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PCB Temperature ratcheting mystery

New to the forums, but I’ve been using BlueRobotics products for a little while. Out of curiosity I wanted to post this plot of the PCB temperature of a blue robotics ping unit I have in a pond being used to measure ice thickness.

Initially I was sort of hoping I might be able to use the PCB temperature to get a sense of the ambient water temperature at the depth of the ping, but obviously it’s a bit too warm for that. However, after watching it for a while I’ve gotten a little curious about the ratcheting in temperature that seems to occur. It’s likely not water temperature fluctuations because I am also separately getting a temperature profile of the pond and it looks like this (oops, new users can only post one media item, will post later if people are interested):


and the regularity of it makes me think it’s not sensor noise. Sensor is in pretty much regular, continuous operation. Ideas?

Hello :slight_smile:

Are you pinging continually, or are there some brief periods where you stop pinging for a little and it gets a chance to cool down? It looks like there are sharp drops and then pretty consistent rises, which would be well-explained by short periods of being off/inactive, followed by relatively constant usage (during which the temperature rises and then reaches equilibrium with the cooling energy from outside.

No, constant pinging at ~1Hz. Could be that the Raspberry Pi zero driving takes a brief break though to do other things, but idk, I’d need to look more closely at the logs which will unfortunately have to wait until ice-out.

Is the vertical scale degC? Like really only changing by 1 degC total? Is it continuously in the water, or could the sharp drops be when it goes in the water?

Yeah it’s degrees C. You’re right that overall it’s fairly stable and doesn’t chance by very much, but I don’t think it’s random. The sensor is continuously submerged so it can’t be the result of plunging it in water and taking it back out.

And is the time scale really like 2 days? If so, I’m gonna guess the water temp actually changed - like a plume of slightly colder water comes along once in a while, OR as was mentioned, for some reason the pings are occasionally stopping for a bit. I wrote the Ping f/w and I can’t think of any non-external cause. Interesting phenomenon anyway!

Don’t think it’s water temp. Here is a temperature profile of the water over the same period of time. Sensor 1 is closest to the surface and Sensor 4 closest to the bottom.

It’s pretty much totally inconsequential as far as I can tell, but glad someone else found it interesting to chew on as well!

So, Arctic Ice Project? Would love to learn more about what you’re doing. I imagine other B/R fans would also.

Sure! We’re a non-profit researching ways to safely replace some of the lost reflectivity in the Arctic as a result of ice loss from climate change. We do full scale climate modeling of possible interventions as well as ecotoxicology and field testing to determine safety and effectiveness. Most of our work to date has been with hollow glass microspheres, which is the subject of the test we’re performing right now in Minnesota and the source of the data we’ve been looking at.

As I mentioned earlier I’m using the ping sonar as a part of an instrument we’ve designed to measure ice thickness. In addition to understanding the impacts on reflectivity of an application of this material we are very interested in getting a better understanding of the first order impacts of a deployment of something like this on the thermodynamics of ice melt.

That should cover the gist of it, but happy to answer more questions if anyone has any about AIP or how we’re using the BlueRobotics gear.

Bit of a long shot, but if your RPi Zero chip is getting to 85℃ it’ll significantly throttle its clock speed. It doesn’t reach that by itself though (even when running on max), so unless you’ve got some other really hot electronics in an enclosure with it that shouldn’t be the cause.

You mentioned it might be stopping to do other things - any idea what those could be? Are there particular components of the software you’re running that could run intermittently, or be transmitting enough information that the USB+Ethernet control port gets overloaded and ignores the ping for a bit?

I’m not sure about the chip temperature on the Pi Zero, but this is a plot of the CPU, GPU and interal temp of the housing for a Raspberry Pi 4B that’s doing significantly heavier duty measuring other sensors and collecting and transmitting over the internet the output from the zero.

The little blue down arrow marks the peak temperature reached by the CPU over the last 48 hours at 41C. Things are generally kept pretty cool since this test is taking place outdoors in Minnesota.