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Topic: reflow (toaster) oven now earning its keep (Read 5571 times) previous topic - next topic

CrossRoads

That stinks. Guess I'll stick with bare probe when I get around to assembling.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

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 knew that :coughs: !!

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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!)
there are only 10 types of people
them that understands binary
and them that doesn't

Riva

Probably breaks the budget but could you use a non contact sensor like this pointed at the PCB?

mmcp42


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 :)
there are only 10 types of people
them that understands binary
and them that doesn't

Riva

Have been trawling eBay and found this that may hack to your needs.

mmcp42

I decided to "adjust" the temperature sensor...

stripped it down again
the plan was to "simply" saw 1/3" or so off the sealed end,
so the thermocouple would hang in the middle of the oven
took a hacksaw to it - no effect
looks like it's stainless steel

tried a Dremel with one of the little "parting" discs
knife through butter!

cleaned the end with the same disc
so now have a slightly shorter tube
with thermostat out in the open

tried a profile run last night
MUCH closer to the first graph (several posts ago)
close enough that the dead time seems to have gone away

so next step is to look at stirring PID control into the equation(s)

modified probe and resultant profile shown below

there are only 10 types of people
them that understands binary
and them that doesn't

mmcp42

ok
PID now implemented
much nicer looking profile
you can see target and actual temp
and also the PID control turning the heater on and off :)

I'm also wondering about using some loft insulation to pack the sides of the oven
might make the up-ramps faster?

need to get cooldown quicker

time to get out the metal cutting tools and install a fan shaped hole :)
there are only 10 types of people
them that understands binary
and them that doesn't

mmcp42

ok took an axe to the oven to day
well almost

decided to move the bottom heaters up to the top
of itself it didn't make much difference

big bonus is I can now put what they call the crumb tray on the top shelf
effectively cutting the heated volume to around a third

by fiddling with the PID parameters I now get this curve
(thanks to retrolefty for a steer there!)

so I'll probably stop playing now and get on with the day job
(apart from adding a fan in the bottom, which now stays at room temperature :) )
there are only 10 types of people
them that understands binary
and them that doesn't

CrossRoads

I thought your other curve followed your desired profile better.
Am guessing its not all that critical if it can be controlled by hand just rotating a temperature control knob and a thermocouple stuck it the tines of a fork to hold in place near the card being reflowed ...
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

mmcp42

further update on the probe that I had to fix
before leaving eBay feedback I emailed the vendor
very responsive - bottom line got £1.00 refund
I'm happy - the probe works and it (now) only cost me £1.52
the fix was dead easy
here's a picture of the problem/fix

the red circle shows the stainless steel outer after I cut it back
the blue circle is where the outer stopped originally
with the frayed wires shorting out the probe

cheers
Mike
there are only 10 types of people
them that understands binary
and them that doesn't

mmcp42

been a while
tinkered a bit (as I tend to)

here's the latest EAGLE files and sketch if anyone is considering going down the same path :)
enjoy

if anyone does find it useful or makes any changes - do let me know :)

cheers
Mike
there are only 10 types of people
them that understands binary
and them that doesn't


ScottG


here's the final circuit
(went through several iterations to get there - as you do!)
and here's the triac heater control


In your circuit, what's the purpose of R5?  Also, I see you have the mains hot connected to MT2 on the triac.  Does it matter which way the triac is wired?  Would it make a difference if MT1 went to mains hot and MT2 went to the oven?

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