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Thread: Hot Water via Immersion Heater

  1. #1
    Automated Home Ninja Andrew Millne's Avatar
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    Default Hot Water via Immersion Heater

    Currently I'm using a combination of a gas AGA and Immersion heater for hot water. I'd like to control the immersion heater using Cortex but would also like to get some feedback from the tank when it is up to temperature. Are there heating elements available that will allow me to get this feedback, perhaps one that will provide an analogue output for use within Cortex?

  2. #2
    Automated Home Sr Member n07tv's Avatar
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    Andrew,

    You can probably use a basic thermocouple attached to an interrface which will give a linear proportional voltage output. I have seen some that do 4-20mA but others with 0-10V outputs. This can then be fed to an analogue input module such as QAI.

    You may need a little searching around as most thermocouple liquid sensors are for such purposes but more industrial, RS may be a good start.

    Cheers,
    N.

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    Automated Home Legend Karam's Avatar
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    Not sure what type of tank you have but the few bog standard older ones that I've seen (no jokes please) tend to have a thermostat touching the surface through a cut out in the insulation. I suppose a simple thermistor placed in a similar fashion (and then re-covered with insulation) might give a good enough proxy. This can be directly wired to the inputs of an analogue input module with suitable resistor to the regulated supply output terminal making up a voltage divider. A hot water object already exists in Cortex to allow different temperature setings at different times of the day.

  4. #4
    Automated Home Ninja Andrew Millne's Avatar
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    Thanks Karam, I'll give that a go. I didn't put any analogue input modules on my recent order so I'll leave it for now until the next installation round.

  5. #5
    Automated Home Legend Karam's Avatar
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    Ok, if you think this method could be suited to your tank we can help by providing a sample thermistor which I think might have a suitable range. You can then use this to see if you can get sensible (indicative) data just by doing some simple measurements with an ohmeter.

  6. #6
    Automated Home Ninja Andrew Millne's Avatar
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    Whoops overlooked this thread. Thanks Karam, The tank is an old copper one that has been wrapped with an insulating jacket so there shouldn't be any obstacles in the way of fitting.

    My dad suggested via skype chat that... "Ideally you'd use some discrete comparators and maybe a couple of FET switches but I bet you could get pretty good results with aforementioned components and a little software to self calibrate"

    Now I've no doubt he knows what he's talking about but when asked questions like this he tends to start talking to himself and it makes it quite difficult for the lay person to get any kind of practical applications out of him.

  7. #7
    Moderator toscal's Avatar
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    Can the Idratek system handle the one wire temperature probes such as the DS18S20. Also if you look on the maxim-IC website you may be able to get a free sample. http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2815. If it can't handle them directly then there are a few one wire to rs232 interfaces available which may be a better option.
    http://www.homechip.com/catalog/
    IF YOU CAN'T FIX IT WITH A HAMMER, YOU'VE GOT AN ELECTRICAL PROBLEM.
    www.casatech.eu Renovation Spain Blog

  8. #8
    Automated Home Legend Karam's Avatar
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    No IDRATEK does not have an interface to 1 wire, however we do use I2C or similar for some onboard devices eg. temperature sensor. Though not intended for long runs I2C will probably be ok for a couple of meters of shielded cable. Its possible, but we're talking DIY job on one of the DTS modules here . If the thermistor route is used then there are already thermistor linearisation mappings for Cortex analogue input object, so you plug in specs. and should get a reasonable result without calibration - certainly I would have thought sufficient for the job. Afterall there's probably not much point having high accuracy at the sensor when the measurement is itself a bit of an estimate of bulk temperature inside. If you do use a DIYed DTS then you get 0.03125C resolution and +/- 0.5C accuracy up to 70C and a little worse up to 125C. More than sufficient I'd say ... If you don't need an analogue input module for any other signals then perhaps the DTS route has some attractions - its just potting the sensor in something sutable that's the fiddly bit.

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