Abstract:
A method and system for providing a linear signal from mass flow transducer approximates the error from the original raw signal using discrete sine functions and subtracts the approximated error from the original raw signal. The method and system can be implemented using an ASIC (Application Specific Integrated Circuit) mated with a raw mass flow transducer. The method and system for linearizing the signal can be contained in the ASIC, and allows for improved accuracy in the linear signal with few coefficients and mathematical steps.

Description:
TECHNICAL FIELD 
   Embodiments are generally related to flow sensors. Embodiments are also related to mass flow transducers. Embodiments are additionally related to techniques and devices for providing a linear signal from a mass flow transducer. 
   BACKGROUND OF THE INVENTION 
   Mass Flow transducers are used in a variety of industries to quantify the flow rate of a substance. For example, the medical industry uses mass flow transducers to monitor and control a person&#39;s breathing. One common technique for sensing mass flow is to utilize multiple resistive temperature detectors on each side of a heating element parallel to the direction of flow. As a mass such as a fluid or gas flows across the resistors, the resistors that are located upstream from the heating element are cooled, and the resistors located downstream from the heating element are heated. When a voltage is applied across these resistors, an electrical signal is generated. The signal generated using multiple resistive temperature detectors are highly non-linear and not ideal for use in most “high accuracy” control systems. 
   Two types of methods are currently utilized to approximate a non-linear mass flow signal into a linear output: piece-wise linear functions or polynomial approximation. In piece-wise linear functions, the linear signal is approximated by many linear equations distributed throughout the range of the signal. In polynomial approximation, a polynomial expression is used to describe the signal. 
   A need exists for improved accuracy in the generation of linear signal with less coefficients and mathematical steps as a part of mass flow transducer. It is believed that a solution to this problem involves the implementation of an improved method and system for linearizing the raw output of a mass flow transducer as described in greater detail herein. 
   BRIEF SUMMARY 
   The following summary is provided to facilitate an understanding of some of the innovative features unique to the embodiments disclosed and is not intended to be a full description. A full appreciation of the various aspects of the embodiments can be gained by taking the entire specification, claims, drawings, and abstract as a whole. 
   It is, therefore, one aspect of the present invention to provide for an improved flow sensor method and system. 
   It is another aspect of the present invention to provide for a method and system for generating a linear signal from a mass flow transducer. 
   It is another aspect of the present invention to provide a method and system for linearizing a raw output signal from a mass flow transducer. 
   It is a further aspect of the present invention to provide for a method and system for providing a linear signal from a mass air flow and liquid flow transducer. 
   The aforementioned aspects and other objectives and advantages can now be achieved as described herein. The method for providing a linear signal from mass flow transducers approximates the error from the original raw signal using discrete sine functions and subtracts the approximated error from the original raw signal. This invention can be implemented using an ASIC (Application Specific Integrated Circuit) mated with a raw mass flow transducer. The method for linearizing the signal will be contained in the ASIC. This method allows for improved accuracy in the linear signal with less coefficients and mathematical steps. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying figures, in which like reference numerals refer to identical or functionally-similar elements throughout the separate views and which are incorporated in and form a part of the specification, further illustrate the embodiments and, together with the detailed description, serve to explain the embodiments disclosed herein. 
       FIG. 1  illustrates a schematic diagram of a bridge circuit that can be adapted for use with a mass flow transducers, in accordance with a preferred embodiment; 
       FIG. 2  illustrates a schematic diagram of a process for linearizing a non-linear raw signal, in accordance with a preferred embodiment; 
       FIG. 3  illustrates a graph depicting the voltage signal verses airflow of the non-compensated and compensated (desired) signals, in accordance with a preferred embodiment; 
       FIG. 4  illustrates a block diagram showing a process of linearizing a non-linear signal using an ASIC, in accordance with a preferred embodiment; 
       FIG. 5  illustrates a high level flow chart of operations depicting a linearization method for a mass flow transducers, in accordance with a preferred embodiment; and 
       FIG. 6  illustrates a graph depicting a percentage error verses normalized flow for the linearized output of a mass flow transducer, in accordance with a preferred embodiment. 
   

   DETAILED DESCRIPTION 
   The particular values and configurations discussed in these non-limiting examples can be varied and are cited merely to illustrate at least one embodiment and are not intended to limit the scope thereof. 
     FIG. 1  illustrates a schematic diagram of bridge circuit  100  that can be adapted for use with a mass flow transducer, and implemented in accordance with a preferred embodiment. Circuit  100  generally includes a group of resistors  104 ,  106 ,  108 ,  110 , which are connected to an excitation voltage  120  and an amplifier  115 . The resistors  104 ,  106 ,  108 ,  110  are arranged as a Wheatstone bridge circuit and are connected to the amplifier  115  at nodes V 1  and V 2 . The circuit  100  can be implemented in the context of an ASIC (Application Specific Integrated Circuit). 
