Choosing the proper PT1000 sensor version

[Vlad]

Hi guys, question to David primarily. I am still in a process of choosing the sensor and as you syggested I am looking into PT1000 sensors now. This page says they are the least accurate: https://duet3d.dozuki.com/Wiki/Temperature_sensors , is that info outdated?

Another question is the number of wires I should pick. I think 4 wires in not really necessary for 3D printer application, assuming all 3 wires are same material and length. 2 wires could probably reduce accuracy. So, is 3 wires PT1000 the best choice at this time? And also, I know Duet should have native support for this sensor(does it support 3-wire configuration?), which is awesome, but how about the other boards? I know this a little off topic but I am trying to make sure the hotend that I work on is compatible with the most boards and not only premium ones. If not compatible (which is likely), could you suggest if there is any amplifier board solution that works on wider variety of boards?

Thanks in advance!

[DjDemonD]

I can help with some part of this in that we sell PT1000's. You can connect directly a 2 wire PT1000 to a thermistor input. Once the firmware knows its a PT1000 not a thermistor then it provides a reasonably accurate temperature reading. However the 10bit DAC cannot resolve more than +/-2 Degrees C so for extremely precise control the much more accurate amplifier in the daughterboard coupled with PT100 is better.

PT1000s are not as affected by interference as they operate over a wider range of resistances, with less amplification.

[dc42]

@vlad said in Choosing the proper PT1000 sensor version:

Hi guys, question to David primarily. I am still in a process of choosing the sensor and as you syggested I am looking into PT1000 sensors now. This page says they are the least accurate: https://duet3d.dozuki.com/Wiki/Temperature_sensors , is that info outdated?

It doesn't say that, it says the precision is Medium, whereas for thermistors it is Low.

Another question is the number of wires I should pick. I think 4 wires in not really necessary for 3D printer application, assuming all 3 wires are same material and length. 2 wires could probably reduce accuracy. So, is 3 wires PT1000 the best choice at this time? And also, I know Duet should have native support for this sensor(does it support 3-wire configuration?), which is awesome, but how about the other boards? I know this a little off topic but I am trying to make sure the hotend that I work on is compatible with the most boards and not only premium ones. If not compatible (which is likely), could you suggest if there is any amplifier board solution that works on wider variety of boards?

A PT1000 sensor needs only a 2-wire connection to a Duet thermistor input.

[dc42]

@djdemond said in Choosing the proper PT1000 sensor version:

... However the 10bit DAC cannot resolve more than +/-2 Degrees C so for extremely precise control the much more accurate amplifier in the daughterboard coupled with PT100 is better.

The Duets have a 12-bit DAC with oversampling to 14 bits. The extra 2 bits from oversampling are not necessarily reliable, but even if you ignore them you have around 0.7C resolution.

[Vlad]

@dc42 Thanks for your reply David. It does say that, here is a quote from that page: "Lower resolution than other sensors". Makes it look like it's the worst choice, not the best. So much conflicting info online everywhere, I am totally lost.

[elmoret]

@vlad said in Choosing the proper PT1000 sensor version:

here is a quote from that page: "Lower resolution than other sensors". Makes it look like it's the worst choice, not the best.

A Ford Mustang has less acceleration than a Corvette. But it has better acceleration than a Honda Civic. A Ford Mustang is neither best nor worst when it comes to acceleration. A PT1000 is neither best nor worst when it comes to resolution.

Resolution is not the only consideration when deciding on a sensor, it is one of many.

[DjDemonD]

The big advantage of PT sensors over thermistors is the near linear response to temperature change, and they can handle much higher temperatures. If you want very accurate PT100 gets you there, but you need a daughterboard £30+ total. If you want 0.7 Deg C resolution (you don't need more to get your filament to melt at the right temperature) then PT1000 gets you there with no daughterboard, just plug it in £6.99.

[Vlad]

@djdemond PT1000 looks like a way to go, just was curious why it says on that page that @elmoret "ford mustang is slower than the rest of cars" I'm more into Tesla type of acceleration. So, trying to apply that vision to 3D printing components. Basically improve everything what can be improved.

As far as resolution goes, I am totally fine with 1C resolution, even 1.5C is very acceptable in 3D printer, imo. My bigger concern is speed response and additional expense of daughter board that may be required on other motherboards apart from duet. As i am working on my hotend, and need to shape the hole in a heatblock accordingly, it is important to choose the right sensor now as they are all shaped differently. I am actually thinking to custom make a 3mm x 5mm PT1000 sensor instead of 3x10 that are available on market. This will improve response time and help it deal with my 100W Dominator series heater cartridges Still need to decide whether to go for a 2-wire PT1000 or a 3-wire version.
Love how DUET handles those by the way. Great job on overpowering the board!

[Vlad]

@dc42 how accurate will that 2-wire connection be, given the fact that the system will not know the resistance of lead wires? Will the third wire improve accuracy on Duet board? Or does it not support 3-wire configuration at all? I do not mind adding an amplifier board if it is what it takes to make it a better thermistor with much higher precision.

[dc42]

@vlad said in Choosing the proper PT1000 sensor version:

@dc42 how accurate will that 2-wire connection be, given the fact that the system will not know the resistance of lead wires? Will the third wire improve accuracy on Duet board? Or does it not support 3-wire configuration at all? I do not mind adding an amplifier board if it is what it takes to make it a better thermistor with much higher precision.

With a PT100 sensor, an extra 1 ohm resistance in the wires causes the temperature reading to increase by 2.5C. But with a PT1000 sensor, an extra 1 ohm resistance causes the reading to increase by only 0.25C, which is less than the resolution we are talking about. So it's much less useful to use a 3- or 4-wire connection with a PT1000 sensor.

The support for PT1000 sensors on the Duets is limited to 2 wire connection, because they plug into an ordinary thermistor input. To use a 3- or 4-wire connection with a PT1000, you would need to use an interface board.

Personally, I don't see the point of using 3-wire connections, because if there are connectors in the circuit then there is no guarantee that the 2 main circuits will have equal resistance.

[Vlad]

@dc42 That makes sense. Thanks a lot David! All noted!