KilnProbe Story and the Wood firing
Philippe Langlois <philippelanglois@free.fr>

The Idea
The idea for the KilnProbe came to me when Francois Eve told me about his huge wood firing project, a kiln of a 100 cubic meters which took Francois, Gaelle and Linda three years to prepare.

I thought to myself "Wow, that would be great to show on the Internet and have realtime temperature data with graphics available there!"

It became more reallistic when Alain Regnier built a special device from a pyrometer.
That device would commute at command between the two temperature probe, and send the result to a computer. The idea was taking shape.

The technology
The computer in charge of taking temperature measurements every 10 seconds from each probe is setup on an old Pentium 200 MMX box running Windows 98. The collecting program was developped in Visual Basic to retrieve the data from the serial port.

The graphing and Internet gateway is setup on my Linux laptop. It runs Apache, RRD Tools (which is a generalization of MRTG), rrdexplorer, rrdcgi,  PHP4 and a variety of custom made scripts to generate and archive these precious data. The upload is then done using lftp on our hosting server.

The network on the site is constructed with a 10/100 Mbit/s ethernet switch, in order to enable easy and fast communication between computers.

The temperature probes themselves are 20 meter long K-couple (Chromel - Alumel) thermocouples. They are linked to a microcontroller-based meter made by Alain Regnier.

The story during the firing

Here, I'll try to sum up the events of the wood firing and the KilnProbe project.

Saturday 20th of september
First time we meet with Alain, we've been working on the project remotely and only knew our voice and email styles. We set up the different computers, switch, thermocouples probes, converters etc...

Francois and Linda fire up the kiln around 19:00 (7 PM). It's the "bassinage" (pre-firing) and the goal is to chase the humidity from the kiln and the pots. The peep holes of the chimney (the "tetin") are closed with a brick during this time to keep the heat in the kiln and prevent "hot pathways". The goal is to keep the heat inside the kiln, that it goes everywhere in the pots piles.

We had a little apero to celebrate the event.

The KilnProbe live experiment starts this afternoon!
No graph yet, but we can see the temperature on the computer.

Sunday 21st of september
Real nice <g> graphics star to show today. Yeah!*^$@($@&*(


Legend: September, Sunday 21st and Monday 22nd.

The green curve "cheminee" [###] represents the heat in the back of the kiln, one meter from the chimney. The probe is placed in the middle of a pile of pots. It reflects the temperature inside the kiln load, at the coldest spot of the kiln.
The red curve "alandier" [###] represents the heat in the firebox.
All temperature are in Celsius Degrees.

On this graph, you can see the impact of the warm weather of the afternoon on the "cheminee" [###] curve. In the evening, the atmospheric temperature  cooled down and so the temperature inside the kiln did also.

We noticed with Linda that the speed of the air in the chimney was much more intense in the afternoon (17:00, 5 PM) than at noon time (12:00, 12 AM). Francois explained that there was an intense "tirage" (draft) for this very early period of the bassinage, and that meant that a lot of air was going in the kiln, including cold air.
He suggested to reduce the entry of air by removing the bricks from under the logs so that no air would flow around them. So we blocked the entry of air in front of the burning logs with bricks, and lowered the logs on to the coals.

You can notice on the previous and following graphs that this way of placing the logs has an effect on the temperature inside the kiln. The temperature read by the "cheminee" [###] curve is increasing at 01:00 (1 AM) monday morning. This cannot come from the atmospheric temperature outside.

Monday 22nd of september
The "bassinage" firing at this point is concentrated on getting the temperature up inside the kiln load. The curve to watch for this is the "cheminee"  [###] curve indicated the temperature of the pots which will be the hardest to heat.
The temperature in the alandier [###] must not cross the 100 Celsius degrees because water would then boil in the pots and then the pots would explode. Neither the "cheminee" [###] curve should cross 100 Celsius but it's highly unlikely ;-)


Legend: Night from September, Sunday 21st to Monday 22nd.

During this night between sunday and monday, the laptop harddrive got filled up and I started to look for an alternative so that a tower computer sit there, dedicated to making the graphs and pushing content to the Internet.

You can see during this night that new wood was placed in the firebox around midnight and around 03:00 and left there to burn without touching.
The effect of the human activity constantly touching the burning wood is noticeable starting at 08:00 this morning as you can see the spike happening much more than during the night, with no effect on the "cheminee" [###] curve.




Around 13:00, the weather started to turn to rain. And the wind before the rain started. The flames were boosted quite a bit by this wind and the temperature in the alandier [###] "clicked" twice over 100 degree Celsius between 13:00 and 14:00.

The temperature of the "cheminee" [###] grows steadily, reaching 25 degrees Celsius, maybe due to the warmth of the day (which is less warm than sunday).



Tuesday 23rd of september


It rained this morning and the air temperature dropped, so did the temperature inside the kiln.

We are a little bit worried about the variation of temperature inside the kiln ("cheminee" is "probe2", here on this special graph). I suggested the idea to put hay in the rose holes in the chimney, at the back of the kiln. Linda corrected that by the fact we want to have the kiln open somewhere for the humidity to come out. She also wants to block the top holes so that no draft is coming there.

The difficulty here comes with the chimney that is being built to reinforce the back of the kiln. It will prevent us from accessing the bricks there, removing or adding them if needed. So we need to foresee what needs to be done on the chimney before finishing the back wall.

Wednesday 24th of september
Last night, it was really cold and the outside temperature dropped a lot.

We are trying to check if the probe at the back of the kiln (chimney probe) is working.
Either it's not working or it's so deep in the pot piles that it doesn't register any temperature change because the heat is going around the pots.