Northland
Posts: 8
Joined: Fri May 06, 2016 6:07 am

temperature sensor for water heater

Sun May 08, 2016 7:05 am

Recommendations please for a temperature sensor. It will be in contact with the outside of a copper tank with insulation over the top. It will be 30m from the pi. Range 40-80 degrees Celsius but down to maybe 10 would be a bonus. Important : easiest to code (python)

Thanks

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joan
Posts: 14686
Joined: Thu Jul 05, 2012 5:09 pm
Location: UK

Re: temperature sensor for water heater

Sun May 08, 2016 7:48 am

Are there sensors which work with 30 metres of lead? I doubt it. You need to find a way of reading a sensor locally and transmitting the data 30 metres to the Pi.

Northland
Posts: 8
Joined: Fri May 06, 2016 6:07 am

Re: temperature sensor for water heater

Mon May 09, 2016 4:54 am

I thought some were digital so distance is irrelevant?

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rpdom
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Joined: Sun May 06, 2012 5:17 am
Location: Chelmsford, Essex, UK

Re: temperature sensor for water heater

Mon May 09, 2016 5:00 am

Northland wrote:I thought some were digital so distance is irrelevant?
Voltage will drop due to the resistance in the cable.

If it drops too much even a digital sensor won't work correctly.

Having said that, with decent cable a DS18B20 sensor can work over a fair distance, but 30m may be pushing it a bit without some sort of one-wire repeater or signal amplifier.

fruit-uk
Posts: 609
Joined: Wed Aug 06, 2014 4:19 pm
Location: Suffolk, UK

Mon May 09, 2016 5:32 am

1-wire may work over that distance, difficult to be sure without trying and 30m of cable just to test may yield disappointing results.
Take a look at the Dallas 1-wire docs for spec etc. as well as much other online.

An alternative may be to set up a wireless node, with a DS1820 or something else. I am using panStamps as remote sensors here with SI7021 sensors and getting 4-6 months on a single AA cell.
There are many other wireless possibilities of course

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