How many PT1000 sensors can I have with Duet 3 Expansion boards.

[lee7670]

The last topic to address this was here: https://forum.duet3d.com/topic/9918/how-many-temperature-sensors-on-duet
This seems to be applicable for RRF2 and Duet 2 bards, but how many are supported with Duet 3 expansion boards. I have an application where it would be nice to have >20 PT1000 inputs.

[A Former User]

i believe (initial) target is to support 8 expansion boards, each 3HC board can have

3 Thermistor/PT1000 inputs and support for 4 PT100/thermocouple inputs via the optional daughterboards.

@lee7670 said in How many PT1000 sensors can I have with Duet 3 Expansion boards.:

would be nice to have

can you elaborate on the requirement? "nice to" have implies its of less importance, maybe you could get away with multiplexing inputs or rigging up external sampling and using the object model to get the data in?

those 3 HC boards quickly add up to some serious £

[dc42]

You could connect more than 2 daughter boards to a Duet 3 main or expansion board, by wiring the CS pins of the boards after the first 2 directly to spare output pins on IO connectors.

[A Former User]

@dc42 said in How many PT1000 sensors can I have with Duet 3 Expansion boards.:

You could connect more than 2 daughter boards

will the daughter boards work with PT1000 sensors?

[dc42]

@bearer said in How many PT1000 sensors can I have with Duet 3 Expansion boards.:

@dc42 said in How many PT1000 sensors can I have with Duet 3 Expansion boards.:

You could connect more than 2 daughter boards

will the daughter boards work with PT1000 sensors?

Ah, I thought we were talking about PT100s. To use a daughter board with PT1000 sensors, you would need to change the reference resistors on the daughter board for higher value ones. The standard ones are 400 ohm +/- 0.1% but for PT1000 you should use 4000 or 4300 ohms. It would also be possible to use third-party boards based on MAX31865 chips that already have suitable reference resistors for PT1000 sensors.

[deckingman]

@lee7670 In addition to other answers, be aware that there are currently limitations on what you can use temperature sensors connected to expansion boards for. The latest limitations list:

A heater on an expansion board can only be controlled by a temperature sensor on the same expansion board.

and ....

A thermostatically-controlled fan on an expansion board can only be controlled by a temperature sensor on the same expansion board.

[lee7670]

Thanks for all the answers! This application isn't especially price sensitive and I only need to read temperatures, not control too many heaters. so that should work. Thanks!

[A Former User]

@lee7670 said in How many PT1000 sensors can I have with Duet 3 Expansion boards.:

This application isn't especially price sensitive

then you're in the right candy store:D