DIY Kiln Contoller

Hi all,

Does anyone know of a DIY electonic kiln controller kit. I need one but am
short of funds. But I do have a soldering iron. I've googled for one but no
luck.

cheers

Rob (England)

"Dave {Reply Address in.sig}" wrote in
:

In message m, Rob
wrote:

Hi all,

Does anyone know of a DIY electonic kiln controller kit. I need one
but am short of funds. But I do have a soldering iron. I've googled
for one but no luck.

I keep meaning to design and build a posh one but so far I've not
found the time. The principle isn't hard and a kiln is a relatively
benign load compared to motors and other nasty inductive things.

Dave

Hi Dave, go on have a go !

what are the basic components needed? some sort of programmable voltage
controller ?


cheers

Rob

On Fri, 20 Feb 2004 23:48:57 GMT, Rob nospam@nospamreq wrote:

"Dave {Reply Address in.sig}" wrote in
:

In message m, Rob
wrote:

Hi all,

Does anyone know of a DIY electonic kiln controller kit. I need one
but am short of funds. But I do have a soldering iron. I've googled
for one but no luck.

I keep meaning to design and build a posh one but so far I've not
found the time. The principle isn't hard and a kiln is a relatively
benign load compared to motors and other nasty inductive things.

Dave

Hi Dave, go on have a go !

what are the basic components needed? some sort of programmable voltage
controller ?

I'm also interested in this, and have gone so far as rounding up parts
but haven't built anything yet.

For electric kilns, there are two basic ways of controlling the
heat. The simplest one is like that used by the "infinity"
controllers you find on an electric range: When the temperature
falls below a setpoint, they turn on the element; when above
the setpoint they turn it off.

The more sophisticated kind is proportional, so that the
current to the element is proportional to the temperature.
This is done by turning the current on only for some portion
of each mains cycle. The elements see a lot of partial
waveforms that average out to a lower effective current.

The first kind is easy to build, but due to thermal cycling
is reputed to be hard on certain kinds of kiln element,
namely silicon carbide "glow-bar" elements, which are
what I'm using. (It's a home-built kiln.) So I need to
use the fancier proportional control.

However, for most kilns, the simple inifinity control
may in fact be better since it produces less noise
on the power lines. (I have a huge transformer to
help block that.) The basic idea is that you have
a comparator that looks at a setpoint and a thermocouple
and toggles the current via an opto-isolated TRIAC
or something similar. (Mercury relays were very
popular for this in the past, and may still be the best
choice in some applications, since they have less
losses than TRIACs.)

Then the setpoint is placed under computer control,
to set up differetn firing schedules, and there you have
it! In fact, depending on the computer, you may want
to have it read the thermocouple, do the comparison,
and activate the TRIAC itself. The you can have it
plot a graph of the thermocouple temperature vs
time, integrate to find an approximation to heat work,
etc.

Someday, just as soon as a few other projects get
out of the way.... ;-)






Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com

On Fri, 20 Feb 2004 23:48:57 GMT, Rob nospam@nospamreq wrote:

what are the basic components needed? some sort of programmable voltage
controller ?


cheers

Rob

Hi Rob,

I've been giving just such an idea a lot of thought and testing of
late.

The route I'm currently taking is perhaps a little odd, but here goes.

#1 A digital Multimeter with a K-Type thermo-couple and a serial
connection to a computer.

#2 A Solid State Relay for each of the 6 elements in the kiln. Each
SSR is triggered On/Off thru the parallel printer port of the
computer.

#3 Some Visual Basic code to read the thermo-copule gauge, compare the
temp to a firing schedule, then adjust the PWM rate being sent to each
SSR, after being filtered thru some proportional derivative software.

#4 For Safety, the kiln still has its old Kiln Sitter installed set a
temp just above the peak in the firing schedule.. (to prevent
over-temp if/when the computer decides to lock up!)

To date I've had great success controlling a simple 110V toaster oven
:0 I'm currently researching a source for the 220v SSRs needed to
control the kiln...


Take Care,
James Lerch
http://lerch.no-ip.com/atm (My telescope construction, Testing, and Coating site)

Press on: nothing in the world can take the place of perseverance.
Talent will not; nothing is more common than unsuccessful men with talent.
Genius will not; unrewarded genius is almost a proverb.
Education will not; the world is full of educated derelicts.
Persistence and determination alone are omnipotent.
Calvin Coolidge

You should be able to find SCRs and most anything else here.
http://dkc1.digikey.com/ca/digihome.html
This is the Canadian site of Digikey but you can click on the flag of your
choice. They have 24 hour shipping.
Best of luck
Don

"James Lerch" wrote in message
...
On Fri, 20 Feb 2004 23:48:57 GMT, Rob nospam@nospamreq wrote:

what are the basic components needed? some sort of programmable voltage
controller ?


cheers

Rob

Hi Rob,

I've been giving just such an idea a lot of thought and testing of
late.

