| 摘要 |
PURPOSE:To detect a disconnection without exerting any influence on an input scan by generating an AC constant-current having a frequency stopped by a noise eliminating means when the disconnection is detected, applying it to a thermocouple, and comparing a generated voltage of an input part by the AC constant-current, with a reference voltage. CONSTITUTION:An output of a thermocouple 1 is inputted to a controlling circuit 15 through a noise eliminating signal conditioner 8 provided with a semiconductor protecting circuit 23, etc., and by a command of a disconnection detection controlling circuit 21 of the circuit 15, a current I of an AC constant-current source 22 is applied to the thermocouple 1, and an input part voltage (e) of the conditioner 8, which is generated at that time is inputted to the primary side of a pulse transformer 291 through a noise eliminating filter circuit 27, etc. Also, its secondary side voltage is inputted to a comparator 35 through an amplifier 31, etc., compared with a reference voltage VREF, and its disconnection detecting signal 100 is inputted to the circuit 15 and the circuit 21 is operated, by which the output of the thermocouple 1 is inputted to the conditioner 8. |
