How to connect PT1000 sensors to Homey

Questions & Help
1

Hello,

I have a Solar water heater system. But unfortunately the controller did yesterday. I was think, maybe I can do the control via Homey. Does some know how I can connect a PT1000 sensor with two wires to a device that can be used in Homey?

Thanks,
Sjors

2

If you can use an other temperature sensor, then this might be an idea:
https://shop.shelly.cloud/temperature-sensor-addon-for-shelly-1-1pm-wifi-smart-home-automation
Combined with a Shelly 1/1PM and a DS18B20 sensor

3

Thanks, I will have a look

4

Typical devices to connect external sensors are the Fibaro Smart Implant (Z-Wave) and the Shelly Uni (WiFi). Both support DS18B20 temperature sensors, but also analog 2- or 3-wire sensors.
Both devices are supported by Homey.
I donā€™t know, if a PT1000 will work.

5

The Fibaro Smart Implant works well with analogue temperatur sensors like the PT1000, ie. a common type of Platinum Resistance Thermometer (PRT) with 1000 kilo-Ohm resistance at 0 dg C. I connected a simple 2-wire PRT straighforward according to Section ā€œ4.5: Connection with 2-wire 0-10V sensorā€ of the ā€œOperating Manual - FIBARO SMART IMPLANT FGBS-222 - v1.2ā€:

  • Initially I use 12V DC batteries for power supply, connected as per the wiring diagram.
  • The PRT connects to Input 1 (IN1), with Parameter 20 set to ā€œ5 ā€“ Analog input with internal pull-upā€.
  • The ā€œinternal pull-upā€ resistance is simply the temperature-dependent resistance that makes a PRT like this work as intended, I guessā€¦ :wink:

However, the output shows up at the Homey Pro smart hub as a voltage, which I then need to calibrate / convert to a temperature (by figuring out the linear V vs T relationship, which should be straighforward enough):

  • with this PRT the output reads 4,22V at 21 dgC. Measured resistance was 12 800 Ohm at 21 dgC (12.8k).
  • That suggests a modest 1.0 mA of current drawn from my (temporary) 8x AAA battery pack, which should provide for useful battery life, before ā€˜upgradingā€™ to a (permanent) 230V AC to 12V DC adapter.

As far as I understand, while the Smart Implant can handle up to six external Temperature sensors (in addition to the one internal), they must all be digital sensors, of the DS18B20 and/or the DHT22 types.

Does anybody know/ use a better way to capture Temp readings from an existing (built in) PT1000 or similar analogue PRT?
ā€¦without any need for ā€˜manualā€™ conversion from Voltage to Temperature?
ā€¦such that this sensor temperature easily integrates with other temperatures, e.g. when trends are analysed on a Homey Pro Insight plot?

6

I got 10 of these Blebox Tempsensor

I use them for
Hotwater tank/ ventilation/ sauna/ buffer/ pool/ sun heater etc.

7

Did you take into account that the resistance / temperature relationship is not linear?
Pt1000 Resistance Table.

8

Thanks for sharing this insight with the link, Adrian,
as Iā€™d just assumed that the Temp vs Resistance relationship was linear and now stand corrected :wink: Much appreciated!

Two follow-up questions, if you donā€™t mind:

  • I also thought hat a separate ā€œpull-up resistorā€ should not be required when I connect a PT1000 to a Fibaro Smart Implant, in order to measure/ transmit/ record & convert the voltage signal?
  • Given the inevitable voltage drift as my initial battery pack inevitably drains, will there also be drift in the readings of P1000 voltage => temperature ? I had planned to just try the batteries over some time to just see how it perfomed, but perhaps I need to ā€˜just bite the bulletā€™ and ā€˜upgradeā€™ to a (permanent) 230V AC to 12V DC adapter, right from the start?
9

Thanks, Lichtenberg,
That looks like a useful device, which Iā€™ll certainly consider for other applicationsā€¦

For the case at hand, unfortunately Iā€™m ā€˜stuckā€™ with an existing PT1000 sensor embedded into a roof-integrated solar PV system, underneath the PV panels high up on the roof - in other words, not easily accessed/ replaced :wink:

ā€¦so in the first instance, Iā€™ll try to work with the existing PT1000 sensor, connecting whatever is easiest to the pair of sensor wires coming down from the roof :wink:

This as part of monitoring panel temperature vs solar power yield, perhaps also playing with rinsing & cooling the PV panelsā€¦

10

Iā€™m not sure how you have wired the PT1000 in to L1, but as it is a resistance devices you need to pass a current through it via a series resistor to create a voltage drop. I guess the internal pull-up is providing that function (the 1kOhm in the diagram, but Iā€™m not sure what the actual value of it is).
image

Ideally you want a regulated voltage supply to prevent any drift as you mentioned.

11

Aha!
Well then hassio for the rescue:

Theres an excellent Hassio to homey integration from the dear @RonnyW

Do notice that an RPI is kinda golden these daysā€¦

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