First, check the IP address of Subnet Mask. If the calculation results are matched after the AND operation, it indicates that the domain names of the human machine interface and the personal computer are the same. If not, it indicates that the personal computer and human machine interface are not in the same domain. For example, if the IP address of Subnet Mask is 255.255.255.0 and the IP address of the personal computer is 192.168.1.5, after the AND operation, the calculation result is as follows: If the IP address of the human machine interface is 192.168.2.5, after the AND operation, the calculation result is as follows: Conclusion: The calculation results do not match. This indicates that the personal computer and the human machine interface are not in the same domain.