Hi all,

Maybe a daft question, I've got some lm35's in the t220 package, I want to use it to sense the temp of a copper pipe.

I'm soldering the joints on the copper pipes, if I solder the tab to the pipe will I do any damage to the sensor?

If it works after I solder it does that mean it will continue to work or could damage show up later?

Has anyone else done it like that? I know I could just use a jubilee clip but solder would be tidier and transfer heat better.

Cheers Geoff

 

Should be okay as long as you don't solder longer than recommended and the copper pipe is at the same potential as circuit ground.

 

Both the tab and the pipe would need to be heated to above solder melting temperature. The thermal conduction from the tab to the silicon is good and the heat stored in the copper pipe would keep the temperature high for a good while. I don't think there is any chance of keeping the silicon below the specified maximum of 150C with lead-based or lead free solder. There is some low melting point solder 70C and 138C but I don't know whether they will 'stick' to the copper and the pipe.

 

Hi all,

Maybe a daft question, I've got some lm35's in the t220 package, I want to use it to sense the temp of a copper pipe.

I'm soldering the joints on the copper pipes, if I solder the tab to the pipe will I do any damage to the sensor?

If it works after I solder it does that mean it will continue to work or could damage show up later?

Has anyone else done it like that? I know I could just use a jubilee clip but solder would be tidier and transfer heat better.

Cheers Geoff

Maybe solder a copper sheet to the pipe and then the LM35 to the sheet?

 

Screw it, or glue it. Don't solder it, it will not survive.

If you glue use thermally conductive glue. That's expensive, so screw it.

 

You can eliminate almost any sensing problem by applying a good chunk of pipe insulation around the area with the sensor. Think about it: Inside that insulation, everything must be the same temperature within a minute or so, even if the TO-220 tab barely touches that pipe.

 

Hi all,

Maybe a daft question, I've got some lm35's in the t220 package, I want to use it to sense the temp of a copper pipe.

I'm soldering the joints on the copper pipes, if I solder the tab to the pipe will I do any damage to the sensor?

If it works after I solder it does that mean it will continue to work or could damage show up later?

Has anyone else done it like that? I know I could just use a jubilee clip but solder would be tidier and transfer heat better.

Cheers Geoff

I've seen a lot of people solder TO220s to copper pipe without ill effects. I would use solder paste made for reflow and cool the pipe right afterwards.

 

Eventhough you have the copper tab, any screw or additional mass will increase the thermal time constant. That is, the lag time from the actual temp change until the chip is able to equilibrate and deliver the new temperature.

If you need to quickly adjust the hot and cold taps to deliver a specific temp, I would recommend super-gluing a TO-46 package flat to the pipe. Our test showed the the mass to be most important to decrease the lag. The TO-46 chip stabilized in about 1/10th the time it takes the TO-220 (If they are both glued to the pipe). The TO-92 chip took about half the time of the TO-220.

Edit: I actually looked at my old notes and edited values. Solder changes the lag - increases the mass that must adjust. It does not adjust as fast as copper.

 

Thanks everyone,
I've got more help than I expected !
I think I will screw and insulate the to220 to the underfloor heating pipes, the lag on the heating the floor up makes sensor lag nearly irrelevant!

However I think I will get some to46 ones for the closed loop on the generator/heat store as response is more important there!

Never know what your going to find out here!
Cheers Geoff