PIR sensor always gives HIGH
I finally found a solution to this problem
First you should adjust the delay knob to the left as min delay time.After connecting the power to the sensor, you should wait 1 min for the sensor to warm up, Now the sensor is ready to use and before this time its performance won't be stable.
Also remember when you the sensor signal moves from high to low, it take around 5 seconds out of service, after than you can trigger it again.

After make sure it work properly you can increase the delay a little bit to increase the on time ^_^...