Field transmitter with diagnostic self-test mode

摘要

A field transmitter for transmitting signals representative of process variables has both a normal operating mode and a diagnostic self-test mode. The field transmitter has a physical sensor for sensing a process variable and generating a physical sensor signal which is representative of the process variable. A signal processing circuit converts the sensor signal to a measurement which is transmitted to a control room. The field transmitter also has a surrogate sensor for producing a surrogate sensor signal which is independent of the process variable. During the diagnostic self-test mode, the surrogate sensor is connected to the signal processing circuit in place of the physical sensor. If the output of the signal processing circuit does not correspond to an expected value, a diagnostic code is produced.