What are my options if I want to install a bed levelling sensor capable of operating at 100 °C?

Question

I currently use a BLtouch 3.1, which is known to stop operating at about 35-40 °C. In fact, when I preheat the bed at 100 °C close to the probe, I sometimes get issues with the pin not retracting correctly.

I would like in the future to enclose and heat the printer chamber, therefore I need a probe capable of operating at higher temperature. My target is 100 °C.

As of now, I'm aware of this solution:

https://hightemp3d.com/products/remoteht-bed-level-probe-3d-printer

This high temperature probe uses a mechanical switch in combination with a servo motor to probe the bed. The servo motor is outside the enclosure and retracts the probe pin by pulling on a steel string inside a spring guide tube.

Microswitches are known to work at high temperatures (that's what the link above uses), but usually need a servo or other mechanism to extend/retract them when needed. Servos typically don't operate at such high temperature, not to mention that they are usually not very accurate.

I saw a Hall filament sensor which uses Hall effect sensors "ss49e" and which could be easily modified to be used as bed probe. Those Hall effect sensors are rated up to 100 °C but at that temperature they have up to 8% shift of the null value and +3/-9% change in sensitivity. The linked project uses two of them in differential mode so the temperature compensation should be much better, but it is not clear how much better. A discussion about it on a Russian forum does not talk about this.

Are there other options operating at 100 °C?

Answer 1

Have you considered using or adapting Prusa’s P.I.N.D.A. V2 or SuperPINDA? Seems that within some bounds they’ve solved the temperature compensation issue.

The older P.I.N.D.A. V1 sensor seems to be temperature-sensitive. See more information in P.I.N.D.A./SuperPINDA Sensor testing article of Pruse Knowledge Base.

Answer 2

There are various designs which can be made to work at 100 °C.

For example this solenoid probe uses a solenoid to lift a plunger during print, letting it drop during probing. The design uses a rare earth magnet which usually loses strength at 60-80 °C, but there are high temperature versions or a ferrite magnet will do. It also uses an Attiny13, rated 80 °C, but there are higher temperature versions of the chip. It is likely that it would work out of specs at 100 °C too, but it uses an optical endstop, which is the limiting factor with 85 °C typical.

This other design uses a solenoid to push up and down a tactile switch. I see no reason why the solenoid would not work at 100 °C, maybe only the external wires may require replacement to withstand the temperature. There is no electronics limiting the operating temperature.

Other designs with a servo are limited by the temperature range of the servo, which is typically 50-60 °C max. I think they would work fine up to 80 °C since they are not operated continuously and they are loaded with little force, but there is no guarantee.

Another design working perfectly and with an even lower total weight is based on a microswitch and... the user placing the probe in position manually. It can probably be automated by mounting it on a hinge and by using something on the side of the bed to move it in an upright position and in a tilted position, where it could be held by (ferrite) magnets.