Clay Times Back Issues Vol. 2 Issue 4 • May/June 1996 - Page 26

MASTER KILN BUILDERS Preventing Thermocouple Burn-Out WITH 18 YEARS EXPERIENCE DESIGNING AND BUILDING BEAUTIFUL, SAFE CUSTOM KILNS BY MARC WARD CAR • SALT/SODA • WOOD • STONEWARE CALL OR FAX DONOVAN PALMQUIST (612) 789-1056 S INGLE-FIRE WORKSHOPS TUSCARORA POTTERY SCHOOL DENNIS PARKS (702) 756-6598 TUSCARORA, NEVADA 89834 Largest selection of pottery equipment, books & supplies, in the known universe! FREE 192 PAGE CATALOG Phone: 800-843-7057 RAKU KILNS 20-gallon, $125 30-gallon, $150 Propane Burner, $65 Raku Videos, $20 each — Free Shipping — (941) 359-0773 VISA • MASTER CARD • AMERICAN EXPRESS DOLAN Precision TOOLS Tools for Artists and Craftsmen 26 ▼ 12612 N. 60th St. • Scottsdale, AZ 85254 1 (800) 624-3127 • Fax (602) 991-4509 Q: The thermocouples on my burners are continually burning out. Is there something I can do to keep this from happening? whatever type of thermocouple you are using, if the back end or "cold junction" gets too hot, you'll have a shutdown. A: Thermocouples are designed to be low-maintenance items. I just replaced one on my kiln that was installed ten years ago. A thermocouple works by sending a signal to a safety valve, telling that valve, "There's a pilot flame burning on me, so everything’s fine.” This signal is a very small voltage current that is produced by the pilot flame. The flame heats up the bulb at the end of the thermocouple while the back end of the bulb stays relatively cool. This "tension" between the front and back of the bulb produces the current. The current is anywhere from 10mV (10 millivolts or 1/100 of a volt) to 35mV (35 millivolts or 3.5/100 of a volt). If the back end of the bulb gets too hot in relation to the end on which the pilot flame is burning, the signal "drops out". In other words, the safety valve is no longer getting the message from the thermocouple and the safety valve shuts the burner down. If the back end of your thermocouple bulb gets con