Need to detect sudden increase in temp

[Chris Pitman]

When i did the shower I fitted a 1 wire temp sensor to the mixed flow pipe (out) of the mixer to detect when shower was in use, thought it would be more reliable than a flow switch but logic is a lot harder. 

Anyone got an idea how to detect a temp increase over a certain time?

Basically if the temp increases say 2deg in less than 30 seconds switch output.

[Duncan]

Will a threshold temperature not pick up the shower being used eg >35 degrees?

[Rydens]

Hi, I used threshold to detect hot water, but then found as my sensor is in the loft on a hot day in the summer it triggers!

So I now use analogue memory, which takes in a value and holds it for x seconds - so I can compare rate of increase.

Hopefully my logic is attached

Cheers David

[Chris Pitman]

Thanks for the help.

Will have a play around with the ideas

Ryden - had a similar problem with temp sensor first person to shower works fine, but second person may not cause a trigger as temp not dropped enough but looking for a quick increase in temp using the analogue memory should work.

[Rob_in]

TBH, taking a difference from 30s ago doesn't sound that great for accuracy. It might work and if it does, stick with it, but...

I actually do a similar thing with humidity and built something like this: Read the sensor every 10s then feed that into a chain of 6 analogue memories that cascade values through each other every 10s. Use a comparator block from the last of these to the input (live) value. This way you get a 1 minute delta that is updated every 10 seconds.

Yeah, maybe this is slightly over-complicated by then again I am a developer ;)

Cheers,

Rob

[Tico]

There’s an image in the attached link that depicts the analogue memory cascade concept. This works well for both On (heating) and Off (cooling).

https://www.loxforum.com/forum/hardware-zubeh%C3%B6r-sensorik/205326-welchen-automationsluxus-habt-ihr-im-bad-verbaut?p=205449#post205449

[Rob_in]

Interesting. I assume that works, but I created 6 different pulses each 0.1s after the other to make sure they cascade properly. Again, that's the dev. in me :)