Posts: 2
Joined: Mon Sep 17, 2012 1:23 pm

Temp measurement

Mon Sep 17, 2012 1:36 pm

Hello, I'm interested in measuring temp in boiler. Inside the boiler is placed sensor called PT100. I don't own a current converter for this device,so is it possible to measure the boiler temp with https://www.adafruit.com/products/381 . The problem is that the I2C bus is limited by lenght. The wires leading to the PT100 are very long.

Thanks a much.
Please exuse my English.

Posts: 96
Joined: Tue May 29, 2012 6:21 pm

Re: Temp measurement

Mon Sep 17, 2012 3:36 pm

Why are you asking about I2C bus? does PT100 have I2C bus? I thought it has just thermistor inside. And DS18B20 has 1-wire bus which can support enough to measure at any point in the house(unless you leave in castle :))

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Re: Temp measurement

Mon Sep 17, 2012 5:09 pm

Also confused as sensor in link is 1 wire interface.

By the way I2C can run some long distances have run it at least 15m, known it to be used for over 50m cable lengths.

You may have to slow the speed of the I2C clock to get the long distance but it works well.
Just another techie on the net - For GPIO boards see http:///www.facebook.com/pcservicesreading
or http://www.pcserviceselectronics.co.uk/pi/

Posts: 108
Joined: Mon Mar 26, 2012 8:14 pm

Re: Temp measurement

Mon Sep 17, 2012 8:24 pm

As others have pointed out, this sensor uses the so called one-wire bus (which is actually at least two wires and preferably three, but that's marketing for you), not I2C. There is a one-wire library available for Raspi, and it is even included in Adafruit's own Occidentalis distro. And yes, a one-wire bus can be extended for quite a distance.

Note though that Adafruit warns against using this sensor at 100°C or over, as the insulation may be damaged. Of course, you want to keep the temperature inside a boiler below 100°C, which brings me to the point I wanted to make: For the love of $deity, if you are messing with boilers, make sure that the safeties are in place. This means at least one overtemperature thermostat or thermofuse, connected in series with the heating element, and a pressure relief valve. Note that local regulations may be even stricter, but this is the minimum common sense safety equipment for a boiler. If you want to know what can happen when the safeties are disabled, watch this: http://www.youtube.com/watch?v=hWnL8SipXT8

Best regards,

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Joined: Mon Sep 17, 2012 1:23 pm

Re: Temp measurement

Tue Sep 18, 2012 3:58 pm

Thanks for advices. Don't worry there are shut off valves. I've got experiences with boilers and heaters. I worked for some time with steam in company providing steam and heat for city. Lot of systems are old, so they are using PT100 with current coverters.They are actualy preatty expensive, so that's why I asked about the dallas sensor. I want to inovate my steam boiler in a house.

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