Locomotive control loop grounding detection circuit and grounding detection method and wire break detection method

The invention discloses a locomotive car duct pilot earth detecting circuit, which comprises a positive bus-bar, a negative bus-bar, a load resistance, line-to-ground isolated resistances of the positive bus-bar and the negative bus-bar, wherein, two detecting branch circuits are connected between the positive or the negative bus-bar and the earth respectively, one of which is composed of a known resistance and the other one is composed of the known resistance and a switch board in series connection. At the same time, an earth detecting method and a thread break error detecting method are further provided to be used for the locomotive car duct pilot earth detecting circuit. The locomotive car duct pilot earth detecting circuit can not only judges the earth errors existing in the locomotive car duct pilot by detecting the size of the line-to-ground isolated resistance of the positive and the negative bus-bar, but also detects the errors of thread breaking, which overcomes the shortcomings of traditional methods, alarms the earth errors in advance, eliminates the hidden safety trouble caused by the earth errors to regular running of locomotive cars and improves the normal using efficiency of locomotive cars.