PT100 vs PT1000

dc42

The PT1000 works reasonably well on the Duet 2 using the standard 4K7 resistor. It's the older 8-bit boards with 10 bit ADCs (Duet 2 is 12 bit) that really need lower value resistors. However, my calculations indicate that 1K is too low, and 2K2 is about optimum.

Corexy

@dc42 said in PT100 vs PT1000:

The PT1000 works reasonably well on the Duet 2 using the standard 4K7 resistor. It's the older 8-bit boards with 10 bit ADCs (Duet 2 is 12 bit) that really need lower value resistors. However, my calculations indicate that 1K is too low, and 2K2 is about optimum.

It sounds like my OCD will only tolerate the PT100, as reasonably well is not going to be good enough for me unfortunately. And if I'm breaking out the soldering iron, I'd rather solder wires than mess with my motherboard.

So if my PT100 sensor is 2 wires, at what point do I convert it to 4 wires? Do I make the 4 wires as long as possible?

A Former User

@Corexy said in PT100 vs PT1000:

Do I make the 4 wires as long as possible?

yeah, as close to the sensor as possible.

Corexy

@bearer said in PT100 vs PT1000:

@Corexy said in PT100 vs PT1000:

Do I make the 4 wires as long as possible?

yeah, as close to the sensor as possible.

It's so strange that it makes a difference...

A Former User

some background https://en.wikipedia.org/wiki/Four-terminal_sensing

Corexy

@bearer said in PT100 vs PT1000:

some background https://en.wikipedia.org/wiki/Four-terminal_sensing

Copy that, thank you.

Is there a size/type of shielded 4 core cable that's most suitable? Last time I ran 4 separate pieces of wire, and I didn't have any problems, but I understand noise can be an issue and I'd like the wires all in a single cable this time if possible.

A Former User

i'd choose twisted pairs over shielded, but if you can have both go for it.

Corexy

@bearer said in PT100 vs PT1000:

i'd choose twisted pairs over shielded, but if you can have both go for it.

More likely I've got twisted pairs here already in my box of RC plane bits. Thank you

dc42

I use 4-core 7/0.2 unshielded cable.

Corexy

@dc42 said in PT100 vs PT1000:

I use 4-core 7/0.2 unshielded cable.

Cheers David.

Is that 7 strand you are referring to? Any idea of AWG?

dc42

7/0.2 means 7 strands each 0.2mm diameter. https://www.canford.co.uk/TechZone/Article/MetricAWGWireSizeEquivalents may be helpful.

Corexy

@dc42 said in PT100 vs PT1000:

7/0.2 means 7 strands each 0.2mm diameter. https://www.canford.co.uk/TechZone/Article/MetricAWGWireSizeEquivalents may be helpful.

So this might roll my PT100, heat break and cooling fan all into the one insulated cable? Twisted pairs too, so everyone's helpful advice has been heeded!

https://www.jaycar.com.au/cat-5-8-core-stranded-network-cable-sold-per-metre/p/WB2020

dc42

@Corexy said in PT100 vs PT1000:

@dc42 said in PT100 vs PT1000:

7/0.2 means 7 strands each 0.2mm diameter. https://www.canford.co.uk/TechZone/Article/MetricAWGWireSizeEquivalents may be helpful.

So this might roll my PT100, heat break and cooling fan all into the one insulated cable? Twisted pairs too, so everyone's helpful advice has been heeded!

https://www.jaycar.com.au/cat-5-8-core-stranded-network-cable-sold-per-metre/p/WB2020

I would not mix temperature sensor or endstop wires in the same cable as motors, fans or heaters.

My delta uses one 8-core 7/0.2 cable to connect the PT100 (4 wires) and the 4 wires that connect the built-in probe of the Smart Effector. It uses another 8-core 7/0.2 cable to connect the hot end heater and 2 fans. The hot end heater uses 2 wires in parallel to each end, to better handle the heater current.

Corexy

@dc42 said in PT100 vs PT1000:

@Corexy said in PT100 vs PT1000:

@dc42 said in PT100 vs PT1000:

7/0.2 means 7 strands each 0.2mm diameter. https://www.canford.co.uk/TechZone/Article/MetricAWGWireSizeEquivalents may be helpful.

So this might roll my PT100, heat break and cooling fan all into the one insulated cable? Twisted pairs too, so everyone's helpful advice has been heeded!

https://www.jaycar.com.au/cat-5-8-core-stranded-network-cable-sold-per-metre/p/WB2020

I would not mix temperature sensor or endstop wires in the same cable as motors, fans or heaters.

