To reduce the volume of incoming data, even during the test drive, these loggers let users start logging only in response to pre-defined events. In triggered logging, data is continually written to a ring buffer. When the trigger event occurs, this ring buffer is closed, and the data is saved. Logging is then resumed in a new ring memory. This method substantially reduces data volumes compared to continual logging. Depending on the configuration of the ring buffer, logged data may be available for a time period before the trigger and possibly for a configurable post-trigger time after the trigger occurs. The ring buffer is usually configured with special software (Figure 2).
Figure 2: For data loggers, a broad choice of interfaces is mandatory
The special script language Logger Task Language (LTL) can be used to execute complex logging tasks. This can be illustrated by a simple programming example: Creating a classing table during logging. First, the symbolic signals Speed and Brake from a database are automatically converted to LTL code. The test engineer only needs to add supplemental code for classing with the CLASSIFY operator:
VAR Speed = CAN1 DATA 200h [2 3]
Brake = CAN1 DATA 100h [3(0)]
MyClassify COUNT (Brake)
OVER Speed (20 CLASSES OF 10 BASE 0)
In this example, the Variable Speed value is defined in km/h over 20 classes, each class has a width of 10 km/h, and 0 km/h is set as the start value of the first class. This yields the following class distribution:
Value range [km/h]
0 - 9
10 - 19
180 - 189
190 - .....
The data of each classing task is saved in text-based results tables that can easily be read into a program such as MS Excel for post-editing.
Figure 3 Trigger