| 摘要 |
PURPOSE:To protect a disconnected resistor precisely when any one of resistors in a serial temperature resistor is disconnected by detecting the disconnected resistor and shorting both the ends of the resistor. CONSTITUTION:If a temperature measuring resistor 12 is disconnected or a temperature measuring resistor 14 is disloaded from a terminal board 2, the state is detected by an overvoltage detecting circuit 10 and informed to a control circuit 7. The control circuit 7 checks whether the voltage of a constant current power supply 8 is excessive or not under the state that the switches 92-9N other than a switch 91 are closed. In this case, an excessive value is not detected because the resistor 11 is normal. When the switch 92 is closed while the switch 91 is still opened, an excessive value is generated because the resistor 12 is disconnected, so that the disconnection of the resistor 12 can be detected. Similar ly, the unloading of the temperature measuring resistor 14 can be detected by closing the switch 94. |
