Measuring Ground Frosts

[Backtrack]

'Temperature measuring range -25°C to +50°C'

You had a minimum temperature of -15c this year, and that's air temperature. There may be times when ther grass low goes below that -25c mark and it doesn't read.

[Terminal Moraine]

'Temperature measuring range -25°C to +50°C'

You had a minimum temperature of -15c this year, and that's air temperature. There may be times when ther grass low goes below that -25c mark and it doesn't read.

That's very unlikely. Even with an air min' of -15c over a snow surface I wouldn't expect the grass ( snow ) min' to be lower than about -19c. To get a grass min' below -25c you'd be looking at an air min' of lower than -21c which would be pretty unusual even where OON lives.

Edited September 5, 2010 by Terminal Moraine

[Osbourne One-Nil]

Not quite true...I remember my wife once tried to cook a microwave meal for me, as a treat, and I think that was around -25º when she served it up.

I've found the perfect holder for the thermometer. It's the former holder for a green laser I used to attach to my telescope...a bit like this...

.

Because it's adjustable at both ends, it's perfect for ensuring the bulb end is lower than the other, yet still grips it tightly, without causing any shelter at all.I've simply taken off the flanged bottom plate, so it sits flat on the lawn, almost exactly 2" above the ground. Seeing as I cut my lawn to 1.98", this is perfect.

Edited September 5, 2010 by Osbourne One-Nil

[Terminal Moraine]

so it sits flat on the lawn, almost exactly 2" above the ground. Seeing as I cut my lawn to 1.98", this is perfect.

Take note! This is the sort of attention to detail and accuracy we should all strive to achieve, it brought a tear to my eye just reading it.

[Osbourne One-Nil]

You're never alone with a lawn.

I'm glad I didn't leave it out on Sunday night as a hulking huge branch fell from my Ash tree and landed precisely where the thermometer would have been. I guess on windy, mild nights, there's nothing to be gained from leaving it out anyway is there?

[Terminal Moraine]

You're never alone with a lawn.

I'm glad I didn't leave it out on Sunday night as a hulking huge branch fell from my Ash tree and landed precisely where the thermometer would have been. I guess on windy, mild nights, there's nothing to be gained from leaving it out anyway is there?

Well there is if you want to know the mean grass minimum for the month. And what about those occasions where the night starts off mild and windy but turns clear and cold later on? You could miss quite a few of those late night ground frosts.

I have to agree, though, that on this occasion it was fortuitous that you hadn't put the thermometer out.

[Osbourne One-Nil]

Well, I suppose that branch can't fall off again.

[Osbourne One-Nil]

Well, a combination of my youngest daughter and a dog means that the thermometer lasted less than a fortnight.

[Terminal Moraine]

Well, a combination of my youngest daughter and a dog means that the thermometer lasted less than a fortnight.

I can forsee that measuring ground frosts could become quite an expensive hobby.

[Osbourne One-Nil]

I'm certainly not going to replace it like for like. I might lower my standards and get one of these, because at least a probe isn't sheltered like an plastic-cased electronic sensor is.

http://www.metcheck.co.uk/acatalog/K14_In_out_minimum_and_maximum_thermometer.html

[Terminal Moraine]

I'll be interested to hear how you get on with that. Is 3m of cable long enough to be able to site it properly, presumably the base unit has to be somewhere indoors?

There's also the added advantage that, when your youngest daughter is allowed out of the coal house, she can help you site it and thereby gain a sense of ownership.

[Osbourne One-Nil]

I've got a waterproof housing which the unit can sit in and the probe can pop out through the rubber grommet. Good idea about letting Damienetta help place it, but not as good as your idea about putting her in the coal bunker.

[Osbourne One-Nil]

My new thermometer has come. It's German-made and was wrapped in brown paper; the sign of a quality product I think.

The probe is on the end of a 3m length of wire, so as it is, I could place the electronic display unit inside the log store and run the probe into the rabbit's grass area. However, as illustrated on the photos, this isn't the most exposed area of the garden. I was wondering though, seeing as the wire is just plain old bell wire, if I couldn't simply extend its length, so I could still house the unit under cover, but actually have the probe in the middle of the lawn? Do you think this would work? By extending it, would I alter the resistance and therefore the readings, or are the readings taken at the probe itself and merely carried down the wire to the unit? Am I making sense?!

[Terminal Moraine]

My new thermometer has come. It's German-made and was wrapped in brown paper; the sign of a quality product I think.

The probe is on the end of a 3m length of wire, so as it is, I could place the electronic display unit inside the log store and run the probe into the rabbit's grass area. However, as illustrated on the photos, this isn't the most exposed area of the garden. I was wondering though, seeing as the wire is just plain old bell wire, if I couldn't simply extend its length, so I could still house the unit under cover, but actually have the probe in the middle of the lawn? Do you think this would work? By extending it, would I alter the resistance and therefore the readings, or are the readings taken at the probe itself and merely carried down the wire to the unit? Am I making sense?!

