@dc42 said in Polynomial Temp Compensation for Probes?:
...They are also bigger and heavier than the alternatives. Why does anyone use them?
As far as bulkiness goes, the one I’m using is modeled after Prusa’s PINDA2, with a thermistor embedded in the probe. It’s about 7.5mm in diameter by 36mm long. It only weighs a few grams, or 15g with the entire cable assembly on the scale. That’s smaller than a BLTouch, and costs less than half, too (about $15 US / £13.45 GPB, on a quick Googling). Runs on 5V, so it was easy to wire up to a Duet3.
Why did I use it for this project? Well, mostly convenience. This project itself was somewhat less than planned. I’d been going back and forth between building a Railcore or retrofitting my old Prusa MK3S, and ultimately decided to go with the Railcore. But then parts got delayed. While I waited, I got antsy. Needing something to do over a long weekend other than stare at a screen, I finally decided to rip up my already-heavily-modified Prusa MK3S and switch it over to a Duet3 6HC. (Yes, it’s massive overkill for this purpose; I also love it.)
In this case, my main motivation was that I could get the PINDA2 working without redesigning the extruder or ordering more parts. That said, I think inductive probes like these with embedded thermistors may be worth a second look on the merits.
They may have significant temperature drift, but it’s predictable drift. With the thermistor embedded in the probe, I’ve found the compensation to be quite reliable, both before and after the Duet conversion. I’m sure it’s not the most precise probe out there, but I’m used to just hitting print and it works.
Probing is fast, too. Tolerates fast dive speeds, is happy with less than 1mm dive height, and no need to deploy a pin or whatnot. I have no problem setting M558 … S0.001 A20 and even if it has to probe half a dozen times, it still takes less than a second.
I'm no fanboy here, and I'm certainly not claiming that it's the Best Probe Ever. It feels like all the options out there today have some compromises, though. When it comes to inductive probes, you've got compact, lightweight, cheap, fast, convenient, plus reliable and accurate enough for an everyday printer. On the balance, you've got to do some software temperature compensation and avoid magnets. Perfect? Nah. Acceptable? Sure.
There may be better alternatives for a given printer, depending on the compromises one chooses. I’ll head in a different direction with that Railcore eventually. In the meantime, though, the printer is busy laying down plastic. (And that Duet is great!)
