RTD sensor (pt100/pt1000) input card?

[meurig]

#3549

Hello,

Is anyone working on an RTD sensor input card?

It’s my understanding that these probes can be more accurate than thermocouples, though they are tricky to interface to – an open source interfacing card seems to be in order!

The arduino forum links to the following design (the multiplexer might be overkill):
http://openenergymonitor.org/emon/node/75

Regards,
Meurig

[rocketscream]

#3824

Hi Meurig,

We are working on it but will go on a slightly different route from that link (saw that some time ago).
It’ll be a 3-wire RTD card (can be used with 2 wire also) with proper micro current biasing on the RTD sensor.
And yes, they are trickier to interface with.

[meurig]

#3825

Hi Rocketstream,

That is great news, I thoroughly look forward to seeing the design.

Will you be making the cards available individually?

Many thanks,
Meurig

[rocketscream]

#3826

Yes, the cards will be available individually. 🙂

[meurig]

#3827

Page five of the following whitepaper gives a circuit suitable for 3-wire RTDs:
http://ww1.microchip.com/downloads/en/appnotes/00687c.pdf

It looks straight forward enough (though I don’t claim to understand it). Is that the sort of thing you had in mind?

They have suggested a 12bit ADC and note that this gives a resolution of 0.22 degrees C per LSB over the -200 to 600 degree range.
I note the ADC in the ATMega is only 10bit, so the resolution would be less (around 1 degree?).

The whitepaper mentions that with proper calibration, such sensors/circuits can achieve 0.01 degree accuracy, is the plan to include a high resolution ADC to take advantage of some of this accuracy? (assuming the calibration problem can be solved).

The following post links to a few ADCs, though 100k SPS is certainly overkill for anything I could imagine using a pid for:
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1287074482

The MPC342x (first link on that post) certainly looks interesting, 18bit resolution, i2c connection for around $4. Is this considered an acceptable price for components on an input shield? The 3.75 SPS would be plenty for any application I’d consider.

[rocketscream]

#3828

That is some papers that we went through earlier on.
But, we are going with an external ADC thingy.
Resolution wise is still not decided yet though we have few of them lying around (16, 20, & even 24 (overkill)), but definitely not the on-board ADC on ATMega. A pretty slow sampling rate pretty enough for these type of application.

[rocketscream]

#3829

The MPC342x (first link on that post) certainly looks interesting, 18bit resolution, i2c connection for around $4. Is this considered an acceptable price for components on an input shield? The 3.75 SPS would be plenty for any application I’d consider.

They are going for $3.02 for above 100 pieces (4 differential input version). Pretty cost effective compared to other similar product in the same range.

[samward]

#3830

I am interested in using the osPID with the RTD card for my brewing rig I am currently building. Do you have an ETA on when you think the RTD cards might be available for purchase??

Cheers
Sam

[rocketscream]

#3831

I am interested in using the osPID with the RTD card for my brewing rig I am currently building. Do you have an ETA on when you think the RTD cards might be available for purchase??

We were slightly side tracked to release something special for osPID. 🙂
The RTD PCB design is completed but haven’t do a last round check before sending them off for fabrication.
No ETA at the moment.

[meurig]

#3832

@rocketscream wrote:

The RTD PCB design is completed but haven’t do a last round check before sending them off for fabrication.

That’s great news, really looking forward to finding out what design you went for, and getting my hands on an ospid with the new card!

[Roddi]

#3833

You have another potential customer for such a card, as the PID that I retrofitted my coffee machine with broke so I need a new solution. Since it came with a pt100 reusing it would be a nobrainer.

[bananaSkill]

#3834

this card looks very interesting,
can this card be used with a ‘standard’ Arduino and how will it be interfacing with the osPID ?

[Cracked]

#3835

Just wondering if there had been any progress on this? Apologies if this has been posted elsewhere, but the forum software wont let me search ‘RTD’.

[rocketscream]

#3836

Okay guys,

This might seems a bit late. But, there’s a bunch of beta boards of the RTD input card on my table.
The card supports 2 & 3 wire PT100 RTD. Currently we are about to send these out for beta tester out there.

And, did I forgot to mention it’s a dual RTD input?

[Cracked]

#3837

Brilliant! Will we have to make our own firmware/front end software to use it?

[Author]

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