(1) No signal, no air source. The reason is that the air source is not opened or the air source fails, the air duct is blocked or the pressure reducing valve fails due to blockage, and the compressor has a fault light;

(2) There is air source and no signal. The cause is that the positioner fails due to air leakage due to the rupture of bellows, or the converter fails;

(3) The positioner has no air supply. The reason is that the filter and pressure reducer are blocked and fail;

(4) The positioner has air supply but no output. The reason is that there is blockage in the orifice of the positioner and the fault occurs;

(5) Signal, no action. The reason is that the valve core falls off; The valve stem is bent or broken.