/*

  Program:   r_sample_series.c           Revision:   9-Nov-2020

  This program calculates the value of  R_sample  in mOhms
  for a series of  Feedback Signal Voltages  in terms
  of  5  parameters that it asks you to enter.

  The 5 parameters and their  entry and display  units are:

  - known target current from the current sweeper             mAmps
  - known Rref                                                 mOhm
  - known Rfb                                                   Ohm
  - known null detector supperconducting transformer ratio       -
  - known value of Internal FB current per Volt of FB         uAmps

  - and the known equivalence of Input & RF coils
    in putting flux into SQUID

  R-sample  is displayed in mOhms.

  The Feedback Signal Voltages that are used for these
  calculations are:

   0.1  1.0  2.0  3.0  4.0  5.0  6.0  7.0  8.0  9.0  10.0  Volts

 */


#include <stdio.h>
#include <math.h>

#define     PI       3.1415926


main ()

{
        float   R_sample     ;  /*  Resistance of the Sample    Resistor            Ohms  */
        float   R_ref        ;  /*  Resistance of the Reference Resistor            Ohms  */
        float   R_fb         ;  /*  Resistance of the Feedback  Resistor            Ohms  */

        float   I_sweeper    ;  /*  Current to Sample from the Current Sweeper      Amps  */

        float   V_fb[10]     ;  /*  Feedback Voltage used for calculation           Volts  */

        float   I_nulldet    ;  /*  Current across top side of Bridge - Null Det.   Amps  */

        float   R_eref       ;  /*  Thevenin Equivalent Reference Resistor          Ohms  */

        float   V_esample    ;  /*  Thevenin Equivalent Sample Voltage             Volts  */
        float   V_efb        ;  /*  Thevenin Equivalent Feedback Voltage           Volts  */

        float   Range        ;  /*  Amps Internal Feedback per Volt of Feedback     Amps  */
        float   Turns_Ratio  ;  /*  Effective Turns Ratio of Superconducting Transformer  */


        float   temp_1  ;

        int     Index   ;


        /*  Define the 10 Feedback Signal Voltages for which       */
        /*  the value of the Sample Resistor  will be calculated   */

        V_fb[1]   =   1.000  ;
        V_fb[2]   =   2.000  ;
        V_fb[3]   =   3.000  ;
        V_fb[4]   =   4.000  ;
        V_fb[5]   =   5.000  ;
        V_fb[6]   =   6.000  ;
        V_fb[7]   =   7.000  ;
        V_fb[8]   =   8.000  ;
        V_fb[9]   =   9.000  ;
        V_fb[10]  =  10.000  ;



        /*  Ask for and echo back the  various parameters.  */


        printf(" \n ");
        printf("  Enter the various operating parameters.  \n ");
        printf(" \n ");


        printf("  Enter the Current Sweeper Target Current  (mAmps): ");
        scanf( "%f", &temp_1 )   ;
        printf(" \n ")           ;

        I_sweeper  =  temp_1 / 1000   ;


        printf("  Enter the value of the Reference Resistor  (mOhms): ");
        scanf( "%f", &temp_1 )   ;
        printf(" \n ")           ;

        R_ref  =  temp_1 / 1000   ;


        printf("  Enter the value of the Feedback Resistor  (Ohms): ");
        scanf( "%f", &R_fb )   ;
        printf(" \n ")         ;


        printf("  Enter the SQUID Controller Range, i.e. how many   \n ");
        printf("  uAmps of Internal FB per Volt of FB Signal  (uAmps): ");
        scanf( "%f", &temp_1 )   ;
        printf(" \n ")           ;

        Range  =  temp_1 / 1000000   ;


        printf("  Enter the Turns Ratio of the Superdonducting Transformer,  \n ");
        printf("  i.e. how much is the Bridge un-balance current stepped up  \n ");
        printf("  before it is sent to the Input Coil of the SQUID  (ratio): ");
        scanf( "%f", &Turns_Ratio )  ;
        printf(" \n ")               ;
        printf(" \n ")               ;
        printf(" \n ")               ;



        /*  Print out all of this input information.  */

        temp_1  =  I_sweeper * 1000  ;
        printf( "\n  The Sweeper Target Current is = %8.4f mAmps  \n",  temp_1  )  ;

        temp_1  =  R_ref * 1000  ;
        printf( "\n      The Reference Resistor is = %8.3f mOhms  \n",  temp_1  )  ;

        printf( "\n       The Feedback Resistor is = %9.3f Ohms   \n",  R_fb    )  ;

        temp_1  =  Range * 1000000  ;
        printf( "\n       The Internal FB Range is = %6.3f uAmps/Volt \n",  temp_1 )  ;

        printf( "\n The Transformer Turns Ratio is = %6.2f to 1 Pri/Sec \n", Turns_Ratio );


        printf( "\n\n\n"   )  ;
        printf( "     Feedback      R_sample   \n"   )  ;
        printf( "       Volts         mOhms    \n\n" )  ;


        for ( Index = 1;  Index < 11;  Index++ )
              {

               /*  Calculate the Thevenin Equivalent Feedback Voltage     */
               /*  and its equivalent Feedback Voltage Source Resistance  */

               V_efb   =  ( R_ref / (R_fb + R_ref))  *  V_fb[Index]  ;

               R_eref  =  ( R_fb * R_ref )  /  ( R_fb + R_ref )    ;


               /*  Calculate the current in the Bridge Null Detector, i.e.   */
               /*  the current flowing across the top side of the Bridge.    */

               I_nulldet  =  ( V_fb[Index] * Range )  /  Turns_Ratio    ;


               /*  Now calculate the value of the Sample Resistor  */

               R_sample  =  ( V_efb + (R_eref * I_nulldet))  /  ( I_sweeper - I_nulldet )  ;


               /*  Print the value of  V_fb  and   Sample Resistor  */

               temp_1  =  R_sample  *  1000  ;

               printf( "    %8.3f       %8.3f  \n",  V_fb[Index],  temp_1 )  ;
               }


        printf( "\n \n \n"  )  ;

}