Abstract:
Methods and systems for simply and inexpensive converting the signals of solid-state sensors for use by analog systems and indicators. An embodiment of the system receives a DC voltage value from at least one sensor, converts the DC voltage value into one or more analog signals based on a reference AC voltage signal, and performs at least one of outputting or storing the generated analog signals. The conversion is performed digitally then converted to analog or is performed using an analog trigonometric converter.

Description:
BACKGROUND OF THE INVENTION 
   Aircraft sensors and associated recording units or cockpit indicators are typically either communicating all digital or analog information. Newer aircraft have solid-state sensor technology with processing systems and indicators that are designed to operate on the output of the solid-state sensors. Because older aircraft have analog sensors, it is becoming increasingly difficult and costly to maintain these older sensors. Thus, it is preferred to replace old sensors with newer, cheaper, and easier to maintain solid-state sensors, such as Micro Electro Mechanical Systems (MEMS) sensors. 
   The problem with replacing the old style sensors with new solid-state sensors is that the existing systems that connect with the old style sensors still need to receive the data in the same format that was outputted by the old style sensors. One solution is to replace the processing systems and indicators with processing systems and indicators that are compatible with the new sensors. This, of course, is prohibitively expensive. 
   Another solution is to translate the data that is outputted by the solid-state sensors into a format that is compatible with the existing systems and indicators within the aircraft. Current translators or converters utilize look-up tables or oscillators to create the proper formatted signals for input into the existing systems and indicators. However, these methods are costly and difficult to implement. Traditional methods require memory (for look-up tables) and/or oscillators that lower system reliability and utilize sync signals which can be susceptible to EMI. Implementation using look-up tables also has finite resolutions bounded by their digital size. 
   Therefore, there exists a need for simply and inexpensively converting the signals of solid-state sensors for use by the existing systems and indicators on an aircraft. 
   SUMMARY OF THE INVENTION 
   The present invention provides methods and systems for simply and inexpensively converting the signals of solid-state sensors for use by analog systems and indicators. An embodiment of the system receives a DC voltage value from at least one sensor, converts the DC voltage value into one or more analog signals based on a reference AC voltage signal, and performs at least one of outputting or storing the generated analog signals. The trigonometric conversion is performed either digitally then converted to analog, or is performed using an analog trigonometric converter. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The preferred and alternative embodiments of the present invention are described in detail below with reference to the following drawings. 
       FIGS. 1–3  are block diagrams of various embodiments of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1  illustrates an example system  20  formed in accordance with an embodiment of the present invention. The system  20  includes a sensor  30 , a trigonometric converter  36 , and an analog indicator or data acquisition unit  40 . 
   The sensor  30  is a solid-state sensor, such as a MEMS sensor, that outputs a DC voltage signal X based on a sensed condition. The sensor  30  may be any of a number of different types of sensors that are used to sense any number of different type of physical values around the aircraft, such as control surface position, pressure sensors, temperature sensors, etc. The trigonometric converter  36  receives a reference AC voltage signal A and the DC voltage value X from the sensor  30  and converts those into signal formats that are necessary for the analog indicator or data acquisition unit  40 . In this example, a first output of the trigonometric converter  36  is the signal A*SIN(X) and a second output is the signal A*SIN(X+angular offset). For a implementation of a resolver, the angular offset would be 90 degrees. More signals may be produced by the trigonometric converter  36  depending upon the requirements (number or type of phase signals) of the analog indicator or data acquisition unit  40 . 
   The analog indicator or data acquisition unit  40  may include any number of analog indicators or gauges, such as those used in an aircraft cockpit. An example data acquisition unit is the processor associated with a flight data recorder. 
     FIG. 2  illustrates a converter  100  that provides the functions of the trigonometric converter  36  shown in  FIG. 1  in accordance with a first embodiment. The converter  100  includes a phase shift voltage generator  102 , first and second trigonometric chips  106  and  108 , and first and second analog multipliers  112  and  114 . 
   In one embodiment, the first and second trigonometric chips  106  and  108  are off-the-shelf trigonometric processing chips, such as the AD639 produced by Analog Devices™. More than two trigonometric chips can be included depending on the desired output or a single chip may be configured to include multiple inputs and outputs for producing desired outputs. The analog multipliers  112  and  114  may also be off-the-shelf devices. In one embodiment, the phase shift voltage generator  102  includes a voltage divider, but could be any of a number of different off-the-shelf voltage generators. 
   The first and second trigonometric chips  106  and  108  receive the DC voltage value X produced by the sensor  30 . An angular offset input pin on the first trigonometric chip  106  is tied to ground, thus providing a zero voltage value at that pin. An angular offset input pin on the second trigonometric chip  108  receives a DC voltage value outputted from the phase shift voltage generator  102 . The DC voltage value outputted by the generator  102  depends upon what angular offset is desired. Therefore, the output of the first trigonometric chip  106  is the value SIN (X) and the output of the second trigonometric chip  108  is SIN (X+angular offset). The first analog multiplier  112  receives the reference AC voltage signal A and multiples that with the output of the first trigonometric chip  106  to produce the signal A*SIN(X). The second analog multiplier  114  also receives the reference AC voltage signal A and multiples that to the output of the second trigonometric chip  108 , thereby producing the signal A*SIN(X+angular offset). The outputs of the analog multipliers  112  and  114  are sent to the analog indicator or data acquisition unit  40 . Amplifiers (not shown) may be used after the multipliers  112  and  114  to amplify the outputted signals and act as a buffer. 
     FIG. 3  illustrates a converter  140  that provides the functions of the trigonometric converter  36  shown in  FIG. 1  in accordance with a second embodiment. The converter  140  includes an analog to digital (A/D) converter  148 , a non-linear transfer function component  150 , a digital offset component  152 , and first and second multiplying digital to analog (D/A) converters  156  and  158 . The components  150  and  152  may be implemented as a field programmable gate array (FPGA) or other functionally comparable device. The A/D converter  148  receives the DC voltage value X from the sensor  30  and converts it into a digital value. The non-linear transfer function component  150  receives the digital output of the A/D converter  148  and converts that linear signal to output a digital representation of a trigonometric signal to the first D/A multiplier  156  and the digital offset component  152 . Equation No. 1 is an example of a non-linear transfer function that is utilized by the component  150  to generate the digital sine signal: 
   
