S3 flow sensor -- does it even do anything?

[MobyDisk 3]

I purchased an Ultimaker S3 about a month ago, and it does not seem to be able to detect if no filament is flowing.  But I thought the printer had a flow sensor.  I am confused, can someone explain?

 

When I load new filament, if I fail to place the filament into the feeder correctly, the printer just sits there asking me to click "Confirm" once I see material coming out of the nozzle.  But if there is no filament loaded, shouldn't the flow sensor immediately tell me that?  And on one occasion, I had to cancel a print because no filament was extruding from the nozzle.  Shouldn't the sensor have told me that too?  All I did was use the UI to push the filament a little bit and the next print was fine.

 

This article claims the S3 has a flow sensor.  But neither the S3 manual or S5 manual mentions of it.

 

[Dim3nsioneer 551]

Make sure you have the newest firmware version of your update channel installed. IIrc there was a recent update concerning the flow sensor during loading.

As for no filament coming out of the nozzle: the sensor only detects the (in)correct flow but can of course not detect if the filament is at the wrong position (e.g. due to an early confirmation at loading).

[MobyDisk 3]

It is on the latest 7.0.2 firmware.  What do you mean by "the sensor only detects the (in)correct flow" ?  What is the incorrect flow?  What is the correct flow?  What does the sensor actually detect?  What is the purpose of the sensor if it cannot determine if there is no filament flowing?

[Dim3nsioneer 551]

The flow error is displayed if the measured flow is smaller than 80 percent of the flow defined by the print file.

If the end of the filament is still 10cm away from the nozzle, somewhere inside the Bowden tube, it might flow with almost 100 percent but still you would have no extrusion. The sensor measures the flow through the feeder, not through the nozzle.

[MobyDisk 3]

@Dim3nsioneer Thanks for the info.  Is there any documentation on this?  I did finally have the sensor alert me when I was printing too fast with a 3rd-party filament.  So I now can confirm that it does work. And that the printer can recover.👍

[Dim3nsioneer 551]

There is no public documentatioin about the threshold level; just code. For general information about the flow sensors, see https://support.ultimaker.com/hc/en-us/articles/4409038027538-The-flow-sensor-has-triggered