I fixed the pir sensor on the top of servo motor.while the servo motor's rotation the pir was also rotated by servo motor's motion.but the problem I had founded that pir sensor had always indicated motion of human which I realized through a buzzer. When I take of the sensor from servo motor it had worked as well. So my question is that can we use pir sensor while it's moving?
I assume you are using one with a fresnel lens on it, and a driver/detection circuit already built in. If so, it will be basically impossible to use it while moving, since it relies on detecting a change in temperature between two areas, and it will be detecting this constantly. They are meant for detecting motion, and you are moving all the time.
Even if you created your own driver, I imagine it would still be pretty difficult to do it (maybe impossible).
To supplement @BeB00's answer:
The illustrations in the linked MakerGuides article is not quite correct.
Figure 1. Modified sensing diagram. A pair of side-by-side PIR sensors in reverse-series connection sense motion while giving high immunity to changes background radiation due to temperature changes.
Here it becomes clear that due to the reverse-series connection that walking into the purple detection zone would generate a positive going pulse and walking into the orange zone would give a negative going pulse.
Figure 2. The type of Fresnel lens shown in the accompanying article.
The type of Fresnel lens shown in the article is used in lighthouse and theater lamps to give high aperture with short focal length. This is not what is required for a PIR motion sensor.
Figure 3. A top view of a typical PIR motion sensor lens.
As shown in Figure 3, the lens used in a PIR motion sensor is not what is commonly known as a Fresnel lens. Instead, it is designed as an array of cylindrical or spherical lenses to give a pattern of weak and strong sensing zones.
So my question is that can we use PIR sensor while it's moving?
Probably not. You would need to stop the motion for long enough to take a reading and check for motion over a specified time period.