CN-0288 LVDT Signal Conditioning Circuit

HI,

We are using CN-0288 LVDT Signal Conditioning Circuit board for one of our project we need to achieve 7.07 Vrms Input voltage, for that we changing the resistor (R7) on board to get 7.07 Vrms, but the voltage is not stable its slowly increasing as IC(AD598) temperature increasing. so can anyone help on this..?

thank you