I think you might alter the resistance and therefore the readings but I'm basing this, not on personal experience or on expertise in the field of electronics, but on stuff I've read relating to other sensors and the limits of cable length.

I've no idea how much you would have to lengthen the cable to increase the resistance sufficiently to affect the readings but I'll bet there's someone on here who does.

If you haven't had a satisfactory reply by the weekend I'll ask my son, who does know about these things.

[Osbourne One-Nil]

Thank you sir, you're a gent. Someone wrote that I was a gent once, on my car, but their spelling was awful.

My guess is that once extended it will either work or not work, as I suppose the probe itself houses the thingamyjog that measures the temperature?

For now, at least, I can place it in the lawn and protect the sensitive part. It does have a plastic cap on the end of the probe, but I'm not sure if it's metal beneath or bare wires. I might just leave alone!

[Osbourne One-Nil]

Here's the new set up. I've put the electronic part in a waterproof case I've got for keeping my Blackberry safe when I'm on site in the pouring rain. Then, out of the bottom comes the cable with the probe attached to a tent peg just above the grass. If it gets really cold, I'll wrap the electronic bit in bubble wrap. I could even put it in a little guinea pig igloo I've got in the shed.

[Backtrack]

-Removed by Backtrack-

Edited September 18, 2010 by Backtrack

[Terminal Moraine]

I asked my son about this at the weekend and really should have written down the answer as I have already forgotten the details of the electronics involved.

Best summed up as, you would be unlikely to be able to extend the cable very much without compromising the readings as the change in current required by the sensor to register a 0.1c temperature change would be very small and would easily be affected by a small change in resistance.

He did suggest contacting the manufacturers technical department for further advice as to exactly how much you'd be able to extend the cable, which seems like a good first step.

[Osbourne One-Nil]

Thank you sir, and don't worry about forgetting precisely what he said...I forgot my phone and wallet were on the roof of my car at Sleaford and only remembered when I got to Worksop.Needless to say, they weren't there any more.

I think I might be able to get away with the current set-up. It's completely waterproof and the probe can reach into the middle of the lawn. Perhaps when I buy another one, because my daughter's used it for a skipping rope...perhaps I'll try it then?

[Airedalejoe]

I've got a Davis Vantage pro cabled. The temp seems to 'spike' particularly in sunshine. Is this set up the cause, ie. the heat from the fence and decking plank!!

Can't put it in the lawn due to spoiling the footy pitch!

Would I be better getting an alloy pole/mast to use as a bracket from the fence?

[Osbourne One-Nil]

You wouldn't want it on the lawn anyway as the Met Office preferred temperature readings are taken at about 3ft 6" I think? The rain sensor would be better at ground level though, but I guess it's a slight compromise? See the other thread about your pole.

[Terminal Moraine]

I've got a Davis Vantage pro cabled. The temp seems to 'spike' particularly in sunshine. Is this set up the cause, ie. the heat from the fence and decking plank!!

Can't put it in the lawn due to spoiling the footy pitch!

Would I be better getting an alloy pole/mast to use as a bracket from the fence?

The standard height above ground level for the thermometers ( sensors ) is 1.25m. Does the temperature always 'spike' in sunshine or is the effect more noticeable when there's very little wind?

It could well be that you're getting background radiation from the fence, and also from the twigs of the bush which will help to restrict free air movement.

If you can't site the equipment out in the open you could try any or all of the following;

Move the sensor away from the bush using its existing support

Move it away from the bush and mount it on an alloy pole

Paint the fence (and the sensor support) gloss white in the area where the sensor is mounted. One whole panel painted white would be enough, this would virutally eliminate background radiation from that area.

In any event move it away from the bush, you'd be amazed how much the twigs will affect the temperature reading in full sunshine on a still day and also how much they'd restrict radiation on a cold, clear night.

[Airedalejoe]

Thanks for the replies men.

In relation to the lawn I didn't mean literally lying on the lawn!! I meant I can't mount it on a pole on the lawn or the little un would kick the living daylights out of it during one of his footy games!! It would solve my problem though!

TM, that's what I suspected re the bush, maybe I could move it away from the bush for now as the footy is abandoned due to snow, then worry about where to site it come spring!

As for painting the fence, I've been told I've got two hope's.......

Cheers anyway.

[casparjack]

My impressive mast is the talk of the Eden Valley. It's just an aerial mast I got from the local TV shop with the only additional costs being some expensive therapy after being so high up a ladder, and a new pair of pants.

It's been up for three years now, I think, and I've never had to change its battery yet. It also transmits unfailingly to the console inside, which is on the opposite side of the house.

I too have the remote transmitting anemometer and my battery has lasted since September 2006 - clearly the solar panel is pretty effective - having said that I'll now probably get a 'low battery' warning!!

I found a site that sells the replacement lithium CR123 batteries in bulk for about £1.50 each, as opposed to £6-7 in the newsagents as my other remote sensors, the Davis temperature stations you were discussing above, literaly 'eat' them.

I have two temperature stations one for grass min (I too am obsessed) and one measuring 30cm soil temperature, it's gripping stuff this meteorological recording...