My delta uses one 8-core 7/0.2 cable to connect the PT100 (4 wires) and the 4 wires that connect the built-in probe of the Smart Effector. It uses another 8-core 7/0.2 cable to connect the hot end heater and 2 fans. The hot end heater uses 2 wires in parallel to each end, to better handle the heater current.

Nice one. Especially about the heater wires in parallel, that's a handy way to keep it all in the multicore cable.

It's another whole discussion, but I was considering using sensorless homing on the XY axis's, for the very reason of reducing the number of wires.

Corexy

I mentioned it in my other post, but what's the advantage of an PT100/1000 over a thermistor?

I see slice use a thermistor in their Mosquito hot end. Is there any reason I'd go with a PT100/1000 in preference to that?

deckingman

@Corexy said in PT100 vs PT1000:

I mentioned it in my other post, but what's the advantage of an RTD over a thermistor?

I see slice use a thermistor in their Mosquito hot end. Is there any reason I'd go with a PT100/1000 in preference to that?

TBH, I don't understand why Slice Engineering chose to use a high temperature thermistor rather than a PT 100 or 1000. It's inaccurate at ambient temperatures, not that it matters. Maybe they couldn't source a high temperature Prt in the USA? They do like to use locally made stuff, rather than imports.

Corexy

Bugger it, I bought all of them. They cost bugger all from Triangle Labs, so I grabbed an assortment of PT100's, 1000's and other bits for the bits box. Was no point getting their standard thermistor cartridges, as they only rated to 280degC and if I'm buying the ludicrously expensive Mosquito/BMG combo, I at least want the option to heat it right up, even if I never do.

Plus a nice member here sent me a spare Slice thermistor he had laying around (cheers Deckers!!), so I'm now spoilt for choices when the time comes.

Now if only it all gets here before the bombs start dropping or the next exotic disease....

mendenmh

@Corexy The advantage of the Pt sensors over thermistors for wide temperature ranges is that the temperature coefficient is very well defined, and fully standardized across all the sensors. Thermistors have varying beta values, and when used over a wide temperature range can give significantly different results between two nominally identical units. In my day job, I work in a ver highly temperature-controlled lab with 0.01C regulation, and logging to 0.001C. This is a US Government standards lab. For this, we use calibrated thermistors because of their very high sensitivity. They are perfect for narrow-range applications. However, to cover a few hundred C or more, they are far from ideal. Although a Pt sensor is less sensitive (0.3%/C at room temp vs. typically 6%/C for a thermistor), they are very linear and interchangeable. A thermistor has too big a coefficient for wide ranges; a 100k thermistor at 25C is < 100 ohms at 280C. That's a huge dynamic range to cover. One the other hand, a Pt1000 is 1k at 0C and 2k at 273C. This is an easy range to digitize, and the resistance is high enough that modest-length wires don't affect the value too much.
The Pt100 sensors are well liked for heavy industrial and high precision applications because they are fairly robust, and the very low impedance makes them relatively noise resistant. On the other hand, the signal levels are low, and you must use a four-wire Kelvin connection unless the leads are very short, since the wiring resistance will be a big contribution to the total resistance. For high-precision work you can't even correct for the wiring resistance in a 2-wire connection, since you don't know the temperature of the wires.

A Former User

I was gonna say thermistors are cheap and "good enough" for most printers as you can tune the settings to achieve good (enough) accuracy and precision. PT100 are accurate, precise, reliable and pricey - PT1000 somewhere in between, closer to PT100 than thermistors, as evident by the price.

But that guy had abit more meat on the reasoning.

For even higher temperatures, thermocouples are the way to go.

Corexy

@bearer @dc42 @deckingman @mendenmh

At this point I'm pretty sure I'll go with this PT1000:

https://www.aliexpress.com/item/32859917151.html?spm=a2g0s.9042311.0.0.401b4c4duXbwYr

I like the fact that it's got a 1m cable length and only needs 2 wires, as I'd rather have it run all the way through to the crimps on the plug at the board end in one piece. I'll leave the resistors as is for now, and if I'm worried I'll get a temp probe for my multimeter and see how bad it is actually out. I've got a couple of fried boards here, so I can actually have a practice run on resoldering the resistors if it is an issue. It seems it should be comparable or better than the thermistor as is, so that will do for now.

I'll also set one up in the enclosure as well, for exhaust fan control.

Thanks for your advice, and for enabling my obsessive compulsive disorder. I really enjoy the pre planning stage, it's a part of the fun for me.