Calibrating your kiln

Calibrating your kiln

Calibrating your kiln

Home> Calibrating Your Kiln

Basics

Why Calibrate Your Kiln?

  • Most people will be satisfied with the operation of their kiln right out of the box.
  • For precise work, a kiln needs to be calibrated or adjusted to match the clay, the way you load your kiln, what temperature you fire to, the characteristics and condition of the kiln, and the thermocouples (as they age and drift in accuracy).
  • Generally speaking, for firing clay, "calibration" means aligning how the electronic control system matches the desired witness cones.

Know Your Kiln

  • Each kiln is different. Kilns can vary in brand, size, or even between identical kiln models.  
  • Multiple factors can affect how a kiln fires, including the health or age of the electrical components(elements/thermocouples/relays), insulation thickness, the distance from the elements to the center of the kiln, and how the kiln is loaded. etc. 
  • Even external conditions like voltage temperature and humidity in the room affect the firing.
  • It's vital to understand while the controls used in most kilns are perfectly acceptable for ceramics, they are not precision instruments.  

Controls &Thermocouples

  • The controls in ceramic kilns are typically accurate to about 1% of scale (+/- 25 F on a typical kiln.)
  • The thermocouples can read +/- 10°F from the actual temperature even when brand new.  Even though L&L uses the "Special Limit of Error" wire, there are still all kinds of variations in the thermocouples, the thermocouple circuit, and the cold compensation on the control. See this on Wikipedia for more information on thermocouples.
  • In addition, the most common Type K thermocouples will drift over time, primarily when used over 2000°F.
  • Type S platinum thermocouples do not drift at those temperatures. Type S thermocouples are an option for your kiln, but are very expensive due to their materials.
  • The temperature you see on the control will probably not be completely accurate. Even if the temperature reading is precise, it is only one piece of the puzzle.
  • Over time your kiln's firing will become more consistent.  (except when the thermocouple begins to drift) Calibrating your kiln helps the kiln to fire more accurately.
  • Note from 2003-2020, L&L kilns were made with thermocouples with a closed protection tube.  This created an expected offset.  Although this issue was adjusted in the preset kiln settings, the temperature reading still has a possibility to vary.  Meaning that the offset may need to be adjusted. 

Loading Your Kiln

  • How you load your kiln makes a big difference in how heat reaches and affects your work.
  • Don't fire empty an empty kiln.  You will most likely get an error code.
  • Don't fire too densely or too heavily at the top or bottom. This could also cause an error code.
  • Load it with a reasonable amount of work, not too close to the elements, and distribute the work as evenly as possible.
  • Don’t put a shelf right next to an element. Most of the heating about 1200°F is radiant heat. Because not all of the work is exposed directly to the elements you need to make space for the heat to circulate. Also, you need to allow time for the heat to get from the wall elements to the inside of the kiln while not overheating the work towards the outside.
  • There are guidelines for loading a kiln but this is more art than science.

Clay and Glazes

  • Talk to your clay and glaze suppliers to find out their firing recommendations.
  • Some glazes can be very fussy about heat work, others not so much.
  • The main point, however, is to “tune” or “calibrate” the kiln to the appropriate level of precision that you need. Don’t overdo it. If you are satisfied with your glaze results, calibration may not be necessary.
  • Also, be aware that clay and glaze vary with different batches. (how they are made)

Heat Work

  • Ceramics and glazes develop from heat work, which is a function of time and temperature.
  • So, for any given temperature, the amount of time spent at that temperature would determine how much heat work is done.
  • Looking at one part of this equation can be misleading.
  • Assuming you had a perfectly known temperature you would then have to determine how much time at that temperature will give you the desired result.

Cones

  • Pyrometric Cones are probably the best way to “see” ceramic heat work. Pyrometric cones melt at a specific temperature and reflect the actual ceramic process taking place. They are far more representative of temperature than what is shown on the control board.
  • Pyrometric cones tell the most accurate story of what is happening inside the kiln.  Individuals will use cones in addition to the control board to "dial" in their intended temperature.
  • Where the cones are placed does make a difference.  
  • Calibrating the kiln with cones is your best chance of coming close to what you want in temperature.
  • Remember: The kiln calibration must only be as good as what you want your work to look like – not what the cones say.

