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While transporting any PCBs either fresh spares or
defective units, take adequate care to pack them.
If they are carried without proper packing in the
tool kit itself, the possibility of damages to the
PCB is very high. This is strongly advised against.
Even a faulty PCB has to be packed properly to avoid
further damage and to enable proper trouble shooting.
In case of microprocessor based controllers for Hot
beverage vending machines, EASYSET method is adopted
for time setting. In this method better accuracy and
repeatability can be achieved by reducing the number
of breaks during setting up the volume. This is particularly
true for water timing. To clarify the point an example
is described below.
Let
us say you start the water set up process. You press
the set up key; LEDs blink; You press Coffee/Tea;
Water flows out; Now the ideal case is that you keep
pressing till you reach exactly the required quantity
and stop. But this cannot be done since it is not
possible to guess the amount of water in the pipeline,
which will flow out after the button is released.
So you release the button when the volume reaches
say 70ml whereas you actually need 100ml. After the
water in the pipeline comes out you see that the volume
is only 85ml. So you press the button again; You release
button and find the volume is 95ml; So you press again:
You release the button and find that the volume is
100ml.
Wherever
trimpots are used for time setting, it is important
to remember that the range of the trimpot is about
10 to 12 full revolutions (20 to 24 times we may have
to turn as we normally tend to turn half revolutions
in one go). It is quite possible that the trimpot
position is at the other extreme when you start. If
this is so in the particular PCB you attend, then
in certain cases you may not notice any change in
volume / gram throw, for the first few rotations.
If it happens, it is advisable to blindly turn about
20 times in the required direction and then start
the setting process. Any excess rotation of the trimpot
beyond the extreme will not damage the device provided
force applied is not excessive. In most cases a faint
clicking may be heard/felt as the position of the
trimpot reaches an extreme.
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