In a process control network, apparatus and method for periodic testing of a thermocouple element includes a switching mechanism that inserts a circuit with known parameters in series with the thermocouple. Voltages levels with and without the inserted circuit are compared and used to identify a failed...http://www.google.com.au/patents/US4841286?utm_source=gb-gplus-sharePatent US4841286 - Apparatus and method for detection of an open thermocouple in a process control network