   As mass flows across the group of resistors  104 ,  106 ,  108 ,  110 , the resistors  106  and  110  upstream from a resistor  109  (i.e., a heater) are cooled and the resistors  104  and  108  downstream from the heater or resistor  109  are heated. Note that the resistor  109  is connected to an excitation voltage  130 . An electrical signal can be generated when the excitation voltage  120  is applied across the group of resistors  104 ,  106 ,  108 ,  110 . A temperature difference is produced by the fluid stream passing over the heater  109  and then over the resistors  104  and  108 . This temperature difference, unbalances the bridge causing a voltage difference that is amplified using the amplifier  115  and then calibrated to the mass flow rate. The signal obtained from the amplifier  115  generally constitutes a non-linear raw signal with respect to fluid flow. 
     FIG. 2  illustrates a schematic diagram of a system  200  of linearizing the non-linear raw signal obtained from the amplifier  115 , in accordance with a preferred embodiment. Note that in  FIGS. 1-2 , identical or similar parts or elements are generally indicated by identical reference numerals. For example, resistors  104 ,  106 ,  108 ,  110  depicted in  FIG. 1 , generally represent the group of resistors  207  depicted in  FIG. 2 . The amplifier  115  and heater  109  of the bridge circuit  100  are also depicted in  FIG. 2  and can be adapted for use with a mass flow transducer  202 , which is electrically connected to an ASIC  201 . The ASIC  201  generally includes an amplifier  115 , which provides an electrical signal to an approximation mechanism  225 . ASIC  201  also includes a memory  240 , which can store coefficients describing an error realized during calibration. Memory  240  and amplifier  115  are electrically connected to an approximation mechanism  225 . 
   The output signal from the circuit  100  can be provided to the amplifier  115  and is subject to amplification by amplifier  115 . The output signals from a memory storing coefficients describing an error realized during calibration are stored in memory  240 . The data stored in memory  240  and an amplified non-linear signal from amplifier  115  can be provided as input signals to approximation mechanism  225 . Such an approximation method approximates an error from the original non-linear raw signal utilizing a circuit  220  for generating a discrete sine function. A subtractor  230  can then be utilized to subtract the approximated error from the original non-linear raw signal, in order to obtain a linear signal  235 . Thus, the embodiments described herein can be implemented using ASIC  201  (Application Specific Integrated Circuit) mated with a raw mass flow transducer  202 . 
     FIG. 3  illustrates a graph  300  depicting the variation of voltage verses fluid flow for a non-linear, non-compensated, signal  305  and a linear desired signal  235  in accordance with a preferred embodiment. As indicated in graph  300 , a non-linear raw signal  305  obtained from a mass flow transducer  202  is converted into a linear signal  235  as a result of the operations depicted in  FIG. 2  and in association with the circuit  100  depicted in  FIG. 1 . The method for linearizing the signal will be contained in the ASIC  201 . 
     FIG. 4  illustrates a block diagram  400  showing a process of linearizing a non-linear signal using an ASIC  201 , in accordance with a preferred embodiment. Note that in  FIGS. 1-3 , identical or similar parts or elements are generally indicated by identical reference numerals. The  FIG. 4  illustrates a group of resistors  207 , an excitation voltage  120 , an amplifier  115 , a non linear signal  350 , an ASIC  201 , a circuit  220  for generating discrete sine functions, a subtractor  230 , an approximation mechanism  225  and a linear signal  235  as depicted previously with respect to in  FIG. 2  and  FIG. 3 . 
     FIG. 5  illustrates a high level flow chart of operations depicting a linearization method  500  for a mass flow transducer  202 , in accordance with a preferred embodiment. As indicated at block  505 , a linear signal can be obtained from the mass flow transducer  202  depicted in  FIG. 2 . Thereafter, as described at block  510 , a non-linear error obtained from the raw output signal generated by circuit  100  depicted in  FIG. 1  can be approximated using a discrete sine function generated by the circuit  220  depicted in  FIG. 2 . Thereafter, as depicted at block  520 , a linear signal can be obtained by subtracting (e.g., using the subtractor  230  depicted in  FIG. 2 ) the approximated error from the original raw signal as depicted previously at block  515 . 
     FIG. 6  illustrates a graph  600  depicting a percentage error verses normalized flow for the linearized output of mass flow sensor, in accordance with a preferred embodiment. As indicated in graph  600 , an optimized 7 th  order polynomial approximation  610  and a 10 segment piece-wise linear approximation  605  can be compared with the Error Plot of subtracting 7 optimized sinusoidal curves  615  used to approximate the original error from the raw signal. 
   It will be appreciated that variations of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.