Logging data

Logging is handled by the File Data Logger driver — it writes the values of selected variables into a binary file with the .qilog extension. The record is exact (every value is stored with its timestamp) and compact; it can be exported to CSV at any time or replayed directly in QInsight.

Enabling logging

Add the Data Log Recorder driver to the project (Home → Project Configuration → Drivers, the + button). The replay driver for later playback is prepared automatically along with it.
The driver's Settings field is pre-filled with a template listing every parameter — just edit the values (meaning below):
```
file=DataLogs;append=true;flushOnWrite=false;reorderBufferMs=500
```
With this default template the logs are stored in C:\Users\<name>\AppData\Local\Qenex\QInsight\DataLogs.
For every variable you want to record, tick Log to FileDataLogger (the variable detail in the Communicated variables section).

📷 Image placeholder — ticking Log to FileDataLogger on a variable.

Parameters

Parameter	Default	Meaning
`file`	`DataLogs`	The folder the logs are stored in. You do not enter a file name — QInsight always builds it from the project name and the start time (see below). Path details under the table.
`directory`	—	Moves the logs to a different folder while keeping the last part of the `file` path as a subfolder: with the default `file=DataLogs`, `directory=D:\Data` stores the logs in `D:\Data\DataLogs`. You normally do not need it — set the target folder directly in `file`.
`append`	`true`	When the target file already exists (two starts within the same minute): `true` = append, `false` = overwrite.
`flushOnWrite`	`false`	`true` = force a disk write after every value (safer on crashes, slower). `false` = writes are buffered and go to disk in blocks; the remainder is reliably written out when the communication stops. On an application crash the last stretch may be missing — choose `true` for critical measurements.
`reorderBufferMs`	`500`	A sorting window based on timestamps: a record is written to the file once a record with a timestamp at least this much newer has arrived — values from several sources with different latencies end up sorted in the file. Consequence: the last records are written out when the communication stops. `0` = off.

About the file path:

A relative path (the default DataLogs) is resolved against the QInsight data folder — so you will find the logs in C:\Users\<name>\AppData\Local\Qenex\QInsight\DataLogs.
An absolute path (D:\Data\Logs) is used as is. The directory does not have to exist — it is created automatically when the communication starts.
If you enter a file path with an extension (D:\Data\test.qilog), only its folder D:\Data is used — the file name is always built by QInsight from the project.
The settings are part of the project (.qproj); the .qilog files themselves are not — they stay on disk in the configured directory.

How recording works and how files are named

Logging runs together with the communication: it starts with Runtime → Connect and ends with Disconnect. Every start creates a new file named after the project and the start time:

<project name>_<yyyymmdd>_<HHhmm>.qilog

The Logged column of the Variable Watch window shows which variables are currently being recorded.

Example

During an engine dyno test, the EngineDyno.qproj project samples quantities from the ECU over XCP on CAN — EngineSpeed (20 ms), BoostPressure (20 ms), OilTemp and CoolantTemp (100 ms) — and we want every test run stored as a separate file on a data drive:

File Data Logger settings:
```
file=D:\Measurements\EngineDyno;append=false;flushOnWrite=false;reorderBufferMs=500
```
(reorderBufferMs stays at 500 — the fast 20 ms channels and the slower temperatures arrive with different latencies, and this way the records land in the file sorted by their timestamps.)
Tick Log to FileDataLogger on EngineSpeed, BoostPressure, OilTemp, and CoolantTemp; leave helper and computed variables that do not belong in the record unticked.

Three test runs started at 8:00, 10:30, and 13:15 create:

D:\Measurements\EngineDyno\EngineDyno_20260726_08h00.qilog
D:\Measurements\EngineDyno\EngineDyno_20260726_10h30.qilog
D:\Measurements\EngineDyno\EngineDyno_20260726_13h15.qilog

Each file holds the complete record of all four quantities from one run and can be replayed or exported to CSV on its own — e.g. to compare the boost pressure trace between runs.

Play the recorded data back — Replaying a log.

Logging data

Enabling logging

Parameters

How recording works and how files are named

Example

Next