The route I'm currently taking is perhaps a little odd, but here goes.

#1 A digital Multimeter with a K-Type thermo-couple and a serial
connection to a computer.

#2 A Solid State Relay for each of the 6 elements in the kiln. Each
SSR is triggered On/Off thru the parallel printer port of the
computer.

#3 Some Visual Basic code to read the thermo-copule gauge, compare the
temp to a firing schedule, then adjust the PWM rate being sent to each
SSR, after being filtered thru some proportional derivative software.

#4 For Safety, the kiln still has its old Kiln Sitter installed set a
temp just above the peak in the firing schedule.. (to prevent
over-temp if/when the computer decides to lock up!)

To date I've had great success controlling a simple 110V toaster oven
:0 I'm currently researching a source for the 220v SSRs needed to
control the kiln...


Take Care,
James Lerch
http://lerch.no-ip.com/atm (My telescope construction, Testing, and
Coating site)

Press on: nothing in the world can take the place of perseverance.
Talent will not; nothing is more common than unsuccessful men with talent.
Genius will not; unrewarded genius is almost a proverb.
Education will not; the world is full of educated derelicts.
Persistence and determination alone are omnipotent.
Calvin Coolidge

Hi all,

Fab - this thread looks like its yeilding some fruit !

Dont know how many of you are from UK - but there is an old computer here
called a BBC micro which has a built in 8 bit 4 channell A/D convertor
and is simply programmed using an old style basic. Although old - these
machines never fall over (in my experience... touch wood) and are quite
happy sitting in sheds - also people now give them away .... even
better!. Its a simple enough task to take the V output from a
thermocuple, read it and then generate a control signal... to ...
something....
I must admit I dont know what a triac is ... but I'm just about to google
and find out -

Would any of you guys like to share the designs and rationale behind the
controllers you are thinking of or have built ?? Can we post jpg's or
files to this site ??? if not I could put up some webspace for the
sharing of circuit diagrams and programs. if any of you are happy to do
this I will supply an email address to this thread.

Anyway thanks for the info and inspiration - I'm off to find out what the
hell a triac does. hmmm I see a possible world full of cheap, efficient,
programmable home made kiln controllers !

:-)

On Mon, 23 Feb 2004 01:36:06 GMT, Rob nospam@nospamreq wrote:

Hi all,

Fab - this thread looks like its yeilding some fruit !

Dont know how many of you are from UK - but there is an old computer here
called a BBC micro which has a built in 8 bit 4 channell A/D convertor
and is simply programmed using an old style basic. Although old - these
machines never fall over (in my experience... touch wood) and are quite
happy sitting in sheds - also people now give them away .... even
better!. Its a simple enough task to take the V output from a
thermocuple, read it and then generate a control signal... to ...
something....

I like the idea of using old PCs for this. The BBC micro sounds
ideal. (I'll be using an old PC/XT with an add-in A/D board.)

One caveat: If you are trying to read the thermocouple directly,
you will need some "signal conditioning" before it goes to the
A/D. The A/D no doubt has a range of 0-1V or more, whereas
the thermocouple range is more like 0-50 millivolts. So you
definitely need some gain here. But this must be done *very*
carefully, since simple DC amplifiers tend to have drift in their
outputs that would be confused with temperature changes.
So you will probably want a slightly more exotic "chopper stabilized"
op-amp.

My approach will be a variant of this. I will use standard CMOS
switches to alternately send either a normal or inverted version
of the amplified thermocouple voltage to the A/D. Besides the
thermocouple signal, I will also send a temperature-stable reference
voltage, also in normal and reverse polarity. By judicious use of
these values, all the drift can be compensated.

I must admit I dont know what a triac is ... but I'm just about to google
and find out -

A TRIAC is the same gizmo inside a standard lamp dimmer. If you
know what an SCR is (Silicon Controled Rectifier), it's just two of
those wired back-to-back internally. The idea is that when the
incoming AC line voltage rises above some threshold, the SCR for
that polarity is fired (by a little trigger circuit), after which the
SCR will stay on for the rest of that half-cycle. When the polarity
reverses, the same thing happens on the opposite-polarity SCR.

To get a proportional control like a lamp dimmer, you just change
where the trigger point is in the AC half-cycles: Earlier and you get
more of the power, later and you get less. To have the whole
thing act like a simple switch (Solid State Relay), just fire the
trigger right at the zero-crossing.


Would any of you guys like to share the designs and rationale behind the
controllers you are thinking of or have built ?? Can we post jpg's or
files to this site ??? if not I could put up some webspace for the
sharing of circuit diagrams and programs. if any of you are happy to do
this I will supply an email address to this thread.

