[PIC] AC rms voltage measurement problem in precision

void adcInit(void){
    
    ADCON0=0x00; 
    ADCON1=0X07;                // SET ANALOG CHANNELS
    TRISA=0xFF;
    PSPMODE=0;
    TRISEbits.TRISE0=1;
    TRISEbits.TRISE1=1;
    TRISEbits.TRISE2=1;
    ADCON2=0b10001010;         // SET COVERSION CLOCK       //101=15        //010=32
    ADCON0=0x01;                // TURN ON ADC MODULE
}

unsigned int getAdcCount(unsigned char channel){
    //unsigned int count;
    if(channel>13) return 0;  //Invalid Channel

   ADCON0=0x00;

   ADCON0=(channel<<2);   //Select ADC Channel

   ADON=1;  //switch on the adc module
//   DelayMs(3);          // WAITING FOR THE ACQUISITION TIME
   GODONE=1;  //Start conversion

   while(GODONE); //wait for the conversion to finish

   ADON=0;  //switch off adc
   //count = ADRES;
    return ((ADRESH<<8)+ADRESL);
}



void main() {

    unsigned char uctemp = 0;
    double U32Volt;
    unsigned int i = 0;
    CM0 = 1; //turn off comparator
    CM1 = 1; // turn off comparator
    CM2 = 1; // turn off comparator
    adcInit();
    gprs_set_flag = 0;
    EB_ZC_PIN_DIR = INPUT_PIN;
    OUT_ZC_PIN_DIR = INPUT_PIN;
    INV_ZC_PIN_DIR = INPUT_PIN; //zero crossing pins as inputs
    
    while (1) {
     
        U32Volt = 0;
        for (i = 0; i < 50; i++) {                     //50 times averaging
            invVolt = Measure_Rms_value(INVVOLT_CHANNEL, 1);       // taking rms value
            U32Volt += invVolt;
        }
        U32Volt = (U32Volt * 3.24) / 50;                //3.24 multiplicaion factor
        DelayS(1);

    }
}



double Measure_Rms_value(unsigned channel, double Mul_factor) {
    unsigned int i;
    unsigned int sample_Val;
    float offset_Val = 533; //775;//512;       // for 3.3v ref offset val=775; for 5v ref, offset value=512
    double sum_Val = 0;
    float filtered_Val = 0, sq_Val = 0, Rms_val = 0;
    unsigned char neg_cycle_flag;
    unsigned int adc_counts = 1000;
    unsigned int timeout = 0;
     if (channel == INVVOLT_CHANNEL) {
        unsigned int invZC = 0;
        timeout = 0;
        if(INV_ZC_PIN==1)                 // if positive half cycle: wait here
        {
            while (INV_ZC_PIN == 1) {
            timeout++; 
            if (timeout >= 1000) {
                timeout = 0;
                break;
            }
        }
       }
        while (INV_ZC_PIN == 0) {                       // wait until negative cycle is finished
            timeout++;
            if (timeout >= 1000) {
                timeout = 0;
                return 0;
            }
        }
        while (adc_counts--) {                        // start taking measurement for one cycle
            invZC++;
            sample_Val = getAdcCount(channel);
            offset_Val = (offset_Val + ((sample_Val - offset_Val) / 1024));
            filtered_Val = sample_Val - offset_Val;
            sq_Val = filtered_Val * filtered_Val;
            sum_Val += sq_Val;

            if (INV_ZC_PIN == 0) {                // negative cylce: zero crossing pin becomes low
                neg_cycle_flag = 1;
            }
            if (neg_cycle_flag == 1 && INV_ZC_PIN == 1) {
                neg_cycle_flag = 0;
                break;
            }
        }

        Rms_val = Mul_factor * (sqrt(sum_Val / invZC)); //
        sum_Val = 0;
        return Rms_val;
    }

    return 0;
}