Mike Bailey on fri 3 sep 99
In message <00fe01bef3e4$bfa1d620$f141f9c3@pii>, Alisa and Claus Clausen
Dear Alisa,
Ref. your enquiry about kiln controllers.
The first thing to accept is that no system is 100% safe - assume a 99%
success rate and it still means that you have got to be ready for the 1
in 100 firing when something goes wrong.
The main things that go wrong with kiln sitters are:
1. Something holds the rod on the inside of the kiln and stops the
mechanism turning off e.g. kiln shelf or pot put too close, a piece
blows up and jams the rod.
2. Something gets put close to the kiln and when the mechanism is
activated, by the cone bending, the latch catches on this object. e.g.
we once used a fire guard around the kiln and this got pushed up against
the kiln sitter - fortunately we spotted it but it could have been a
disaster.
3. The internal cut off mechanism itself gets stiff and, although the
latch falls, it fails to activate the disconnection. This can be due to
arcing / carbon build up on the contacts or a misalignment of the guide
plate.
4. Putting in the wrong cone!
5. In some earlier models, turning the time clock right back to its
maximum near the end of the firing actually stopped the cut-off
mechanism.
6. You forget to reset the timer and kiln turns off early - can result
in dunting.
The main things that go wrong with electronic controllers are:
1. Power surges / spikes. In some models this jams the kiln on!
2. The thermocouple gets broken, a poor connection, compensating cable
damaged or thermocouple partially removed from the kiln, and hence
under reads the temperature in the kiln. Kiln over fires.
3. The potter sets the program incorrectly / uses the wrong program.
4. Like all electronic devices it doesn't measure heat-work.
...................................................................
So, in recognition of all the above, it is best to set a few rules. The
main one being.
DO NOT RELY ON THE KILN_SITTER OR CONTROLLER!!!!!!
Be around when the kiln should be turning off - do not leave the kiln
to turn itself off.
It's much better to leave the kiln unattended in the early stages so
that, for example, you leave the kiln on low overnight so that you can
be around during work time, at the time when the kiln goes off.
If you can't do this then it is possible to have a 'policeman' which
activates a second mains contactor that will over ride and cut-off 20
deg C. above your set point. But fitting this yourself is getting a bit
complicated.
......................................................................
You make the point that controllers sound easy and exact, but do you
need a back up as far as an extra safety?
Well, you can probably tell from the above that I think you do. We use
both and have the best of both worlds. That is,
A programmer to run the firing.
A kiln - sitter to turn it off, with the programmer set just above top
temp as a guard.
And finally we make sure the firing has been completed before going
home.
Obviously, it's expensive to have both, so if necessary get one or the
other and use yourself as the backup.
You can get both kiln-sitters and electronic controllers from
Potterycrafts. Campbell Road, Stoke on Trent. ST4 4ET England.
Phone 44 (0)1782 745000
or you could contact our friend Clive Shellard who does all the kiln
repairs in our area. I'm sure he'd help with a wiring diagram and give
some good advice. He's at:
Roman Environmental Instruments,77 Upper Bloomfield Road, Bath BA2 5SA
Phone 44 (0)1225 833427
Hope this is of some help - sorry it's taken a few days to reply but we
have had a weekend plus a Bank Holiday and the Clayart newsletter and
other E-mails just backed up.
Best regards,
Mike.
P.S.
>Denmark voltage is 220, or recently upped to 230. Same in UK,
>isn't it?
Yes, although in The U.K. we are notional 240V but receive 230V much of
the time !
--
Mike Bailey. Bath. U.K.
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