Thermocouple Offset Setting and Cone Offset Setting

Knowledgebase FAQ

  • See the Sales FAQs for Frequently Asked Sales and Preorder Questions
  • The Knowledgebase is organized into a series of questions and answers having to do mostly with technical troubleshooting and understanding of kilns.
  • Although we write this for our own kilns many of these articles apply to other makes - although L&L takes no responsibility for that.
  • Many Knowledgebase articles have Actions, PDFs and Videos associated with them.
  • Actions are specific actions for you to take during the troubleshooting or repair process.
  • Each Action may also have Videos and PDFs associated with it and, in addition, specific Cautions.

Search Knowledgebase

Thermocouple Offset Setting and Cone Offset Setting

What they are, how to find them, and when to use which setting.

  1. Thermocouple Offset and Cone Offset are two different settings that allow you to control how much heat-work develops in the kiln by the end of the program. Basically they accomplish this by allowing you to raise or lower the final temperature that the DynaTrol calculates to shut itself off.
  2. The Thermocouple Offset setting allows you to add or subtract degrees from the kiln’s final temperature.
  3. The Cone Offset setting allows you to add or subtract degrees from what the DynaTrol determines the individual cone’s final temperatures to be.
  4. They are both located under the OTHER key. When the display reads IDLE, press OTHER again and again.

Cone Offset:

First up is Cone Offset which looks like CNOS. Press ENTER here to first set which cone you want to offset, then set how much of an offset you want to have. Very early versions of the DynaTrol only came with +/-50 degrees, while later ones come with +/-100 degrees. If the setting is already set to 0 and you want the kiln to fire cooler you must use a “9” in front of the setting; 9020 would 20 degrees cooler that the 0000 setting.

Thermocouple Offset:

A few OTHER presses past CNOS you will find TCOS or Thermocouple Offset. When TCOS comes up press ENTER and first you will see which TC you are about to offset. Press ENTER again and you will see how many degrees are currently offset for that thermocouple. This number is what you will be changing to make this zone of the kiln fire hotter or cooler. RAISE the setting to fire cooler, LOWER the setting to fire hotter. Use the “9” again as a prefix for a setting that is set below 0. While you can set each zone differently it is best to keep the settings within 10 degrees of each other to minimize the chances of producing an error code from the difference between an artificially higher/ lower temperature and the real set point.

Thermocouple Offset and Cone Offset can both be used to calibrate the kiln to a self-standing pyrometric cone. All this means is that when you program the kiln to go to say cone 6, it will do that and bend the cone over perfectly- not too hot or cool. If the cone comes out looking too melted or not melted enough Thermocouple Offset and/or Cone Offset can be used to adjust it hotter or cooler.

Lots of people call up and say the kiln fires too hot or too cool. It seems best to first calibrate the kiln to their glaze cone using Thermocouple Offset only. This usually only takes one firing but sometimes 2 or 3 firings is necessary.

If they say it fired more than a whole cone over where it should have, add 25-35 to the existing Thermocouple Offsets. If they say about a whole cone over add 20-25. If they say the cone was flat but still had the hump in the back add 15-20. 10 seems to be the minimum setting change in order to see a significant change in the cones.

Cone Offset is only seldom used; like for example if the customer complains that although the glaze firing is fine, the bisque firing is too hot or too cool.

Using Cone Offset on the bisque firing adjusts just a single cone number and does nothing to change the glaze firing. It is pretty rare to have to use both though. Usually they just care about the glaze firing.

Another time to use Cone Offset is to get the kiln to fire to cone 5-1/2 instead of cone 5. Just add 20 to whatever is set in the cone offset already for cone 5. Then fire to cone 5 and it should be about ½ a cone hotter.

Additional Actions to Take

Why Calibrate Your Kiln?

Most people will be satisfied with the operation of their kiln right out of the box. However for the most precise or accurate work a kiln needs to be calibrated or adjusted to match the load, the temperature that you typically fire to, the unique characteristics of the kiln, and the thermocouples.

It is important to establish a relationship between you, your kiln and your work. Although we use the word “calibrate” or “tuning” really what is called for is an understanding of the heating characteristics of your particular kiln, and understanding of how thermocouples and controls work and their limitations, how you load your kiln, the clay and glazes that you use, how pyrometric cones work, and the basic concepts of heat-work. Let’s take these one at a time.

