초록 ▼

A fault detection circuit in a boiler-water level system includes a dual-frequency signal generator which develops two AC components with no associated DC component. The two frequencies are mixed and sent through an impedance matching circuit to match the impedance of the signal generating portion o

A fault detection circuit in a boiler-water level system includes a dual-frequency signal generator which develops two AC components with no associated DC component. The two frequencies are mixed and sent through an impedance matching circuit to match the impedance of the signal generating portion of the system with the impedance of the boiler water under measurement. The impedance-matched signal is then directed to two legs, one leg directed through one of a plurality of electrode probes and then to a first filter circuit, and the other leg is directed a second set of filters. In combination, the filters pass either the higher or the lower of the two frequencies to determine an open or short condition in the level sensing circuitry, as well as a steam vs. water condition.

대표청구항 ▼

A fault detection circuit in a boiler-water level system includes a dual-frequency signal generator which develops two AC components with no associated DC component. The two frequencies are mixed and sent through an impedance matching circuit to match the impedance of the signal generating portion o

A fault detection circuit in a boiler-water level system includes a dual-frequency signal generator which develops two AC components with no associated DC component. The two frequencies are mixed and sent through an impedance matching circuit to match the impedance of the signal generating portion of the system with the impedance of the boiler water under measurement. The impedance-matched signal is then directed to two legs, one leg directed through one of a plurality of electrode probes and then to a first filter circuit, and the other leg is directed a second set of filters. In combination, the filters pass either the higher or the lower of the two frequencies to determine an open or short condition in the level sensing circuitry, as well as a steam vs. water condition. nnecting means for setting the potential of the other of the drain and the source of the driving transistor between a state where the light emitting element operates and a state where the light emitting element does not operate; a first means for injecting the model current from a model current source into the one of the drain and the source of the driving transistor in the state where the light emitting element does not operate; and a voltage accumulating means for accumulating a gate voltage generated in response to the injection of the model current. 3. The pixel driving apparatus according to claim 2 further comprising: a first and a second switching means which are connected between the model current source and the one of the drain and the source of the driving transistor and connected between the model current source and a gate of the driving transistor, respectively; a current supplying means for separating the model current source from the one of the drain and the source of the driving transistor through the second switching means and setting the potential of the other of the drain and the source line in a state where the light emitting element operates to supplying a current to the light emitting element by the gate voltage accumulated in the voltage accumulating means; and a second means for holding supply of the gate voltage by the voltage accumulating means through the third switching means until an operation of the current programming means becomes valid. 4. A pixel driving apparatus for a light emitting display comprising: a light emitting element; a driving transistor; a model current source adapted to supply a model current; a first switching section adapted to connect/disconnect one of a drain and a source of the driving transistor and the light emitting element; a second switching section disposed between the model current source and the one of the drain and the source and adapted to connect/disconnect the model current source and the one of the drain and the source; a third switching section disposed between the model current source and a gate of the driving transistor and adapted to connect/disconnect the model current source and the gate; and a voltage accumulating section disposed between the third switching section and the gate and adapted to accumulate a voltage between both ends of the driving transistor. 5. The pixel driving apparatus according to claim 4, wherein the first switching section is a switching element disposed between the one of the drain and the source and the light emitting element. 6. The pixel driving apparatus according to claim 5, wherein the first and second switching sections and the switching element are transistors. 7. The pixel driving apparatus according to claim 4, wherein the first switching section is a power source connected to the other of the drain and the source of the driving transistor; the power source applies a low voltage to the other of the drain and the source to disconnect the drain and the light emitting element, the low voltage not enabling to drive the light emitting element; and the power source applies a high voltage to the other of the drain and the source to connect the drain and the light emitting element, the high voltage enabling to drive the light emitting element.