HDPE , RepRap hardware and 200 Deg C.

I must be using less aggressive m/b settings than you are. My temperature will stabilize at less than 20% over, and I don't think I've ever seen the heater light go dark when I wasn't trying to provoke it. Mine takes nearly forever to arrive at a stable temperature, somewhere in the 30-45 minute range (ugh). I haven't noticed any big swings when I start start extruding, but I haven't left the extruder running for more than a few minutes at a time.

In normal operation, I think Andreas' "reading too high" check would only be hit when we're reading extremely high temperatures or if the host software has died. If the host software is running properly, it should adjust the wdt scaler to keep the timer readings in the middle of the range, well above 0x10. It's a good thing to have in there, but it's not going to help in most normal situations.

I'd love to see this algorithm replaced with something simpler too. I'm a bit worried about what's going to happen in a few weeks when the molded extruders bring another wave of extruders into the mix.

I've been trying to replace the measurement routine with the dual-slope variant I had mentioned. If it works, it could simplify things a bit -- you couldn't enter the wrong capacitor value, and auto-ranging may not be necessary on the host side. I'm anticipating an epic struggle with SDCC this weekend.

Cool,
Post the code and I can test it on my machine. I am still running the default Thermistor.

Bruce W.

from what I have seen my temp is running very low I set my temp to 240 Deg. it barely reached a constant temp to extrude at. But my power settings prob need work..

Bruce,

EMFs work still will need the 100k thermistor.
based on what I have seen at this stage of development you really need to have a seperate thermcouple monitoring temperature.

The risk of frying the PTFE is real. A historical note the first six chemists to discover elemental fluorine did not live to report the discovery. I don't know what the breakdown byproducts are of decomposing PTFE, but they are not good.

If you use the slope and intercept that I listed above (assuming a ~6ohm room temperature heater and ~12 volt power supply), you will be able to drive the heater way hotter than is needed. my heater was not insulated during the cal run so the power slope is greater than I will need for my now insulated heater.

Oh boy another heater profiling run :-)

Best,
Dan

emf Wrote:
-------------------------------------------------------
> In normal operation, I think Andreas' "reading too
> high" check would only be hit when we're reading
> extremely high temperatures or if the host
> software has died. If the host software is
> running properly, it should adjust the wdt scaler
> to keep the timer readings in the middle of the
> range, well above 0x10. It's a good thing to have
> in there, but it's not going to help in most
> normal situations.
>

this check does not safeguard against high temperatures. it protects "only" against heating forever, if the desired temperature is to high for the used thermistor/capacitor. the measurement of the temperature in the firmware needs some machine-cycles (I don't remember exactly but I think its more than 10 and below 16 cycles) at the minimum. therefor if the temperatureLimit (I think we should change the name of the variables in the firmware-code, because its not the temperature its the time to load the capacitor) is lower than the minimal time to measure it, than the heater would heat forever. so if the thermistor/capacitor would allow it, the firmware would heat it up until something burns.

Dan P. Wrote:
-------------------------------------------------------
> I am considering adding a stainless steel
> hose clamp to the base of the PTFE barrel to keep
> it from deforming. For those if you starting to
> run at these higher temperatures PLEASE BE
> CAREFUL,240C HDPE will burn you in a heartbeat. I
> don't know yet whether This was a one off failure.
> Please report your experience.

i've seen this on both my machine and tom owad's machine... i highly recommend adding a stainless steel hose clamp. when i get around to updating the extruder documentation, i'll be sure to make a note of it (as well as include a hose clamp in the kit on the RRRF store.)

I use a 1 inch cube of PTFE for a thermal barrier instead of that flimsy rod stuff. I've never been sorry that I shifted over. The lack of worry and bother has more than made up for the extra cost many times over.