Topic: Differences between Davis Temp Probes?

[JohnN]

The temperature probe I had in my pool went bad, so I'm looking to replace it. I see Scaled Instruments has 3 different options with a wide price range, so I'm wondering what the difference is between the 3 and why I'd choose the most expensive probe over the cheapest one. I can see the basic differences that one is sealed in plastic while the others are stainless steel and one is two wires while the others are RJ-45 connectors, but I don't see how those justify the price differences.

[johnd]

The 6470 non-RJ11 one has sturdier cable suitable for burying is one difference.

[JohnN]

I have a pipe buried that I run the wires in, so I think any wire should be suitable in my case.

[azchrisf]

They are all 10k NTC thermistors.
If you want to save money and have it work like the Davis plug and play,
You can find them in a lot of places.

Here for example:
https://www.ebay.com/itm/383709719796

I’ve used a few of these to replace the Davis ones that have gone bad on my soil stations.

[JohnN]

They are all 10k NTC thermistors.
If you want to save money and have it work like the Davis plug and play,
You can find them in a lot of places.

Here for example:
https://www.ebay.com/itm/383709719796

I’ve used a few of these to replace the Davis ones that have gone bad on my soil stations.

Something like that looks perfect. I was thinking of buying a generic one but wasn't sure the exact specs, and didn't know where to find the resistance range for the Davis ones.

[doubleohwhatever]

Keep in mind that NTC thermistors from different manufacturers have different response curves.

10k NTC thermistors are usually centered around 25C. So two sensors with different response curves will have a similar output within a few degrees of center (25C). However, they will diverge the farther you get from center due to the different response curves.

Take a look at the second page in this Davis datasheet to see what I'm talking about:
https://www.davisinstruments.com/product_documents/weather/spec_sheets/6475_6477_SS.pdf

[azchrisf]

That is correct. Most are but some aren't.
Make sure the centerpoint is 25c.

[azchrisf]

JohnN,

I'm gonna caution on this, even though these will work in most situations since yours is always submerged in water that's probably a case where the Davis might be sealed a little better for that need vs. the generic ones. Eventually though, water will find a way past the potting material and get into the sensor no matter what brand.

If your OK with replacing these sensors every few months (they are so cheap if you find them in bundles) you'll probably save money in the long run, but at the cost of having to replace more often. I'm not saying that WILL happen but it's a definite possibility if they are 100% submerged beyond the top of the metal case.

[JohnN]

I found a 5-pack on Amazon for $10 that I'm going try. Couldn't find the spec sheet so I'm not sure if they'll match the Davis, but for $10 it's worth a shot. This Davis one lasted around 2 years I think, so even that doesn't seem to have the longest life anyway. So even if I have to replace them every few months, I'll probably still come out ahead of replacing the Davis every 2 years.