Passive optical sensors
AssigneeBritish Telecommunications public limited company
InventorsMohammad Zoualfaghari, Michael Fisher, Ian Neild, Michael Williamson
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Abstract
A passive sensor for detecting the operation of a light source includes a photosensor which, when illuminated by the light source, delivers a voltage to a field effect transistor (FET) which can switch a circuit to control a device at a remote location. The FET transitions rapidly between very low resistance (short circuit) and very high resistance (open circuit), allowing a binary indication to be given in the circuit. The circuit can be used to charge an electrical storage device to allow later download of recent status of the lamp by detecting the charge stored in the device.
Claims11
A transducer for detecting the state of a light source, comprising:
- a passive photoelectric sensor generating an electric potential in response to incident light, coupled to a field-effect transistor (FET) which switches between distinct on and off states at a threshold potential, wherein the FET is connected to an electrical storage device arranged to be charged up by the photoelectric sensor, and to be switched to discharge to a further circuit, by the FET when the light sources ceases to be illuminated.
Dependencies are inferred from the claim text.