Repeatable Results

  • The only way to get entirely consistent results is to repeat the same process, with the same time-temperature cycle, with a kiln that changes as little as possible, and with the same materials as possible.
  • This is how industrial ceramics is done but with far higher precision and with process engineers using statistics to process control.
  • Most art ceramics have a much higher degree of variability.
  • Achieving your exact desired results takes a tremendous amount of time and effort.  You have to be able to test, record results, and adjust when needed. Some of the crystalline ceramic artists are good examples of people who understand how to accomplish this.

How to Calibrate Your Kiln

Tools for Calibrating Your Kiln

  • There are two basic tools for calibrating your kiln: thermocouple offset and cone offset.
  • Pyrometric cones are the main tool to "see" what is happening in the kiln.

FIRING A KILN WITH WITNESS CONES

 

EMPTY KILN WILL NOT GET TO TEMPERATURE

  • Sometimes, a new kiln does not get to temperature during the test firing due to the kiln being completely empty.
  • Firing with your kiln furniture during the test firing will put some mass into the kiln and help it reach temperature.  

DIFFERENCES IN AN EMPTY KILN VS. FULL KILN

  • An empty kiln cools a lot quicker, which will freeze the cone very quickly. In a full kiln, there is a lot of mass in the kiln that is just as hot as the kiln around it. It is this mass (the load in the kiln), which is radiating its heat as well, that will continue to melt the cone for a little longer after the kiln has been shut down.
  • Once the kiln is fine-tuned, it is also how you have loaded the kiln that will account for many of the variations you will see from firing to firing. 
  • Loading will affect the speed of firing - an empty kiln will fire differently than a full one. Although the control does compensate for this, the compensation is not totally perfect.

ADJUSTING / CALIBRATING THE KILN WITH THE THERMOCOUPLE OFFSET

  • The kiln should not be calibrated until you have fired to temperature with witness cones.  This allows you to see precisely what is happening temperature-wise and gives you an idea of where to begin. (Kilns are not fired before they ship).
  • You can fine-tune how the kiln reads temperature by adjusting the Thermocouple Offset. (See below for how to do this).
  • Fire the kiln with witness cones. Use the most typical or critical cone you fire to. Typically, the most important cone you will fire to is your glaze temperature. Generally, bisque temperatures are less critical. 
  • Thermocouple offset will change the reading of the thermocouples to the same amount from room temperature to the maximum temperature of the kiln. (Cone Offset, which will be covered later on, will adjust how the kiln reacts to a particular cone/temperature).

 

WHAT IS THERMOCOUPLE OFFSET?

  • Essentially, you are tricking the kiln that it is hotter or cooler than it is to get to the exact desired temperature.  
  • Adding a thermocouple offset lowers the temperature in the kiln (relative to the temperature reading on the control) For instance, let's say the control reads 2000°F, and you add 10°F of thermocouple offset. Now, the control thinks there is 10°F more in the kiln, and, for a setpoint of 2000°F, it will control to 1990°F in the kiln.  
  • Subtracting thermocouple offset raises the temperature in the kiln. For instance, let's say the control reads 2000°F and you subtract 10°F of thermocouple offset. Now the control thinks there is 10°F less in the kiln, and, for a setpoint of 2000°F, it will control to 2010°F in the kiln. 
  • Thermocouple Offset allows you to adjust the temperature of bisque and glaze on an Easy-fire and Vary Fire.  (Available on Dyna-Trol, One-Touch, & Genesis controls) 
  • All temperature readings in your control are determined by the thermocouple signal. Thermocouple readings can be inaccurate from thermocouple drift or electrical noise. ( Inductive Current) The only absolute that you can have good confidence in is a witness cone. When we change the thermocouple offset, we are not changing the setpoint of the control, only the temperature interpretation with the thermocouple offset.
  • You can think of the control setpoint as the other absolute and the thermocouple signal reading as the variable that gets altered in the thermoset offset process.
  • When we add temperature to the thermocouple signal, we make the control believe the kiln is hotter than it actually is, and it will shut off sooner and fire cooler. 
  • When we subtract temperature from the thermocouple signal, we make the control believe the kiln is cooler than it actually is, and it will then shut off later and fire hotter. 

EXAMPLE AND PROCESS

  • Witness cone bent slightly during the first firing, but no more than a little bit -- > Start by reducing the thermocouple offset setting by 5°F to make the kiln fire slightly hotter.
  • Witness cone did not bend at all -- >  Start by reducing the thermocouple offset setting by 10°F to make the kiln fire hotter.
  • Witness cone bent a little too much -- > Wait and see how it does with a full load or start by increasing the thermocouple offset by 5°F to make the kiln fire slightly cooler.
  • Witness cone bent more than a little bit -- > Start by increasing the thermocouple offset settings by 10°F to make the kiln fire cooler.
  • If the witness cone collapsed -- >  start by increasing the thermocouple offset settings by 15°F.
  • There are beginning suggestions - feel free to experiment outside of this.

