Marlin - extra hot end temperature measurement (no replies)

Hi!

Today, I almost got into trouble with my 3D printer. Up until now, I only have one temperature sensor connected to my hot end. That sensor sprang loose during printing, resulting in a almost catastrophic overheating of the hot end.

Happily, I was close by and checked up on the printer regularly.

The solution for this problem would be to install a secondary backup temperature sensor. The Marlin firmware I use includes support for such secondary sensor.

#define TEMP_SENSOR_0 1
#define TEMP_SENSOR_1 0
#define TEMP_SENSOR_2 0
#define TEMP_SENSOR_BED 1

// This makes temp sensor 1 a redundant sensor for sensor 0. If the temperatures difference between these sensors is to high the print will be aborted.
//#define TEMP_SENSOR_1_AS_REDUNDANT
#define MAX_REDUNDANT_TEMP_SENSOR_DIFF 10

I just have to uncomment the TEMP_SENSOR_1_AS_REDUNDANT and set TEMP_SENSOR_1 = 1 and it should work after I connect a second sensor to the hotend.

Sadly it appears not to be this simple.

I use the same sensor type as my default hot end sensor. I installed it on my RAMPS 1.4. The configuration is as follows:

-- HOT END SENSOR 1 +
-- HOT END SENSOR 1 -
-- BED SENSOR +
-- BED SENSOR -
-- HOT END SENSOR 0 +
-- HOT END SENSOR 0 -

I already successfully used the configuration without SENSOR 1. However, when I try to use this configuration, it starts heating up, but after a while, it just stops heating. I assume this is because the temp difference between the two sensors becomes too great.

I looked how to actually extract the temperature measured by SENSOR 1, but that appears not to be possible using G-code? Or is there a G-code command I can use for this?

Anybody an idea why this is not working?

It goes without saying that I am not going to leave my printer work on it's own without solving this :-)

Thanks!
Steph