Hector Martin wrote: > air rework station (which claims it was putting out 480=BAC), and measured > a voltage on the two wires. With the rework station, I managed to get it > to output 5-6mV. At room temperature, it puts out 0.1mV or 0.0mV. I'm > guessing it has a thermocouple in series with the heating element. If it outputs a voltage, that's pretty much what it has to be. The output voltage is not a clear indicator. = One common thermocouple would be a NiCr-Ni (aka "type K"). But only if you got the tip to only some 150=B0C. For the other common thermocouple, PtRh-Pt (aka "type R"), the voltage is a bit too low. There are a few others... maybe you can find one that matches. > I understand thermocouples require a cold junction at the unit side and > compensation for accuracy, though I don't recall seeing a temperature > sensor in the base unit (I took it apart a few times). = They could use a diode as compensation sensor, for example, mounted more or less close to where the wires connect to the board. You don't have to see this. > How can I tell if the wire from the soldering iron is thermocouple wire > or plain old copper wire? = If it puts out a voltage, it's a thermocouple -- how else would the voltage be generated? May not be an intentional thermocouple, though :) > If it's just copper, my guess is the "cold junction" is formed at the > base of the soldering iron. = This is also a possibility. This way, the voltage would indicate the temperature difference between tip and handle of the iron, which they may have considered as good enough. > Consistency would be nice, however. If you get consistent voltages that increase with temperature, you can pretty much be sure that there is a thermocouple in there -- intentional or not. And you can use it. It will be consistent, and precise only if you can find out which one it is. > I'm guessing drive voltage would have to be pulsed (it'll end up being > pulsed once it reaches the set temperature anyway, due to the closed > loop), so I would take the temperature measurements between pulses. This > also means the measuring circuit has to withstand whatever voltage I put > across the iron (or somehow get disconnected during that time). Also, if > the time between pulses is short, I'd have to worry about capacitance > skewing results due to the previous high-voltage pulse. Not really. This is temperature; a few tens or even hundreds of milliseconds of power-off don't do any harm, and that's enough for any capacitance in the iron and input circuit get recharged. Gerhard -- = http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist