The present invention is directed to transient suppression devices, in general, and more particularly, to transient suppression apparatus coupleable in series with an electrical pathway into a potentially explosive environment for limiting current, voltage and energy to levels considered safe for such environments, and to systems utilizing such apparatus.
An aircraft fuel measurement or indication system is an example of a system which utilizes transient suppression devices for limiting current, voltage and energy into a potentially explosive environment. In such a system, sensors are disposed at or in the fuel tank of the aircraft and a sensor excitation system remote from the tank generates excitation signals over electrical pathways to the sensors for measuring the quantity of fuel in the tank. Currently, there are many different types of sensors, comprising capacitive, inductive and/or resistive elements, for example, and different types of excitation signals needed to excite these sensors, like alternating current (AC), direct current (DC) and/or pulsed excitation signals, for example. Because of these differing system applications, the transient suppression solutions therefor need to accommodate differing levels of current, voltage and energy protection.
In addition, recent new requirements have been specified to insure aircraft safety, specifically associated with fuel tank safety which is considered a potentially explosive environment. These requirements apply to multiple threat and failure conditions that could impose unsafe levels of energy, voltage and current into the potentially explosive fuel tank environment if left unprotected. Existing transient suppression devices which are disposed in the electrical pathways use magnetic isolation, such as inductors and/or transformers and band pass circuit filtering, for example, to limit the current, voltage and energy parameters of the electrical pathways to the fuel tank. While an adequate solution, each transient suppression device needs to be tailored or designed for a specific application or group of similar applications in order to accommodate the level of current, voltage and energy protection required therefor while maintaining the level of sensitivity of an existing solution at normal operation taking into account parasitic components of the electrical pathways. Accordingly, there is no known existing transient suppression solution that may be universally used for the many different types of sensor/system applications and requirements therefor.
The present invention intends to overcome the drawbacks of the existing transient suppression devices and systems utilizing the same by offering substantially universal transient suppression apparatus which will provide the specified protection with different types of sensors and sensor excitation signaling and not be subject to the level of sensitivity that the existing solutions have at normal sensor measurement operation.
In accordance with one aspect of the present invention, transient suppression apparatus, which is coupleable in series with an electrical pathway into a potentially explosive environment for limiting current, voltage and energy thereto, comprises: an impedance element coupleable in series with the electrical pathway to conduct current to the potentially explosive environment, the current causing a voltage potential across said impedance element; at least one first semiconductor element coupled to the impedance element in series with the current path upstream of the impedance element, the at least one first semiconductor element operative to impose a resistance to the current of the electrical pathway governed by the voltage potential across the impedance element; and at least one second semiconductor element coupled to the impedance element in series with the current path downstream of the impedance element, the at least one second semiconductor element operative to impose a series resistance to the current of the electrical pathway governed by the voltage potential across the impedance element.
In accordance with another aspect of the present invention, a system for determining a quantity of fuel in a container comprises: at least one sensor disposed at the container for sensing a quantity of fuel in the container; sensor excitation system coupled to each of the at least one sensor through an electrical pathway for providing an excitation signal thereto; transient suppression apparatus as described directly above disposed in series with each electrical pathway for limiting current, voltage and energy to the container.