I want to build circut with 8051 micro controller which detects whether Clock signal is available or not ie I want to detect Clock signal is presetnt or not how to or not do this .
Three posts just to get to the fact that you want to measure the time between pulses. You lost a lot of time by not being explicit in your first post. But you still haven't given all information.
What processor?
What type of sensor do you have?
How is it connected to the processor?
What is the expected frequency of the pulses? Max pulses / second when the wheel is turning fast, and the longest amount of time between two pulses before you consider the wheel as stopped?
You can use a timer in the processor to count the time between two pulses. Depending on how the signal is connected, the timer can do most of the work itself, or you may have a pin-change interrupt where you start/stop the timer, or you may busy-loop while keeping track of your timer.
There are a lot of sample code available for how to use a timer. And there are many threads about it, if you just use the search feature you can see in the upper right of this web page.