L&L's Thermocouple Test Program

MULLITE CERAMIC PROTECTION TUBES OVER 8 GAUGE TYPE K THERMOCOUPLES OFFER SUPERIOR LIFE THAN METALLIC THERMOCOUPLES

L&L TEST PROGRAM

L&L tested 23 different thermocouples in a kiln by firing them to Cone 10 (2350°F) and soaking the kiln for one hour repeatedly and then measuring the thermocouples with a sophisticated datalogger. The main thermocouple to control the kiln was a platinum Type S. The various test thermocouples were our standard 8 gauge thermocouple with a butt-welded end, one with a twisted end, both in a heavy mullite protection tube and exposed to air, 14 gauge Type K exposed thermocouples, Type N thermocouples of various types, a Hoskins 2300mi, several metallic sheathed thermocouples with inconel and various grades of Pyrocil (a replacement for the 2300MI), etc.

One of our standard Type K 8 gauge thermocouples in the industrial protection tube achieved 139 firings. The standard 8 gauge thermocouple without a protection tube made it to 100 firings. The metal-sheathed Pyrocil was good but not as good as the 8 gauge with the protection tube (it worked for 130 firings). An 8 gauge Type N did slightly better (143 firings) but the potential confusion of using this outweighed the simplicity and backward compatibility of the Type K.

The conclusion from the test is that a standard 8 gauge thermocouple with an industrial mullite ceramic protection tube offered the best combination for cost, cleanliness (there is no contamination of the kiln with metal spalling), resistance to contaminants in the kiln like sulfur, backward compatibility, and long life.

Before Thermocouple Test

Thermocouple Test After the test

Thermocouple Test