Homebrew PCBs

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@... [Homebrew_PCBs] wrote:
>
> Where do you mount this device without destroying it and melting 
> solder on the supporting
> chips in the toner work PCB heating  path?
> How far do you mount it from the desired location where you are 
> pinpointing temperature measurment?
>
>
>
>
> While I would agree that a Non contact passive infrared rules..........
>
> I would like to some day compare the accuracy of the $20 passive 
> infrared with
> the K type thermocouple and a simple thermistor.
>
> Noting that my ROYAL laminator heater control was done by a contact 
> thermistor clamped to the aluminum heat shield
> behind a roller heater.
>
>
> When I was looking into thermocouple circuits and supporting chips it 
> looked like about $15 gets that done
> and
> 5 cents buys a thermistor....
> or maybe a dollar if it has wires.
>
> New Reprap NTC 3950 Thermistor 100K with 1 Meter wire for 3D Printer TSCA
>
>
> On 12/30/2016 09:02 AM, AncelB mosaicmerc@... [Homebrew_PCBs] wrote:
>>
>> Non contact passive infrared rules...
>> Get one of these...
>> https://www.sparkfun.com/products/9570
>>
>> ------------------------------------------------------------------------
>>
>
>