Peter Homann wrote:
[snip]
> Basically it worked like this.
>
> 1. The board was put in the oven
> 2. The Start/Stop button was pressed. (The heater and fan turned on.
> The LCD displays the current temperature)
> 3. When the temp reaches the "Hi" set point (218 degs C) the Heater
> turns off and the fan stays on to help cool the oven. (also the oven
> door is opened at this point.
> 4. When the temp reaches the "Lo" set point (50 Degs C), the fan
> turns off.
> 5. Take the board out and start again.
>
> The relays were to control the heating element and the fan. The rotary
> encoder was for entering the Hi and Lo set points.
>
> If a "D" character is sent over the RS232 I/F, the oven will reply
> with the current temp.
>
> Eventually I plan to replace the 84 with a 628 with twice the code
> space. That way I can add to the RS232 command and have it controlled
> by a computer or another PIC. The idea is to control the oven to get
> a proper SMT temp profile.


Peter, it is interesting.  I always tought to test the single temperature
slope as your solution does.

The recommended paste soldering says a dual temperature slope, increase
temperature to a certain point, hold there during some time, then increas=
e
temperature to a second setpoint, hold for a short time and turn off
everything, just keep the fan active to cool it down.  The first
temperature slope is to heat everything, board, components, solder paste,
and create a pre-solder environment, the second slope quickly melts the
paste instantly, so, melting temperature is applied very briefly reducing
the probable thermal damage to components.

How long your oven takes to reach 218=B0C ?
How long to cool down to 50=B0C ?

Probably you found a simpler way to do the same job.
Did you ever logged the internal temperature in time (plotted a graph) ?

Thank you.
Wagner.

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