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December 1999

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Subject:
From:
Brian Stumm <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 16 Dec 1999 11:39:43 -0800
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Hey Phil,

Don't you mean the PID controller, not the PDI controller? Probably a typo.

Anyway, Phil is correct - the SIMPLE approach is usually the best (and most reliable).
My company manufactures reflow systems and the methods Phil speaks of are similar to
our methods. Due to the amount of calibration done at our facility we do have slightly
fancier methods. The profilers provided with our equipment are calibrated using a hot
pot. 3 temperature measuring devices are used to compare the profilers accuracy. It is
also a good idea to have your profiler calibrated by the manufacturer at least once a
year (or whenever you suspect it is out of calibration). Conveyors are checked in the
fashion that Phil mentions except that we verify the speed over a longer duration (full
length of oven) in addition to the short length test. Conveyor speed should be accurate
to within one percent or less.

Hope that helps,

Brian Stumm
ETS, Inc.

Phil Zarrow wrote:

> Jim -
> The simplest approach is the direct approach.  Regarding conveyor speed, mark
> off a measured length on the on-load (or off-load) and time how long it takes
> a mark on the conveyor (or a link or pin) to cover the distance.  Calculate
> the speed and compare it to the setpoint.  Most ovens have closed-loop
> conveyor speed control but it is a good idea to test it.
> The way I used to measure accuracy of temperature was to attach a
> thermocouple to the the PDI controller (or you can use the inputs for
> on-board profile tracking your oven might have come with) and place the
> thermocouple first into a beaker of ice and then into a beaker of boiling
> water.  The temperature measured by the machine should be 0 deg. C and 100
> deg C respectively.
> I suppose there are fancier, more "academic" approaches, but this is
> practical, simple, economical and can even be incorporated as part of your
> ISO-9002 procedures.
>
> Phil Zarrow
> ITM, Inc.
> Durham, NH  USA
> www.ITM-SMT.com
>
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