mmcp42:
if anyone is interested I'll post the sketch as well
I'm interested. Does the opto isolator do everything (switching on the zero crossing) or does the sketch have to do that?
mmcp42:
if anyone is interested I'll post the sketch as well
I'm interested. Does the opto isolator do everything (switching on the zero crossing) or does the sketch have to do that?
seems the zero-crossing bit does all that
you just send a logic high to the input side and magic does the rest
sketch here...
if there's any bit that needs explanation ...
ReflowOven.zip (10.3 KB)
Looks pretty neat, thanks.
RE: profile.jpg
Are you using PID to control the temperature?
Have you considered adding a servo connected to the oven door to speed up the cool-down cycle? How about a fan?
Nice work mmcp42 - I'll get mine assembled one of these months
not using a PID, yet
need to get the temperature ramping fast enough
at the moment there's nothing to control!
and yes, I have seriously considered a servo to open the door
also a fan
watch this space...
@CrossRoads
cheers - and thanks for the initial inspiration
Thanks, but I am just following in the footsteps of many others here.
that's what I like about this forum
so many generous people leaving footprints for lesser mortals to follow
shiny new temperature probe arrived today
doesn't work
took it to pieces (what else! )
found the problem
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
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!
added link to probe
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.
That stinks. Guess I'll stick with bare probe when I get around to assembling.
I knew that :coughs: !!
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
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
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
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 )
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 ...
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