Duet + PT100 thermocouple

[Viking]

Has anyone used the combination of the duet 0.8.5 and e3d's PT100 amplifier board ?

[Jimustanguitar]

I'm about to use the Duet with a thermocouple board. I'd assume that it's a similar process.
I'll post my lessons learned here, once I've screwed up and learned those lessons

[Great_Thark]

Did you learn anything?

[Jimustanguitar]

I haven't gotten anywhere with it yet, because I was fighting a firmware issue that effects Win8.1 (look in MHackney's guide, if you're curious). Now that I'm good to go again, I'll know how well it works this week some time. This is the resource that I was going to work from.
http://reprap.org/wiki/Using_thermocoup ... apFirmware

[U.S. Water Rockets]

You can't hook a PT100 RTD to a thermocouple input board.

Thermocouples sense temperature by means of the thermoelectric effect inducing a voltage that varies with temperature in the range of around 0 to 80 millivolts. A very sensitive voltage ADC is used to measure them. Their voltage output is nonlinear, and so software linearization is used to translate the voltage to a temperature, which varies based on what metals the thermocouple is made from.

PT100 is jargon referring to a 100 ohm Platinum RTD. RTD's are Resistance Temperature Devices, and they are actually a resistor that varies with temperature. To read an RTD, you must provide a current source known as "Excitation Current" and then read the voltage drop across the RTD to determine the resistance using Ohms Law. The resistance in RTDs is also nonlinear and must be linearized with software, which varies based on the materials used in making the RTD.

You cannot use one in place of another or vice versa, unless you have a specialized input circuit designed to be switchable between the two sensor types. Even then, you must make sure you have the input configured for the sensor it is connected to, otherwise it will not work.

I'm not sure if improper sensor configuration is why people are having issues with RTDs and Thermocouples, but it's a good place to start looking if you have trouble.

[dc42]

I have just finished implementing PT100 support in my fork of RepRapFirmware, and tested it with the E3D PT100 sensor. I will release and document it in the next few days. You will need a MAX31865-based RTD interface board such as this one http://www.ebay.co.uk/itm/PT100-PT1000- ... 1677140557. Make sure you get one that is designed to run for use with 3.3V electronics, not one that includes 5V level shifters.

I chose to support this type of board rather than E3D's amplifier board for a couple of reasons. First, E3D states that their board is 5V only. Second, a digital interface board eliminates many of the potential sources of error that you have with an analog one.

[Jimustanguitar]

That's great to hear!

I got my thermocouple running successfully last night, no trouble to speak of. I was using the Logxen amplifier board that I purchased with a Smoothie a while back. Add 5 dual female jumper wires, hook them up according to the pinout that you choose, make the quick switch in the firmware, and it just works.

If the PT100 board works similarly to how my thermocouple install went, you'll have no problem.

[Xenocrates]

Heh. Unless the Replicape's delta support improves dramatically before I have the budget to buy a new controller+FSR's, consider me sold. Since it's digital, I assume I can run the wiring to the converter up to the top of the printer, and thus not need to have the lead for the PT100 extended, potentially spoiling accuracy or needing actual RTD extension cables. Now if only there were alternative (Non-fleabay) sources for PT100's with the right price and package size (Although I did find an M4 PT100, but it's 71$ (I should stop browsing the Omega Catalog))

[dc42]

The digital interface is SPI running at 4MHz so the wiring between the Duet and the RTD interface board should be short. Increasing the wire length on the PT100 is no big deal. You can calculate the effect on the reading. Best to avoid introducing additional.connectors, or if you do then make sure they use gold plated contacts. If you want really high accuracy, you can use a 4 wire PT100.

[dc42]

The wiring instructions are now live at http://reprap.org/wiki/Using_PT100_temp ... apFirmware.

[dc42]

I have now released firmware version 1.12 with PT100 support. See the separate thread about that release.

[Eaglezsoar]

I have now released firmware version 1.12 with PT100 support. See the separate thread about that release.

Sir, do you have anything to do with the production of the Duet boards?
The USA distributor, http://www.filastruder.com, seems to be having a problem receiving enough boards. Just thought I would ask Sir.

[Xenocrates]

David is mostly involved in the Paneldue, the mini IR probe, and the Duet NG. I think he has some input into the latest revision of the hardware, but I do not think he does the actual manufacturing.

But has anyone done any testing/setup with this yet? If not, I suppose I get to go first, since unless I want to order thermistors again (Which I would rather not do, considering the frailty and in-accuracy of them), I'll need to do it to get my printer operational again, as my Rambo appears slightly toasted. (I didn't intend to upgrade controllers this soon, but since it looks like the alternative is having the Rambo repaired in some fashion, and it uses a chip known to lose it's bootloader at times (Remind me why Atmel thought that releasing that was a good idea, and Arduino turned it into a core product>?, and the core board is cheaper than a new rambo, there's really no contest)

Also thanks David (or whoever your documentation guy is) for putting together some really clear documentation rapidly, so that there are few undocumented or mis-documented features. An example to all the other firmware/hardware folks (Now to find a physical pinout guide and put together a picture showing the pins involved, so that those who are new to the Duet can have an easy reference (I don't expect you to do so, I plan to do it myself if someone else doesn't)

[dc42]

Correct, I am not involved in the production of the current Duet boards, although some of my suggestions were taken into account in the design of the Duet 0.8.5.

I understand that Think3DPrint3D has been caught out by the rapidly rising demand for the Duet 0.8.5, so although they have been ramping up production, it hasn't been fast enough. I understand that T3P3 has recently taken delivery of another batch of Duets, and they are once again showing as in stock on T3P3's web site. Filastruder is showing an estimated dispatch date of 13 May.

The next-generation Duet is a joint development between my own company and Think3DPrint3D. The wiring for thermocouple and PT100 adapters will be simpler, because they have a dedicated connector.

You asked for a photo of the wiring, so here are a couple.

[img]https://dl.dropboxusercontent.com/u/193 ... .09.12.jpg[/img] [img]https://dl.dropboxusercontent.com/u/193 ... .10.28.jpg[/img]

Further testing revealed a problem with SPI initialisation needed to communicate with PT100 interface boards in some configurations, so I will shortly release version 1.12a of the firmware to correct this.

[Eaglezsoar]

Thanks for your answer and the pictures!
The demand has exceeded the ability to produce, and as you indicated, they are ramping up.
I believe the Duet is going to become as common as Ramps, I hope the manufacturer can handle the demand.
Will a K type thermocouple work with the board shown in the pictures and if not where is a good source for
the PT100 RTD shown in the pictures?

[dc42]

The PT100 sensor in the pictures is the one sold by E3D here http://e3d-online.com/E3D-v6/Spares/PT100. You will also need the new heater block here http://e3d-online.com/E3D-v6/Spares/V6- ... ater-Block if you intend to fit it to an E3D hot end (there is a different block if you use the Volcano nozzles).

A thermocouple is quite different from a PT100 sensor and needs a different interface board. See http://reprap.org/wiki/Using_thermocoup ... apFirmware for how to interface thermocouples to the Duet.