Logging

A unit with an SD card writes logs: files of sensor values over time, in the MDF4 format that analysis tools open. Its logging configuration has two parts, the settings with the sensors to log, and the bindings that start and stop it.

Settings

• Interval. How often a row of values is written, in milliseconds, 10 at the least. A sensor that is read more often than that is logged at the interval; a CAN frame sensor logs every frame.
• File size. When a file grows past it, in MB (1024 at most), the unit closes it and starts the next one, so that a long drive is a run of files that continue one another. 0 never starts a new file.

Sensors to log

Each sensor you add to the list is logged. For each one you may also log:

• its raw value, for an input that has a math expression: the value before the expression, the calibrated reading of an analog input or the level of a digital one;
• only new data: a row only when the value changed, which keeps a slow value from filling the file.

A sensor not in the list is not logged. A sensor in the list that is disabled in the sensors configuration logs nothing until it is enabled.

Starting and stopping

Logging starts and stops in three ways:

• A binding. An on-or-off value on the unit’s event bus, such as an indicator sensor (rpm > 500, a switch on a digital input), starts logging when it turns on and stops it when it turns off. A binding names the unit it is for: this one, a unit of the network by its ID, or every unit that writes logs. Up to sixteen bindings.
• The app. Start and Stop on the unit’s Logging page, with the status beside them: whether it logs, the file being written and its size.
• The network. A unit without a log writer, such as one with a display, can start and stop the units that have one.

Note

Writing any configuration to a unit stops logging on every unit of the network, and nothing starts it again but a binding turning on or a Start. The app says so before it writes while a unit is known to be logging.

The files

A log is named after the time it started on the unit’s clock, which counts from power-on and is not a date. The app lists a unit’s logs with their length and size, saves them to the computer or the phone one at a time or all at once, and deletes them; the log being written is closed first. A log can be plotted in the app straight from the unit, with cursors, several logs laid over one another and a CSV export, and a set of logs saved together as a session file.

What the unit checks

The unit refuses a logging configuration it cannot run, and the app shows the same findings before you write it: an interval under 10 ms, a file size past the limit, more than sixteen bindings. The app also warns of a setting that does nothing: a raw value on a sensor that has none, only new data on a CAN frame sensor, a sensor the list names that the sensors configuration lacks.