Digital thermometer for diving?

[Pitlamp]

I'm trying to source a digital thermometer which will withstand depths of, say, 30 m, read to +/- 0.1 degree C and work in the range 0 degree to 20 degrees C. (I want to swim along two underwater passages with it and determine if they're hydrologically unconnected based on temperature readings.) Oh - and I'm a caver, so obviously it wants to be cheap.

Data loggers probably won't do as I need to read the result there and then (and don't want to have to devote subsequent dives to recovering equipment).

I don't want to buy (yet another!) dive computer which also measures temperature; I just want a thermometer which I can take diving.

Can anyone point me at anything suitable? Thanks.

 

[Cantclimbtom]

I don't drink the koolaid of the Apple cult so this might be way off, but would a recent Apple watch do that? (If you can borrow one). I've heard of people using them as dive computers for rec dives.

Edit: think it must be Apple Watch Ultra https://support.apple.com/en-gb/guide/watch/apd9073c83d6/watchos

 

[IanWalker]

Not sure if this is egg-sucking or not but...

Could you buy a cheap thermometer with remote probe, and then seal the thermometer into a clear box with a gland or resin? Leaving just the wire and probe sticking out? If its not a pressure tight box you could add a shraeder valve and pre-pressurise

Something like this:

Fridge or Freezer Thermometer | Internal/External Sensors 810-225

Dual temperature sensor, Fridge/Freezer Thermometer, records max/min temperatures with large LCD display & programmable high/low audible alarm. ETI 810-225

thermometer.co.uk

 

[Pitlamp]

Thanks both - but I was trying to avoid repurposing other stuff and / or trying to bodge something waterproof. Surely there must be something available off the shelf?

 

[Pitlamp]

Also, the point where the cable goes into the cylindrical sensor proably isn't very waterproof.
I've actually got one of those cheap temperature probes; I think it cost the princely sum of £3-99 and has a very large and clear read out. Reads to +/- 0.1 degree C and I find it very useful for measuring temperatures of surface streams. Did consider potting that but I'd rather just buy the real thing, if possible.

 

[Babyhagrid]

ChillChek Waterproof Thermometer

Ideal for swimming, diving, fishing, and other water sports, this thermometer is designed with a fully enclosed IPX8-rated housing, ensuring it can handle depths of up to 150 feet (45 meters). The ChillChek also comes with a high-visibility reflective break-away lanyard and a durable brass split...

suncompany.com

This is a tenner and designed for up to 45M depth but is analog (no electricity to get wet) so might fit what you need

https://www.scuba.com/p-aquwt/wrist-watch-mount-thermometer?srsltid=AfmBOoouDeU_VOhSeLsMprvB2Hr-WdiKIMmIh2x9lhFzGKlxbJLlGzsl

Or something like this
Although both are on US websites sadly

 

[Blueberry]

Can't you borrow a dive computer that will give you a profile of the temperture along with the profile of the dive i.e shearwatrer perdix

 

[Pitlamp]

Thanks Babyhagrid - was hoping to avoid analogue but I'll take a look. The problem there might be reading with enough precision, as graduations are only every 5 degrees.

 

[PeteHall]

I've just sent you a message with a suggestion, but borrowing a suitable dive computer might be easier if it's for a one off.

 

[Pitlamp]

Thanks for the suggestions Blueberry & PeteHall; yes, I probably could. But I'd not want to keep pestering folk as I'd anticipate the thermometer being used fairly often. I'd much rather buy something simple that just does the job reliably.

 

[Blueberry]

Thanks for the suggestions Blueberry & PeteHall; yes, I probably could. But I'd not want to keep pestering folk as I'd anticipate the thermometer being used fairly often. I'd much rather buy something simple that just does the job reliably.

Yes but being from Yorkshire you should really have said, I need something reliable, simple and cheap.

 

[Ian Ball]

I suspect by the year 2040, Pitlamp will have made everyone aware he is not a Yorkshireman.

 

[Pitlamp]

I suspect by the year 2040, Pitlamp will have made everyone aware he is not a Yorkshireman.

 

[Pitlamp]

That's right; I'm from the left hand side of northern England's equivalent of the Berlin Wall!

 

[langcliffe]

I have as Brannan digital thermometer I bought for hydrological purposes. I've looked at it, and with a bit of sealant I reckon it could be made reasonably waterproof. It only costs a few quid, so it's probably worth trying. I think the main problem would be reading the display underwater.

https://www.amazon.co.uk/Brannan-Thermometer-Traceable-Calibration-Certificate/dp/B09ZHZ5V8P

 

[ChrisB]

I've just been looking at places I've bought thermometers from. There are lot of 'pool' thermometer, that float - I don't imagine anything that floats will really be designed for 30m submersion, irrespective of what it says. IPX7 is only 1m, IPX8 is over 1m but you need to read the specs to see how much over, there's no standard depth after IPX7.

The other thing I think you may need a reasonably rapid response. A swimming pool will only change temperature slowly - I assume you'll want to know as soon as you move into a different flow, not wait minutes for it to stabilise.

On the other hand, you don't need accuracy, just resolution and repeatability. Whether the two streams are 4.5ºC and 5.2ºC, or 5.0ºC and 5.7ºC doesn't matter, you only need the difference, and consistency.

The choice seems to be pool thermometers, which probably don't have the depth rating, or general purpose industrial types, which will be expensive and probably have a much bigger range (eg, up to 200ºC) which you don't need.

 

[Steve Clark]

I don't really have anything immediately useful to add. I've got a Shearwater Peregrine you're welcome to take for some dives. It does live display visible in the dark and data logging. Totally sealed, wireless charging and Bluetooth download. Very difficult to break. It only has a whole digit degree C resolution though.

For interest's sake, there is a tool in the making that is going to make this very easy. Halcyon are currently testing and refining the electronics system for their new Symbios rebreather. This has a miniature HUD unit that mounts directly in the corner of a mask, like a tiny computer monitor with OLED display. You can configure it to display lots of different things, but it will display temperature to 0.1deg, depth and compass bearing. (Plus all the deco stuff and multiple tank pressures).

Write-up for the whole system here : https://indepthmag.com/halcyon-symbios-rebreather/

Specs for the 'near-eye' dive computer : https://symbios.halcyon.net/hud/index.html?cover.htm

As a standalone computer, it will have some significant advantages for low-vis diving. It will be a while before you can get one in the Aldi middle aisle!

 

[PeteHall]

Have a look at your WhatsApp @Pitlamp.
You may have an offer of something made for the job.

 

[Pitlamp]

Thanks for the further information fellas. (Pete - we've swapped WhatsApps now directly.)

 

[Pitlamp]

Just for completeness, quite a few years ago we did some temperature measurements in Hurtle Pot with a liquid in glass thermometer. (For those not familiar, it's a large water-filled cave system where the upstream route descends from zero depth to almost -30 m.) We found that it got "warmer" the deeper we went. (This was replicated on a few occasions.) in fact we concluded that the greater pressure at greater depths (almost 4 x atmospheric pressure at almost -30 m) was probably deforming the thermometer bulb, causing the thread of mercury to extend further up the narrow tube.

I agree with Chris that this wouldn't matter in an ideal world - but it does matter if two passages are at different depths so results can't be compared.

I think we wrote up this little experiment in a CDG Newsletter at the time but it'd take some finding.
Thought it was worth mentioning, so it's on record here.