ANOTHER STARTING POINT METHOD

  • To determine a good starting point for thermocouple offset (or cone offset) you can fire the kiln a cone or so hotter than your witness cone.
  • Then carefully observe when the cone bends and note the temperature displayed on the control.
  • Compare this number with what you think it ought to be using an Orton Cone Chart. You will have to have some idea of the speed of firing to get an accurate number.

CREATING A THERMOCOUPLE OFFSET - DYNATROL

  • Turn kiln on with toggle switch. Wait 5 seconds.
  • Press 1, wait 5 seconds. The kiln display will say STOP and then go into IdLE mode.
  • Press OTHER about eight times until you see TCOS
  • Press ENTER. See TC 1
  • Press ENTER again
  • It will flash between °FOS (which stands for Deg F Offset) and 0018 (The 0018 stands for a thermocouple offset of 18°F - which comes preprogrammed into the control to compensate for the ceramic protection tubes. By changing the offset to 0010 we are REDUCING the offset by 8°F- making it fire 8 deg hotter). (NOTE: On older kilns, with a slightly different composition thermocouple protection tube the preprogrammed value is 0050).
  • Press 0008 to reduce thermocouple offset by 10°F.
  • Press 0013 to reduce thermocouple offset by 5°F.
  • Press ENTER to accept your input.
  • Do the same for all your thermocouples. The prompts will scroll past in the order of TC1, TC2 and TC3.

THERMOCOUPLE OFFSET - DYNATROL

 

CREATING A THERMOCOUPLE OFFSET - ONE-TOUCH CONTROL

  • Access the Thermocouple Offset by getting into the Options.
  • Options are accessed by holding the ENTER button while turning the power onto the control (turn on the kiln with the toggle switch) and continuing to hold onto the ENTER button until EdIt is displayed.
  • This activates the Options Menu.
  • The first thing you will see after turning the power on while pressing ENTER is LL-G or 1t-1 (This is the software version).
  • Then you will see 1288 if it is a Cone 10 control or 1249 if it is a Cone 6 control.
  • Then you will see EdIt, and you will hear a beep. You can now let go of the ENTER button.
  • Press ENTER again. You will see °F or °C.
  • Press ENTER again, and you will see OFFS
  • Press the UP arrow to enter a positive offset OR press the DOWN arrow to add a negative sign to the offset. All this first button press does is get you in the right range.
  • You can NOW use the UP or DOWN arrow to change the value of the offset. 
  • When in the positive range, you can only go as low as 0000. The UP arrow increases the offset setting, and the DOWN arrow decreases it.
  • When in the negative range, you can only go as high as -000. The UP arrow, when you are in the negative range, is moving the setting in the negative range. For instance, if you start at -000 and hit the UP arrow, you will be at -001 (negative by one degree). If you hit the DOWN arrow, you will go back to -000 (which is actually in the "positive" direction). Some of this is counterintuitive, so it takes some getting used to by just experimenting.  
  • Once you are done with your setting, hit ENTER, and in a few seconds, the control will flash between IDLE and some temperature and STOP.
  • If you want to redo the offset setting, turn the control off and start over.
  • Older kilns with closed-end protection tubes came with a pre-programmed +18 Deg F offset to compensate for the thermocouple protection tube. Newer kilns with open-end protection tubes do generally not need an offset (except for fine adjustment).
  • Note that the control does not convert the offset setting to deg C or F. If you are operating in Deg C then the offset setting should be +8 Deg C.
  • Note: If you first press the DOWN button, you can only set a negative value, or if you first press the UP button, you can only enter a positive value.
  • You can go back and change this later if you make a mistake. 

