APPLICATIONS

Fuses are often counted upon for extinguishing fires within a housing based on the circuit producing a short circuit or overload that will eventually clear the fuse. Other mechanisms such as thermal fuses and thermal switches have also been used with limited results as the point of thermal stress must be mechanically connected to the thermally overstressed component in order to perform its intended function. Many smaller events and transient events may cause smoke but not be of adequate magnitude to trip either a thermal limit or an input fuse. This leaves a wounded or failing product in operation until such time as the unit fully fails, many time causing additional stress on personnel within a small area, such as a passenger cabin of an aircraft, of the failing device.

Disclosed herein is a volatile organic compound (VOC) controlled relay that is utilized as a switching relay to enable and disable power to electronic circuits. This VOC controlled relay is particularly suited to power conversion electronics where high power and manipulation of high power or voltage carries risks of failures due to overstress, unforeseen input variations, thermal overstress, component failures, poor design practices and other failure mechanisms.

It is a feature of the VOC controlled relay that miniaturization and

microelectronics enable integration of a sensor, microcontroller and power relay in an integrated package to become a single sensing and power control device.

Figure 1 is an isometric view of a VOC controlled relay as described herein.

Figure 2 is a cross-sectional view of the VOC controlled relay.

Figure 3 is a block diagram of the VOC controlled relay.

Figure 4 is a schematic of the VOC controlled relay.

Figure 1 is an isometric view of a VOC controlled relay 10 having a housing 12 and gas ports 14. A plurality of leads provide electrical interconnect between the VOC controlled relay and external circuitry. These leads include controller leads 16 and relay leads 18.

Figure 2 is a cross-sectional view of the VOC controlled relay 10. Contained within housing 12 are a controller portion 20 and a relay portion 22. The controller portion 20 includes a gas sensor 24 and a microcontroller 26. Optionally, radio 28 may be included. Data and power is provided through bus 30 that is electrically interconnected to controller lead 16. The gas sensor 24 and microcontroller 26 can either be powered from the power input to the relay portion 22 or from a secondary circuit separate from the relay assembly. A self-contained power relay portion 22 with separate power supply to power the gas sensor 24 and the microcontroller 26 is one preferred embodiment.

The gas sensor 24 receives a gaseous input through gas port 14 and measures a level of VOC. The gaseous input is typically ambient air. The sampling may be continuous or periodic as required by the system to adequately monitor for fault events. The VOC level is communicated with the microcontroller 26 to monitor the VOC level. Dependent on the concentration of VOC and the rate of change of VOC concentration, the microcontroller sends the data over the optional radio 28 to an external monitor. If a programmed threshold level is exceeded, the microcontroller 26 opens the relay 32 removing power from the unit under supervision. As one example, the microcontroller may instruct the relay to open when the VOC concentration exceeds a nominal level based on the environment by a predetermined amount, such as by 50%, by concentration. The nominal level may be determined by taking several measurements over time to establish a baseline. An elevated VOC concentration is an indication that there is overheating or outgassing of components. Opening the relay causes power to be removed from the device under supervision. As an example, if the baseline VOC concentration is 480 parts per billion (ppb) and when a reading is taken the concentration increased to over 700 ppb, the relay would be actuated to remove power.

VOC gases enter through the gas ports 14 extending through housing 12 where they are analyzed for content of materials. This information is processed by the microcontroller 26 which compares the gross value of VOC particles to the maximum value allowed based on a programmed value. The programmed value could include an offset for other environmental contaminants such as dust or other organic compounds to ensure no false triggers of the system occur. Setting of the trip value could be done at the factory or with the use of the optional radio 28. This value could be set on location for the device it is monitoring. The radio would report the continuously or periodically monitored value of the VOC level. One suitable gas sensor is a micro VOC integrated circuit, such as the ultra-low power digital gas sensor for monitoring indoor air quality sold by AMS USA Inc. (Cupertino, CA) as the CCS811 Gas Sensor Solution. Relay 32 is normally in the closed position, in electrical contact with a first contactor 34, so that first relay lead 18A and third relay lead 18C are electrically interconnected and the device controlled by the VOC controlled relay 10 functions normally. When a threshold level of VOC is exceeded, magnetic coil 36 is powered causing the relay 32 to break contact with the first contractor 34 and make contact with the second contactor 38. When the relay 32 is in electrical contact with the second contactor 38, second relay lead 18B and third relay lead 18C are electrically interconnected and the device controlled by the VOC controlled relay 10 does not receive power.

