How to get the stable temperature data from external temperature sensor (RTD)?

HI:

I connected a external temperature sensor in VINTP and VINTN on EVM with TP29 and TP27, as follow:

and I had a configured with PGA900_cfg.c as follow:

CONFIG_ALPWR(POWER_UP_PT_PGA_FD | ADC_EN_VREF | GATE_CTRL_SD_DISABLE);

DAC_Config(DAC_ENABLE, DAC_RATIOMETRIC_MODE_DISABLE, DAC_GAIN_10V | B_4_20MA_DISABLE | DACCAP_DISABLE );

AMUX_CONFIG(TEST_MUX_DAC_EN | TEST_MUX_P_EN | TEST_MUX_T_EN);

ADC_Tchannel_Config(ADC_ENABLE| ADC_ENABLE_24BIT | ADC_DECI_RATE_128US | ADC_INT_RATE_EVERY_SAMPLE, T_GAIN_20_V_V );

 TEMP_CTRL=0x30; //500uA

I made a output in PGA900_adc.c, the program as follow:

interrupt void PADC_Handler(void)
{

signed long xx,yy;
yy = (TADC_DATA_24BIT & 0x00FFFFFF);/* Mask the upper 8 bits */

if(yy & 0x00800000) /* If sign bit is set */
{
yy = yy | 0xFF000000; /* Sign extend the sign bit */
}
/* Accumulate the value of P channel */
FIR_AccadcValue[0] = xx;
/* Accumulate the value of T channel */
FIR_AccadcValue[1] += yy;

coeffP = (NtempCoeff[VarI] * FIR_AccadcValue[0]);

coeffP = (coeffP >> 14);
coeffP = coeffP + GtempCoeff[VarI];
coeffP = (coeffP * FIR_AccadcValue[0]);
coeffP = (coeffP >> 14);
coeffP = coeffP + HtempCoeff[VarI];
DAC_Value = (US)(coeffP);

DAC_Value=(yy>>10);

then, I have detected the voltage in vout (TP30), the voltage which shown in voltage meter was continued changed even the temperature is keeping a 20 degrees.

would you please tell me what's going on?

didn't I missed something?

Thanks