I've been working on a reflow oven
(and hijacking other people's threads to boot)
so now decided to have my very own bragging thread
started with a 1 kW 9litre toaster oven
4 heating elements; 2 top 2 bottom
I added a K type thermocouple
(actually took a couple of goes as the ifrst one melted!)
I took it apart, cut off the smouldering ends, joined the new ends together
used heat resistant (fibre glass?) insulation this time
disconnected all the oven control gear and wired it via a triac
triac controlled by 'duino of course
software attempts to match the profile for reflow ovens
anyway - time for some pictures
here's the triac driver board
it's inside the oven to keep mains voltage well away from small children and idiots
(er and me )
2nd picture shows the much reduced internal wiring
3rd picture shows the first board "wot I made"
it's a micro 'duino
once Nick Gammon helped me with the bootloader - it worked!
4th picture is part of a range of camera kit we're selling
all the SMD parts sorted in < 10 minutes!
the two wires are insulated with what looks like glass insulation
then slipped inside a stainless steel "knitted" (thank you Mrs Noah) outer jacket
trouble is at the business end the trimming was awful
with strands of wire touching the probe
and shorting it out intermittently
so - trimmed it back - much easier said than done stainless steel is tough!
wrapped the end of the metal in heat shrink - just to hold it while I re-assembled
temperature readings now rock steady
but
as the probe is inside a metal sleeve, there does seem to be some inertia in the measurement now
the graph below shows the problem
(apparent) delay in getting started
overshoot at the intermediate temperature points
a naked thermocouple is much more responsive
(see the original curve posted earlier)
I may well add PID processing - which should stop the overshoot
next decision after that's all working
oh and for amusement here's a picture of the first probe
not completely heat proof methinks!
mmcp42:
as the probe is inside a metal sleeve, there does seem to be some inertia in the measurement now
"Dead-time" in PID jargon.
I may well add PID processing - which should stop the overshoot
Not necessarily. There is a conflict between getting the response you want, the dead-time, and overshoot. If possible, you should first strive to reduce the dead-time as much as possible. That will make working with PID much much easier.
I may well add PID processing - which should stop the overshoot
Not necessarily. There is a conflict between getting the response you want, the dead-time, and overshoot. If possible, you should first strive to reduce the dead-time as much as possible. That will make working with PID much much easier.
indeed
I'm looking at removing the end of the metal sleeve
that way the thermocouple will be nicely inside the oven
but still in free air (aka dangling!)
Riva:
Probably breaks the budget but could you use a non contact sensor like this pointed at the PCB?
good thought
a) cost exceeds £$€ spent so far!
b) will it work through the glass door?
c) actually measuring PCB temp would be really neat!
still good thought though