wats the difference between pyrometric detectors and pyroelectric detectors?

"what is the use of fresnel lense and how it can be used?" Review the information you have of a fresnel lens, and compare it's characteristics to the KRX11 datasheet. Where does it appear it may have any effect on the sensor? Is it a desireable effect?

"Is that is a component?" It can be. Do you think it should be?

"can i connect output of this circuit to relay circuit?" Refer once again to the datasheet. What does it tell you? My review of the datasheet tells me...

If you will answer these questions, I (or someone else more capable) will visit with you about this. We will not provide homework answers here, but we will try to help you to understand how to solve questions.

Where does a pyrometric device come in here?