The heating characteristics of your kiln

Each kiln is different. They vary from brand to brand, kiln series to kiln series, kiln size to kiln size, and even for identical models from kiln to kiln. The age of the elements, the insulation thickness, the distance from the center of the kiln to the elements, the kiln height, how tight the kiln is, if there is a vent, the condition of the thermocouples as they age, whether there is a protection tube on the thermocouple, etc. Even external conditions like voltage and temperature in the room affect the firing. Moreover, the controls used in most kilns, while perfectly acceptable for ceramics, are not military precision instruments. So – just assume and know that the kiln is not a standardized “instrument” – it is more like a violin that needs to be tuned and understood.

Controls and Thermocouples

The controls in ceramic kilns are typically accurate to about 1% of scale vs. something like .1% of scale in an expensive industrial control. The thermocouples can read +/- 10°F from actual temperature even when when they are brand new. (This is a function of the variation in materials in the thermocouple. Even though L&L uses "Special Limit of Error" wire, there are still all kinds of variation in the thermocouples, the thermocouple circuit, and the cold compensation on the control. See this on Wikipedia for more information on thermocouples. On the other hand, to put things in perspective, ceramic kilns cost about 10% to 25% of what a comparable industrial kiln or furnace would cost. In addition to this Type K thermocouples, the most common ones used in ceramic kilns, will drift over time, especially when used over 2000°F. Type S platinum thermocouples do not drift at those temperature. Although they are available as options on most L&L kilns and most other brands, they cost on the order of $200 each and most people are not willing to pay for them. The thermocouple protection tube that L&L uses introduces a known 18°F offset into the thermocouple reading. Although it is a known constant and is adjusted for, the exact amount can vary slightly based on individual tubes (this does not change with time). The long story short here is that the absolute temperature that you see represented on the control may not be completely accurate (and even if it were it is only one piece of the information you need to understand what is happening in the kiln). On the other hand it tends to be consistent over time (except for the thermocouple drift). Hence, when you “calibrate” the control to meet the requirements of your work, the experience of many thousands of customers tells us that you will get consistent results firing to firing, all other things being equal.

How you load your kiln

How you load your kiln makes a huge difference in how heat reaches and affects your work. For example, fire an empty kiln and you will probably get error codes. Fire it too densely or too heavily in the top or bottom and you might get different error codes. Ideally you will load it with a reasonable amount of work, not too close the elements, and distribute the work as evenly as possible. Also 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 convective 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. Also know that clay and glaze varies with different batches.

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 right result.

Cones

Pyrometric Cones are probably the best way to “see” ceramic heat-work. They represent and reflect the actual ceramic process taking place. They are far more representative of what you want to see than temperatures as shown on the control. Still, even pyrometric cones are telling a story that is only representative of what your work will experience. Where they are placed in the kiln can make a difference, for instance. They will always need to be interpreted based on your experience with your own work. However, calibrating the kiln with cones is your best chance of coming close to what you want.  Do not get hung up on perfection because you will, if you can, only perfect a representation. It only has to be as good as what you need to produce the work you want – not what the cones say.

Repeatable Results

Given all the variables involved the only way to get completely 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 statistical process control. Most art ceramics has a much higher degree of variability. There are exceptions to this rule and those who pursue those exceptions need to and often do put a tremendous amount of time and effort into this achievement. Some of the crystalline ceramic artists out there are good examples of this.

How to Calibrate Your Kiln

Tools for Calibrating your Kiln

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

FIRING A KILN WITH WITNESS CONES

Click here is the video above about using witness cones does not display.

SOMETIMES AN EMPTY KILN WILL NOT GET TO TEMPERATURE

  1. Sometimes a new kiln does not get to temperature during the test firing. This is generally because of an empty kiln. It is generally a good idea to fire with your kiln furniture to put some mass in the kiln even during the test firing.

DIFFERENCES IN AN EMPTY KILN VS. FULL KILN

  1. One difference between an empty and full kiln is that 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 it’s heat as well, that will continue to melt the cone for a little longer after the kiln has been shut down.
  2. Once the kiln is fine-tuned, it is the variable of how you have loaded the kiln that will account for many of the variations you will see from firing to firing. 
  3. Loading will affect the speed of firing - an empty kiln will fire differently than a full one. Although the control does compensate for this that compensation is not totally perfect.

