PIR Motion Sensor(D203B)

Dear Experts,

I am working with D203B PIR sensor, I have attached my schematic for your reference,

this circuit is working fine for 2-3 hours after that this sensor deduction range is automatically reducing, I can’t understand the reason if you have any solution for that kindly let me know,

Note: I have some changes in schematic VR1 value change to 1M ohm fixed resistor, I got pulse value 3.02v t0 0v at detection time so I set VR3 output volt is 2.9v

regards

kannannatesh