Solid/Liquid State Sensor

A common problem in industrial processes, particularly those involving electroheat, is the holding of metallic charges at their solid/liquid state interface temperature. A transducer has been developed that achieves this by plunging and widthrawing a probe in an induction-heated metallic charge. The probe is driven by a servomotor whose armature current senses the state of the charge. Successful results have been obtained with induction-heated metals and alloys. In many cases the degree of control is so precise that the limit cycle amplitude is undetectable. Preliminary investigations into nonmetallic charges have also been conducted. These can be successful provided the induction heater output is low. The new transducer is simple, rugged, inexpensive, and constructed from items readily available in industrial instrumentation laboratories. The presentation is intended for the professional engineer concerned with the control of industrial processes.