At Skutt we believe in giving the customer the choice to match the thermocouple that best suits your needs.
There are currently 4 types of thermocouples used on the market today and each have their advantages. For more detailed information on choosing a thermocouple read What is a Thermocouple and How To Evaluate Thermocouples.
8-Gauge Type K – Standard with Every KilnMaster Kiln
- Double the Life – We supply a free replacement with each new kiln.
- Accurate – We use only Special Limit Wire, which is tested to very highest standards.
- Responsive – Because it does not have a heavy protection tube, this thermocouple is extremely responsive.
- Durable – The 8-Gauge wire with low mass ceramic insulators is tough.
- Value – Replacement thermocouples are inexpensive and easy to install.
Recommended Applications – Low Fire Ceramics. Occasional High Fire OK.
Type S – Special Order Upgrade
- Cone 10 – This thermocouple can hold up to the high demands of High Fire applications firing after firing.
- Accurate – Type S wire is the most accurate thermocouple wire available.
- Responsive – The low mass ceramic protection tube insures that this thermocouple remains responsive.
- Long Life – This thermocouple does not degrade and will virtually last forever if not broken.
- No Drifting – Since this thermocouple does not degrade it will not drift.
- Sealed tube – Protects probe from kiln atmosphere.
Recommended Applications – High Fire Ceramics and Applications where high precision is critical.
Type K MI Cable – Standard with Every GlassMaster Kiln
- Accurate – At low fire temperatures this thermocouple is very accurate.
- Responsive – The low mass thermocouple shield insures responsiveness and eliminates flaking.
- Durable – The low mass shield is tough.
- Long Life – At low fire temperatures this thermocouple will last a long, long time.
Recommended Applications – Low Fire Ceramics and Glass
8-Gauge Type K w/Ceramic Protection Tube – Special order only
- A low mass protection tube is currently not available for this thermocouple and therefore we are only recommending this unit for specialized applications. Please contact the factory for details.
Important – Type S thermocouples may only be used with a Type S controller and Type S thermocouple lead wire and vice-a-versa. Misuse could result in an overfire.
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What is a Thermocouple?
A thermocouple is a component of the kiln used to read the temperature within the kiln chamber. The controller uses the information it receives from the thermocouple and makes decisions on whether or not to turn the element on or off. Your oven at home most likely has a thermocouple that performs the very same function.
The thermocouple is constructed of 2 pieces of dissimilar metal (usually wire) that are joined together at one end. When heated this junction creates a very small electrical signal (measured in millivolts) that changes as the temperature is raised or lowered. Since the signal moves predictably it can be converted by the controller into a temperature reading.
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How To Evaluate Thermocouples
The 5 most important things to consider when evaluating a thermocouple are:
The Accuracy of a thermocouple is measured by the difference between what a thermocouple is reading and the actual temperature of the chamber. This is measured when the kiln is at a steady state (not ramping up or down).
A Type S thermocouple is considered to be the most accurate thermocouple and is therefore used as the standard to measure against. The material used to construct a Type S thermocouple will not degrade in most atmospheres and therefore the thermocouple will not drift with age.
Type K thermocouple wire is also very accurate however as the wire degrades the thermocouple will began to drift towards an overfire. This is a gradual process and is not something to be concerned about. Use self supporting Pyrometric cones to monitor your firings and indicate when it is time to change the thermocouple.
High mass protection tubes can also affect the accuracy of a thermocouple even during a long soak. This is because the end of the tube that is not exposed to the kiln chamber wicks heat through conduction causing a falsely low reading (see Illustration). This will cause the kiln to fire too high. The higher the temperature the more dramatic the effect.
You can compensate for this affect by entering Cone offsets (altering cone correlation temperatures in Cone Fire Mode) however this must be done for every cone value and does not compensate for temperature ranges prior to cone correlation.
The Responsiveness of a thermocouple is determined by the accuracy of the thermocouple while the kiln is increasing or decreasing in temperature. This is determined primarily by the type and mass of the protection tube used if any. The greater the mass of the protection tube the less responsive the thermocouple becomes.
Thermocouples that are not responsive will lag behind the actual temperature of the kiln when it is ramping up. Since the controller thinks the kiln is cooler than it actually is, this will cause the kiln to overshoot the desired temperature. Generally, the faster the rate the more dramatic the overshoot.
This can be compensated for by entering thermocouple offsets (tricking the controller to read a higher temperature than the thermocouple is indicating), however once the kiln enters a soaking temperature the temperature balances out and the actual temperature of the kiln will be too low. For obvious reasons this is not recommended.
The life of a thermocouple, how long it lasts, can be affected by a multitude of factors. The most influential factors are Wire Type (see Wire Type section) and temperature. The temperature range in which it is used can have a huge impact on the life of the thermocouple. For example, a thermocouple used at glass temperatures may last for over 1000 firings where the same thermocouple used at cone 10 may only last for 20 firings.
The life of the thermocouple will also be affected by the gauge of thermocouple, and gases it is exposed to from clay and glazes.
Durability is determined mostly by the thermocouples impact resistance. In certain applications, especially when inexperienced people are loading the kilns, it is possible to bump the thermocouple with a piece of ware or a shelf. The stronger the thermocouple the more it will hold up to this abuse.
Type K thermocouples will oxidize as they age. If a protection tube is not used they will drop small black particles below the thermocouple. This is generally not a problem since the thermocouples do not protrude too far into the kiln chamber and the particles drop straight down. It will be necessary to vacuum the kiln chamber occasionally. Type S thermocouples will not flake however a protection tube is needed for dimensional stability.
Type S thermocouples are approximately 20 times more expensive than Type K thermocouples due to the materials used to make them. At Skutt we give you a spare type K thermocouple with every purchase of a new Skutt Kiln therefore your initial cost per firing is cut in half. Since a Type S thermocouple will virtually last forever, unless you break it, your cost per firing decreases with every firing.