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Emonpi temperature monitor sensor Ω

Hello all,

My brother has one emonpi and he wants to measure the temperature of the solar thermal panel.
He talk with the local installer about sensors he could use to monitor and the local installer asked what Ω have emonpi and ds18b20.
From what i have reading but never get sure, DS18b20 has 100Ω, am i correct?
Can you give-me an idea of what sensors could i connect to emonpi or if the ds18b20 is suitable for my purpose?
This is the type of solar panel that my brother has.( but not the exact model).
It has integrated water reservoir inside it.
If it would be me, i would use a esphome node-mcu with compatible sensor to transmit to emonpi by mqtt but my brother wants everything integrated, so why i ask this.

Thanks in advance!

The local installer clearly expects the DS18B20 to be a resistance thermometer. It is not, the output is a DIGITAL SIGNAL representing the temperature. He cannot connect it to anything other than the One-wire input of an emonTx or emonPi (or an equivalent device).

Your brother should ask the installer to fit a “pocket” - a short tube with a sealed end, which will be surrounded by the hot water - into the system, then your brother can insert the temperature sensor into the pocket (with some silicone grease to transfer the heat) and take the wires back to his emonPi.

I’ve found some pictures:
Here (yellow) is the emonPi asking the sensors to read and “convert” the temperature into a number:

and two sensors replying with their temperatures (with a different time scale):

(The blue is just a digital output to trigger the oscilloscope.)

Or to put it another way - the DS18B20 is a digital device. It is not an analog, i.e. resistive measurement device which are commonly used on solar thermal panels.

But as Robert says, just place it in a pocket, or alternatively with some insulation around it on one of the pipes into or out of your solar thermal system and the emonPi or emonTx will read the temperature and you can log it.


Thank you all for your answers.
I didn’t understand why the local installer asked that but now i know why it doesn’t work. Thanks @Robert.Wall for the graphics to help me understand it better!
i will ask him if the solar panel has that pocket in it, but another option suggested by my brother and by @Bramco is to, in case of doesn’t have a pocket, and to avoid drilling the panel, to place it in touch with the pipes.

Thanks for your help @Robert.Wall and @Bramco!
Helped me alot!


If the panel has the resistance thermometer fitted, then that is probable fitted in a pocket already. Our sensor is 7 mm diameter over the heat-shrink sleeve that gives a water-resistant seal.

Look at ‘Learn’ for notes about long wiring back to the emonPi.

Already did when i was looking for the Ohm values. And i was able to check for allot other things too that i didn’t know.

If the panel has the resistance thermometer fitted, then that is probable fitted in a pocket already.

From what my brother said, it doesn’t have a resistance thermometer.
But i will ask the local installer if does have a preinstalled pocket to install the sensor.
Either way, its good to know that we have an alternative for the place we will use for the sensor, just in case…
I am planning to install one in my house in a couple of months so, it will be useful for me too.

Thanks @Robert.Wall


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