The relay 32 may be a single pole single throw (SPST) relay or a multi-pole double throw relay depending on the application.

Once the microcontroller 26 determines that the VOC level exceeds the programmed level, the microcontroller 26 signals to the relay portion to "set" the relay 32 latching it OPEN. This removes power from unit under supervision. To reset the latching relay 32, either an additional electrical signal or a mechanical push button may be used to move the relay 32 back to the normally closed position, in electrical contact with first contactor 34.

While Figures 1 and 2 illustrate the gas sensor 24 contained within the same housing 12 as the relay 22, alternatively, the gas sensor may be contained in a separate housing and be located remotely from the relay. Communication between the gas sensor and the relay would then be by any suitable wired or wireless communication system.

Figure 3 is a block diagram depiction of one embodiment. Power is supplied via the power bus 138 and power return 40 lines. The power may be AC or DC power depending on application. For an exemplary passenger cabin of an aircraft application, the power is typically 115 volts AC at 400 Hz. Minor adjustments to the circuit could be required depending on the power bus source of choice. Power is fed through the normally closed first contactor 34 of the relay portion 22 to the device under supervision 42 through the power output 48 of the relay portion 22. The VOC sensor (Gas Sensor 34) continuously monitors the air quality within the unit under supervision 42. The VOC content is requested by the microcontroller 26 through an Inter-Integrated Circuit (I2C) interface 46. When a measurement is complete, the VOC sensor 24 responds over the I2C interface 46 to the microcontroller 26 with the VOC content. The microcontroller 26 determines if the value of the response is greater than the programmed limit. The programmed limit can be set at the factory or loaded through a wireless interface to the microcontroller 26 through a radio. Microcontrollers 26 with integrated radios are a design method that keeps the device 10 as small as possible.

Figure 4 schematically depicts electrical connections from component to component. The I2C interface 46 between the microcontroller 26 and the sensor 24 allows for bidirectional communication between these devices. Power for the microcontroller and sensor is derived from an appropriate power supply taken from the input power. The method of this is determined by the input power bus 138 voltage and form chosen.

Jl of Figure 4 is a programming port to allow firmware to load into

microcontroller (26) U2. Ul is a voltage regulator to convert the 5VDC of the Universal Serial Bus (USB) interface to a regulated 3.0VDC used by the microcontroller for operation during programming. Yl is a crystal oscillator to set the operating frequency of the microcontroller instruction cycle timing to operably execute the firmware instructions. The firmware loaded is operable to monitor the VOC sensor 24 through the inter integrated circuit (I2C) interface 46. The microcontroller 26 contains non-volatile memory for storing the firmware as well as the nominal value of the VOC sensor under nominal operating conditions for comparison to operational readings taken.

When the microcontroller receives a reading from the VOC sensor 24 showing a dramatic increase in VOC value, the microcontroller determines that a smoke, heating or outgassing event is occurring. The microcontroller though port PFO sets the port to a logic 1 enabling relay control Kl. Kl in turn drive relay (22) LS I to the open state removing power 52 to the unit under supervision. Driving the relay ON only during a fault decreases the power consumption of this circuit. Either drive ON, OFF or the use of a latching state relay may be effected by minor modifications of the circuit.

Power to the microcontroller 26 during operation is taken from the POWER IN 50. Converting power from the POWER IN form is required to produce a 3.0VDC bias supply to operate the microcontroller 26 and VOC sensor 24 as well as the relay drive circuit Kl. Power conversion from line voltage or DC voltage is well known in the industry and is not included in this disclosure.