CREATING A THERMOCOUPLE -  GENESIS CONTROL

  • Turn kiln ON with toggle switch
  • Press MENU
  • Press # - ADJUSTMENTS
  • Press # 2- TC OFFSETS
  • Select TC 1
  • Enter the degrees you would like to offset your top TC(if negative, make sure to put - symbol before the number)
  • Press SAVE
  • Press MENU
  • Press # - ADJUSTMENTS
  • Press # 2- TC OFFSETS
  • Select TC 2
  • Enter the degrees you would like to offset your middle TC (if negative, make sure to put - symbol before the number)
  • Press SAVE
  • Press MENU
  • Press # - ADJUSTMENTS
  • Press # 2- TC OFFSETS
  • Select TC 3
  • Enter the degrees you would like to offset your bottom TC (if negative, make sure to put - symbol before the number)
  • Press SAVE
  • Press BACK to return to the main menu screen

ADJUSTING TEMPERATURE VARIATION - TOP TO BOTTOM IN THE KILN 

  • Note that you can use different Thermocouple Offsets for the three (or two) different thermocouples. 
  • This allows you to make the top or bottom hotter or cooler to even out the temperatures in a kiln.

 

WHAT IS A CONE OFFSET?

  • A Cone Offset will only change the temperature for the specified cone that you offset.  For example, if created a cone 6 offset for your glaze firing, it would not affect your 06 bisque. 

 ONE-TOUCH CONTROL

  • There is no Cone Offset Option on the One-Touch Control

Creating CONE OFFSETS - DYNATROL

  1. Tune your kiln using the Thermocouple Offset for your most critical firing (typically glaze firings). 
  2. Typically, bisque firings are not very critical. 
  3. CNOS (Cone Offset) - is used to fine-tune what the Dynatrol thinks the final cone temperature should be in EASY-FIRE programs. The final cone temperature can be raised or lowered to a maximum of 99°F (or 55°C). When entering the offset temperature, the following code is used: the left two digits designate whether to raise (00) or lower (90) the cone temperature, that is, “00” means plus (+) and “90” means minus (-). The right two digits are the number of degrees the cone temperature will be raised or lowered. This offset will remain programmed only for the specific cone number until you reprogram the cone offset differently

Examples:

Number

Meaning

0020

Raise the final cone temperature by 20°F

0040

Raise the final cone temperature by 40°F

9030

Lower the final cone temperature by 30°F

9005

Lower the final cone temperature by 5°F

NOTE: This option does not affect the VARY-FIRE (Ramp-Hold) mode but it will show up on the menu.

NOTE ABOUT PREPROGRAMMED CONE OFFSETS:

  • The Cone Offsets come preprogrammed. From cone 022 to cone 017 the cone offsets are set at 9020. All other cones are preset at 0000.
  • Note on Blue DynaTrols made before Oct 1 2004, the cone offset was 9030 for cones 022 to 017 and 9020 for other cones. (The offsets were changed when we switched to a more responsive thermocouple protection tube).
  • You can always change offsets.
  • The RESET option in Other menu will NOT reset these cone offset settings.
  • This is part of the compensation necessary for the mullite thermocouple protection tubes.

Cone Offset Example:

Adjust cone 07 to shut off the kiln at 20°F below Orton’s prescribed cone temperature.

Press

Display

Comment

OTHER
OTHER

CNOS

If CNOS does not show on the display, press the Other key until CNOS displays.

ENTER

Alternately flashing:
CONE & #

Cone Offset has been selected; the word CONE and the last entered cone number will alternately flash on the display. Now enter the cone number which you want to adjust (in this example cone 07)

07

Alternately flashing:
CONE & 07

The word CONE and the entered cone number (07) will alternately flash on the display. If you type a wrong number, press 0 three times, press ENTER, then type the correct number.

ENTER

Alternately flashing:
°F0S & 0

°F0S and the previous offset setting alternately flash. Enter the new offset temperature using the rules above, in this example, 9020

9020

9020

The selected offset temperature is displayed. If you type a wrong number, press 0 four times, then type the correct number.

ENTER

IdLE flashes then the current temperature

IdLE indicates the offset temperature adjustment has been accepted. The current temperature then flashes in the display.

VIDEO SHOWING HOW TO CHANGE CONE OFFSET IN A DYNATROL

CREATING A CONE OFFSET - GENESIS CONTROL

  • Turn kiln ON with toggle switch
  • Press MENU
  • Press # 3 - ADJUSTMENTS
  • Press # 1 - CONE OFFSETS
  • Press EDIT
  • Use the scroll to the right to select the cone you are offsetting. 
  • Enter the degrees you would like to offset your cone. (if negative, make sure to put - symbol before the number)
  • Press BACK to return to the main menu screen

TROUBLESHOOTING WITH CONES

See our various instruction sheets about cones, specifically troubleshoot-cones.pdf.