This post is an input for discussion.

I have done some measurements in an instrument I built. It will measure the force on a 1.75mm filament entering an E3Dv6 with a 0.4mm nozzle. I use a Bondtech to feed the filament. The filament used is ColorFab Ngen. To make it easier to understand the result (for me) I use the ratio between 1.75 an 0.4 to express the extrusion speed. The plastic is extruded into open air, so no back pressure.

Equipment used

The graph below shows the force for different temperatures (210C to 260C). Note that the force doesn't converge on origo. For higher extrusion speeds the curves would probably be less linear.

When the extrusion stops slowly there is a remaining force that almost always is around 1N. It is possible that this force is caused by the friction between the hot, semi melted filament and the nozzle and lower part of the heat break. I the force is subtracted from the earlier graph it looks like the graph below. For the higher temperatures the curves now can be extrapolated to origo.

It is also possible to to measure the enthalpy for melting the plastic as shown below.

And the total power used, graph below.

The first graph can also be plotted in an other way and will then show, for a given print speed, how the force decreases with increasing temperature.

I have some thoughts regarding Pressure Advance

1. If there is a remaining force of 1N the trapped volume between the nozzle tip and the non sliding section of the filament would heat up, expand and ooze out.
2. Is Pressure Advance (M572) and non-linear extrusion(M592) overlapping.
3. These measurements are steady state measurements. Do they confirm the theory behind Pressure Advance?

Any other comments?

@brunofporto I have done some dynamic measurements, mostly with the intent to study retract.

The graph shows three repeated tests. I don't remember the exact settings.

1. The graph starts with an S-curve type acceleration. The hotted was primed a few minutes before the test.
2. The force build up to close to 8N initially
3. The force is reduced once everything gets going
4. The retract takes place and the force is reduced to -1 N. This is the holding force and independent of how much you retract it will not be lower. I think this is caused by plastic deformation of warm filament near the heat break. 1N is the force you get for all filaments I have tested.
5. The plastic deformation relaxes the force to zero in less than a second.
6. The force build quickly after the un-retract when the retract state have been for one second. The un-retract length was the same as the retract length.

The waviness you can see in curves from 4-10s (peak to peak around 1 s) are caused by the gears in the planetary gear used in the extruder.

The very smal jitter in the curve is the full steps of the stepper. I use a Trinamic with 16 micro steps and interpolation to 256 micro steps.

@droftarts I installed HomeBrew and installed wxwidgets as described, and BOSSA worked after that. I am running Catalina 10.15.7.

@dc42

1. The wiki links to an earlier post, no picture on the wiki.
2. The capacity recommended is different from the 100nF you recommended in this post
3. I mounted two 100nF for one channel between the inner pins and ground. I have a four wire configuration with maybe 2m cable. When I use the jumpers on the board to make it a 2-wire configuration the signal is improved significantly. When I remove the jumpers the signal deteriorate.
4. The signal is poor even before the first usage of the steppers in the extruder.
5. Shouldn't all four pins into the Wheatstone bridge have this capacitor?

I am using the 2-wire connection now (with jumpers) and the result is really good. I will try to add two more capacitors to the same channel (total of 4 per channel ) to see if this improves the 4-wire connection.

@dc42 said in Different versions of Pt100 Temp Daughterboard:

Alternatively, wire-leaded ones can be soldered on the underside of the board

I could solder the underside with normal capacitors . However, there is no drawing (that I have found) and the text on the board is almost unreadable. I assume the capacitors should be between the two pin pair that can be closed by a jumper?

@bearer Thank you for the info! You know your own hometown least! And maybe I should give SMT a try someday.

@dc42 I checked the solder pads this morning and I can't solder that small. If you would like you could send me a board with the capacitors on so that I can test it since I have the problem very consistent.

The M301 command. When you do the autotune the PID parameters are printed at the end of the tuning.

Hmm.. I also remember that I forgot to insert the ADC values in the config.g once and they disappeared somehow. Maybe that happened to you as well?

PID is the way you normally control a temperature. This is a good site to explain it:
http://brettbeauregard.com/blog/2011/04/improving-the-beginners-pid-introduction/

@dc42 OK, thank you.
I have the 1.1a.
Yes, they are isolated and the cable shielded.

Maybe you could try the PID settings instead, these should be listed when you autotune. To me it looks like the P part is to high, so try cutting it to half. I would also tune at the temperature that you intend to keep, so 300 in this case.

@Veti Thank you for responding!
@dc42 OK, Thank you for the info. What type and size of capacitor do you recommend?
I have two daughterboards and one is used for the chamber and bed. These signals are good. For the board used for the two extruders the signal i jittery. I have done an extensive work trying to improve the situation but it is clear that it can't be as good as for the bed-chamber sensors.

I have done everything except grounding the hotted itself (tried by holding a ground wire manually, and it did not help). I have a better version of Pt100 that I don't think connect to the heater block, and I have tried several. The jitter can be seen for both channels on one board, but not the other board.

Would it be a good idea for the Duet 3 to have a separat ground connection that you can take to the common ground for the machine?

Does anyone know the difference between version v1.1 and v1.1a of the Pt100 temperature daughterboard for the duet3D? I can not find 1.1a on GitHub.

I have the problem with spikes in the temperature reading (2000C) that many have reported on the forum, and is wondering if the revision change have been made to improve that. The problems probably come from the steppers used for the extruders by inductance despite having separate, shielded cabels and motor phase twisted pairs.

@iamturbo1978 You could check out this:
SimplexMotion
They use Out-runners and Hall sensors to read the magnetic field instead of encoders. Contact them directly with a project description if you are interested. I do not think they support linear encoders for position feedback.

One advantage with a servo is that you can use a stiffer Polyurethane belt to get a stiffer system with better response and accuracy. The downside is the tuning of the servo that can be time consuming.

In my experience from industrial servo application with linear encoders, the inner loop is the encoder in the rotating servo and the outer loop is from the linear encoder. I think it would be difficult to control a servo with only the linear encoder.

I have build a screw based system that can go fast (1m/s) and accurate and the limiting factor I found was the extruder (with gear) that has difficulties providing a smooth flow during accelerations, specially with pressure advance that creates higher pressure. The effect is similar to ghosting, so it took a while to figure out the cause. I print at 150mm/s (limited by the melting of plastic) and with conservative values for acceleration.