     
       
         
           
             
               
                 
                   SIN 
                   ⁡ 
                   
                     ( 
                     X 
                     ) 
                   
                 
                 ≈ 
                 
                   
                     
                       X 
                       ⁡ 
                       
                         ( 
                         
                           1 
                           - 
                           
                             X 
                             2 
                           
                         
                         ) 
                       
                     
                     ⁢ 
                     
                       ( 
                       
                         2.83 
                         - 
                         
                           X 
                           2 
                         
                       
                       ) 
                     
                   
                   
                     0.9 
                     ⁢ 
                     
                       ( 
                       
                         1 
                         + 
                         
                           0.3 
                           ⁢ 
                           
                             X 
                             2 
                           
                         
                       
                       ) 
                     
                   
                 
               
             
             
               
                 ( 
                 1 
                 ) 
               
             
           
         
       
     
   
   Other types of equations may be utilized to perform the non-linear transfer function at the component  150 . The digital offset component  152  performs a digitally implemented pre-defined angular offset based on the desired angular offset that is desired for an output of the converter  140 . The first D/A multiplier  156  receives the reference AC voltage signal A and the output of the component  150  to produce the signal A*SIN(X). The second D/A multiplier  158  also receives the reference voltage signal A and combines that with the output of the digital offset component  152  to produce the signal A*SIN(X+angular offset). The output of the multipliers  156  and  158  are sent to the analog indicators or data acquisition unit  40 . Amplifiers (not shown) may be used after the multipliers  112  and  114  to amplify the outputted signals and act as a buffer. 
   While the preferred embodiment of the invention has been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. Accordingly, the scope of the invention is not limited by the disclosure of the preferred embodiment. Instead, the invention should be determined entirely by reference to the claims that follow.