I'd be glad to share whatever I come up with.
Can't post JPGs here. I thnk such things are usually posted to some
..alt.binaries NGs that exist just for this purpose. though a Website
has the advantage that it keeps related stuff together, and can
include descriptive text pages, etc.

Anyway thanks for the info and inspiration - I'm off to find out what the
hell a triac does. hmmm I see a possible world full of cheap, efficient,
programmable home made kiln controllers !


I suspect this world will be on the small side, consisting only
of electronically-inclined potters. But we'll have fun!


Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com

On Mon, 23 Feb 2004 01:36:06 GMT, Rob nospam@nospamreq wrote:

Hi all,

Fab - this thread looks like its yeilding some fruit !

Dont know how many of you are from UK - but there is an old computer here
called a BBC micro which has a built in 8 bit 4 channell A/D convertor
and is simply programmed using an old style basic. Although old - these
machines never fall over (in my experience... touch wood) and are quite
happy sitting in sheds - also people now give them away .... even
better!. Its a simple enough task to take the V output from a
thermocuple, read it and then generate a control signal... to ...
something....


Oops! Just re-read your post regarding the A/D converters.
I'm afraid 8 bits won't do the job, since it only encodes 256
levels. If you scaled the thermocouple range to fit this,
you'd end up with several degrees per A/D step. True,
that may be closer than you'd control it manually, but
it would be better to use something like a 12-bit A/D
(4096 levels) or better yet 16 bits (65536 levels).

One of the benefits of my complicated chopper scheme
is that the signal output from there to the computer is
AC, so it can be monitored with a cheapo 16-bit sound
card. (Sound cards don't pass DC or low frequency
signals like thermocouples put out.) Plus, as a side
benefit, it is easily expanded to any number of input
channels just by using CMOS switches with more
channels.

When I get this ready, I'll post full info with schematics
and circuit board layout on my site and announce it here.
Probably not any time soon, but it's definitely in the works!





Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com

To me, a controller running the schedule, with a kiln-sitter switching
it off is the best of both worlds: the convenience of a controller with
the heat-work reaction of a cone. This is exactly how I fire my electric
kiln and it can't be beat!

Steve
Bath
UK

In article , James
Lerch writes
On Fri, 20 Feb 2004 23:48:57 GMT, Rob nospam@nospamreq wrote:

what are the basic components needed? some sort of programmable voltage
controller ?


cheers

Rob

Hi Rob,

I've been giving just such an idea a lot of thought and testing of
late.

The route I'm currently taking is perhaps a little odd, but here goes.

#1 A digital Multimeter with a K-Type thermo-couple and a serial
connection to a computer.

#2 A Solid State Relay for each of the 6 elements in the kiln. Each
SSR is triggered On/Off thru the parallel printer port of the
computer.

#3 Some Visual Basic code to read the thermo-copule gauge, compare the
temp to a firing schedule, then adjust the PWM rate being sent to each
SSR, after being filtered thru some proportional derivative software.

#4 For Safety, the kiln still has its old Kiln Sitter installed set a
temp just above the peak in the firing schedule.. (to prevent
over-temp if/when the computer decides to lock up!)

To date I've had great success controlling a simple 110V toaster oven
:0 I'm currently researching a source for the 220v SSRs needed to
control the kiln...


Take Care,
James Lerch
http://lerch.no-ip.com/atm (My telescope construction, Testing, and Coating
site)

Press on: nothing in the world can take the place of perseverance.
Talent will not; nothing is more common than unsuccessful men with talent.
Genius will not; unrewarded genius is almost a proverb.
Education will not; the world is full of educated derelicts.
Persistence and determination alone are omnipotent.
Calvin Coolidge

--
Steve Mills
Bath
UK

Look at www.bartinst.com. I built a single zone controller for a test kiln
using one of their controller boards. Was not too hard to do. Hardest part
was making the enclosure.Bartlett offers plans at the website.

"Dave {Reply Address in.sig}" wrote in message
...
In message m, Rob
wrote:

"Dave {Reply Address in.sig}" wrote in
:

In message m, Rob
wrote:

Hi all,

Does anyone know of a DIY electonic kiln controller kit. I need one
but am short of funds. But I do have a soldering iron. I've googled
for one but no luck.

I keep meaning to design and build a posh one but so far I've not
found the time. The principle isn't hard and a kiln is a relatively
benign load compared to motors and other nasty inductive things.

Dave

Hi Dave, go on have a go !

what are the basic components needed? some sort of programmable voltage
controller ?

In its simplest form it's just a triac per element (three elements on all
the kilns here) and a small microprocessor to turn them on as required.
Obviously there's a lot more work than just that.

Dave
--
mail: da (without the space)
http://www.llondel.org/
So many gadgets, so little time...