| 摘要 |
PURPOSE:To make it possible to select the overrange directions to the upper and lower limits at the time of wire breakdown, by the constitution wherein the inverted or non-inverted output of a power source voltage can be selectively applied to the input of a temperature measuring amplifier at the time of wire breakdown of a temperature resistor. CONSTITUTION:When a temperature resistor Rt is broken at a point P, the voltage ea at a point A becomes VR1, and the voltage eb at a point B becomes eb=0. Therefore, the output of a comparator 4 becomes ON, and the output of a comparator 5 becomes OFF. An analog switch 7 is turned ON by the ON output of the comparator 4. The voltage of a +B power source is applied to the positive input terminal of the amplifier 2. Thus the output of the amplifier 2 is overshot to the upper limit. A point (c) of a jumper 8 is connected to a point (b), and the value of a resistor R5 is made smaller than that of the resistor R. Then the output is overshot to the lower limit. When the temperature measuring resistor Rt is broken at a point Q or a point S, the same action follows. The power source voltage is selectively applied to either the inverted input terminal or the non-inverted input terminal of the amplifier. Thus the overrange directions to the upper and lower limits can be selected, and the fail safe action for the wire breakdown fault can be implemented. |
