Rain Sensor

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  • chris_j_hunter
    Automated Home Legend
    • Dec 2007
    • 1713

    Rain Sensor

    'been a bit wet lately, and wondered about having a rain sensor in teh system. There seem to be three types available, any of which might do the job (see below), with various obvious pros & cons. Anyone tried one, by any chance ?




    Rain sensors ... for irrigation systems are available in both wireless & hard-wired versions, most employing hygroscopic disks that swell in the presence of rain & shrink ... again as they dry-out - an electrical switch is in-turn depressed or released ... some ... use tipping bucket or conductance type probes to measure rainfall ...

    Nowadays, rain sensors are integrated in a system to automatically start the windscreen wipers ... the most common rain sensor implementation is based on the principle of total internal reflection: an infrared light is beamed at a 45-degree angle into the windshield from the inside, near the lower edge - if the glass is wet, less light makes it back to the sensor, and the wipers turn on.
    Our self-build - going further with HA...
  • Karam
    Automated Home Legend
    • Mar 2005
    • 863

    #2
    I think popular ones tend to be just conductance based. I'm guessing that alternating the current direction and applying enough current to slightly warm the conductors might be the only other tweaks to apply, but I really am guessing here so someone can let me know when they've done the research :-)

    So perhaps a suitably tinned pcb and a tweaked DIO module?

    Karam

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    • chris_j_hunter
      Automated Home Legend
      • Dec 2007
      • 1713

      #3
      having Googled & Googled for rain sensors, I found these :



      Rain Sensor ... avoid unnecessary wastage ... £22.95 Code: 570161

      Suitable for use with ... Water Timer ... avoids unnecessary wastage ... when rainfall reaches 5mm, programmed watering shuts down, resuming when the water in the sensor evaporates. Install outdoors in an area exposed to rain up to 2m (6'6") from the timer using the stainless steel bracket provided.

      and :



      The Mini Click II is the best-selling rain sensor in the world ... measures rainfall through moisture absorbing (hygroscopic) disks ... no collection cup to clog up ... requires no regular maintenance ... set the sensitivity to allow 1/8, 1/4, 1/2, 3/4 or one inch (25mm) of rain to fall before it switches the system off ... housing is made of UV resistant thermoplastic, and the mounting bracket is aluminium ... unlike sensors that are buried in the ground to measure soil moisture, the Mini Click II will not get in your way ... mounted safely above ground, often on the side of a building ...

      RS24 - Mini Click II @ £33.62 +VAT

      ... primarily to prevent water draining back from your system into your household supply ... can be used to stop water flow unless a preset pressure is reached ... can be set to open at any pressure, from 1.7 to 14 psi ... useful on overhead irrigation systems ... prevents water held in the suspended pipe work from leaking through the emitters after operation ... install it in-line just before the first outlet for maximum effect ... also for 13mm systems to prevent water retained in pipework from draining down slopes & causing flooding, through spray heads, pop-ups, etc ...

      HCV - Hunter Check Valve @ £6.38 +VAT

      [Garden Irrigation Supplies, Withytree Farm, Broadway Road, Near Winchcombe, Gloucestershire, GL54 5NT ... tel: 01242 604 604]

      plus, there was mention of something on the Velux web-site, but no details ... !

      From what I've read, while Googling, the hydroscopic ones seem reliable & very common. My only experience is of the one in the car, which presumably works by the IR / internal reflection method, and it has been very effective for seven-years (compeletely reliable, sensitive, and clearly giving information on amount of rain, because 'wiper operation varies automatically according to need) ...

      Also found some weather-station types, all of which seemed less good, sometimes because they would be difficult to inteface, but always because (or so it seemed to me, anyway) they might be too-easily overwhelmed by the downpours we have & they would / might need regular attention (emptying, leaves, etc).
      Last edited by chris_j_hunter; 15 March 2008, 09:33 AM. Reason: missed words & a few typos !
      Our self-build - going further with HA...

      Comment

      • Kevin
        Moderator
        • Jan 2004
        • 558

        #4
        I've been looking too ...

        I believe that some of the sensors used in irrigation systems are purposed to reduce the watering cycle times dependent on the amount of rain that has fallen. As such they might be (intentionally) slow to react initially or remain in a hold off state for a longer period afterwards.

        Velux do some sensors that are used to close their windows so I assume they work quickly. I too haven't found much info on these yet though - eg if they can be used standalone.

        The car ones I thought rely on the water droplets being removed from their field of vision by the wipers so probably aren't much use. But then this seems to work without.


        On eBay there are these - which operate much as Karam said and are very low cost...I just bought one so I'll let you know how it works - if I ever get it installed...


        and there is a Finnish company that makes a probably expensive device that looks like a cheese..


        and I found this from Germany - again really expensive looking...


        K

        Comment

        • Karam
          Automated Home Legend
          • Mar 2005
          • 863

          #5
          Chris,

          Sorry perhaps I didn't quite get the gist .. The sensory method I suggested would just tell you that its raining without giving information about rate. So to some extents it may depend what the sensing is for. If you want a quick reaction to rainfall, eg. to close a window, then this type of sensor might be suitable. Whereas for garden irrigation soil moisture content might be better to measure rather than just amount of rainfall, though I suppose one might be roughly inferred from the other.

          Comment

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