In reply to dave_59:
Sorry for the typo here. The ##delay_b is 200.
The sequence is like:
sequence check_b;
$rose(enable_b) ##200 $rose(sig_b);
endsequence
The delay between enable_b and sig_b is 2000ns and the reference clock is of 100Mhz frequency. So the ##delay_b (i.e.,the number of clock cycles)is derived as 2000ns/10ns which is 200.
Please correct me if the method followed is inappropriate.