Recording Limits in ALTRON: Size, Time and Frame Count for Long Recordings

You started recording, went off to do something else, and when you came back the whole recording was only a few seconds long. Nothing is broken; one of the three recording limits was reached. Every saving node in ALTRON has three limits. Whichever is reached first ends the recording. The default values suit a short test recording, not a full shift.

The three limits and their defaults

• Max Capt. Size (MB): the maximum size of recorded data. Default: 200 MB.
• Max Capt. Time (s): the maximum recording duration. Default: 20 seconds.
• Max Capt. Count: the maximum number of received data items; the default is 2,000,000. If the input is line-based, each line counts as one. If the input is frame-based, each frame counts as one.

So with the default settings, recording stops after 20 seconds or after 200 MB, whichever comes first. That is the "stops by itself" behavior you saw.

In video nodes, you enter the count limit in Max Capt. Count (K), in thousands of frames.

Why have limits at all?

An industrial camera, especially a line scan running at a high rate, produces a large amount of data in a short time. If someone leaves recording on and walks away, the disk fills up and the rest of the system suffers too. The limits guard against exactly this.

For long recordings, do not remove the limits; just raise them to suit the job. Their allowed ranges are large; for example, time can go up to 315,360,000 seconds.

Setting up a long recording, step by step

1. Measure the data rate. In the diagnostics panel, go to the Internal Info tab. There, Main Data Rate shows the data rate of each port.
2. Enter the duration you need in Max Capt. Time.
3. Multiply the data rate by the recording duration. Set Max Capt. Size slightly above this number, but make sure it does not exceed the free disk space.
4. Set Max Capt. Count so that it is not reached before the other two limits, unless you deliberately want a specific number of lines or frames.
5. Press Start. These values are read at the moment you press Start, so changing them mid-recording has no effect on the current recording.

Read the four percentage bars

Next to Cache, Size, Time and Count there are four percentage bars. Each bar shows how close that limit is to being reached. Whichever of the Size, Time and Count bars reaches 100% first ends the recording. The Cache bar is not a limit; it only shows whether the disk has fallen behind the camera. If recording stops earlier than expected, just check which bar is full.

If the Cache bar is full, the story is different. The problem is not the limits; the disk has fallen behind the camera. In that case, look at the cache size, the disk speed or the save format.

Several nodes, one setup

If you have several saving nodes or record several cameras at once, you do not need to enter the limits one by one. Use Tools › Record › Set Common Params to set the save path, cache size and the three limits for all saving nodes in one place.

Then use Tools › Record › Begin Record All to start them all together. This is the only reliable way to keep several output files in sync. To stop, press End Record All.

Low disk space warning

The same Set Common Params window has a threshold for the disk space warning (Low disk warning below (GB)). Every few seconds, ALTRON checks the free space on the drives the saving nodes write to. If the space drops below this value, it shows a warning message for each drive. Unless you change it, the threshold is 5 GB.

A common mistake

Many people raise Max Capt. Size and forget Max Capt. Time. The default time is 20 seconds, and recording ends right there, no matter how much you raised the size. Before every long recording, review all three values once.

To learn more about disk write speed, Wikipedia article (English).

If you need help estimating the size and duration of recordings for your own project, ask us your question.