ADJUSTING / CALIBRATING  THE KILN WITH THE THERMOCOUPLE OFFSET

  1. The kiln cannot be calibrated until it has reached temperature and affected a witness cone. The reaction of the witness cone to the firing is how you begin the calibration process. (Kilns are not fired before they ship).
  2. You can fine-tune how the kiln reads temperature by adjusting the Thermocouple Offset.
  3. 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. 
  4. Thermocouple offset will change the reading of the thermocouples 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?

  1. Adding thermocouple offset lowers the temperature in the kiln (relative to the temperature reading on the control. For instance lets 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 actually control to 1990°F in the kiln. 
  2. Subtracting thermocouple offset raises the temperature in the kiln. For instance lets 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 actually control to 2010°F in the kiln. 
  3. Thermocouple Offset affects both Easy-Fire programs and Vary-Fire programs (Cone Offset, on the other hand, only affects Easy-Fire programs).

EXAMPLE AND PROCESS

  1. If the witness cone bent slightly during the first firing, but no more than a little bit, then start by reducing the thermocouple offset setting by 5°F to make the kiln fire slightly hotter.
  2. If the witness cone did not bend at all, then you can start by reducing the thermocouple offset setting by 10°F to make the kiln fire hotter.
  3. If the witness cone bent a little too much, you might wait and see how it does with a full load, or you could start by increasing the thermocouple offset by 5°F to make the kiln fire a little cooler.
  4. If the witness cone bent more than a little bit start by reducing the thermocouple offset settings 10°F which will make the kiln fire cooler.
  5. If the witness cone collapsed start by reducing the thermocouple offset settings 15°F.
  6. There are beginning suggestions - feel free to experiment outside of this.

HOW TO CHANGE THERMOCOUPLE OFFSET IN A DYNATROL: STEP BY STEP

  1. Turn kiln on with toggle switch. Wait 5 seconds.
  2. Press 1, wait 5 seconds. The kiln display will say STOP and then go into IdLE mode.
  3. Press OTHER about eight times until you see TCOS
  4. Press ENTER. See TC 1
  5. Press ENTER again
  6. 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).
  7. Press 0008 to reduce thermocouple offset by 10°F.
  8. Press 0013 to reduce thermocouple offset by 5°F.
  9. Press ENTER to accept your input.
  10. Do the same for all your thermocouples. The prompts will scroll past in the order of TC1, TC2 and TC3.

ADJUSTING FOR TEMPERATURE VARIATION TOP TO BOTTOM IN THE KILN

  1. 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.

CONE OFFSETS

  1. Tune your kiln using the Thermocouple Offset for your most critical firing (typically glaze firings). Typically bisque firings are not very critical. 
  2. 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 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

0015

Raise the final cone temperature by 15°F

9030

Lower the final cone temperature by 30°F

9005

Lower the final cone temperature by 5°F

9045

Lower the final cone temperature by 45°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 preprogramed. 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 this. The RESET option in Other menu will NOT reset these 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 appears indicating the offset temperature adjustment has been accepted. The current temperature then flashes in the display.

TROUBLESHOOTING WITH CONES

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

  1. Carefully examine thermocouple tip. This is the exposed welded joint at the end of the thermocouple that is not covered up by the ceramic tube.
  2. To do this you will have to remove the thermocouple from its protection tube (if it is a kiln that has one of our protection tubes). You can do this with the kiln disconnected from power.
  3. Look for corrosion - especially if it severe. These thermocouple tips will oxidize and otherwise corrode over time. That is normal. There is some point, however, at which the corrosion affects the ability of the tip to work (thermocouples work by generating a small voltage at the tip caused by two different metals reacting to each other).
  4. Make sure the two wires are securely joined. One of the things that can cause an intermittent problem is a bad weld. If the two wires touch each other (even if they are not welded) they may work temporarily. However, if the weld is not secure then the wires could separate when the kiln heats up and cause an intermittent failure.
  5. If the thermocouple tip looks healthy then test the control board.
  1. Unplug kiln.
  2. Remove or hinge open the control box.
  3. Remove the Thermocouple Lead Wire from the Thermocouple.
  4. Unscrew the Thermocouple from the kiln.
  5. Remove Thermocouple.
  6. Install a new Thermocouple and screw in place.
  7. Replace Thermocouple Lead Wire and tighten. Be sure to get red matched to the MINUS (Negative) sign and the Yellow matched to the PLUS (Positive) sign.

See this video: