Homebrew PCBs

How  HIGH is what you say is high heat conditions that weaken the 
soldered thermocouple ?
Considering that some  are rated at over 2,000 F degrees
while others only are rated to 400 F.





On 12/30/2016 03:15 PM, 'keith printy' keethpr@... 
[Homebrew_PCBs] wrote:
>
> The lead wires on thermocouples usually are soldered with some type of 
> lead based solder. In high heat conditions this can come loose or 
> oxidize to where it is weak . when I worked in an electronics plant 
> and we dealt with high heat we always used thermocouples. When we used 
> a packaged temperature controller they were usually type j . when we 
> used microprocessor control they were type k .
>
> +++++++++++++++++++++++++++++++++++++++
>
>

> Which one?
>
> RE:
>  approach in favor of a purchased controller with a type K 
> thermocouple. This cost USD 8.99 on e-bay from China. I have not yet 
> put it into service because of the melted gears.
>
> On 12/30/2016 01:04 PM, Harvey Altstadter hrconsult@... 
> <mailto:hrconsult@...> [Homebrew_PCBs] wrote:
>
>     Rob,
>
>     The Passive IR gun type thermometer is only used for making
>     initial measurements, not for a feedback type control system. The
>     PIR thermometers have a distance to spot ratio. The Sparkfun unit
>     mentioned previously has a ratio of 12:1, meaning that at a
>     distance of 12 inches, the detector is reading the temperature in
>     a 1 inch circle. The thermistor and thermocouple approaches
>     measure the temperature at the point of contact, a much smaller
>     area. With the PIR thermometer, I could not read the rollers in my
>     laminator at all because they are surrounded by the heater
>     structure except where the paper path is. Those slots were too
>     narrow for either of my PIR thermometers. Another issue with the
>     PIR thermometers, usually ignored in the advertising, is that the
>     emissivity of the surface being measured has an effect on the
>     readings. In plain English, this means that two surfaces made with
>     different materials could be at the same temperature, but give
>     different readings on the PIR. Surfaces with multiple materials,
>     if they fall in the reading area, will give a reading that
>     integrates the two readings, rather than providing a true reading.
>
>     I tried to use the RepRap thermistor in my original control
>     circuit, and found that while it works, the resistance vs
>     temperature curve is very flat near 200�C, making the controller
>     action sluggish. I abandoned the thermistor approach in favor of a
>     purchased controller with a type K thermocouple. This cost USD
>     8.99 on e-bay from China. I have not yet put it into service
>     because of the melted gears.
>
>     As far as the location of the thermistor in the Royal laminator,
>     this is a mechanically simple location to use, and if we think
>     about it, we understand that there is no need to measure the
>     actual temperature of the rollers, at least in the original
>     application of the laminator. As long as the temperature drop
>     between the heater and the roller is known, the system can be
>     calibrated for proper operation with the thermistor mounted on the
>     heater structure. The Harbor Freight unit uses mechanical
>     thermoswitches mounted on the heater structure.
>
>     In our toner transfer case, it is not clear (at least to me) that
>     measuring at the heater is sufficient. Since we are putting single
>     or double sided thermally conductive boards of different sizes
>     through the rollers, I am not sure that the temperature drop is
>     sufficiently constant that we don't have to measure the
>     temperature at the roller. I was experimenting with this when my
>     gears turned to mush.
>
>     Harvey
>
>     On 12/30/2016 8:24 AM, Rob roomberg@...
>     <mailto:roomberg@...> [Homebrew_PCBs] wrote:
>
>