connected VBOX.   You can see in the screenshot above right, that the last four entries in this case are the four Wheel Speed channels for the test vehicle.

Step 3: Creating the Maths Expression

The equation for wheel slip of one of the wheels as a percentage is:
 

(Speed – Wheel speed) / Speed * 100.
 

Click the required channels from the list to add them to the expression and type the symbols and numbers necessary to create the expression.
 

The formula should read as shown:

As this expression was created in the Formula 1 section, Maths channel 1 will now show the results from this equation. The window Formula 2 can be used to create a percentage slip channel for the other front wheel. Now the Maths Channel screen can be closed.

Maths Functions and Custom Formulae

Both the Maths Channel and New Channel features are capable of using advanced maths functions, such as square root and cosine, as well as allowing you to save your own formulae for future use. Formulae saved in the Maths Channel screen can be used in the New Channel screen, and vice versa.
 

To save a formula, it must first be entered in the ‘Expression’ text box (in the case of the Maths Channel screen, it can be entered in any of the ‘Expression’ text boxes). When the formula has been entered, click the ‘Save Formula’ button. You will then be prompted for a name for the formula. If you do not wish to save that formula (either because it is incorrect or because you only wish to save a different formula in the Maths Channel screen), press cancel. Otherwise, enter a suitable name and select ‘OK’.
 

Saved formulae can then be re-used by clicking the ‘Maths Functions’ icon and then selecting the required formula from within the ‘User Defined’ category. This menu also displays a list of standard maths functions, which can be inserted into the formula in the same way.

Rate Of Change

Maths Channels can also make use of a Rate Of Change (‘ROC’) function, which will output the rate at which the selected channel is changing at every sample. This feature assumes that each sample occurs at the file’s normal logging rate, so erroneous results may occur if data has been lost.
 

It is important to note that the Rate Of Change function cannot be used in combination with any other maths functions within a single channel. However, a Maths Channel that uses the ROC function can be used as a data channel within other Maths Channels. So if, for example, a channel was required that showed:

Maths Channel = ‘Channel A + Rate Of Change of Channel B’
 

It could be created by making two Maths Channels:

Maths Channel 1 = ‘Rate Of Change of Channel B’

Maths Channel 2 = ‘Channel A + Maths Channel 1’.

Maths Channel 2 can then be used to show the required data.