Request for support on design: reading 24pcs PT1000 sensors for heating system.

Thread Starter

Koen568

Joined Jul 22, 2021
1
Hi all,
I'm new to this, have some knowledge of electronics.
I want to read 24pcs PT1000 sensors to automate my home heating system.
Outputs are some relays switching the 220VAC pumps and valves.
My questions:
1) I made a design Whitestone bridge with cd4051 to switch sensor. Will this work as I draw it, what can be done better?
2) I putted a Arduino due in as this has 12bit ADC onboard and is fast controller. Are there better choices?
3) I want this this to be connected to my internet (preferable wired) so I added a ENC 28j60 board.
4) goal is that this runs on it own and send data to IOT tool or database (I want graphs of changes,...)

1626953226907.png
 

bassbindevil

Joined Jan 23, 2014
171
You might be better off with digital sensors like the Dallas DS18B20; but unless you buy the sensors from a vendor like Digikey you'll be getting fakes, which are less accurate and less reliable but are also a fraction of the price. A bunch of DS18B20 can be hung off one Arduino (or Pi) input and addressed individually.
For the control software and stuff, consider Pihome and a Mysensors network. Arduinos running Mysensors read the temperature sensors and activate relays to control the valve actuators, communicating over wireless or ethernet or RS485, all under the supervision of a Raspberry Pi running Pihome. The main problem I've encountered is that (last time I checked), Pihome doesn't handle Arduino nodes that combine temperature sensing and actuators (zone controllers), unless maybe you dig deeper into the underlying code, which I'd rather not do. Pihome software is free, you get the download link after buying it for 0.00 Euros in the shop.
https://www.pihome.eu/
https://www.mysensors.org/
 
Last edited:

andrewmm

Joined Feb 25, 2011
1,752
Hi all,
I'm new to this, have some knowledge of electronics.
I want to read 24pcs PT1000 sensors to automate my home heating system.
Outputs are some relays switching the 220VAC pumps and valves.
My questions:
1) I made a design Whitestone bridge with cd4051 to switch sensor. Will this work as I draw it, what can be done better?
2) I putted a Arduino due in as this has 12bit ADC onboard and is fast controller. Are there better choices?
3) I want this this to be connected to my internet (preferable wired) so I added a ENC 28j60 board.
4) goal is that this runs on it own and send data to IOT tool or database (I want graphs of changes,...)

View attachment 244139
The problem I for see with this design , is noise

The sensors you have, have a very low voltage that has to be amplified,
Amplification , amplifies any drift and noise picked up
If as I read it, this is around a house , then its likely to mean long cables to the sensors

An active sencors , can give out a much higher voltage, or even a digital signal that can be less noise sensitive.

If you have long wires on the sencors, your other worry is ESD

For a quick job it should be OK,
but for a long term project, then you need to put ESD / over voltage protection on the IO of the board.

Generaly , make the thing as robust as you can,

Re arduinos
there are rugged version available
https://www.rugged-circuits.com/
 

crutschow

Joined Mar 14, 2008
27,691
PT1000 sensors are very accurate but as noted, they require precise detection circuits and have a very small resistance change (and thus signal change) with temperature making them sensitive to noise, and would seem to be overkill for your requirements.

Look for solid-state analog or digital output temperature sensors, depending upon your preference.
 

Marley

Joined Apr 4, 2016
416
I would have a dedicated IC for each PT1000 sensor. This would correctly provide each sensor with the correct current and apply the correct linearisation. Something like the MAX31865. Then interface the sensors digitally with their /CS inputs.
You can purchase these already mounted on a PCB with all the correct connections and terminal blocks. For PT1000 sensors, change the "R ref" resistor to 1k00. There are cheaper Chinese copies on Ebay.
 
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