Water Resistant Temperature Measurement

Hi there,

What's the best way of measuring ambient temperature but having some sort of water resistance (splashes, etc, not necessarily waterproof, although it could be). The trick here is that I would prefer a surface-mounted temperature sensor, and if I have a plastic enclosure around it this means that there will be some thermal resistance since the air is trapped inside the water resistant enclosure.

Here are the options:

  • Let's say that using an external probe (like the waterproof DS18B20 sensors) is not an option for now.
  • If I poke a hole in the enclosure near the sensor, it will allow air to flow through but will no longer be water resistant.
  • Is there some sort of mesh that is water-resistant but lets air through? Kind of like the ones they use on the Samsung Galaxy phones for their microphones and speakers that are waterproof.
  • Is there a small temperature sensor that allows panel mounting (mounts in a hole in the enclosure) and has a very short metal casing, unlike the DS18B20's very long metal tube? This would allow me to make a hole for it and epoxy it in place.
  • I was thinking to get a through-hole sensor (standard TO-92 3-pin package or similar) and bend it at a right angle so that the head barely sticks outside a cutout on the side of the enclosure, then epoxy it. Could that work?

Thanks!

EDIT:

  • The sensor shouldn't be very expensive, like IR temperature sensors.

What about infrared temperature measurement?

MK1888:
What about infrared temperature measurement?

They're really expensive compared to traditional temperature sensors.

androidfanboy:
They're really expensive compared to traditional temperature sensors.

Then let's add your budget for sensors to the options.

Paul

Epoxy-coated thermistors are the most accurate and one of the cheapest methods to measure temperature.

Then there's a thermocouple.

Pick one.

http://www.yourduino.com/sunshop/index.php?l=product_detail&p=151

On the downside the 18B20 is less desirable than the 18B30.

I'm not affiliated with this store but have bought parts there. Due to shipping charge I buy more than a couple of bucks worth of parts, it's not free shipping. But look at the parts prices, especially chips at 5/$1 prices, a lot of those can be added without raising the shipping price.

OTOH there is ebay where you might find the same or similar with free shipping.

Use whatever sensor you want. Drill a hole and stick it through. Then a little dab of silicone to fill the hole. Waterproofing done.

I bet that a thin metal covering will insulate the sensor less.

For a surface mount sensor, I would build it on a breakout board that can be attached to the side of the enclosure. Then use a small brass screw through the enclosure to touch the temperature SMT sensor via thermal compound. The small the screw, the faster it will react to temperature changes. The trick will be aligning the (tiny) SMT sensor with the screw so nothing shorts out.

For a through hole sensor, drill a hole in the enclosure and expose and mount the sensor to/through the hole. Not really an external sensor (ie., dangling by a cable). If using the smooth sides variety, then epoxy in place (and hope it stays) or use the (smallest) threaded version and thread the hole in the case. With either method, mount from the inside so the working end sticks out.

Thanks guys! I think I'll end up using a through hole sensor and stick it into a hole flush with the surface of the enclosure, or an epoxy thermistor. With the thermistor in a voltage divider configuration, could I switch the positive voltage with an Arduino digital pin to reduce current?

Can... but thermistor + pull-up resistor = about 20 kOhm resistance for a typical 10k thermistor, or about 0.25 mA on 5V, and 0.185 mA on 3.3V. Is that really an issue? You can easily reduce this by a factor 10 by using a 100k thermistor and 100k pull-up resistor (assuming your temperature changes slowly, fast changes the ADC won't be able to follow with these resistances). There exist even higher nominal resistance NTCs.