Re: [ATM] Making glass blanks.

["Stuart Hutchins" <stuart452@earthlink.net>]

Timm,

What is the signal from your thermocouple?  Is it the direct millivolt
output, or is it signal conditioned to 0-5 volts or 4-20mA?
Are you presently reading the thermocouple with a computer interface?

Latching the output byte from the printer port is trivial.  Converting the
byte to an analog voltage representing the setpoint is trivial. Comparing
the setpoint voltage to another voltage  representing the temperature from
the thermocouple and turning the solid state relay off and on is also
trivial.

This is the control scheme suggested by Martin Cibulski.  I presume you are
thinking of writing a simple program to output the temperature setpoint to
the printer port, which will change over several days following the cooling
schedule you wish to implement.  It seems that you will have to make sure
your computer and your program run continuously for the whole annealing
cycle.  If that is done, then I don't think you have to latch the printer
port output.  I believe the value you write to the port stays there until
you change it.

Stuart


----- Original Message ----- 
From: "Timm Simpkins" <poduck@poducksworld.com>
To: "'Stuart Hutchins'" <stuart452@earthlink.net>
Sent: Saturday, May 15, 2004 12:28 PM
Subject: RE: [ATM] Making glass blanks.


> Stuart,
>
> How difficult would it be to set up something that would take a
temperature
> setting from a parallel port on a computer and compare it to the
temperature
> read from a thermocouple and if it is lower send current to a solid state
> relay, and if it is higher stop that current?  It would have to store the
> setting internally, otherwise there would have to be a constant signal
being
> sent.  That would probably be much easier than limiting the current
wouldn't
> it?  Might it also be less expensive?  I have figured out how to convert
the
> temperature read from a thermocouple exactly to mv, so we would only have
to
> compare voltage to the setpoint, and nothing extra.
>
> I've calculated the wattage needed, and for the design I have made,
> specifically for making mirror blanks, I need about 7.5 kilowatts.  That
> would allow for melting glass, as well as annealing.
>
> Anyway, let me know if you can help.
>
> Thanks,
>
> Timm Simpkins
>
>
>


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