Rain sensor with snow.

[Gina]

Tried to post a diagram but it came out far too big I'll have another go later.

[beteljuice]

BTW - for those of a mathematical bent - the spoon 'size' of the Fine Offset rain gauge is 0.2794mm

Although I would still expect you to have to do a few tweaks if change your 'collector' size.

[Gina]

Here are the two different funnel arrangements. The small funnel is what I have now but I'm going to use the large funnel instead and have a wood preserver container which will fit between the top of the large funnel and the flower pot. I could then put a heater in that. I can insulate the container with polystyrene wall insulation (sort that goes between wallpaper and wall). If freezing up of the rain gauge is a problem, that could also have a heater.

Small-Funnel.png

Large-Funnel.png

[Gina]

Modified design for rain gauge with the large funnel. The outer casing is now a plastic bucket that wood preserver came in. By cutting half the spout off the funnel it will fit nicely above the rain gauge with it's top bit sitting in a large hole in the bottom of the bucket.

Rain_Gauge-3.png

[Gina]

Here's a photo of the finished rain gauge (sitting on a little table). See see attachment for cross-section.

Rain_Gauge-4.png

[Repairman77]

Interesting Gina; I may do something similar when the weather improves.
Incidentally what have you set the multiplier (or strictly speaking divisor) in Cumulus to in order to calibrate?
Mike.

[Gina]

I have the rain multiplier set to 0.33. Sometime I want to get a measuring cylinder and take manual readings to compare. The catchment area is about 4 times the original and I've included a factor of 30% low standard reading from what those who've made manual measurements have found. This gives 0.33 or one third rather than a quarter. I think the right value will probably be between 0.25 and 0.33.

One thing I've noticed is that changing the "multiplier" does not change previous data so you can change your rain gauge and the multiplier (at the same time) and everything will be fine Good thinking Steve

BTW - the"Rain" reading is actually snow melt.

[RCE]

BTW - the"Rain" reading is actually snow melt.

Which is why I have changed most of my stuff to read precipitation rather than rain.

The heater seems to work well, will make a separate post with details as soon as I get a few minutes.

Only thing I did find was that loading the unit with snow, all the snow melted from on it but no rain reading, think the slow melt must have meant it evaporated before reaching the mechanism. We have had some more snow, and some sleet and it seems to measure these fine.

[Gina]

That snow melt today was from natural thawing - I haven't built my heater/thermostat unit yet - waiting for some parts. I don't think it will want much heat. My thermostat and heater runs off 12v and uses an NTC bead thermistor as temperature sensor with a 741 op-amp used as a comparator, to switch current on and off in a ceramic resistor. I'll post the circuit diagram tomorrow.

[RCE]

What value resistor you going for, I have found my 8 ohm ceramic running from an old 5v power supply gives plenty of heat (just over 3W).

I reckon for places regularly hitting -10 probably 6W would be the aim, I would split that over two resistors.

One thing I haven't needed is temperature control, mine is effectively under proportional control using my PC and home automation stuff and only comes on for part of each hour depending how cold it is.

[Gina]

What value resistor you going for, I have found my 8 ohm ceramic running from an old 5v power supply gives plenty of heat (just over 3W).

I'm using a 33 ohm ceramic resistor which will give about 4W (with 12v supply).

[beteljuice]

As a matter of interest, found this on the Austrailian BOM site.

They do like to simplify things

Snow Intensity

Light:Gives a water equivalent of up to 2 mm per hour.

Moderate:Gives a water equivalent of 2.2 mm to 6 mm per hour.

Heavy:Gives a water equivalent of more than 6 mm per hour.

Maybe they only have one 'kind' of snow

[RCE]

As a matter of interest, found this on the Austrailian BOM site.

They do like to simplify things

Snow Intensity

Light:Gives a water equivalent of up to 2 mm per hour.

Moderate:Gives a water equivalent of 2.2 mm to 6 mm per hour.

Heavy:Gives a water equivalent of more than 6 mm per hour.

Maybe they only have one 'kind' of snow

Maybe never even seen snow

[Gina]

Thermostat/heater circuit diagram attached The thermistor is a NTC type and obtained from Maplin. The resistance quoted is at 25C. At around zero (freezing) it is 50K for this one. The variable resistor sets the temperature at which the heater switches on. The 270K resistor provides some hysteresis so that it switches cleanly and doesn't switch on and off too frequently. Without hysteresis, the transistor in series with the heater resistor, would turn on gradually and dissipate too much heat and fail.

[RCE]

Thought I would report how things went as we had a bit of snow yesterday... heater was a great success

I recorded 5.7mm of precipitation yesterday, with another 0.3mm overnight.

I keep an eye on another private weather station near me, his station showed 0mm yesterday and 6mm today coinciding with a quick thaw starting (we haven't had any rain today).

Well chuffed.